Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
254 AM EDT Thu Mar 20 2025

Valid 12Z Sun Mar 23 2025 - 12Z Thu Mar 27 2025


...Overview and Guidance/Predictability Assessment...

Progressive upper flow into the weekend in two streams will
amplify into next week with the development of a warming/building
West Coast ridge and a cooling/deepening and unsettling east-
central U.S. trough.

Models and ensembles again seem well clustered with the weather
pattern evolution through the medium range period, with reasonably
good agreement on individual storm systems as well. Forecast
confidence remains above average overall with a guidance blend,
albeit with more uncertainty in details later period. However,
these seem well mitigated consistent with predictability by the
blend process and targeted manual adjustments. The WPC forecast was
mainly derived from a GFS/ECMWF/CMC/UKMET model composite Sunday
into Tuesday before switching to a blend of the better compatible
and consistent GEFS/ECMWF/Canadian ensemble means into longer time
frames. This forecast is overall mainly in line with the National
Blend of Models, machine learning and latest 00 UTC model guidance
while also offering good WPC product continuity.

...Weather/Hazards Highlights...

West Coast upper ridge riding shortwave troughs shift from the
northeast Pacific into BC Sunday with a potent moisture plume to
the south that pushes across western WA. A Marginal Risk for
excessive rain is maintained only into Day 4/Sunday for coastal
Washington as compounding effects of multiple preceding bouts of
precipitation may lead to local runoff issues. Amplified upper
trough development and deep system genesis early-mid next week
should prove slow to approach the West Coast, but should spread
orgainzed precipitation back into the Northwest in about a week.

The amplifying low over the northern Plains into the Great Lakes
Sunday will draw broad scale Gulf moisture up the MS Valley and
support a heavy rain and a severe weather threat for parts of Mid-
South and lower MS Valley into the TN Valley. The Day 4/Sunday ERO
Marginal Risk area is maintained for the Lower Mississippi and
Tennessee Valleys. Enhanced rains then spread as a wavy cold front
sweeps across the Southeast/Eastern Seaboard Monday into Tuesday. A
WPC Day 5/Monday ERO Marginal Risk area was introduced to cover
lingering and training cell potential over the eastern Gulf Coast.

Meanwhile on the northern periphery of the expanding precipitation
shield, reinforcing cold air wrapping around the main deep low
appears to support a heavy snow threat for the Great Lakes region
Sunday into Monday, spreading over the northern and interior
Northeast into Monday and Tuesday with closed upper low/trough
approach and with coastal New England triple-point low development.

Schichtel


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