Valid Thu Mar 28, 2024
Valid Fri Mar 29, 2024
Valid Sat Mar 30, 2024
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NWS Weather Prediction Center College Park MD
318 AM EDT Thu Mar 28 2024
Valid 12Z Thu Mar 28 2024 - 12Z Sat Mar 30 2024
...Rainy, stormy weather continues along the East Coast through today,
lingering in New England Friday...
...Unsettled weather for the West, with a late season Atmospheric River
impacting California Friday...
...Warming trend begins over Central U.S. today...
Two slow moving frontal boundaries will continue to push towards the East
Coast today, with the leading front pushing into the Atlantic by early
afternoon and the second front slowing approaching the coast while
weakening through this evening. Chances for showers and thunderstorms will
continue through today along the East Coast but taper off from south to
north as the leading front exits. Locally heavy rainfall will be possible
over portions of the eastern Mid-Atlantic and coastal New England, which
may cause isolated to scattered instances of flash flooding. The highest
risk for flash flooding will be over eastern North Carolina and far
southeastern Virginia as a wave of low pressure moves along the frontal
boundary today, and there is a Slight Risk of Excessive Rainfall (level
2/4) for this area. Precipitation chances will likely linger through
Friday for portions of New England as low pressure strengthens just east
of the region. Colder air moving in from the north will allow rain to
switch to wintry mixed precipitation and snow overnight into Friday for
inland areas. Winds will also become gusty in the Northeast on Friday and
Saturday as the low strengthens and the pressure gradient tightens.
Meanwhile, a frontal system will push southeast across much of the West
with unsettled weather today into Friday. Mountain snow and low elevation
rain will impact the region, and locally heavy snow will be possible for
regional mountain ranges from the Pacific Northwest southward into
northern/central California, as well as for the eastern Great Basin into
the northern/central Rockies. Low pressure associated with the
southeastward moving frontal system will push into the northern and
central Plains on Friday and reach the Great Lakes region by Saturday
morning. This will bring chances for wintry precipitation to the Upper
Midwest and northern Great Lakes and chances for showers and thunderstorms
to portions of the Midwest and Ohio Valley.
On Friday afternoon, a Pacific low pressure system will approach the
California coast. This system will aim a plume of moisture (an atmospheric
river) at central and southern California Friday night into Saturday,
which will result in heavy rainfall and potentially flash flooding. There
is a Slight Risk of Excessive Rainfall (level 2/4) for portions of coastal
southern California on Friday and Saturday where upslope flow along
terrain will likely enhance rainfall totals and could lead to scattered
instances flooding.
Temperature-wise, lows this morning will be chilly, dropping into the low
to mid-30s across portions of the Mid-South into the Tennessee Valley
following a cold front passage, and Frost/Freeze-related advisories and
warnings are in place for newly greening sensitive vegetation. Increasing
upper-level ridging over will bring warmer, above average temperatures to
portions of the Central U.S. today, to the Plains, Mississippi Valley, and
Midwest on Friday, and to the Southeast and Mid-Atlantic on Saturday.
Below average high temperatures are forecast for much of the West through
the weekend due to expected cloud cover and precipitation and for the
northern high Plains Friday through the weekend as colder air moves in
behind a cold front.
Dolan
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php
NWS Weather Prediction Center College Park MD
257 PM EDT Thu Mar 28 2024
Valid 12Z Sun Mar 31 2024 - 12Z Thu Apr 04 2024
...A low pressure/frontal system will spread potentially heavy
rain and mountain/northern tier snow to much of the country next
week...
...Overview...
Upper troughing with one or more embedded lows will move across
California and the Four Corners states early next week. This
feature and its surface low pressure system will direct moisture
into California and the Southwest/Great Basin into the Rockies on
Sunday and produce heavy rain and higher elevation snow. These
upper/surface features will interact with northern stream troughing
in the north-central to northeastern U.S. to consolidate a surface
low that should move from the central Plains to the Northeast
during the workweek. Expansive precipitation coverage is likely
with this system, with snow and freezing rain possible on its north
side, and heavy rain in the warm sector as moisture pools along
the surface low's fronts. Well behind this system, an upper trough
and leading cold front pushing into the Northwest should spread
precipitation southeastward across the region by next Wednesday-
Thursday.
...Guidance/Predictability Assessment...
