139
FXUS02 KWBC 161900
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Fri May 16 2025

Valid 12Z Mon May 19 2025 - 12Z Fri May 23 2025

...Severe weather and flash flooding forecast for parts of the
central U.S. Monday-Tuesday...

...Hazardous and record heat could continue especially across Texas
and Florida into mid-next week...


...Overview...

The primary weather feature next week will be an upper trough/low
over the Rockies Monday that tracks east as the week progresses
along with its associated surface low pressure/frontal system. This
pattern will provide ample lift and instability for rain and
thunderstorms in the Plains, Mississippi Valley, and Ohio Valley
early week and spreading into the East for midweek and beyond.
Meanwhile a subtropical upper ridge will continue to cause hot
conditions to areas of the Southeast, particularly into southern
Texas and Florida, where the heat could be hazardous and/or record
setting.


...Guidance/Predictability Assessment...

Model guidance begins the medium range period Monday in reasonably
good agreement with the primary upper trough and embedded upper
low(s) in the Interior West and spinning up a surface low in the
central Plains. Models diverge rather quickly with the evolution of
the ejection of embedded upper-level energies and subsequent
details at the surface. A second upper-level shortwave looks to
lead to secondary low development over the central/southern Plains
Tuesday south of the initial surface low development. The 00Z
ECMWF/UKMET and 00/06Z GFS maintain the more northern low before a
complex evolution that generally tends to favor the southerly low
becoming the main low as the system progresses northeastward into
the Midwest/Ohio Valley by mid-next week. The evolution of the
surface low pattern in the 06Z GFS is a bit more similar to the 00Z
ECMWF compared to the 00Z run initially in feature
location/progression. The 06Z then shows a much faster progression
of leading energy eastward out of the Ohio Valley and into the Mid-
Atlantic/Northeast while the 00Z GFS remains more similar to the
00Z ECMWF with a slower progression. The progression of the low(s)
is also faster in the deterministic guidance compared to the
ECENS/GEFS means, which is also faster compared to the prior
guidance as well as WPC forecast. The 00Z CMC is more aggressive in
having the southerly low become the solo, primary low quickly in
the subsequent evolution of the pattern with a much slower and
southerly track. Another complex evolution looks to occur heading
into later next week as the upper-trough merges with northern
stream energy, and a coastal low develops off the coast of the Mid-
Atlantic, lifting northeastward in parallel with the coast. Both
the 00Z GFS/ECMWF and the respective means are in generally good
agreement despite typical location/timing differences with
increasing lead time. The 06Z GFS remains much faster, bringing the
coastal low well offshore compared to the other guidance,
suggesting a higher level of uncertainty despite the good
agreement. The updated WPC forecast begins with a blend of the 00Z
ECMWF/UKMET and 00/06Z GFS given the transition between the 06Z to
00Z with respect to better agreement with the other guidance. The
00Z CMC was not included because of the outlier nature of the
southerly system track. A contribution from the ensemble means is
added for the mid- to late period given the loss of the time-
limited UKMET, removal of the 06Z GFS given a diverging solution,
and general increase in uncertainty. The blend results in a
forecast that maintains generally good continuity with the prior
WPC forecast, with the greatest differences being a faster
progression of the system eastward through the Ohio Valley and a
stronger coastal low towards the end of the period.

...Weather/Hazards Highlights...

The notable surface low pressure system consolidated over the
central Plains by Monday will draw in above average moisture (with
precipitable water values around the 90th percentile for this time
of year) and ample instability ahead of its associated cold front.
The upper low spinning aloft will provide good dynamical lift, and
this combination of ingredients will lead to widespread rain and
thunderstorms and mesoscale convective systems, with best chances
slowly progressing east from the central to east-central to eastern
U.S. as next week progresses. The greatest chances for heavy rain
causing flash flooding look to be across the Mid-Mississippi and
western Ohio Valleys Monday, and a more expansive area from the
Mid- Mississippi east through the Ohio Valley and into the central
Appalachians Tuesday, as moisture and instability pool near a warm
front stretching west-east that could promote training storms. Thus
Slight Risks are in place for the Day 4/Monday and Day 5/Tuesday
ERO over pretty similar areas before the upper/surface lows eject
eastward. Broad Marginal Risks surround the Slights to the south
and east where convection may be more scattered, and on Monday a
Marginal curls back west closer to the low track. Severe weather is
also possible per the Storm Prediction Center, as they delineate a
severe area on Monday for the south-central Plains to Missouri
Valley Monday, with the greatest threat over eastern Oklahoma, and
another area for the Lower/Middle Mississippi Valley on Tuesday.
Rain and thunderstorm potential should press toward the Eastern
Seaboard by mid to late week with moderate to locally heavy
rainfall possible for the Mid-Atlantic Wednesday into coastal New
England Thursday.

Some precipitation is forecast in the Intermountain West under the
upper trough/low for the first half of next week. The cool
temperatures aloft could lead to May snow in higher elevations of
the Rockies particularly Monday. Convective showers are possible
near the Four Corners region. Meanwhile rounds of modest
precipitation may be possible in the Northwest. Light rain may
linger in the Northeast early next week under the influence of a
northern trough.

Warm to hot temperatures are likely across the southeastern U.S.
as the subtropical upper ridge reaches the region. Southern Texas
in particular will remain hot, with temperatures well into the 100s
leading to Major to Extreme HeatRisk through Tuesday. The Florida
Peninsula should see warm temperatures in the mid to upper 90s.
Both areas could see record or near record warm lows and highs.
Meanwhile the trough aloft will promote below normal temperatures,
especially for highs, across the Interior West Monday and into the
northern Plains Tuesday. Below average highs by around 10 degrees
are also possible in the northern tier. As the trough tracks east,
cooler than average temperatures should shift into the eastern
third of the country under it. This may also moderate the
temperatures somewhat in the South. But upper ridging poking into
the West will raise temperatures to above normal there by later
week, bringing highs well into the 100s for the Desert Southwest.

Putnam/Tate


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




$$