Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
245 PM EST Mon Feb 24 2020

Valid 00Z Tue Feb 25 2020 - 00Z Thu Feb 27 2020

...A developing storm will bring heavy snow potential across portions of
the Northern Plains and portions of the Mid West into the Great Lakes...

...Strengthening winds from the Southern High Plains into portions of the
Southwest and southern California will increase the wild fire risk...

...Much colder temperatures to spread southeast from the Rockies into the
Plains and Mississippi Valley Tuesday & Wednesday...


The mid to upper level pattern across the mid section of the nation will
undergo amplification over the next few days, setting the stage for a very
active weather pattern across large sections of the nation. Accumulating
snows will develop initially over portions of the Northern Plains Monday
night into Tuesday and farther east later Tuesday, continuing into
Wednesday, from the Mid West into the Great Lakes. This will support a
highly impactful storm with snow totals of 4-8"+ across portions of the
Northern Plains and a heavier stripe of 6-12"+ snows from far northeast
Missouri, far southeast Iowa, across northern Illinois, including the
Chicago Metro area, into far northwest Indiana and the southern portions
of the Lower Peninsula of Michigan, including the Detroit metro area.
Travel will be significantly affected in these heavy snow areas,
especially in the more urbanized areas from the Mid West into the Great
Lakes where strengthening winds Tuesday into Wednesday will produce
considerable blowing and drifting of snow along with greatly reduced
visibilities.

On the southeastern peripheries of this storm system, a large region of
rain and thunderstorms are expected to push eastward Monday evening into
early Tuesday across portions of the South into the Southeast. This will
result in heavy precipitation potential and an isolated flooding threat,
especially across portions of south central Georgia where ongoing moderate
river flooding is already occurring. The good news with this heavy rains
event is that it will be primarily to the east of portions of Mississippi
and Alabama that have experienced very heavy rains and flooding recently.

In the wake of the above mentioned developing snow storm from the Northern
Plains into the Great Lakes, much colder air will be pushing southeastward
from the Rockies and across the Plains and Mississippi Valley Tuesday and
Wednesday. High temperatures Tuesday will be 15 to 20 degrees below
average through the Central to Southern Rockies, eastward into the High
Plains and 15 to 20 degrees below average on Wednesday across much of the
Plains and Lower to Middle Mississippi Valley.

Above to much above average temperatures expected across much of the West
coast and Great Basin Tuesday and Wednesday with high temperatures
expected to be 15-20 degrees above average. Along with the warm
temperatures, increasing winds and low relative humidities will increase
the fire weather threat across portions of southern California and western
Arizona Tuesday into Wednesday.

The fire weather threat will also increase across portions of the Southern
High Plains from eastern to southern New Mexico into far west and
Southwest Texas from Monday afternoon through Tuesday. Winds across these
areas are expected to increase with the passage of a cold front this
evening and remain strong through the day on Tuesday. This combined with
lowering relative humidifies and expected dry weather will increase the
wild fire threat across these areas.

Oravec

Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
134 AM EST Tue Feb 25 2020

Valid 12Z Fri Feb 28 2020 - 12Z Tue Mar 03 2020

...Overview...

Upper pattern on Friday will feature a western ridge and eastern
trough that will flip as the longwave pattern progresses
downstream. Building ridging to the north/northeast of Hawai'i and
south of the Gulf of Alaska late this week favors the development
of a sharp/digging trough through California Sun/Mon that may
close off over the deserts. Northern stream will continue across
the northern tier or southern Canada, trending northward in time
east of 100W as subtropical ridging again builds through the
western Caribbean.

...Guidance/Predictability Assessment...

The 12Z/18Z models/ensembles generally showed good agreement on
the longwave evolution through the period. The GFS and UKMET were
displaced a bit with a couple features that made their forecasts
less desirable. For the former, both the 12Z/18Z runs were quite
aggressive with a sfc low Sat/Sun offshore OR/CA that was not
supported by the ensembles, resulting in a slower speed of the
longwave upper trough by Mon compared to the 12Z ECMWF ensemble
mean and NAEFS mean. For the latter, it has had trouble resolving
incoming Pacific systems (too strong and/or displaced) in recent
days compared to the ensembles but was considered acceptable
elsewhere. The 12Z Canadian may be too strong with a sfc low off
SE New England late Sat into early Sun as well. Overall the 12Z
ECMWF offered the most reasonable solution through the period.
Trended toward the ensemble consensus by next Mon/Tue with the
developing system over the Southern Plains as the upper trough
lifts out of the Southwest.


