016
FXUS02 KWNH 060709
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
308 AM EDT Mon May 6 2024

Valid 12Z Thu May 09 2024 - 12Z Mon May 13 2024


...Central Gulf Coast States to Appalachians/Southeast U.S. Heavy
Rainfall Threat into Thursday/Friday...


...Guidance/Predictability Assessment...

The 12 UTC GFS/ECMWF/Canadian model solutions seem best clustered
for Thursday and Friday in a pattern with good ensemble support and
above normal predictability and continuity, mainly in line with
the 01 UTC National Blend of Models (NBM). A composite blend offers
good system detail. However, model forecast spread and cycle to
cycle continuity issues now increase rapidly by the weekend aloft
out West, but especially with wetter weather systems moving through
the East/South and western Atlantic coastal low developments that
are quite varied and without a clear signal to follow. Accordingly,
WPC products at these longer time frames have been mainly derived
from more compatible guidance from a 12 UTC GEFS/ECMWF/Canadian
ensemble means composite and the 01 UTC NBM to maintain max
product continuity but limited system detail pending new guidance.

...Weather/Hazards Highlights...
Main lows and associated fronts to focus mainly moderate rainfall
seem set to work from the Great Lakes/Ohio Valley through the
Northeast/Mid-Atlantic later this week with complex system/energy
interactions forging offshore low developments downstream.
Meanwhile, a wavy/trailing frontal system and impusles aloft will
gradually work across the South to intercept return flow with
deeper instability and moisture. Accordingly, a WPC Marginal Risk
Excessive Rainfall (ERO) area is now in place from the lower
Mississippi Valley through the central Gulf Coast states to the
Appalachians for Day 4/Thursday. A small embedded Slight Risk area
is in place from NE Louisana to central Alabama given slow system
translation. A favorable pattern will continue for rain and
thunderstorms across the Southeast with the wavy front where a
Marginal Risk ERO has been introduced for Day 5/Friday. Downstream
energy track may lead to additional but uncertain coastal lows,
while additional rainfall potential back to the south-central U.S.
is highly speculative in guidance at this time for into next week.

Expect cooler than normal temperatures for parts of the West into
Thursday under upper troughing. Meanwhile, mean upper ridging will
favor lingering warmth from the far South through the Mid-Atlantic
to threaten record seasonal values Thursday. 90s are still forecast
across the far southern tier, with potential for south Texas
excessive heat with temperatures over 100F and higher heat indices.
Temperatures broadly cool later week onward across the South and
East, with warming across broad portions of the West in more
benign weather pattern underneath a building upper ridge.

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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