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FXUS02 KWBC 150659

PMDEPD



Extended Forecast Discussion

NWS Weather Prediction Center College Park MD

259 AM EDT Mon Apr 15 2024



Valid 12Z Thu Apr 18 2024 - 12Z Mon Apr 22 2024





...Overview...



A low pressure system exiting the Great Lakes on Thursday will

continue to bring some showers and storms across parts of the East.

Behind this, another upper low will skirt the northern tier states

eventually dragging some troughing through the Ohio Valley and

Northeast this weekend/next week. This may allow a secondary cold

front to briefly stall across the Central Plains-MS Valley region,

and aided by weak shortwave energy through the Southwest/Southern

Plains, may help to enhance precipitation across the ArkLaTex

region on Saturday. The next system should move into the Northwest

late weekend, with a very uncertain evolution still. This should

push upper ridging from the West this weekend into the Central U.S.

early next week.





...Guidance/Predictability Assessment...



Model guidance remains reasonably agreeable on the large scale at

least the first half of the period, though some differences in the

smaller scale details. A second broader upper low across south-

central to southeastern Canada continues to show some variation in

timing of shortwaves rounding its base into Ohio Valley/Northeast,

but models have overall trended toward less amplification of

troughing across the East late period, and stronger ridging across

the Southeast U.S.. Later in the period, yesterdays 12z/18z

guidance showed some significant variation in energy entering the

Northwest late weekend, and eventual tracking eastward. The ECMWF

was notably weaker/faster than other guidance with this energy,

while the GFS/CMC suggested a closed low would hang back over the

Northwest early next week. There wasn't as much support for the

GFS/CMC closed low from the ECMWF-initialized AI/ML models, and the

ensembles means were extremely washed out suggested a lot of

uncertainty. The new 00z runs tonight (available after forecaster

generation time) of the GFS and CMC have trended much faster with 

the system and timing wise, are in better agreement with the ECMWF

(just much stronger). 



The WPC forecast tonight utilized a blend of the deterministic

guidance for days 3-4 (Thursday-Friday), but trended more towards

the ensemble means later in the period (with some ECMWF) to account

for significant uncertainty in the western U.S. system.





...Weather/Hazards Highlights... 



Some generally light precipitation is expected as the period begins

on Thursday associated with an initial cold front. The next system

though right on its heels will renew rain and convection across the

East late week, while lingering across the south-central U.S. as 

the frontal system stalls briefly. Given anomalous moisture and

instability present, felt a low-end marginal risk was warranted 

from eastern Oklahoma into southern Missouri where storm training 

seemed most likely with some higher rain rate potential. This area 

however has been rather dry as of late, which should inhibit the 

overall flash flood threat. Weak shortwave energy into the Southern

Plains should help to further enhance precipitation across Texas on

Saturday with increasing moderate to heavy rain potential. After

this, some precipitation should move into the Southeast as the

Northeast dries out, and depending on upper pattern evolution,

precipitation should return to the Northwest late week/early next

week.



Expect a broad area of above normal temperatures by 5-15 degrees 

over the southern half of the country into Thursday, while the 

northeastern quadrant of the U.S. gradually cools behind a cold 

front. Meanwhile the upper trough across the northern tier states 

will bring below normal temperatures (with greater anomalies for 

highs than lows) starting in the northern Rockies/Plains midweek. 

Cooler temperatures gradually expand farther south and east behind 

the secondary cold front late week into the weekend, with near to 

below average temperatures expected to reach everywhere but Florida

by next weekend. Meanwhile, above normal temperatures across the 

Southwest should gradually expand northward underneath a building 

Western U.S. ridge and progress eastward into the Rockies early

next week.





Santorelli





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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