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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Mon May 20 2024

Valid 12Z Mon May 20 2024 - 12Z Wed May 22 2024

...Continued severe weather and excessive rainfall threats over the
central U.S. into mid-week...

...Cool conditions with periods of shower and storm chances from the
Rockies to the Pacific Northwest...

...Well above average, Summer-like temperatures to start the week across
much of the central/eastern U.S...

An energetic upper-level pattern featuring multiple shortwaves emitting
from a broader long-wave trough over the western U.S. will continue a
period of active weather over the central U.S. this week. An initial
shortwave/accompanying surface frontal system will bring showers and
thunderstorms to portions of the Upper Midwest/Great Lakes Region by early
Monday. A few more robust thunderstorms will be possible immediately ahead
of the wave over northeastern Illinois and adjacent Wisconsin/Indiana,
where the Storm Prediction Center has issued a Slight Risk of severe
weather (level 2/5) for the threat of some damaging winds and large hail.
Some locally heavy downpours and isolated flash flooding will also be
possible. Further west, lee cyclogenesis is expected over the central High
Plains as the long-wave trough further amplifies, helping to reinforce a
frontal boundary draped across the region. Moist upslope flow north of
this boundary is expected to lead to thunderstorms by Monday afternoon,
with an Enhanced Risk of severe weather (level 3/5) over northeastern
Colorado and southwestern Nebraska as some of the more robust storms may
produce very large hail, significant damaging winds, and a few tornadoes.
A broader Slight Risk extends northeastward along the front through the
central Plains into the Upper Midwest. Increasing storm coverage Monday
evening with the potential for some locally heavy downpours will also
bring the threat for some isolated flash flooding from northeastern
Colorado northeast into northwestern Iowa. Moisture spreading
northwestward into portions of the northern High Plains/Rockies will bring
moderate precipitation chances here as well, with some locally heavy
snowfall totals possible for higher mountain elevations.

Another shortwave ejecting from the longwave western trough will bring a
broader, greater chance for severe weather and flash flooding to portions
of the Midwest Tuesday. The accompanying surface low pressure/frontal
system will deepen and lift northeastward from the Plains into the Upper
Midwest, with an expansive warm sector from the Southern Plains
northeastward through the Lower Missouri and Upper Mississippi Valleys.
Both supercells and more organized convective systems are expected amidst
strengthening low and upper-level wind fields and strong instability. An
Enhanced Risk of severe weather is in place for the threat of tornadoes,
some strong, significant damaging winds, and large hail. In addition, a
deep influx of moisture as well as the strong forcing associated with the
deep surface low will help to promote heavy downpours. With more numerous
storms expected in vicinity of the surface low, a Slight Risk of Excessive
Rainfall (level 2/4) has been issued for portions of central/southern
Minnesota and northwestern Wisconsin for the risk of some scattered
instances of flash flooding. Lingering shower and thunderstorm chances
will also extend back west through the central Plains into the
central/northern Rockies.

Elsewhere, a few thunderstorms will remain possible over the Florida
Peninsula through at least Tuesday. An upper-low/frontal system dropping
southward from northwestern Canada will spread showers and storms into the
Pacific Northwest/northern Great Basin Tuesday, with some locally heavy
rainfall possible along the coastal ranges and Cascades. A broad area of
well above average temperatures is expected over much of the
central/eastern U.S. with ridging in place ahead of the trough over the
West. Highs in the 80s and even low 90s will be common, even in more
northerly locations from the Great Lakes into the Northeast. Sweltering
heat continues over portions of southern Texas into the southern High
Plains as highs soar into the 90s and 100s. In contrast, much cooler,
below average temperatures are expected to the north and west of the
system over the Plains under the influence of the western trough. Highs
from the Pacific Northwest into the Great Basin, northern/central Rockies,
and northern/central Plains will be in the 50s and 60s. Highs will be
closer to average in the Southwest with 80s and 90s forecast.