Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
330 AM EDT Thu Oct 03 2024

Valid 12Z Thu Oct 03 2024 - 12Z Sat Oct 05 2024

...Showers and thunderstorms return to the Gulf Coast from Thursday
evening into Saturday...

...Rain develops over the Pacific Northwest and scattered showers over
parts of the Midwest, Central/Southern Appalachians, and Northeast...

...There are Excessive Heat Warnings and Heat Advisories over parts of
Southern California and the Southwest...

On Thursday, tropical moisture will start to build over the
Central/Eastern Gulf Coast and Florida. Upper-level energy over the
Western Gulf Coast and Northern Gulf of Mexico will move into parts of the
Southeast and Central Gulf Coast, producing showers and thunderstorms over
parts of the Gulf Coast from Thursday evening into Saturday. In addition,
showers and thunderstorms will develop over parts of Florida through
Saturday. Furthermore, the moisture will also build over the
Central/Southern Appalachians, as upper-level energy moves over the area,
showers and thunderstorms will develop from Thursday afternoon into Friday
evening.

Meanwhile, a front extending from the Upper Great Lakes to parts of the
Central Plains will move eastward to just off the Northeast and
Mid-Atlantic Coast by Saturday. The boundary will produce rain with
embedded thunderstorms over parts of the Middle Mississippi Valley on
Friday morning into the early afternoon. As the front moves into the
Northeast and Mid-Atlantic, showers and thunderstorms will develop over
parts of the region late Friday evening into Saturday.

In addition, on Friday morning, a second front will move onshore over the
Pacific Northwest, moving to the Northern Plains by Saturday. The system
will produce rain over parts of the Pacific Northwest from Friday into
late Friday evening. Overnight Friday, wet snow will develop over the
highest elevations of the Cascades. The rain will expand into the Northern
Intermountain Region Friday evening into Saturday.

Moreover, the upper-level ridge over the Four Corners Region will create
high temperatures over Southern California and the Southwest, ranging from
the upper 90s to 110s. Low temperatures will be in the upper 80s to low
90s, providing little relief from the heat overnight. The temperatures
have prompted Excessive Heat Warnings and Heat Advisories over parts of
Southern California and the Southwest.

Record-breaking heat is expected across portions of the Southwest this
week. Moderate to major heat impacts are possible in areas near San
Francisco, Las Vegas, and Los Angeles. Extreme Heat Risk impacts are
forecast for parts of the Southwest. Remember, Heat is the Deadliest
Weather Phenomenon in the U.S.! People spending more time outdoors or in a
building without cooling are at an increased risk of heat-related illness.
Visit www.weather.gov/safety/heat and check local media and government
websites for information on cooling centers.


Ziegenfelder


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Thu Oct 3 2024

Valid 12Z Sun Oct 06 2024 - 12Z Thu Oct 10 2024

...Anomalous heat will persist across the Southwest into early next
week...

...Chances for heavy rainfall across the Florida Peninsula will
increase into next week...


...Overview...

Latest models and ensembles still show the upper pattern settling
into a slower-evolving pattern dominated by large scale features.
Expect an upper ridge covering the western-central U.S. to produce
a broad area of much above normal temperatures over that part of
the country while a trough settling over the East (anchored by an
upper low that may track over or near New England) will bring a
cooler trend. The leading edge of a Pacific trough will produce
gradual height falls over the Pacific Northwest and bring some
precipitation to the northern parts of the region. Ahead of the
dynamics that will ultimately establish the eastern upper trough, a
front crossing the Great Lakes and Northeast should produce some
organized rain. Farther south, expect the heaviest rainfall over
the lower 48 to be over parts of Florida, due to the combination of
abundant moisture plus a combination of one or more Gulf of Mexico
surface features and a front draped across the peninsula.

...Guidance/Predictability Assessment...

Guidance continues to show typical detail differences for the
evolution of the upper trough settling over the East and the
anchoring upper low. General trends of the GFS/ECMWF and their
means over the past couple days have been a little slower with the
upper low, offering some support for ideas from recent CMC runs
that have been on the western side of the spread. However by the
end of the period the full array of dynamical and machine learning
(ML) guidance would recommend a farther east position (over or east
of northern Maine) versus the CMC. The 12Z UKMET held the core of
the upper trough northwest of consensus by the end of its run but
the 00Z version compares better to consensus. An average of the
GFS/ECMWF and their means has good support from the average of ML
models by late in the period.