Latest guidance agrees in principle on most aspects of the large
scale pattern evolution and dominant surface systems, but with some
typical detail uncertainties that are still to be resolved.
For the initial western system ultimately affecting the
central/eastern U.S., the first issue to arise involves the latest
GFS runs depicting a closed upper system tracking northeastward
across the Plains early next week in contrast to most other
guidance showing a more open depiction across this region. The
GEFS mean is more open but both solutions lead to a farther
west/northwest track for low pressure and extent of heaviest QPF.
00Z ECMWF-initialized machine learning models (MLs) show various
ideas for how upper dynamics may evolve during that time but still
are not very supportive of the GFS specifics.
The next question involves amplifying Canadian/northern tier U.S.
energy by around next Tuesday-Wednesday. The best clustering of
dynamical models and MLs suggest that this northern stream energy
should yield a fairly deep upper low over the central-eastern Great
Lakes by early Wednesday. The 00Z CMCens mean was a fast extreme.
On the other hand, the new 12Z UKMET/CMC/ECMWF all stray to the
southwest of consensus for the upper low at that time. Time will
tell if this is an emerging trend. The majority scenario would have
the upper low and deepening surface low pressure reach New England
or vicinity by next Thursday, with slowly improved clustering
yielding a deeper trend in a blended forecast at the surface and
aloft. Given some of the trends by Wednesday, confidence thereafter
declines especially with the surface track becoming quite sensitive
to upper low specifics.
Meanwhile there is decent agreement for the overall upper trough
forecast to move into the Northwest by midweek or so. Some GFS runs
have leaned a bit on the deep/sharp side of the spread (but with
some support from the MLs), while the 00Z ECMWF showed two discrete
shortwaves--each faster than the single trough depicted in the
GFS/CMC, ensemble means, and MLs.
Finally, the latest dyanmical models and means are strongly
support the idea of lingering Southwest U.S. energy settling into
northwestern Mexico as a trough/upper low later in the period.
Interestingly, most 00Z MLs suggest this energy will eject out
much more quickly.
Guidance comparisons among 00Z/06Z guidance favored updating the
forecast with an operational model composite, with sufficiently
modest GFS weight not to have undue influence on the forecast over
the Midwest early next week. The blend transitioned to a half
model/half ensemble mean mix by day 7 Thursday, reflecting the
large scale guidance agreement but decreasing confidence in
details.
...Weather/Hazards Highlights...
A potent storm system will move west to east next week and lead to
widespread precipitation across much of the country. On Sunday, a
weak atmospheric river should be pushing into Arizona. A Marginal
Risk remains in place in the Day 4 Excessive Rainfall Outlook over
portions of Arizona on Sunday where heavy rainfall may occur.
Meanwhile snow is the likely precipitation type in higher
elevations from the Mogollon Rim northward across the Intermountain
West to the Rockies, with moderate to heavy totals possible.
Additionally, though the atmospheric river will have passed beyond
southern California by Sunday, convective rainfall could occur
there as steeper lapse rates come in with the upper low overhead.
These showers may have some higher rain rates that could cause some
isolated flooding concerns especially after a wet couple of days,
so the Day 4 ERO depicts a Marginal Risk along/near southern
coastal California too. Expect a drying trend over much of the West
Monday-Tuesday. A trailing upper trough/cold front moving into the
Pacific Northwest/northern Rockies should spread rain and mountain
snow across the region late Tuesday onward.
The initial Southwest upper low/trough will continue shifting
inland through early next week, and with consolidating surface low
pressure in the central Plains, a period of gusty winds is possible
across much of New Mexico and southwest Texas. Farther east,
moisture from the Pacific and Gulf will likely combine and produce
rain and thunderstorms especially near frontal boundaries. The
Ohio Valley will be one area of focus for potentially heavy
rainfall. Some rain is likely there on Sunday but amounts are
forecast to increase by Monday. A Marginal Risk remains in place
from the Middle Mississippi Valley into the Ohio Valley on Monday
as a starting point for the Day 5 ERO, with some potential for
future position adjustements and upgrades. Moisture and
instability are anomalously high for this time of year, and showers
and storms could train along the west to east oriented warm front
nearby. By Tuesday the cold front and low should continue to push
east and the heaviest rainfall at that point may focus across the
Tennessee Valley into the Appalachians. Also the Storm Prediction
Center is monitoring severe potential in the warm sector from the
Plains to just west of the Appalachians early next week.
