Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
217 PM EDT Wed May 7 2025

Valid 12Z Sat May 10 2025 - 12Z Wed May 14 2025


...Multi-day Southeast U.S. Heavy Rainfall/Flooding Threat...


...Overview...

Closed low energy will meander over the Southeast and cool daytime
temps, finally lifting out of the region around next midweek. This
will support deeply pooled moisture to fuel daily heavy
rainfall/convective threats through the weekend into next week
over the Southeast including Florida, albeit with an eventual
gradual translation up through the Mid-Atlantic with slow system
ejection. To the north, a northern stream shortwave will close off
a new compact upper low over the Northeast into early this weekend
with moderate surface low/system genesis and lingering wrap-back
flow rains. Elongated upper troughing off the West Coast, stemming
from an upper low moving out of the Gulf of Alaska, will send an
initial shortwave into the West/Northwest Sunday. Upstream closed
low development off the Northwest coast will lead into an amplified
and cooling upper trough digging down the coast and subsequent
slow push of widespread precipitation inland across the West into
Tuesday/next Wednesday, including elevation snows.

...Guidance/Predictability Assessment...

Model and ensemble guidance continues to be reasonably well
clustered valid through the weekend into early Monday in a slowly
evoloving pattern with seemingly above average predictability with
the main weather features. A model composite is favored to offer
maximum forecast detail. Most guidance remains decently clustered
through early-mid next week, albeit with the 00 UTC ECMWF and to a
lesser extent the 00 UTC ECMWF ensemble mean becoming somewhat more
progressive with upper trough/system energies working over the
West at these longer time frames. Favor a slower solution in line
with a composite of the GFS/Canadian and GEFS/ECMWF ensemble means.

...Weather/Hazards Highlights...

A wavy frontal system and a closed upper low meandering over the
Southeast will continue to support a multi-day heavy
rainfall/runoff threat into next week as fueled by the pooling of
highly anomalous moisture. Relatively dry antecedent conditions
and higher flash flood guidance may limit the overall flash
flooding potential, at least initially. For now, opted to maintain
WPC Excessive Rainfall Outlook Marginal risks for Days 4/5
this weekend, especially considering lingering uncertainty in the
details/local focus. However, repeat cells/training along with
subsequent cumulative effects from prior days will likely lead to
threat level upgrades as the supporting guidance signal continues
to increase closer to the wet event. Rainfall may gradually lift
northward with time into the Mid-Atlantic early-mid next week.

Elsewhere, rainfall will be exiting the Northeast after Saturday
with the upper low. Out West, rain and higher elevations snows will
become more widespread through the weekend and become more
widespread with main amplified system cooling and slow progression
inland through early and mid next week.

General troughing across the South will keep temperatures near or
below normal at least through the weekend and longer for the
Southeast. Upper ridging out West will support much above normal
temperatures with daytime highs 20-25+ degrees above normal in the
Northern Plains. Above normal temperatures may also extend across
the Upper Midwest/Great Lakes/Northeast by next week. Parts of the
Southwest should approach 100 degrees with at least some localized
heat threat given earlier in the season timing. The WPC Hazards
Outlook continues to depict a weekend Hazardous Heat Threat area.


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