...Weather/Hazard Highlights...

Lake-effect snow will continue late this week into the start of
the weekend with broad cyclonic flow around the departed system.
Some record cold max temperatures may be approached in the East,
even into south Florida where some areas may not reach 70F.

By contrast, the West will see a couple more mild/warm days
Fri-Sat with some potential record highs in California on Friday.
Pacific system will bring an increasing coverage of light to
modest terrain-enhanced rain/snow as the upper trough digs in.
Temperatures will trend much cooler by Sun/Mon but only about 5
degrees below average overall. Milder air will get pushed to the
east of the Rockies next week, with readings about 5-10 degrees
above average (moreso overnight) in advance of the exiting
Southwest system.


Fracasso


Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php


WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:

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/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
321 AM EST Mon Feb 24 2020

Valid 00Z Tue Feb 25 2020 - 00Z Tue Mar 03 2020

...Heavy rain possible for the Big Island this coming weekend into
next week...


A surface front will stall/dissipate near Kauai on Tuesday.
Generally light showers are expected as precipitable water values
fluctuate around an inch and upper heights rise. Troughing to the
east of the region will drift northeastward but another piece will
dig southward just to the east of the Big Island late Fri into
Sat. The models/ensembles generally stall this upper low near the
Big Island into next week thought the 00Z ECMWF takes it westward
past 160W by late next Mon. Prefer to stay near the ensemble
consensus which was just west of the 00Z GFS/Canadian but east of
the 00Z ECMWF. This position would help to draw in higher
precipitable water values to at least the Big Island next weekend
and then possibly through the rest of the islands into next week.
This could lead to an increase in showers and locally heavy
rainfall over at least the Big Island. The modestly tight pressure
gradient (1035mb high near 37N/157W 12Z Fri) will support elevated
trades for much of the week with mainly light/modest showers until
the weekend.


Fracasso

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
732 PM EST Mon Feb 24 2020

Day 1
Valid 01Z Tue Feb 25 2020 - 12Z Tue Feb 25 2020

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST...

...Southeast...
A steady increase in surface/low level confluence near/along the
Emerald coast of the FL panhandle and some modest instability up
to around 500 J/kg has seen a steady uptick in shallow convective
activity across the Panhandle into Southeast AL/Southwest GA, yet
the instability rapidly decreases along/just north of a draped
stationary from south of Troy, AL to just north of Albany, GA.
Hi-Res CAMs, particularly recent runs of the HRRR suggest
continued increased activity across this region with slow eastward
progress through the early overnight hours, with some potential of
2-3" totals particularly if best convergence remains stationary
over the next 3-6hrs, providing the greatest risk for rates up to
1.5"/hr. HREF probabilities are around 70% to produce over
1"/3hrs but rapidly decrease to 20-30% of greater than 2"/3hrs,
generally south of the stationary front. This frontal zone is
also the general demarcation of drier (south) and above normal
precipitation and more susceptible ground conditions over the last
7 to 14 days. So with solidly drier conditions suggesting FFG is
reasonable, and hourly FFG values of 2.5-3" and three-hourly FFG
values over 3" it is becoming increasingly less likely that they
would be exceeded.

North of the frontal zone, where National Water Model 40cm
saturation ratios are much higher and AHPS precipitation anomalies
are greater than 200% of normal, the lack of building instability
sufficient for extreme rates is also reduced though .5-1.5" totals
may occur, the duration is also likely to limit any flooding
conditions to highly isolated. As such, have restricted the
Marginal Risk of Excessive Rainfall even further to only the areas
of Southeast AL/Southwest GA and extreme north-central Florida
Panhandle where more than one Hi-Res CAM member even suggests the
potential for 2-3" totals through 12z tomorrow morning.

Gallina

Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
257 PM EST Mon Feb 24 2020

Day 2
Valid 12Z Tue Feb 25 2020 - 12Z Wed Feb 26 2020

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.


Pagano


Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
259 PM EST Mon Feb 24 2020

Day 3
Valid 12Z Wed Feb 26 2020 - 12Z Thu Feb 27 2020

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Pagano



Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
417 PM EST Mon Feb 24 2020

Valid 00Z Tue Feb 25 2020 - 00Z Fri Feb 28 2020


...Northern High Plains to the Central Plains...
Day 1...
Models continue to show a well-defined northern stream shortwave
dropping southeast along the northern to the central Rockies and
High Plains. In addition to the favorable upper forcing, strong
low-to-mid level convergence along a developing low and lingering
inverted trough is expected to support light to moderate snows
across portions of the northern High Plains, from eastern Montana
and southwestern North Dakota to eastern Wyoming and western South
Dakota Monday evening into the overnight. Orographic enhancement
is expected to enhance totals across the Black Hills region, where
locally heavy amounts are most likely.

