285
FXUS02 KWBC 240626
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
226 AM EDT Fri May 24 2024

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


***Heavy Rainfall for the Northeast on Monday, and hazardous heat
 will continue through early next week for Southern Texas and South
 Florida***


...General Overview...

An amplifying upper trough over the Great Lakes region early in
the week will result in a pattern change across much of the
northeastern quadrant of the U.S. through midweek. A relatively
strong cold front will bring a quality airmass from the Northern
Plains to the East Coast after recent warm and humid conditions.
Another cold front is also forecast to cross the Pacific Northwest
and then the Intermountain West through mid-late week, while an
upper ridge tries to build northward across the Plains. The
heatwave across the Gulf Coast region is expected to abate some by
midweek, although it will still be quite warm and humid for the
remainder of the week across southern Texas.


...Guidance/Predictability Assessment...

Model guidance shows good agreement on the overall large scale
upper level pattern through the medium range period, but there are
some small/mid scale differences between models and runs that will
affect how upper lows and shortwaves interact. Shortwave energy
should move into the Pacific Northwest and cross the northern tier
of the nation mid-next week, but there is still some uncertainty
regarding the speed and amplitude of this feature.

The WPC fronts/pressures forecast incorporated a blend of the
deterministic GFS/ECMWF/CMC/UKMET along with some previous WPC
continuity through Tuesday, with slightly more weighting applied to
the ECMWF and GFS. For the Wednesday through Friday time period,
the WPC blend used a combination of the deterministic GFS/ECMWF/CMC
and ensemble means to help smooth out model differences, with
ensemble means accounting for about 40% of the blend by the end of
the week.


...Weather/Hazards Highlights...

Scattered to numerous showers and thunderstorms are likely across
the Mid-Atlantic and into the Northeast U.S. for the beginning of
next week, compliments of an amplifying upper trough and an
incoming cold front. The models are coming into better focus with
an area of more concentrated convective rains from eastern
Pennsylvania to southern New York during the new Day 4 period
Monday afternoon into Monday night. Therefore, a small Slight Risk
area is planned for this region.

Elsewhere across the nation, moisture convergence along and south
of a frontal boundary across Texas and Oklahoma, along with a
dryline, will likely generate scattered storms with heavy rainfall
on both Days 4 and 5 (Monday through Tuesday), but the models vary
on the placement of the QPF maxima. A Marginal Risk area is planned
on both days across portions of the southern Plains to account for
this potential.

Early summer heat and humidity will continue to make weather
headlines across the southern half of Texas, especially in the Rio
Grande Valley, through Memorial Day before slight improvement
arrives. The combination of daytime highs from the upper 90s near
the coast to 105-110 degrees well inland, along with dewpoints of
75-80 degrees closer to the coast, will combine to produce
hazardous heat indices of 110 to perhaps 120 degrees for these
areas. Farther to the north, a more refreshing change is coming
from the Midwest to the Mid-Atlantic as a cold front advects a
cooler and drier airmass into the region to close out the month of
may, with highs in the 60s and 70s for many of these areas by
Wednesday and Thursday.

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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