On the northern side of the storm system, snow and freezing rain
are potential threats from the north-central Plains on Sunday,
stretching into the Upper Midwest and Great Lakes region Monday and
higher elevations of the Northeast by Tuesday-Wednesday. However,
there is still considerable uncertainty in the placement and
amounts of snow and ice, so continue to monitor forecasts. The
Interior Northeast may see the heaviest snow amounts overall
because of the duration of the potential snow event there compared
to the north-central U.S./Midwest/Great Lakes.
Through Monday, a strong front across middle latitudes east of the
Rockies will separate chilly temperatures across the north-central
U.S. (highs at least 10-15F below normal) from very warm readings
across the southern half of the Plains and Mississippi Valley into
the Tennessee Valley and Southeast/southern Mid-Atlantic with
upper ridging helping to enhance the warmth. Warm sector
temperatures of 10-20F above average will become widespread, with
highs well into the 70s reaching Kansas to Virginia while highs
climb into the 90s to even 100F in southern Texas. Developing low
pressure will then push a trailing cold front eastward, dropping
temperatures in the south-central U.S. by Tuesday and focusing the
warmth in the Southeast before the front pushes through there too
by midweek. Meanwhile in the Southwest, cooler than average
temperatures particularly in terms of highs are likely underneath
the upper low early next week before a moderating trend. The
Pacific Northwest could see a brief period of above average
temperatures early next week.
Rausch/Tate
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:
https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw
Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Thu Mar 28 2024
Valid 00Z Fri Mar 29 2024 - 00Z Fri Apr 05 2024
Breezy to windy trades are forecast for the next day or two as a
strong surface high sets up well north of Hawaii. Meanwhile some
weak troughing aloft may decrease stability a bit and allow for
some showers. These would generally favor windward/mauka areas
with some potentially spilling leeward. By the weekend, the
pressure gradient looks to relax somewhat as the surface high
pulls northeast, leading to moderate trades while moisture levels
dry out a bit and sit around average.
Then into next week, mid-upper troughing is likely to stretch
southward through much of the Pacific over Hawaii. This trough
will push a surface cold front ahead of it, but models vary
regarding if and when this front would push through the state. The
00Z GFS stalls the front for a bit but then pushes it through
around Wednesday-Thursday, while the 00Z ECMWF never has it
passing through. In any case, moisture is likely to pool near and
south of the front, leading to increasing rain potential early to
mid-next week. Another strong surface high building north of
Hawaii will lead to increasing trades again as well.
Tate
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+ Forecast Discussion
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1154 AM EDT Thu Mar 28 2024
Day 1
Valid 16Z Thu Mar 28 2024 - 12Z Fri Mar 29 2024
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID ATLANTIC AND NORTHEAST U.S....
16Z Excessive Rainfall Discussion...
...New England...
Introduced a Slight Risk of excessive rainfall over portions of
New England through tonight. Satellite imagery showed another
region of cooling cloud tops upstream from the area as of late this
morning...so any respite from rainfall overnight and early this
morning should be short-lived. The expectation is that neither
rainfall rates nor rainfall amounts will be blockbuster in
magnitude and that most places would be handled under most
circumstances (as suggested by the 12Z HREF neighborhood
probabilities showing less than 5 percent risk of 1-/3-/6-hour QPF
exceeding respective Flash Flood Guidance). But discussions with
the National Water Center and offices in the area indicate that the
amount of water added by melting and compaction of the snowpack
may be enough for more than isolated problems with runoff in areas
of poor drainage. 12Z HREF guidance shows better coverage of
rainfall along and near the coastal regions of New England with
nearly 1.5 inches of additional rainfall.
...Eastern Carolinas...
Maintained the Slight Risk for the time being as rain continues to
call over eastern North Carolina as higher reflectivities continue
to move from south to north across the region. The entire area of
rain should be shifting off-shore during the afternoon but
localized higher rainfall rates may still occur before rain ends.
Bann
08Z Excessive Rainfall Discussion...
...Eastern North Carolina - Southeastern Virginia...