Farther to the south, models have trended upward -- indicating a
stronger signal for at least light to moderate precipitation
developing, with rain changing to snow, along a narrow axis of
strong low-mid-level forcing extending north-south across central
Nebraska early Tuesday and northwest-southeast across northeastern
Kansas by late morning and continuing into the afternoon.


...Mid Mississippi Valley to the Upper Great Lakes...
Days 1-2...

Shortwave trough dropping southeast into the central Plains
Tuesday morning, is forecast to pivot northeast across the mid
Mississippi valley toward the western Great Lakes late Tuesday
into early Wednesday, with a band of moderate to heavy snow
expected to develop in the low-to-mid level frontogenesis and
deformation zone. The daytime model runs continued the ongoing
trend toward a more southerly axis, with the 12Z GFS showing a
significant shift farther south. Latest model consensus now shows
the heaviest amounts centering from far northeastern Missouri to
southern Lower Michigan. Models are still showing the potential
for some lake enhanced, heavier amounts along the southeastern to
southern shores of Lake Michigan beginning Tuesday and continuing
into Wednesday.


Northeast...
Day 3...
As the upper trough crosses the Great Lakes, an upper jet maxima
is forecast to move along the spine of the Appalachians, with a
well-defined 300 mb divergence maxima crossing PA/NY into interior
New England Thursday morning. This will combine with low-mid
level warm advection to produce widespread precip across the
northern mid Atlantic to the northeast on Thursday. The
combination of synoptic lift and upslope flow into the NY
Adirondacks, the VT Green Mountains, and NH White Mountains to the
ranges of interior Maine will support the potential for several
inches of snow at these locations. Meanwhile, expect warm
advection will likely limit snowfall potential at lower
elevations, including the major cities.

For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Pereira

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
134 AM EST Tue Feb 25 2020

Valid 12Z Fri Feb 28 2020 - 12Z Tue Mar 03 2020

...Overview...

Upper pattern on Friday will feature a western ridge and eastern
trough that will flip as the longwave pattern progresses
downstream. Building ridging to the north/northeast of Hawai'i and
south of the Gulf of Alaska late this week favors the development
of a sharp/digging trough through California Sun/Mon that may
close off over the deserts. Northern stream will continue across
the northern tier or southern Canada, trending northward in time
east of 100W as subtropical ridging again builds through the
western Caribbean.

...Guidance/Predictability Assessment...

The 12Z/18Z models/ensembles generally showed good agreement on
the longwave evolution through the period. The GFS and UKMET were
displaced a bit with a couple features that made their forecasts
less desirable. For the former, both the 12Z/18Z runs were quite
aggressive with a sfc low Sat/Sun offshore OR/CA that was not
supported by the ensembles, resulting in a slower speed of the
longwave upper trough by Mon compared to the 12Z ECMWF ensemble
mean and NAEFS mean. For the latter, it has had trouble resolving
incoming Pacific systems (too strong and/or displaced) in recent
days compared to the ensembles but was considered acceptable
elsewhere. The 12Z Canadian may be too strong with a sfc low off
SE New England late Sat into early Sun as well. Overall the 12Z
ECMWF offered the most reasonable solution through the period.
Trended toward the ensemble consensus by next Mon/Tue with the
developing system over the Southern Plains as the upper trough
lifts out of the Southwest.


...Weather/Hazard Highlights...

Lake-effect snow will continue late this week into the start of
the weekend with broad cyclonic flow around the departed system.
Some record cold max temperatures may be approached in the East,
even into south Florida where some areas may not reach 70F.

By contrast, the West will see a couple more mild/warm days
Fri-Sat with some potential record highs in California on Friday.
Pacific system will bring an increasing coverage of light to
modest terrain-enhanced rain/snow as the upper trough digs in.
Temperatures will trend much cooler by Sun/Mon but only about 5
degrees below average overall. Milder air will get pushed to the
east of the Rockies next week, with readings about 5-10 degrees
above average (moreso overnight) in advance of the exiting
Southwest system.


Fracasso


Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php


WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:

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/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml