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FXUS02 KWBC 061929

PMDEPD



Extended Forecast Discussion

NWS Weather Prediction Center College Park MD

329 PM EDT Mon May 6 2024



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





...Gulf Coast States to Appalachians Heavy Rainfall Threat into 

Thursday/Friday...





...Overview...



Positively tilted upper troughing atop much of the lower 48 to 

start the period will push rain and thunderstorms through the South

and East along and ahead of a cold front Thursday-Friday. By the 

weekend into early next week, this trough should consolidate and 

linger atop the eastern U.S. with split flow across the West.





...Guidance/Predictability Assessment...



The early medium range period shows reasonably good agreement with

a train of energy embedded within the positively tilted trough, 

with some energy focused in the central Great Basin lingering into 

late week while some tracks from the Midwest into the Northeast. 

With the latter, associated surface lows are in reasonable 

agreement but with typical spread. Thus the early period was based 

on a blend of the 06Z GFS and 00Z ECMWF and CMC, which maintained 

good continuity with the previous forecast. 



By early Saturday or so additional energy looks to dive into the 

north-central U.S., with the 00Z GFS an outlier in how much and how

far west it fed in. Meanwhile, the 00Z CMC took southern stream 

energy east while other models had it lingering in the Southwest 

through Saturday. The newer 12Z CMC looks to be in better 

agreement. But then, the ECMWF holds this energy farther southwest 

longer than other guidance--and longer/southwest than the EC-based 

AI/machine learning models. With many of the deterministic models 

showing increasing spread, quickly increased the proportion of 

ensemble means in the model blend by days 5-7 to minimize the 

individual differences.





...Weather/Hazards Highlights...



Main lows and associated fronts to focus 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 in place from eastern Texas across the Lower 

Mississippi Valley through the central Gulf Coast states to the 

Appalachians for Day 4/Thursday. The Marginal for this forecast 

cycle will expand farther north into portions of the Lower Great 

Lakes region. Despite lower instability than farther south, 

anomalous moisture will be in place there while the surface low and

a coupled jet (right entrance/left exit region) aloft could lead 

to flooding concerns in a somewhat sensitive region. An embedded 

Slight Risk is in place from portions of 

Louisiana/Mississippi/Alabama (expanded eastward from the previous 

forecast) because ample instability and the west-east orientation 

of the front and thus the convection will provide an environment 

favorable for training storms with very heavy rain rates. By Day 

5/Friday, the front will continue to press eastward and areas from 

southern Alabama and Georgia into northern Florida could see some 

thunderstorms with flooding concerns, so a Marginal Risk remains in

place there with a trend slightly southward from the previous 

issuance. Downstream energy may lead to additional but uncertain 

coastal lows with wrapback precipitation in the northeastern 

quadrant of the country. 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.





Tate/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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