051
ACUS02 KWNS 201759
SWODY2
SPC AC 201758

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1258 PM CDT Mon May 20 2024

Valid 211200Z - 221200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN
IOWA...NORTHWEST ILLINOIS AND FAR NORTHEAST MISSOURI...

...SUMMARY...
Severe storms are expected Tuesday across the Midwest, especially
including portions of Iowa and Missouri into Wisconsin and
western/northern Illinois. Tornadoes (a few strong), damaging wind
gusts, and large hail are expected.

...Lower/Middle Missouri Valley to the Upper Great Lakes...
A notably strong belt of cyclonically curved westerlies (70+ kt 500
mb) will extend from the south-central Great Plains to the Upper
Midwest and Upper Great Lakes on Tuesday, with a lead/convectively
augmented shortwave trough likely to spread from the central High
Plains toward the Lake Superior vicinity late Tuesday night. An
elongated surface low over eastern Nebraska Tuesday morning will
deepen and lift northeast to northern Wisconsin/Upper Michigan by
evening, with a surface warm front lifting northward ahead of the
surface low, although its effective position will likely be
influenced by the early day precipitation. Meanwhile, a trailing
cold front will surge east across Iowa/eastern Kansas/northern
Missouri from mid-afternoon into the evening.

Remnant clusters of storms will likely be ongoing Tuesday morning
across central/eastern Nebraska, with the possibility of additional
storms farther east across southern Iowa/northern Missouri in
association with a warm-advection regime. Some key uncertainties
persist about the influences of this early day convection, but
trends will be for quick air mass recovery given a
progressive/highly dynamic pattern.

Very steep mid-level lapse rates will overspread the increasingly
moist warm sector, supporting aggressive diurnal destabilization
especially on the southern fringe of lingering convection/cloud
cover. Significantly strengthening mid-level winds and a diurnally
persistent strong low-level jet will support initial supercells
capable of large hail and a few tornadoes, including strong (EF2+)
tornado potential. But a mixed/transitional mode is expected
overall, as upscale growth occurs given the degree of forcing for
ascent, with likely evolution into a well-organized/fast-moving QLCS
capable of increasingly widespread/intense damaging winds and a
continued QLCS-related tornado risk. This scenario currently appears
to be most probable across southern/eastern Iowa into northwest
Illinois and nearby far northern Missouri. The severe risk will
persist into the Upper Great Lakes region and middle Mississippi
Valley overnight.

...Southern Plains...
Convective coverage will likely decrease with southward extent as
large-scale ascent focuses northward toward the Great Lakes.
Nevertheless isolated storms are possible into northeast
Oklahoma/northwest Arkansas by late afternoon/evening, and more
conditionally with southwest extent near a dryline from central
Oklahoma into central Texas. Large hail and severe gusts will be
possible with this activity.

...Northeast States...
A weak upper shortwave trough will move across southern Quebec and
northern New England. This will result in a band of enhanced
westerly deep-layer flow from northern New York into Maine. A
seasonally moist airmass will be in place with surface dewpoints
into the low 60s F, with strong heating and steepening low-level
lapse rates. MLCAPE to around 1000 J/kg and effective shear
magnitudes around 35 kt will support organized cells. Elongated
hodographs and favorable vertical shear suggest marginally severe
hail will be possible along with locally damaging wind gusts.

..Guyer.. 05/20/2024

$$