202
FXUS02 KWBC 111853
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
253 PM EDT Sun May 11 2025

Valid 12Z Wed May 14 2025 - 12Z Sun May 18 2025

...Heavy rain for the Northern Plains and heat builds across Texas...


...General Overview...

It generally remains the case that a slow moving upper low across
the Southeast U.S. will be weakening and evolving into an open
trough by Thursday as it exits the East Coast. Another cooling upper
trough and closed low across the Northern Rockies mid-week will
sustain a well organized surface low crossing the Northern Plains
and then into south-central Canada by the end of the week, with
heavy rain for the Dakotas/Minnesota and late season mountain snow
for the northern Rockies. A second cooling trough will likely
develop over the interior West by next weekend with an upper ridge
trying to re-develop across the Plains. Elsewhere in this pattern,
widespread above normal temperatures are likely for most of the
south-central and eastern U.S. for much of the forecast period.

...Guidance/Predictability Assessment...

Models and ensembles along with the growing suite of machine
learning guidance continue to offer a reasonably similar mid-
larger scale pattern evolution through medium range time scales,
albeit with lingering smaller scale system specific variances that
vary from cycle to cycle. Opted to blend better clustered guidance
from the GEFS/ECMWF/Canadian ensemble means coupled with WPC
continuity and the National Blend of Models. This now seems to best
offer a solid forecast and threat messaging starting point, with
the broad blend tending to mitigate differences as consistent with
individual predictability. This plan maintains good WPC product
continuity in line with latest 12 UTC guidance trends.

...Weather/Hazards Highlights...

The region with heaviest rainfall going into the second half of the
work week will be across the Northern Plains on the back side of
the developing surface low. Although rainfall rates are not
expected to be all that high, multiple hours of moderate rainfall
with rates of half an inch per hour in some cases may just be
enough to cause some minor flooding issues in vulnerable areas, and
therefore the Marginal Risk area has been maintained for Wednesday
(Day 4) from eastern Montana into western North Dakota. Going into
Thursday (Day 5), the heavier rainfall reaches eastern North Dakota
into northern Minnesota where a Marginal Risk area is now planned,
with some of the guidance indicating the potential for 1-2 inch
rainfall totals with some embedded convection.

Elsewhere across the nation, explicit QPF has recently trended a
little lower for the Mid-Atlantic region for Wednesday as the
forcing associated with the upper low weakens and convection is
more scattered and less organized. After recent consultation with
affected WFOs, a prior issued WPC ERO Marginal Risk threat area was
dropped for the Day 4/Wednesday period. However, lingering moisture
and slow translation of remaining activity could be locally
problematic for areas the end up getting precursor heavy rainfall.
The Storm Prediction Center shows a threat for some severe storms
on Thursday across portions of the Midwest. Out West, Old Man
Winter will continue to make its presence known across the Northern
Rockies with heavy snow for the highest ranges of southwestern
Montana and northern Wyoming, with the potential for 6-12 inches of
accumulation in some cases. Lighter snows are likely elsewhere for
higher terrain of the Northern Rockies and Intermountain West.

Very warm weather will continue across the Upper Midwest for the
middle of the week, with highs reaching 85-90 degrees on Wednesday
across the eastern Dakotas and much of Minnesota. The anomalous
warmth then shifts eastward to the Great Lakes and Ohio Valley
regions to close out the week, and much of the East Coast Friday
into Saturday ahead of the cold front. Very hot conditions are
expected across southern Texas for the entire forecast period with
highs exceeding 100 degrees near the Rio Grande, and HeatRisk
reaching the major category for these areas. In contrast, chilly
conditions are likely for the Intermountain West and Northern
Rockies with highs running 5-15 degrees below average with the
upper level trough and increased cloud cover.

Hamrick/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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