Some aspects of the forecast over and near the Gulf of Mexico
still have low predictability due to a combination of smaller-
scale features. One wave may track into the central/east-central
Gulf from the northwestern Caribbean while another feature may
evolve over the western Gulf, with the surface/QPF details also
potentially affected by multiple impulses aloft. Lately there has
been some improvement in the signal for these features to phase
early next week as they approach and interact, with this
potentially messy evolution involving fronts and moisture
gradients possibly yielding a more conventional wavy front that
sags just south of the Florida Peninsula by the end of the period.
Continue to monitor outlooks from the National Hurricane Center for
the latest information on features of interest over the Gulf.

A blend of most guidance looks good for the height falls reaching
the Pacific Northwest by the latter half of the period. The one
exception was the 12Z CMC which brought a stronger shortwave into
the region. The new 00Z CMC looks better in this regard.

Based on 12Z/18Z guidance, the early part of the forecast started
with an operational model composite. The forecast phased out the
last part of the UKMET mid-period and then the 12Z CMC, while
increasing 18Z GEFS/12Z ECens weight. This yielded a half GFS/ECMWF
and half GEFS/ECens mix by the end of the period next Thursday.

...Weather/Hazards Highlights...

The majority of the lower 48 should see dry weather for most or all
of the Sunday-Thursday period, with most precipitation focus
around the corners. By far the heaviest rainfall potential should
be over the Florida Peninsula, with slow-moving low pressure over
the Gulf of Mexico along with a wavy front draped over the state
and a broad area of anomalous moisture extending over/east of the
Gulf. There is still a fair amount of uncertainty for details
though. During Day 4 Sunday, most dynamical models/ensemble
probabilities keep the highest rain rates just offshore the western
peninsula but machine learning models show faster progression of
Gulf low pressure and leading enhanced rainfall. For now will
maintain no risk area in the Day 4 Excessive Rainfall Outlook until
a dynamical model trend toward the ML models becomes evident. On
Monday there is better consensus that enhanced moisture and
potentially heavy rainfall will extend farther eastward across at
least the southern half of Florida, meriting the introduction of a
Marginal Risk area for the Day 5 ERO. Southern Florida may continue
to see periods of significant rainfall for another day or so, with
the axis of highest totals sagging south with time along with the
focusing wavy front.

Elsewhere, the frontal system crossing the eastern Great Lakes and
Northeast Sunday-Monday may generate rainfall of varying
intensity. This region may then see showery conditions at times as
shortwave impulses flow around an upper low expected to track over
or near northern New England and the Canadian Maritimes. A mean
frontal zone with one or more embedded waves should reach near the
northern Pacific Northwest by early-mid week, producing some
periods of light to locally moderate rain and nonzero chances of
snow in the highest elevations.

The strong and persistent western-central U.S. upper ridge will
promote an extended period of well above normal temperatures over
that part of the country. Gradual eastward drift of the ridge axis
will shift the highest anomalies from the West on Sunday, with
some highs at least 10-15F above normal, more into the Plains by
Tuesday-Thursday when some northern locations could reach 20-25F
above normal. Expect numerous daily records for warm minimum and
maximum temperatures, especially over the Southwest through
Sunday-Monday. Height falls slowly pushing in over the West Coast
will support a trend toward near normal temperatures there by
Wednesday or Thursday. Moderately above normal temperatures over
most of the East as of Sunday should then decline to near or
somewhat below normal as upper troughing sets up near the East
Coast. This may lead to frost/freeze concerns across portions of
the Upper Great Lakes region and interior Northeast, with the
timing around the median to a bit late for the first frost/freeze
of the season.

Rausch


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
339 AM EDT Thu Oct 03 2024

Valid 00Z Fri Oct 04 2024 - 00Z Fri Oct 11 2024

Latest guidance is consistent in showing a period of lighter
trades Friday through the weekend as fronts weaken high pressure
to the north and upper troughing develops overhead. This may
allow for sea/land breezes to affect the distribution of rainfall
during Friday-Sunday. Trades should rebound to moderate speeds
Monday onward with a return of windward shower focus as high
pressure to the north strengthens. Meanwhile, the improved
clustering aloft seen 24 hours ago for the upper trough developing
over the area by the weekend has held up fairly well into today's
runs with only modest refinements. Now consensus shows a better
defined compact upper low settling over or barely north of the
main islands during at least Sunday-Monday. Most solutions show
the upper low ejecting northeastward thereafter but likely with a
lingering weak trough/shear axis over the area at least into
midweek. 00Z machine learning models show a similar evolution.
The destabilizing influence of the upper low will likely support
some heavier showers, especially during the weekend into early
next week.