An upper trough moving over the lower Mississippi Valley and
northern Gulf will begin to assume a negative tilt as it moves into
the Southeast today. Right-entrance region upper jet forcing will
support a deepening low that will track north along the Southeast
to the southern Mid-Atlantic coast later this morning. This will
support continued southwest to northeast training showers and
thunderstorms into the afternoon, with additional heavy rainfall
amounts expected over the region. Although instability will be
limited, strong forcing interacting with sufficient moisture (PWs
1.25-1.5 inches) will be enough to support rainfall rates up 1
inch/hour and accumulations 1-3 inches. HREF neighborhood
probabilities indicate that additional totals of 2 inches or more
are likely within the Slight Risk area. These amounts on top of
wet antecedent conditions can be expected to cause additional
runoff concerns.
...New England...
As the previously noted low develops and approaches from the south,
a slow-moving front will provide the focus for deepening moisture
and soaking rains across much of coastal New England. Overall,
models have remained consistent in showing a long stripe of 1-3
inch amounts extending from eastern Connecticut to DownEast Maine.
Rainfall rates will be limited by a lack instability, likely
topping out near 0.25 inch/hour. However, given the recent rainfall
and saturated soils, there remain some runoff concerns, promoting
the continuation of a Marginal Risk.
Pereira
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1154 AM EDT Thu Mar 28 2024
Day 2
Valid 12Z Fri Mar 29 2024 - 12Z Sat Mar 30 2024
....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHERN CALIFORNIA...
A well-defined shortwave diving west of a closed low centered west
of Vancouver Island is expected to support the development of a
closed low further south that will drop south along the northern
California coast Friday into Saturday. Models continue to advertise
an anomalously deep system for this time of year, with 500 mb
heights dropping 1-3 standard deviations below normal across much
of California this period. Deep southwesterly flow ahead of the low
will support increasing IVTs, with the highest values dropping
south along the coast from Monterey Bay into the Transverse Ranges.
A Slight Risk was maintained over Santa Barbara and Ventura
counties, where the models continue to show a decent signal for
locally heavy amounts in the favored terrain. The consensus of the
deterministic guidance shows amounts of 1-3 inches in the region,
with locally heavier amounts possible by 12Z Saturday. There is
also some signal for locally heavy amounts further to the north
along the immediate coast, indicating the Slight Risk area may need
to be drawn further to north into central California. But for now,
maintained a broad Marginal Risk that covers much of central
California from the coast into the Sierra foothills.
....DownEast Maine...
Rain developing across the region on Day 1 is expected to carry
over into early Friday with an additional 1-2 inches of rain
expected before precipitation changes over snow and diminishes
behind of the departing low. As on Day 1, a lack of instability
will limit rainfall rates and the potential for flash flooding.
However, areal flooding will remain a concern given the saturated
soils.
Pereira
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1154 AM EDT Thu Mar 28 2024
Day 3
Valid 12Z Sat Mar 30 2024 - 12Z Sun Mar 31 2024
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHERN CALIFORNIA..
As an anomalously deep low continues to drop south, excessive
rainfall concerns developing on Day 2 are expected to continue and
expand further south across portions of southern California this
period. Increasing IVTs associated with a well-defined frontal
boundary will push across southern California on Saturday, with
PWs reaching 0.75-1 inch (2-3 standard deviations above normal). A
Slight Risk remains in place from the Transverse into the
Peninsular Ranges, where areal average amounts of 1-3 inches are
expected.
Moisture spreading east of the mountains will support widespread
precipitation, with locally heavy amounts possible into the lower
Colorado Basin, where a Marginal Risk was maintained for portions
of southern Nevada and western Arizona.
Pereira
NWS Weather Prediction Center College Park MD
259 AM EDT Thu Mar 28 2024
A potent storm system will move west to east next week and lead to
widespread precipitation across much of the country. On Sunday, a
weak atmospheric river should be pushing into Arizona. A Marginal
Risk is in place in the Excessive Rainfall Outlook for much of
Arizona on Sunday where heavy rainfall may occur, but from the
Mogollon Rim northward across the Intermountain West to Rockies,
snow is the likely precipitation type in higher elevations.
Moderate to heavy snow totals are possible. Additionally, though
the atmospheric river will have passed beyond southern California
by Sunday, convective rainfall could occur there as steeper lapse
rates come in with the upper low overhead. These showers may have
some higher rain rates that could cause some isolated flooding
concerns especially after a wet couple of days, so a Marginal Risk
is delineated in southern California too. A drying trend is
expected in the West Monday-Tuesday, except for the Pacific
Northwest that will see increasing support for precipitation by
Tuesday and beyond.
The upper low will continue shifting inland through early next
week, and with consolidating surface low pressure in the central
Plains, a period of gusty winds is possible across much of New
Mexico and southwest Texas. Farther east, moisture likely from the
Pacific and Gulf will combine and produce rain and thunderstorms
especially near frontal boundaries. The Ohio Valley will be one
area of focus for potentially heavy rainfall. Some rain is likely
there on Sunday but amounts are forecast to increase by Monday. A
Marginal Risk is in place from the Middle Mississippi Valley into
the Ohio Valley on Monday as a starting point for the Day 5 ERO,
with certainly some potential for future upgrades. Moisture and
instability are anomalously high for this time of year, and showers
and storms could train along the west to east oriented warm front
nearby. By Tuesday the cold front and low should continue to push
east and the heaviest rainfall at that point is forecast to focus
in the Tennessee Valley into the Appalachians.
On the northern side of the storm system, snow and freezing rain
are potential threats from the north-central Plains on Sunday,
stretching into the Upper Midwest and Great Lakes region Monday and
higher elevations of the Northeast by Tuesday-Wednesday. However,
there is still considerable uncertainty in the placement and
amounts of snow and ice, so continue to monitor forecasts. The
Interior Northeast may see the heaviest snow amounts overall
because of the duration of the potential snow event there compared
to the north-central U.S./Midwest/Great Lakes.
Chilly temperatures linger across the north-central U.S. through
Monday, but across the southern half of the Plains and Mississippi
Valley into the Tennessee Valley and Southeast/southern Mid-
Atlantic, notable warmth is expected into Sunday as upper ridging
builds. Temperatures of 10-20 degrees above average will become
widespread, with highs well into the 70s reaching Kansas to
Virginia while highs climb into the 90s to even 100F in southern
Texas. A cold front is forecast to drop temperatures in the south-
central U.S. by Tuesday, focusing this warmth in the Southeast
before the front pushes through there too by midweek. Meanwhile in
the Southwest, cooler than average temperatures particularly in
terms of highs are likely underneath the upper low. The Pacific
Northwest could see above average temperatures for a period early
next week though.
Tate
NWS Weather Prediction Center College Park MD
259 AM EDT Thu Mar 28 2024
A potent storm system will move west to east next week and lead to
widespread precipitation across much of the country. On Sunday, a
weak atmospheric river should be pushing into Arizona. A Marginal
Risk is in place in the Excessive Rainfall Outlook for much of
Arizona on Sunday where heavy rainfall may occur, but from the
Mogollon Rim northward across the Intermountain West to Rockies,
snow is the likely precipitation type in higher elevations.
Moderate to heavy snow totals are possible. Additionally, though
the atmospheric river will have passed beyond southern California
by Sunday, convective rainfall could occur there as steeper lapse
rates come in with the upper low overhead. These showers may have
some higher rain rates that could cause some isolated flooding
concerns especially after a wet couple of days, so a Marginal Risk
is delineated in southern California too. A drying trend is
expected in the West Monday-Tuesday, except for the Pacific
Northwest that will see increasing support for precipitation by
Tuesday and beyond.
The upper low will continue shifting inland through early next
week, and with consolidating surface low pressure in the central
Plains, a period of gusty winds is possible across much of New
Mexico and southwest Texas. Farther east, moisture likely from the
Pacific and Gulf will combine and produce rain and thunderstorms
especially near frontal boundaries. The Ohio Valley will be one
area of focus for potentially heavy rainfall. Some rain is likely
there on Sunday but amounts are forecast to increase by Monday. A
Marginal Risk is in place from the Middle Mississippi Valley into
the Ohio Valley on Monday as a starting point for the Day 5 ERO,
with certainly some potential for future upgrades. Moisture and
instability are anomalously high for this time of year, and showers
and storms could train along the west to east oriented warm front
nearby. By Tuesday the cold front and low should continue to push
east and the heaviest rainfall at that point is forecast to focus
in the Tennessee Valley into the Appalachians.
