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FXUS02 KWBC 081836

PMDEPD



Extended Forecast Discussion

NWS Weather Prediction Center College Park MD

236 PM EDT Wed May 8 2024



Valid 12Z Sat May 11 2024 - 12Z Wed May 15 2024



...Emerging Texas/Gulf Coast/Southeast Heavy Rainfall Threat...





...Pattern Overview and Guidance/Predictability Assessment...



Guidance continues to show pretty good agreement that mean

troughing will linger over the Great Lakes/Eastern U.S. into early

next week as a blocky pattern out west takes some time to de-

amplify. By early next week, shortwave energy into western Canada

will amplify over the Northwestern U.S. allowing a closed low over

the Great Basin to shift eastward into the Plains/Midwest Monday-

Wednesday. This should also help push troughing over the East out

and upper ridging to build across the Southeast. Additional

shortwave energy may move into the Southwest late period as well.



Overall, the latest models and ensembles show good agreement on the

large scale pattern, but plenty of uncertainty in the timing and

details of individual systems. The differences in the central U.S.

shortwave in particular could have bigger implications on heavy

rainfall across parts of the southern Plains into the Gulf

Coast/Southeast this weekend and into next week, including areas

that have been very wet in the past week. So these areas may be 

more sensitive than normal to smaller changes in the

pattern/details.



Despite the differences, it seemed that a general model compromise

worked well as a starting point and offered the best continuity

with the previous WPC forecast. For days 3-5, was able to use an

equal blend of the deterministic solutions, incorporating

increasing amounts of the ensemble means into the blend for days 

6-7 to mitigate the smaller scale details that are impossible to 

resolve at these longer time scales.





...Weather/Hazards Highlights...



Moderate rainfall will linger this weekend over the Northeast with

wrapback moisture and upper trough support as downstream energy 

transference leads to coastal low genesis, but details remain 

uncharacteristically uncertain even as we enter short range time 

frames. Upstream northern stream systems will then periodically 

offer bouts of mainly lighter rains from the north-central U.S. to

the Great Lakes/Northeast this weekend to next midweek, albeit 

also with uncertainty in focus/timing, but with limited impact.



Meanwhile to the south, a cooling/slowing trailing front along 

with a reinforcing front and upper shortwaves are expected to 

periodically focus precipitation from the southern Rockies/Plains 

out through the Gulf of Mexico and Gulf Coast/Florida this weekend

through early-mid next week. A growing but still not solidified 

guidance signal offers support for moisture to increase along the 

Gulf Coast and vicinity ahead of the returning warm front. Heavy 

rain may work inland over time as the front edges northward. The 

WPC Day 5/Sunday into Monday Excessive Rainfall Outlook update this

afternoon expanded the previous marginal risk area significantly

northward into eastern Texas to far southern Oklahoma. Given

soil/streamflow sensitivities across especially southeast Texas,

also expanded the slight risk farther north. Heavy rain and a 

threat of runoff issues may also spread through the central Gulf 

Coast to the Southeast early-mid next week to monitor.



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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