ACUS02 KWNS 200601
SWODY2
SPC AC 200600

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Mon May 20 2024

Valid 211200Z - 221200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
MISSOURI VALLEY TO CENTRAL WISCONSIN...

...SUMMARY...
A broad area of severe-thunderstorm potential is expected from the
southern Plains to the upper Great Lakes. The highest concentration
of severe storms is expected from eastern Kansas to southwest
Wisconsin. Tornadoes (a few strong), damaging gusts, and large hail
are possible through Monday night.

...Lower Missouri Valley to the Upper Great Lakes...

An upper shortwave trough over the central High Plains Tuesday
morning will spread northeast to the upper Great Lakes through the
forecast period. This will result in strong height falls
(particularly across IA/MN/WI) and strengthening surface
cyclogenesis. An elongated surface low over eastern NE Tuesday
morning will deepen and lift northeast to northern WI/Upper MI by
evening. A surface warm front will lift north ahead of the surface
low, becoming positioned across central WI by 00z. Meanwhile, a
trailing cold front will surge east across IA/eastern KS/northern MO
from mid-afternoon into the evening. The cold front will continue
east overnight, becoming positioned from western Lower MI to central
MO and northwest OK by Wednesday morning.

One point of uncertainty on Tuesday is expected morning convection
across IA into southeast MN and WI. Most guidance quickly moves this
activity northeast with airmass recovery occurring quickly in a
strong warm advection regime and progressive/dynamic large-scale
pattern.

An EML plume, characterized by midlevel lapse rates greater than 8
C/km, will overspread the region along with an increase 850-700 mb
jet (50-70 kt) by afternoon and into the evening. This should
support airmass recovery in the wake of morning convection. A broad
warm sector, with surface dew points in the mid/upper 60s F will be
in place. The moist boundary layer beneath steep to very steep
midlevel lapse rates will result in a corridor of strong instability
(greater than 2000 J/kg MLCAPE) from eastern KS into southwest WI.
Large and favorably curved low-level shear profiles will be present
as indicated by forecast hodographs. While supercell wind profiles
are evident, a mixed mode scenario is possible with discrete
supercells developing initially with potentially rapid upscale
growth into a QLCS given both strong large-scale ascent and frontal
forcing. Regardless, tornadoes will be possible with either
convective mode, and a few strong tornadoes are possible.
Severe-gust potential will increase a upscale growth ensues, with
some potential for significant gusts (greater than 65 kt). Large
hail will also be possible with any more discrete or line-embedded
supercells.

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
OK/northwest AR by late afternoon/evening, and more conditionally
with southwest extent near a dryline from central OK into central
TX. Large hail and severe gusts will be possible with this activity.

A QLCS will likely continue through the overnight hours into parts
of Lower MI, northern IN, and central IL/MO. Damaging gusts will
become the primary risk overnight, but a couple of tornadoes also
will be possible.

...Northeast...

A weak upper shortwave trough will move across southern Quebec and
northern New England through Wednesday evening. This will result in
a band of enhanced westerly deep-layer flow from northern NY into
ME. A seasonally moist airmass will be in place with surface
dewpoints into the low 60s. Strong heating will result in 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 gusts.

..Leitman.. 05/20/2024

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