Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
156 PM EDT Sat Apr 19 2025

Valid 12Z Tue Apr 22 2025 - 12Z Sat Apr 26 2025


...Heavy rain threat for the South-Central U.S. next week...


...Guidance/Predictability Assessment...

There remains decent agreement on the overall upper level flow
evolution next week into next weekend, but still 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 the details
of southern stream shortwaves/energy along multiple frontal
boundaries will have direct implications on heavy rainfall
distribution and amounts across the southern-central Plains and
vicinity. By Friday an upper low or deeper shortwave energy will
move into the West Coast with growing uncertainty still in the
timing and evolution. The WPC forecast for today used a blend of
the deterministic guidance, anchored by the ECMWF, for Tues/Wed,
gradually increasing the contributions of the ensemble means to 70
percent by Day 7, with the other 30 percent made up of the ECMWF
and GFS. Overall, this helped to smooth out the less predictable
details and maintained good continuity with the overnight WPC
forecast as well.


...Weather/Hazards Highlights...

A protracted 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 April weather,
but there is a growing signal to amplify the flow from the eastern
Pacific into the West heading into next weekend.

A WPC Excessive Rainfall Marginal Risk area for portions of the
Southern Plains for Day 4/Tuesday and Day 5/Wednesday (with an
extension northward into the central Plains) are in place given the
potential for repeat/training of cells during the day and with
overnight activity with emerging moist and unstable return flow
into and over several frontal boundaries. Portions 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
greater uncertainty on the details.

An expectation for upper trough amplification, wavy surface system
genesis and slow translation from the eastern Pacific to the West
Coast Friday into next weekend has the potential to offer increased
moderate rain chances with unsettled/cooling weather conditions.

Santorelli/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