Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 PM EDT Mon Mar 24 2025

Valid 12Z Thu Mar 27 2025 - 12Z Mon Mar 31 2025

19Z Update: The 12Z model guidance suite maintains good synoptic
scale agreement across the Continental U.S. for the end of the work
week. For the storm system developing across the Plains and Upper
Midwest this weekend, the UKMET is a bit more to the northwest of
the model consensus with the front placement, but not a major
outlier. More substantial diffences become apparent with the next
Pacific storm system, with the GFS taking the main low center well
to the north of the CMC and GFS, and lingering model spread in the
wake of that system. For the East Coast, the GFS is faster with the
front exiting the coast Monday night.

Taking these factors into account, Thursday and Friday incorporated
a general deterministic model blend, and then the ensemble means
were gradually increased to about 40% by early next week. The
previous forecast discussion is appended below for reference.
/Hamrick
-------------------

...Overview...

Most guidance shows a reloading mean trough over the eastern
Pacific with a strong system affecting the Pacific Northwest
Thursday into Friday with potential for another meaningful system
to affect the West Coast by Sunday-Monday. The downstream pattern
looks moderately progressive, with a very warm Rockies/Plains ridge
eventually moving off the East Coast while trailing shortwave
energy supports low pressure that should track northeastward from
the Plains during the weekend into early next week. The eastern
Pacific systems will bring areas of enhanced precipitation to the
West Coast while the system affecting the central/eastern U.S. by
Saturday-Monday should spread a broad area of moisture east of the
Rockies with some wintry weather possible over far northern
latitudes. A southern stream shortwave crossing northern Mexico and
Texas late this week may also produce some heavy rainfall along
and inland from the western half of the Gulf Coast.

...Guidance/Predictability Assessment...

Latest guidance agrees decently with the larger scale aspects over
the overall pattern but there is still plenty of uncertainty for
details of shortwave energy moving into the West late this week and
continuing inland thereafter, affecting the forecast for low
pressure that should ultimately track northeastward from the
Plains. Trends over the past couple days have been leading toward
an intermediate solution for the leading energy reaching the West
while significant differences develop for the relative emphasis of
leading energy versus trailing energy arriving from the Pacific. At
least there is a somewhat coherent clustering of GFS/ECMWF runs
and most ensemble means as the overall shortwave trough reaches the
eastern half of the country, with surface low pressure near the
eastern Great Lakes as of early next Monday. CMC runs had been too
eager to close off an upper low but the new 00Z run seems to be
tempering that tendency. Machine learning (ML) model spread is
disconcerting though, with a couple suggesting potential for a
faster leading wave and another one hanging back to the southwest,
while another subset is closer to the model/ensemble majority. Off
the West Coast, there is decent clustering for the strong system
near the Pacific Northwest late this week though the new 00Z UKMET
looks somewhat disjointed. There is still a lot of spread for
specifics of the Sunday-Monday system but with the average of
guidance trending somewhat stronger. ML models are still not
developing this system too strongly though.

Latest guidance comparisons based on 18Z/12Z guidance led to
starting Day 3 Thursday with an operational model composite. The
CMC was removed thereafter in favor of the CMCens mean, while the
blend introduced some 18Z GEFS/12Z ECens after early Saturday. Day
7 Monday featured an even weight of models (18Z GFS/12Z ECMWF) and
the means.

...Weather/Hazards Highlights...

Guidance continues to show a late-week threat of locally heavy
rainfall over parts of Texas and then extending eastward, as low
level Gulf moisture and a warm front interact with an upper trough
progressing across northern Mexico and Texas. There is still
considerable spread for details, tempering confidence. The Day
4/Thursday Excessive Rainfall Outlook stays close to continuity in
depicting a Marginal Risk area over central-southern Texas.
Initially dry ground conditions and guidance spread continue to
preclude an embedded Slight Risk area, though will continue to
monitor trends for improved clustering on the heavier side of the
envelope for any potential upgrade. As this activity likely drifts
eastward, the Day 5/Friday ERO shows a Marginal Risk area along and
somewhat inland from a majority of the Texas and Louisiana coast.
This reflects the best overlap of guidance and is where heavier
rainfall should be more likely based on instability. The Day 4
period maintains a couple regions of interest with no risk areas
for now but require continued monitoring. Dynamical and machine
learning guidance is very mixed regarding potential warm frontal
rainfall over the Midwest. Meanwhile there has been a fair amount
of spread and variability for rainfall along the Pacific Northwest
coast. The best moisture reaches inland by Thursday but instability
under the upper trough could lead to some enhanced rain rates.

In addition to supporting Pacific Northwest precipitation, the
strong storm offshore on Thursday may produce some strong winds
near coastal areas. As the system's front and shortwave dynamics
continue eastward, moderate amounts of rain and high elevation snow
will progress across the northern half or so of the West late this
week. Expect Low pressure developing over the Plains and tracking
northeastward to spread an increasingly broad shield of
precipitation across the central and eastern U.S. from the end of
this week into next Monday. Some wintry weather will be possible
over far northern latitudes but otherwise most precipitation should
be in the form of rain, with some potentially on the heavy side.
How much snow falls over the northern Plains during the weekend
will depend on how strongly the system develops, with confidence in
specifics remaining in the lower half of the spectrum. Another
potentially vigorous eastern Pacific system may bring areas of
enhanced precipitation to the West by Sunday-Monday.

The strong upper ridge reaching the Rockies/Plains by Thursday
will bring very warm temperatures to the region, with some areas
over the Plains and eastern Rockies/Midwest seeing up to plus
20-30F anomalies for highs and/or morning lows during Thursday
and/or Friday. Some daily records are possible over the High
Plains. System progression will push a moderated form of this
warmth farther eastward by the weekend, with plus 10-20F anomalies
for highs. However a front settling into the Northeast/Mid-Atlantic
may define a sharp gradient between the warm air and cooler
readings just to the north. Behind the front anchored by the
developing Plains low, near to slightly below normal highs will
progress from the West through the central U.S., followed by a
rebound over and near the Rockies by next Monday.

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