983
FXUS02 KWNH 240700
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Sat May 24 2025

Valid 12Z Tue May 27 2025 - 12Z Sat May 31 2025


...Heavy rain/flash flooding threats from the South through the
south-central Appalachians/Mid-Atlantic early-mid next week...


...Overview...

This upcoming medium range period will feature an amplified and
slow to progress upper level pattern with a couple cutoff lows
that will drive surface frontal systems across the lower 48. One
low will wander across the north-central U.S. and Midwest while
the others gradually approach the Southwest. The eastern low
should gain momentum late in the period as it tends to sync with a
broad upper level trough, but Southwest lows will move slowly as
ridging builds heat over the West. This pattern will result in a
lingering period with areas of wet unsettled weather to focus from
the South up through the south-central Appalachians/Mid-Atlantic.
A series of Pacific frontal approaches toward/north of the Pacific
Northwest may offer some modest coastal rains chances next week.

...Guidance/Predictability Assessment...

Guidance offers a reasonably similar mid-larger scale pattern
evolution for Tuesday into Thursday despite complex and slow to
transition flow. Best clustered guidance of the 18 UTC GFS and 12
UTC ECMWF/Canadian have good ensemble and machine learning model
support, and a composite blend seems to mitigate much of the
smaller scale system and weather focus details as consistent with
individual predictability. Forecast spread characteristically
increases later next week, but a blend of best clustered guidance
of the 18 UTC GEFS mean and 12 UTC ECMWF/Canadian ensemble means
best maintains continuity, with a solution in line with latest 00
UTC guidance composite trends through these longer time frames.

...Weather/Hazards Highlights...

Main developing lows along a wavy frontal system over the South
should are slated to progress northeastward Tuesday and Wednesday.
This will expand a threat of localized heavy rain up through the
south-central Appalachians region/Mid-Atlantic, while the moisture
pooling trailing front lingers back across the South to focus
locally heavy convective downpours chances that may extend well
into next week with advent and reinforcement from Midwest
cyclo/frontogenesis from northern stream energies. The WPC
Day4/Tuesday Excessive Rainfall Outlook (ERO) depicts an elongated

Marginal Risk threat area from Texas into the south-central
Appalachians region/Mid-Atlantic given deep moisture and upper
support. A Day 5/Wednesday WPC ERO Marginal Risk shows best focus
lingering over the southeast Mid-Atlantic with lead low passage and
also back over the southern Plains/Lower Mississippi Valley with
ejecting southern stream impulse induced return flow.

In the West, a building upper ridge will lead to an expanding area
of heat from the Intermountain West into the West Coast states,
with temperatures rising upwards to 10 to 15+ degrees above normal
during the second half of next week that in particular may lead to
a hazardous heat focus over the California Central Valley heading
into and through next weekend.

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





$$