Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
302 PM EDT Wed Mar 19 2025

Valid 12Z Sat Mar 22 2025 - 12Z Wed Mar 26 2025


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

Progressive flow with activity over the northern tier continues
into Sunday before amplification through early next week with the
development of a warming/building West Coast ridge and a
cooling/deepening and unsettling east-central U.S. trough.

The main low pressure feature is a trough that rounds a Gulf of
Alaska low Thursday night, crosses Vancouver Island Friday, then
amplifies over the northern Plains Saturday night and deepens into
a low over the Great Lakes Sunday night that slows is reinforcing
into midweek as ridging amplifies over the west. Global guidance is
in good agreement with this low and the ridge through Monday night
with uncertainty rising with the timing and strength of the
reinforcing shortwave troughs rounding the Great Lakes low.

Forecast confidence remains above average overall with a
deterministic blend of the GFS/ECMWF/CMC/UKMET through Day 5 with
some GEFS/ECENS included for Days 6/7 (which is after input from
the UKMET ends). This blending is mainly in line with the National
Blend of Models and WPC continuity.

...Weather/Hazards Highlights...

Northern tier activity working with continental air masses results
in no excessive rainfall risk for the CONUS on Day 4/Saturday.

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 for Day 5/Sunday coastal Washington as compounding
effects of multiple preceding bouts of precipitation may lead to
local runoff issues.

The amplifying low over the northern Plains into the Great Lakes
Sunday night draws 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 5 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.

Meanwhile, reinforcing cold air wrapping around the main low
appears to support a heavy snow threat for the Great Lakes region
Sunday into Monday, possibly spreading over the northern and
interior Northeast into Monday and Tuesday with closed upper
low/trough approach and as triple-point low development is
additionally possible near the coast of New England.

Jackson


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