Rausch

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1131 AM EDT Thu Oct 3 2024
Day 1
Valid 16Z Thu Oct 03 2024 - 12Z Fri Oct 04 2024

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

A continued depiction of locally heavy rainfall exists within this
morning CAMs around Southeastern LA into the coastal areas of
AL/MS. The threat within the latest hi-res is a bit less
ostentatious compared to even the previous forecast outputs
correlating to lower probabilities for heavier precip necessary to
attain a risk area. Still anticipating some localized totals of
2-4" across the Southeast Parishes with the areas of highest threat
for any flash flood concerns still residing within urban corridors
like New Orleans, Biloxi, and Mobile. Considering all those
locations are running <45% within the 3" precip probability, the
threat will remain non-zero, but still falling short of the MRGL
risk threshold necessary to implement a low-end risk. A secondary
area of note resides over the Tampa metro where locally enhanced
rainfall from sea breeze convection will drop a quick 2-4" with
locally as much as 5" within some CAMs output. Rainfall rates, both
hourly and intra-hour will be the defining point for flash flood
concerns over the area and current prospects are borderline for
flash flood concerns, but again non-zero in the grand scheme. The
nil ERO across the CONUS was maintained, but will still monitor the
two areas above for targeted upgrades pending radar evolution.
Mesoscale Precip Discussions might be more beneficial in this setup
considering the smaller footprint of flash flood potential.

Kleebauer

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1131 AM EDT Thu Oct 3 2024
Day 2
Valid 12Z Fri Oct 04 2024 - 12Z Sat Oct 05 2024

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

During this period there will be broad cyclonic over the Western
Gulf along with deep tropical air that advects into the flow. This
will result in convection that breaks out across the Gulf and
creeps inland into South Texas. A majority of the guidance
maintains the highest QPF offshore however there could be 0.75 to
1.5 inches that occurs in South Texas that should provide
beneficial moisture to the area rather than pose as an threat for
local flooding concerns.

Campbell

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1131 AM EDT Thu Oct 3 2024
Day 3
Valid 12Z Sat Oct 05 2024 - 12Z Sun Oct 06 2024

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

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Thu Oct 3 2024


The majority of the lower 48 should see dry weather for most or all
of the Sunday-Thursday period, with most precipitation focus
around the corners. By far the heaviest rainfall potential should
be over the Florida Peninsula, with slow-moving low pressure over
the Gulf of Mexico along with a wavy front draped over the state
and a broad area of anomalous moisture extending over/east of the
Gulf. There is still a fair amount of uncertainty for details
though. During Day 4 Sunday, most dynamical models/ensemble
probabilities keep the highest rain rates just offshore the western
peninsula but machine learning models show faster progression of
Gulf low pressure and leading enhanced rainfall. For now will
maintain no risk area in the Day 4 Excessive Rainfall Outlook until
a dynamical model trend toward the ML models becomes evident. On
Monday there is better consensus that enhanced moisture and
potentially heavy rainfall will extend farther eastward across at
least the southern half of Florida, meriting the introduction of a
Marginal Risk area for the Day 5 ERO. Southern Florida may continue
to see periods of significant rainfall for another day or so, with
the axis of highest totals sagging south with time along with the
focusing wavy front.

Elsewhere, the frontal system crossing the eastern Great Lakes and
Northeast Sunday-Monday may generate rainfall of varying
intensity. This region may then see showery conditions at times as
shortwave impulses flow around an upper low expected to track over
or near northern New England and the Canadian Maritimes. A mean
frontal zone with one or more embedded waves should reach near the
northern Pacific Northwest by early-mid week, producing some
periods of light to locally moderate rain and nonzero chances of
snow in the highest elevations.