On the northern side of the storm system, snow and freezing rain
are potential threats from the north-central Plains on Sunday,
stretching into the Upper Midwest and Great Lakes region Monday and
higher elevations of the Northeast by Tuesday-Wednesday. However,
there is still considerable uncertainty in the placement and
amounts of snow and ice, so continue to monitor forecasts. The
Interior Northeast may see the heaviest snow amounts overall
because of the duration of the potential snow event there compared
to the north-central U.S./Midwest/Great Lakes.
Chilly temperatures linger across the north-central U.S. through
Monday, but across the southern half of the Plains and Mississippi
Valley into the Tennessee Valley and Southeast/southern Mid-
Atlantic, notable warmth is expected into Sunday as upper ridging
builds. Temperatures of 10-20 degrees above average will become
widespread, with highs well into the 70s reaching Kansas to
Virginia while highs climb into the 90s to even 100F in southern
Texas. A cold front is forecast to drop temperatures in the south-
central U.S. by Tuesday, focusing this warmth in the Southeast
before the front pushes through there too by midweek. Meanwhile in
the Southwest, cooler than average temperatures particularly in
terms of highs are likely underneath the upper low. The Pacific
Northwest could see above average temperatures for a period early
next week though.
Tate
» Interactive Winter Weather Map (Day 4-7)
» Winter Storm Severity Index
+ Forecast Discussion (Day 1-3)
Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
219 PM EDT Thu Mar 28 2024
Valid 00Z Fri Mar 29 2024 - 00Z Mon Apr 01 2024
...The West...
Days 1-3...
An increasingly active period of winter weather is likely across
the West into the weekend as an impressive closed low digs along
the CA coast, forcing a broad trough to encompass the West with
waves of energy and moisture shifting onshore.
The period begins with a weakening closed low west of the WA coast
shedding vorticity lobes to the east and forcing increasing height
falls into the Pacific Northwest as the trough amplifies. At the
same time, a potent shortwave rotating around this closed low will
dive southeast and interact with the lead closed low, causing it to
shear and weaken, while the secondary impulse becomes the primary
closed low off the CA coast by Saturday morning. The evolution from
there becomes quite complex as this closed low continues to dive
along the CA coast into Sunday, while shearing potent shortwaves
downstream into the impressively divergent flow over the Great
Basin, leading to a positively tilted by amplified longwave trough
over the West by the end of the forecast period. The resultant
subtropical jet streak pivoting downstream of this trough axis will
additionally enhance ascent, and by the weekend there is likely to
be pronounced but broad ascent across much of the region.
At the same time, moisture will steadily increase into the area as
onshore flow becomes increasingly backed leading to deeper moist
advection on SW /warm/ flow, with IVT increasing to above 250
kg/ms leading to PW anomalies reaching above +2 sigma, highest
across southern CA and the Great Basin late D2 into D3. The
expansive synoptic ascent noted above will lead to waves of low
pressure moving eastward, including a strong low which may move
into southern CA D3. The accompanying fronts will drive varying
snow levels as well, although NBM 75th percentiles hover around
5000 ft, and the result of this ascent into the higher moisture
content within varying snow levels will result in widespread heavy
snow across the West.
For D1, WPC probabilities above 70% for 6+ inches extend from the
Olympics into the WA/OR Cascades, east to the NW WY ranges and the
Uintas, and then down into northern CA and the northern Sierra. By
D2 the forcing and moisture shift to become more focused across CA
and into the Central Rockies, with WPC probabilities for more than
6 inches reaching 70% or more focused in the Sierra and
Shasta/Trinity/Siskiyou region. Heavy snow will continue across
the Sierra on D3, but will become more expansive as well, with WPC
probabilities above 50% for 6+ inches reaching the Transverse and
Peninsular ranges, as well as surging across the terrain of NV and
lifting into the Wasatch and Uintas as well. Although most of the
snow will be terrain focused, the setup may support some enhanced
banding and heavier snow rates along the 700mb WAA/fgen in NV/UT
which could produce light snow into much lower elevations as well.
Even if that occurs, the heaviest accumulations should remain in
the Sierra and other high terrain of CA where 3-day snowfall of 2-3
feet is likely.
...New England...
Day 2...
