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FXUS02 KWBC 030648

PMDEPD



Extended Forecast Discussion

NWS Weather Prediction Center College Park MD

248 AM EDT Fri May 3 2024



Valid 12Z Mon May 06 2024 - 12Z Fri May 10 2024





...Northern Plains to Midwest Heavy Rain Threat early next week...





...Overview...



An upper low that is strong for this time of year is forecast to 

move through the West by early next week and track/meander into 

the Plains and Midwest as the week progresses. This will support 

cooler than normal temperatures, gusty winds, and precipitation 

including higher elevation snow in the West early in the week. Rain

that could be locally heavy shifts into the northern Plains and 

downstream through the Midwest. Meanwhile farther south, mean upper

ridging will lead to warming pre-frontal temperatures for much of 

the central and eastern U.S. that could yield some record values. 

Upstream, Pacific upper trough energy will work inland over an 

unsettled West and to the south-central U.S.. This may interact 

with a wavy and stalling lead front and combine with pooling 

moisture and instability to fuel rain and thunderstorms over the 

south-central states/Mid-South and onward into later next week,

still also under some influence from the lead upper low/trough.



...Guidance/Predictability Assessment...



Model and ensemble solutions overall seem reasonably clustered for

Monday-Wednesday and generally in step with National Blend of 

Models (NBM) guidance. This bolsters forecast confidence in a 

composite GFS/ECMWF/UKMET/Canadian model blend to provide maximum 

system detail as consistent with feature predictability. Opted to 

switch preference to a composite of best clustered GFS/ECMWF and 

GEFS/ECMWF ensemble means along with the NBM for later next week 

to temper detail some, acting to mitigate growing but managebale 

forecast spread. WPC product continuity is decently maintained in 

this manner. Latest 00 UTC guidance has mainly stayed in line.



...Weather/Hazards Highlights... 



As a main/closed upper low tracks out of the West as addiitonal 

energies feed back through the West Coast, widespread precipitation

will include some enhanced snow potential given cooled 

temperatures. The higher elevations of the Sierra Nevada, north 

into the Cascades, and east into the Intermountain West/Rockies 

will see May snow. Troughs/low aloft and frontal boundaries could 

also produce some high winds across the Great Basin to Rockies to 

High Plains. Precipitation is forecast to move steadily eastward 

through early next week, reaching the northern Plains to Midwest 

Monday and Tuesday. Rainfall on the west side of the strong surface

low could be heavy across eastern Montana into the Dakotas given 

strong upper-level support for lift. 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 in the Day 

4/Monday and into Day 5/Tuesday for this area given the potential 

for protracted heavy rain, but likely without widespread 

significant flooding impacts. The Marginal Risk extends southeast 

into the Upper/Mid-Mississippi Valley, where more instability will

be in place for higher rain rates, but storms will likely be 

faster moving. The Storm Prediction Center also has portions of the

Plains delineated with potential for severe weather on Monday. 

Convective rainfall is forecast to shift east into the Great Lakes 

and Ohio Valley Tuesday into Wednesday with system progression and 

intercecting return flow. A Day5 Marginal Risk ERO was introduced.



Upstream, aforementioned Pacific upper trough energy will work 

inland over an unsettled West and over the south-central U.S. into

later next week, riding under the base of the lingering main upper

low/trough. These will interact with wavy and stalling fronts and 

combine with pooling moisture and instability to fuel a favorable 

pattern for rain and thunderstorms across the south-central 

states/Mid-South and onward to the East where downstream energy 

track may support moderate late next week coastal low development.



Much cooler than average maximum temperatures will slowly moderate

while spreading next week from the West to the northern Plains 

with slow ejection of a closed upper low. But farther southeast, 

mean upper ridging will meanwhile spread quite warm pre-frontal 

temperatures from the South through the Appalachians/Mid-Atlantic

to threaten record seasonal values. 90s are forecast to become 

more widespread across the southern tier, with temperatures over 

100F (and even higher heat indices) into south Texas and the 

possibility for the first excessive heat days of the year.



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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