008
FXUS02 KWBC 051852
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
252 PM EDT Sun May 5 2024

Valid 12Z Wed May 08 2024 - 12Z Sun May 12 2024


...Mid-South/Ohio Valley Excessive Rain/Severe Threat midweek
shifts to the Central Gulf Coast States/Appalachians Thursday...


...Guidance/Predictability Assessment...

Latest guidance continues to show good agreement for the overall
synoptic pattern, but offer plenty of uncertainties in the details,
especially later in the period. The biggest area of concern during
the period is with an upper low as it ejects out of the Northern
Plains into the Great Lakes/Northeast. There are uncertainties with
the speed of this trough early in the period, and then with the
evolution of additional energy dropping into the trough from
central Canada around late week/next weekend. On the large scale at
least, the guidance all suggests that the pattern across the CONUS
will shift from a West trough-East ridge mid-week to West ridge-
East trough set up by next weekend.

A general blend of the deterministic solutions worked as a good
starting point for the Wed-Fri WPC forecast, incorporating more
ensemble mean guidance by next weekend to mitigate the differences
across mainly the Eastern U.S. next week. This maintains good
continuity with the previous WPC forecast as well.


...Weather/Hazards Highlights...

Amplified upper trough/low energies will shift slowly from the
northern Plains midweek to the East next weekend along with
a main/reforming parent surface lows then moderate coastal low.

There will be higher elevation snows back over the north-central
Rockies into mid-late week on the backside of the main trough/low
as depicted in the WPC Winter Weather Outlook. Rainfall on the
west side of the strong surface low could be heavy across eastern
Montana given upper-level support. However, this region is not
particularly sensitive to flooding concerns, and instability should
be limited wrapping around the low. A WPC Excessive Rainfall
Outlook (ERO) Marginal Risk area remains in place Day 4/Wednesday
for this area given the potential for heavy rainfall which should
start towards the end of the short range period.

Meanwhile, an associated lead and wavy/trailing frontal system
will gradually work downstream across the central and eastern
states to intercept and pool return flow instability and moisture.
This will set the stage for a widespread and generally broad comma
shaped area of rainfall to include a threat for excessive rainfall
and strong to severe thunderstorms for areas near the Mid-South
and Ohio Valley midweek and the Central Gulf Coast States to
Appalachians into the Southeast Thursday into Friday.

A Marginal Risk and embedded Slight Risk ERO is in place from the
Mid-Mississippi Valley through the Ohio Valley states for Day
4/Wednesday. These risks shift to the lower Mississippi Valley
through the northern central Gulf Coast states to the Appalachians
Day 5/Thursday as fronts push farther toward the east and northeast
and interact with pooling moisture and instability. The Storm
Prediction Center highlights a broad area of the Midwest to
Mississippi Valley/parts of the Southern Plains for severe weather
potential into midweek. A favorable pattern will continue for rain
and thunderstorms across the Southeast with the trailing cold front
and broadly across the East next weekend. Downstream energy track
may also lead to a moderate New England coastal low.

Expect much cooler than normal temperatures for parts of the West
Wednesday/Thursday under upper troughing. Meanwhile, mean upper
ridging will favor quite warm temperatures from the South through
the Appalachians/Mid- Atlantic to threaten record seasonal values.
90s are forecast across the southern tier, with potential for south
Texas excessive heat with temperatures over 100F and higher heat
indices. Temperatures broadly cool later week into next weekend
across the East, while warming across the West underneath a
building upper ridge.

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



















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