Southern stream impulse lifting along the Atlantic coast will
phase with northern stream energy near the Mid-Atlantic states,
leaving a negatively tilted and eventually closed-off mid-level
low moving into the Canadian Maritimes by Saturday morning. This
mid- level evolution combined with modestly coupled upper jet
streaks and along a surface baroclinic gradient will drive rapidly
intensifying cyclogenesis, and an impressive surface low is likely
to be positioned well east of Maine by Friday night. The guidance
has trended a bit east with this feature, and while this keeps the
highest moisture farther offshore, it also allows for colder air to
filter more rapidly into northern New England. Additionally, a
potent deformation axis strengthening on the west side of this low
will help enhance ascent, and combined with the somewhat colder
column to produce a swath of moderate to heavy snow from far
northern NH into downeast ME. The heaviest accumulations should
remain in the higher terrain as the column is still marginal
otherwise until dynamic cooling can overlap with the slowly
filtering CAA, but WPC probabilities are as high as 50% for far
northern NH and northern ME, especially at higher elevations.
...Northern Plains and Upper Midwest...
Day 2....
A lobe of vorticity shedding from the closed low west of the
Pacific Northwest will surge eastward across the Northern Rockies
and then begin to amplify over the Northern High Plains Friday
morning. This feature will maintain amplitude as it advects
progressively to the east, reaching the Great Lakes Saturday
morning, and will interact with modest upper diffluence along the
LFQ of a jet streak to the south, to produce a weak wave of low
pressure along the surface front. While this wave will be weak and
progressive, the accompanying 850-700mb WAA will surge northward
and lift isentropically with mixing ratios of 3-4 g/kg. This will
expand an area of precipitation from the Dakotas into MN/WI/MI. The
column into which this ascent is occurring appears more than cold
enough for snow, but the DGZ id elevated and only partially
saturated, so expect SLRs will be somewhat compromised as the best
moisture and lift is warmer than -12C. This should still result in
an axis of accumulating snow, but WPC probabilities for more than 4
inches of snow reach as high as 20-30% across northern ND and into
western MN.
Weiss
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NWS Weather Prediction Center College Park MD
257 PM EDT Thu Mar 28 2024
Valid 12Z Sun Mar 31 2024 - 12Z Thu Apr 04 2024
...A low pressure/frontal system will spread potentially heavy
rain and mountain/northern tier snow to much of the country next
week...
...Overview...
Upper troughing with one or more embedded lows will move across
California and the Four Corners states early next week. This
feature and its surface low pressure system will direct moisture
into California and the Southwest/Great Basin into the Rockies on
Sunday and produce heavy rain and higher elevation snow. These
upper/surface features will interact with northern stream troughing
in the north-central to northeastern U.S. to consolidate a surface
low that should move from the central Plains to the Northeast
during the workweek. Expansive precipitation coverage is likely
with this system, with snow and freezing rain possible on its north
side, and heavy rain in the warm sector as moisture pools along
the surface low's fronts. Well behind this system, an upper trough
and leading cold front pushing into the Northwest should spread
precipitation southeastward across the region by next Wednesday-
Thursday.
...Guidance/Predictability Assessment...
Latest guidance agrees in principle on most aspects of the large
scale pattern evolution and dominant surface systems, but with some
typical detail uncertainties that are still to be resolved.
For the initial western system ultimately affecting the
central/eastern U.S., the first issue to arise involves the latest
GFS runs depicting a closed upper system tracking northeastward
across the Plains early next week in contrast to most other
guidance showing a more open depiction across this region. The
GEFS mean is more open but both solutions lead to a farther
west/northwest track for low pressure and extent of heaviest QPF.
00Z ECMWF-initialized machine learning models (MLs) show various
ideas for how upper dynamics may evolve during that time but still
are not very supportive of the GFS specifics.
The next question involves amplifying Canadian/northern tier U.S.
energy by around next Tuesday-Wednesday. The best clustering of
dynamical models and MLs suggest that this northern stream energy
should yield a fairly deep upper low over the central-eastern Great
Lakes by early Wednesday. The 00Z CMCens mean was a fast extreme.
On the other hand, the new 12Z UKMET/CMC/ECMWF all stray to the
southwest of consensus for the upper low at that time. Time will
tell if this is an emerging trend. The majority scenario would have
the upper low and deepening surface low pressure reach New England
or vicinity by next Thursday, with slowly improved clustering
yielding a deeper trend in a blended forecast at the surface and
aloft. Given some of the trends by Wednesday, confidence thereafter
declines especially with the surface track becoming quite sensitive
to upper low specifics.
