974
FXUS02 KWNH 200700
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Sun Apr 20 2025

Valid 12Z Wed Apr 23 2025 - 12Z Sun Apr 27 2025


...Multi-day Heavy rain threat for the South-Central U.S....


...Guidance/Predictability Assessment...

Recent guidance offers decent agreement on the overall upper level
flow evolution this week into next weekend, but still with plenty
of uncertainty in the details of individual shortwaves. Questions
of timing and intensity of weaker shortwaves through the west to
north-central U.S. even early period are evident, and specifics of
southern stream shortwaves/energy on multiple frontal boundaries
will have direct implications on heavy rainfall distribution and
amounts across the southern-central Plains and vicinity. By Friday
or so, an upper low or deep shortwave energy should move into the
West Coast, albeit with uncertainty in the timing and evolution.
Accordingly, the WPC forecast used a blend of GEFS/ECMWF/Canadian
ensemble mean guidance through medium-range time scales. Overall,
this acts to smooth out the less predictable details and maintains
reasonable WPC product continuity now more in line with latest 00
UTC guidance model cycle and recent machine learning model trends.

...Weather/Hazards Highlights...

An scattered series of generally progressive upper features and
associated surface based systems are set to work over the lower 48
next week in multiple stream flows to locally focus late April
weather, but there is some signal to amplify the flow from the
northeast/eastern Pacific into the West heading into next weekend.

WPC Excessive Rainfall Marginal Risk areas for portions of the
south-central Plains for Day 4/Wednesday and Day 5/Thursday are in
place despite lingering local focus uncertainties given the
potential for repeat and training of cells during the day and with
overnight activity with emerging moist and unstable return flow
into several frontal boundaries. Parts of this area are also
forecast to have enhanced rainfall this weekend that would lead to
wet soil conditions. Heavy rain and runoff threats along with
strong convective potential in this region and into the Mississippi
Valley will also be monitored for mid-later next week given
lingering support and multi-day potential, albeit with even greater
uncertainty on the details.

The extent of upper trough amplification and digging is not a done
deal in guidance, but the prospect of wavy surface system genesis
and slow but steady translation from the northeast/eastern Pacific
to the West Coast Friday and inland over the West next weekend
still offers increased light to moderate widespread rain chances.
Unsettled and cooling weather conditions support mountain snows.

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














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