579
FXUS02 KWNH 250654
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
253 AM EDT Sat May 25 2024

Valid 12Z Tue May 28 2024 - 12Z Sat Jun 01 2024

***Hot and humid conditions continue for southern Texas and the
 Florida Peninsula***

...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...

The 12Z model guidance suite initially has a good overall synoptic
scale depiction of the incoming trough for the Pacific Northwest
and the downstream ridge over the Rockies on Tuesday. The 12Z CMC
differed considerably from the model consensus across the Great
Lakes region with the details of the amplifying upper low here, and
becomes stronger with the trough axis near the East Coast going
into Tuesday. This run was also broader with the Western U.S.
trough late in the week. The 12Z UKMET was considerably faster
with the progression of this trough across the Rockies through
midweek. Neither of these two solutions had much support from the
machine learning guidance from the ECMWF nor the ICON model, and
taking all of these factors into account, the fronts/pressures
forecast only used the GFS and ECMWF, along with some previous WPC
continuity since the previous forecast was close to those solutions
through Thursday. The 00Z run of the CMC trended more in the
direction of the preferred GFS/ECMWF blend, although the UKMET
remains progressive with the northwestern U.S. upper trough.

Looking ahead to Friday and Saturday, there is good agreement with
the upper ridge axis across the Midwest states, but more
differences emerge with the trough crossing the Rockies with a
faster CMC solution, and also with the trough just off the East
Coast, with the 12Z ECMWF slower in moving the trough off the
coast. The ensemble means accounted for 30-50% of the forecast for
this time period, while having slightly more of the operational GFS
compared to the ECMWF and CMC.

...Weather/Hazards Highlights...

Moisture convergence along a frontal boundary and east of a dryline
across Texas and Oklahoma will likely generate scattered to
numerous showers and thunderstorms, with the potential for episodes
of locally heavy rainfall early to mid week as some MCS activity
develops. 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 now a planned Day 4 (Tuesday) Slight
Risk in the ERO across portions of north-central Texas where the
potential exists for storms with rainfall rates approaching 2
inches per hour. Some strong to severe storms are also likely. The
coverage of showers and storms will likely expand north across the
central and northern Plains later in the week as an organized
frontal system moves into the central U.S. from the Rockies.
Locally heavy rainfall will be possible across portions of the
Rockies going into late Friday and early Saturday as the cold front
intercepts an increasingly humid airmass.

In terms of temperatures, the Gulf Cast region will continue to
remain hot and humid on Tuesday before some limited relief arrives
by midweek as a cold front drops southward. However, the heat and
humidity will likely continue across Deep South Texas and South
Florida with highs running up to 10 degree above average, and heat
indices in the 100-110 degree range, especially for southern Texas.
Some triple digit heat is also likely for the lower elevations of
the Desert Southwest, but very low humidity here will help keep
heat indices in check.

A quality airmass will deliver a refreshingly cooler airmass from
the Upper Midwest to the Mid-Atlantic and points northward as a
pair of cold fronts pass through. courtesy of a building upper
level trough centered over the Great Lakes and Northeast. Cooler
weather is also forecast to reach the northwestern quadrant of the
nation as the next upper trough moves inland across the
Intermountain West, with highs running 5-15 degrees below normal by
the end of the week.

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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