Meanwhile there is decent agreement for the overall upper trough
forecast to move into the Northwest by midweek or so. Some GFS runs
have leaned a bit on the deep/sharp side of the spread (but with
some support from the MLs), while the 00Z ECMWF showed two discrete
shortwaves--each faster than the single trough depicted in the
GFS/CMC, ensemble means, and MLs.
Finally, the latest dyanmical models and means are strongly
support the idea of lingering Southwest U.S. energy settling into
northwestern Mexico as a trough/upper low later in the period.
Interestingly, most 00Z MLs suggest this energy will eject out
much more quickly.
Guidance comparisons among 00Z/06Z guidance favored updating the
forecast with an operational model composite, with sufficiently
modest GFS weight not to have undue influence on the forecast over
the Midwest early next week. The blend transitioned to a half
model/half ensemble mean mix by day 7 Thursday, reflecting the
large scale guidance agreement but decreasing confidence in
details.
...Weather/Hazards Highlights...
A potent storm system will move west to east next week and lead to
widespread precipitation across much of the country. On Sunday, a
weak atmospheric river should be pushing into Arizona. A Marginal
Risk remains in place in the Day 4 Excessive Rainfall Outlook over
portions of Arizona on Sunday where heavy rainfall may occur.
Meanwhile snow is the likely precipitation type in higher
elevations from the Mogollon Rim northward across the Intermountain
West to the Rockies, with moderate to heavy totals possible.
Additionally, though the atmospheric river will have passed beyond
southern California by Sunday, convective rainfall could occur
there as steeper lapse rates come in with the upper low overhead.
These showers may have some higher rain rates that could cause some
isolated flooding concerns especially after a wet couple of days,
so the Day 4 ERO depicts a Marginal Risk along/near southern
coastal California too. Expect a drying trend over much of the West
Monday-Tuesday. A trailing upper trough/cold front moving into the
Pacific Northwest/northern Rockies should spread rain and mountain
snow across the region late Tuesday onward.
The initial Southwest upper low/trough will continue shifting
inland through early next week, and with consolidating surface low
pressure in the central Plains, a period of gusty winds is possible
across much of New Mexico and southwest Texas. Farther east,
moisture from the Pacific and Gulf will likely combine and produce
rain and thunderstorms especially near frontal boundaries. The
Ohio Valley will be one area of focus for potentially heavy
rainfall. Some rain is likely there on Sunday but amounts are
forecast to increase by Monday. A Marginal Risk remains in place
from the Middle Mississippi Valley into the Ohio Valley on Monday
as a starting point for the Day 5 ERO, with some potential for
future position adjustements and upgrades. Moisture and
instability are anomalously high for this time of year, and showers
and storms could train along the west to east oriented warm front
nearby. By Tuesday the cold front and low should continue to push
east and the heaviest rainfall at that point may focus across the
Tennessee Valley into the Appalachians. Also the Storm Prediction
Center is monitoring severe potential in the warm sector from the
Plains to just west of the Appalachians early next week.
On the northern side of the storm system, snow and freezing rain
are potential threats from the north-central Plains on Sunday,
stretching into the Upper Midwest and Great Lakes region Monday and
higher elevations of the Northeast by Tuesday-Wednesday. However,
there is still considerable uncertainty in the placement and
amounts of snow and ice, so continue to monitor forecasts. The
Interior Northeast may see the heaviest snow amounts overall
because of the duration of the potential snow event there compared
to the north-central U.S./Midwest/Great Lakes.
Through Monday, a strong front across middle latitudes east of the
Rockies will separate chilly temperatures across the north-central
U.S. (highs at least 10-15F below normal) from very warm readings
across the southern half of the Plains and Mississippi Valley into
the Tennessee Valley and Southeast/southern Mid-Atlantic with
upper ridging helping to enhance the warmth. Warm sector
temperatures of 10-20F above average will become widespread, with
highs well into the 70s reaching Kansas to Virginia while highs
climb into the 90s to even 100F in southern Texas. Developing low
pressure will then push a trailing cold front eastward, dropping
temperatures in the south-central U.S. by Tuesday and focusing the
warmth in the Southeast before the front pushes through there too
by midweek. Meanwhile in the Southwest, cooler than average
temperatures particularly in terms of highs are likely underneath
the upper low early next week before a moderating trend. The
Pacific Northwest could see a brief period of above average
temperatures early next week.
Rausch/Tate
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:
https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw
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