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FXUS02 KWBC 200652

PMDEPD



Extended Forecast Discussion

NWS Weather Prediction Center College Park MD

252 AM EDT Sat Apr 20 2024



Valid 12Z Tue Apr 23 2024 - 12Z Sat Apr 27 2024





...General Overview...



The forecast period begins on Tuesday with an amplifying upper

trough over the Great Lakes and then over the Northeast U.S., and

this will propel a cold front across much of the Eastern U.S. for

the middle of the week. Surface high pressure then builds in across

the Midwest and then across the East to close out the week along

with cooler temperatures. Meanwhile, a synoptic scale trough

develops across the Western U.S. by Friday and into Saturday with a

couple of shortwaves ejecting out across the Plains, and 

supporting surface cyclogenesis across the western High Plains.

This will likely result in developing showers and storms for the

Central U.S., with some heavy rain and strong storms possible by

the end of the week.



...Guidance/Predictability Assessment...



One of the main forecasting challenges early on will be across the

Northeast U.S., and this regards the degree of phasing between an

incoming shortwave from the Midwest and an arctic trough dropping

from the Hudson Bay region. The GFS and to a slightly lesser extent

the GEFS mean support a stronger system with a closed low

developing across portions of New England, whereas the non-NCEP

guidance and the machine learning guidance from the ECMWF supports

the idea of a broader trough. Otherwise the models are in pretty

good agreement for the Tuesday-Wednesday time period, and a multi-

deterministic model blend with slightly more weighting towards the

ECMWF works well as a starting point in the forecast process. There

is growing consensus for a trough developing across the West to

close out the week, although timing differences remain for the

shortwave crossing the Southwest and then the Southern Plains (GFS

is most progressive), and also for the shortwave/closed low 

originating from the Gulf of Alaska. The use of the ensemble means 

accounted for about 40-50% of the forecast blend by Friday-

Saturday.



...Weather/Hazards Highlights... 



Upper trough and frontal passages through the Midwest/Great Lakes 

and then the Northeast will be accompanied by some widespread light

to moderate rains early-mid next week. Given the overall 

progressive nature of this storm system, and the lack of 

appreciable instability and QPF most places in this period, no 

flash flood threat areas are currently warranted for the WPC 

Excessive Rainfall Outlook for Tuesday. On Wednesday, warm air

advection across Texas and Oklahoma will bring a return to

scattered showers and storms across this region, with some of the

model guidance suggesting the potential for some local one inch

rainfall totals. However, the guidance is not locked in on the

location of these scattered QPF maxima, and therefore it seems 

prudent to hold off on any risk areas for the Day 5 outlook on 

Wednesday until a better model signal develops for placement. More 

widespread showers and storms are then expected to develop across 

the Plains and Midwest states into later next week as moisture and 

instability increase with surface low pressure system development, 

and the potential exists for some strong storms ahead of the 

dryline in the Southern Plains, so this will continue to be 

monitored.



Initial upper level ridging out West should support above normal 

temperatures through about Wednesday, and then a return to near or

slightly below normal levels for much of the West Coast and

Intermountain West starting Thursday. Warmer temperatures and 

increasing humidity are forecast for the south-central U.S. by 

next Friday and beyond as the upper ridge axis builds back, and 

southerly flow from the western Gulf advects moisture northward 

ahead of a developing surface low. Highs could get over 100 degrees

for portions of southern Texas by Saturday.



Hamrick





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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