The strong and persistent western-central U.S. upper ridge will
promote an extended period of well above normal temperatures over
that part of the country. Gradual eastward drift of the ridge axis
will shift the highest anomalies from the West on Sunday, with
some highs at least 10-15F above normal, more into the Plains by
Tuesday-Thursday when some northern locations could reach 20-25F
above normal. Expect numerous daily records for warm minimum and
maximum temperatures, especially over the Southwest through
Sunday-Monday. Height falls slowly pushing in over the West Coast
will support a trend toward near normal temperatures there by
Wednesday or Thursday. Moderately above normal temperatures over
most of the East as of Sunday should then decline to near or
somewhat below normal as upper troughing sets up near the East
Coast. This may lead to frost/freeze concerns across portions of
the Upper Great Lakes region and interior Northeast, with the
timing around the median to a bit late for the first frost/freeze
of the season.

Rausch

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Thu Oct 3 2024


The majority of the lower 48 should see dry weather for most or all
of the Sunday-Thursday period, with most precipitation focus
around the corners. By far the heaviest rainfall potential should
be over the Florida Peninsula, with slow-moving low pressure over
the Gulf of Mexico along with a wavy front draped over the state
and a broad area of anomalous moisture extending over/east of the
Gulf. There is still a fair amount of uncertainty for details
though. During Day 4 Sunday, most dynamical models/ensemble
probabilities keep the highest rain rates just offshore the western
peninsula but machine learning models show faster progression of
Gulf low pressure and leading enhanced rainfall. For now will
maintain no risk area in the Day 4 Excessive Rainfall Outlook until
a dynamical model trend toward the ML models becomes evident. On
Monday there is better consensus that enhanced moisture and
potentially heavy rainfall will extend farther eastward across at
least the southern half of Florida, meriting the introduction of a
Marginal Risk area for the Day 5 ERO. Southern Florida may continue
to see periods of significant rainfall for another day or so, with
the axis of highest totals sagging south with time along with the
focusing wavy front.

Elsewhere, the frontal system crossing the eastern Great Lakes and
Northeast Sunday-Monday may generate rainfall of varying
intensity. This region may then see showery conditions at times as
shortwave impulses flow around an upper low expected to track over
or near northern New England and the Canadian Maritimes. A mean
frontal zone with one or more embedded waves should reach near the
northern Pacific Northwest by early-mid week, producing some
periods of light to locally moderate rain and nonzero chances of
snow in the highest elevations.

The strong and persistent western-central U.S. upper ridge will
promote an extended period of well above normal temperatures over
that part of the country. Gradual eastward drift of the ridge axis
will shift the highest anomalies from the West on Sunday, with
some highs at least 10-15F above normal, more into the Plains by
Tuesday-Thursday when some northern locations could reach 20-25F
above normal. Expect numerous daily records for warm minimum and
maximum temperatures, especially over the Southwest through
Sunday-Monday. Height falls slowly pushing in over the West Coast
will support a trend toward near normal temperatures there by
Wednesday or Thursday. Moderately above normal temperatures over
most of the East as of Sunday should then decline to near or
somewhat below normal as upper troughing sets up near the East
Coast. This may lead to frost/freeze concerns across portions of
the Upper Great Lakes region and interior Northeast, with the
timing around the median to a bit late for the first frost/freeze
of the season.

Rausch

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
158 AM EDT Thu Oct 3 2024

Valid 12Z Thu Oct 03 2024 - 12Z Sun Oct 06 2024

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Weiss

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Thu Oct 3 2024

Valid 12Z Sun Oct 06 2024 - 12Z Thu Oct 10 2024

...Anomalous heat will persist across the Southwest into early next
week...

...Chances for heavy rainfall across the Florida Peninsula will
increase into next week...


...Overview...

Latest models and ensembles still show the upper pattern settling
into a slower-evolving pattern dominated by large scale features.
Expect an upper ridge covering the western-central U.S. to produce
a broad area of much above normal temperatures over that part of
the country while a trough settling over the East (anchored by an
upper low that may track over or near New England) will bring a
cooler trend. The leading edge of a Pacific trough will produce
gradual height falls over the Pacific Northwest and bring some
precipitation to the northern parts of the region. Ahead of the
dynamics that will ultimately establish the eastern upper trough, a
front crossing the Great Lakes and Northeast should produce some
organized rain. Farther south, expect the heaviest rainfall over
the lower 48 to be over parts of Florida, due to the combination of
abundant moisture plus a combination of one or more Gulf of Mexico
surface features and a front draped across the peninsula.

