191
FXUS02 KWBC 241852
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
252 PM EDT Fri May 24 2024

Valid 12Z Mon May 27 2024 - 12Z Fri May 31 2024


...Heavy Rain and flooding possible for the Northeast on Monday...

...Hazardous heat will continue through early next week for
South Texas, the Central Gulf Coast, and South Florida...


...Overview...

Multiple shortwaves will pivot around a deep upper low positioned
north of the Upper Midwest over southern Canada, which will drive
multiple surface fronts south across the central and eastern U.S.
next week. Precipitation chances will be highest in the Great Lakes
and Northeast in the vicinity of the upper low and near the Gulf
Coast where one of the frontal boundaries will stall. By mid-week,
another deep upper low is forecast to push into the Pacific
Northwest and southern British Columbia and bring a frontal system
across the Northwest and Intermountain West. This frontal system
will emerge into the Plains later in the week, producing
widespread shower and thunderstorm chances. A ridge will build
over the Midwest during the second half of the week as the leading
upper low/trough shifts east. Hazardous heat is forecast to
continue for portions of South Texas, the central Gulf Coast, and
South Florida through early next week, but the Gulf Coast may see
some relief mid-week with a cold frontal passage.


...Guidance/Predictability Assessment...

Model guidance shows good agreement on the overall large scale
upper level pattern through the medium range period. As usual,
there are some differences in the details, which will likely affect
the sensible weather forecast. The highest uncertainty in the
forecast concerns interactions between the Great Lakes/Northeast
upper low and pieces of shortwave energy rotating around and
through the upper trough. The strength, timing, and location of
these features will have an affect on one another and the surface
features moving across the central and eastern U.S.. Models have
come into better agreement on the timing and strength of the upper
low moving into the Northwest mid-next week, but solutions diverge
later in the week as the low moves into the Upper Midwest/southern
Canada.

The WPC blend for the afternoon forecast was comprised of a blend
of the deterministic GFS/ECMWF/CMC/UKMET for the first two days
(Monday-Tuesday). For Wednesday, the UKMET strayed away from the
other model guidance, so the previous WPC forecast blend was
substituted in its place. For the rest of the period, ensemble
means from the GEFS/ECE were added to the blend to smooth out
differences between the deterministic GFS/ECMWF/CMC.


...Weather/Hazards Highlights...

Scattered to numerous showers and thunderstorms are forecast
across the Mid-Atlantic and Northeast on Monday, compliments of an
amplifying upper trough and an incoming cold front. Model guidance
continues to show heavy rain focusing over eastern Pennsylvania,
northern New Jersey, and southern New York, so a Slight Risk of
Excessive Rainfall was maintained for this area in the Day 4
(Monday) ERO.

Elsewhere across the nation, moisture convergence along a frontal
boundary and dryline across Texas and Oklahoma will likely
generate scattered thunderstorms with the potential for locally heavy
rainfall early next week. The threat of heavy rainfall will be
highest in Texas Tuesday into Wednesday as an upper level
shortwave moves over the southern Plains, so there is a Marginal
Risk of Excessive Rainfall for this region in the Day 5 (Tuesday)
ERO. Shower and thunderstorm chances will expand north across the
central and northern Plains later in the week as a frontal system
moves into the central U.S. from the northwest.

Early summer heat and humidity will continue to impact the
southern half of Texas, especially in the Rio Grande Valley, and
portions of the Gulf Coast and South Florida through Memorial Day.
Conditions will improve for the Gulf Coast and South Florida as a
cold front sinks south mid-week, but heat, though less widespread,
will likely hang on a little longer for some locations in South
Texas as the front stalls then lifts back north as a warm front.
The combination of daytime highs ranging from the mid 90s to 110
degrees and dewpoints of 70-80 degrees will produce dangerously
high heat indices that could exceed 115 degrees in some places.

Above average temperatures are also forecast across much of the
western and central U.S., but below average temperatures will
develop in the Pacific Northwest as the upper low and associated
frontal system push inland mid-next week. Below average
temperatures will also shift from the Upper Midwest to the Mid-
Atlantic and Northeast behind a series of cold fronts next week.


Dolan


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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