...Guidance/Predictability Assessment...

Guidance continues to show typical detail differences for the
evolution of the upper trough settling over the East and the
anchoring upper low. General trends of the GFS/ECMWF and their
means over the past couple days have been a little slower with the
upper low, offering some support for ideas from recent CMC runs
that have been on the western side of the spread. However by the
end of the period the full array of dynamical and machine learning
(ML) guidance would recommend a farther east position (over or east
of northern Maine) versus the CMC. The 12Z UKMET held the core of
the upper trough northwest of consensus by the end of its run but
the 00Z version compares better to consensus. An average of the
GFS/ECMWF and their means has good support from the average of ML
models by late in the period.

Some aspects of the forecast over and near the Gulf of Mexico
still have low predictability due to a combination of smaller-
scale features. One wave may track into the central/east-central
Gulf from the northwestern Caribbean while another feature may
evolve over the western Gulf, with the surface/QPF details also
potentially affected by multiple impulses aloft. Lately there has
been some improvement in the signal for these features to phase
early next week as they approach and interact, with this
potentially messy evolution involving fronts and moisture
gradients possibly yielding a more conventional wavy front that
sags just south of the Florida Peninsula by the end of the period.
Continue to monitor outlooks from the National Hurricane Center for
the latest information on features of interest over the Gulf.

A blend of most guidance looks good for the height falls reaching
the Pacific Northwest by the latter half of the period. The one
exception was the 12Z CMC which brought a stronger shortwave into
the region. The new 00Z CMC looks better in this regard.

Based on 12Z/18Z guidance, the early part of the forecast started
with an operational model composite. The forecast phased out the
last part of the UKMET mid-period and then the 12Z CMC, while
increasing 18Z GEFS/12Z ECens weight. This yielded a half GFS/ECMWF
and half GEFS/ECens mix by the end of the period next Thursday.

...Weather/Hazards Highlights...

The majority of the lower 48 should see dry weather for most or all
of the Sunday-Thursday period, with most precipitation focus
around the corners. By far the heaviest rainfall potential should
be over the Florida Peninsula, with slow-moving low pressure over
the Gulf of Mexico along with a wavy front draped over the state
and a broad area of anomalous moisture extending over/east of the
Gulf. There is still a fair amount of uncertainty for details
though. During Day 4 Sunday, most dynamical models/ensemble
probabilities keep the highest rain rates just offshore the western
peninsula but machine learning models show faster progression of
Gulf low pressure and leading enhanced rainfall. For now will
maintain no risk area in the Day 4 Excessive Rainfall Outlook until
a dynamical model trend toward the ML models becomes evident. On
Monday there is better consensus that enhanced moisture and
potentially heavy rainfall will extend farther eastward across at
least the southern half of Florida, meriting the introduction of a
Marginal Risk area for the Day 5 ERO. Southern Florida may continue
to see periods of significant rainfall for another day or so, with
the axis of highest totals sagging south with time along with the
focusing wavy front.

Elsewhere, the frontal system crossing the eastern Great Lakes and
Northeast Sunday-Monday may generate rainfall of varying
intensity. This region may then see showery conditions at times as
shortwave impulses flow around an upper low expected to track over
or near northern New England and the Canadian Maritimes. A mean
frontal zone with one or more embedded waves should reach near the
northern Pacific Northwest by early-mid week, producing some
periods of light to locally moderate rain and nonzero chances of
snow in the highest elevations.

The strong and persistent western-central U.S. upper ridge will
promote an extended period of well above normal temperatures over
that part of the country. Gradual eastward drift of the ridge axis
will shift the highest anomalies from the West on Sunday, with
some highs at least 10-15F above normal, more into the Plains by
Tuesday-Thursday when some northern locations could reach 20-25F
above normal. Expect numerous daily records for warm minimum and
maximum temperatures, especially over the Southwest through
Sunday-Monday. Height falls slowly pushing in over the West Coast
will support a trend toward near normal temperatures there by
Wednesday or Thursday. Moderately above normal temperatures over
most of the East as of Sunday should then decline to near or
somewhat below normal as upper troughing sets up near the East
Coast. This may lead to frost/freeze concerns across portions of
the Upper Great Lakes region and interior Northeast, with the
timing around the median to a bit late for the first frost/freeze
of the season.

Rausch


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