883
ACUS01 KWNS 150551
SWODY1
SPC AC 150550

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1250 AM CDT Mon Jul 15 2024

Valid 151200Z - 161200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS EASTERN IOWA
INTO NORTHERN ILLINOIS AND FAR NORTHWEST INDIANA...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE CENTRAL
HIGH PLAINS...MUCH OF THE MIDWEST...AND PARTS OF NEW YORK AND
PENNSYLVANIA...

...SUMMARY...
Severe thunderstorms are expected this afternoon and evening across
portions of the Midwest, central High Plains, and the lower Great
Lakes. The greatest potential for severe/damaging winds appears to
be across eastern Iowa into Illinois and Indiana. More isolated
strong to severe thunderstorms are possible across southeast Arizona
and the New England region.

...Synopsis...
A complex severe-weather setup is anticipated for today across the
Midwest with the potential for one or more severe MCSs. The details
of how the severe threat will evolve this afternoon/evening will be
conditional on convective evolution of ongoing MCSs across ND and
IL/IN through 12 UTC, which introduces considerable uncertainty into
the forecast. In general, a broad surface cyclone is forecast to
deepen slightly over the upper Great Lakes over the next 12-24 hours
as a low-amplitude mid-level wave traverses the northern CONUS. As
this occurs, a weak cold front (noted in surface obs across MT and
the western Dakotas as of 05 UTC) will migrate south into the
Midwest and central Plains by late afternoon. Thunderstorm
development and/or re-intensification is anticipated along this
boundary and on the northern periphery of a reservoir of a high
theta-e air mass in place over the central Plains.

...Midwest...
Recent CAM guidance depicts a range of possible scenarios for the
next 24 hour period. The most probable scenario involves the cluster
of thunderstorms ongoing across the Dakotas as of 05 UTC, which will
likely weaken by 12 UTC as it approaches the mid-MS River Valley.
The remnants of this complex may act as foci for re-development by
mid to late afternoon on the northeastern periphery of a reservoir
of high theta-e air (denoted by dewpoints in the low to mid 70s)
across IA, southern WI, and northern IL. Thunderstorms emerging from
this zone will likely organize and intensify into an organized MCS
as it propagates southeast into eastern IA and northern IL.

If the ND cluster weakens substantially by late morning, convective
initiation will likely be focused along the cold front as it
migrates south and/or along a residual outflow boundary from ongoing
storms. The location of initiation varies in latest model solutions,
which introduces uncertainty on where the corridors of relatively
higher severe-wind potential will be established. Higher wind
probabilities were placed based on where ensemble guidance shows the
best QPF signal, which likely correlates to where deep convection
will most likely occur. Additionally, forecast soundings suggest
sufficient low-level SRH may be in place to support a tornado threat
across eastern IA into northern IL; however, this threat will likely
be conditional on realizing a predominantly discrete storm mode
prior to upscale growth and/or embedded circulations with an
organized MCS.

...Northeast...
05 UTC regional radar imagery reveals a mature MCS ongoing across
northern IL/IN. A vorticity maximum associated with this system is
apparent over lower Lake Michigan, and is expected to migrate east,
reaching the lower Great Lakes by around 18 UTC. Mid-level lapse
rates are fairly modest across New England per 00 UTC soundings, but
dewpoints in the upper 60s/lower 70s should support around 500-1000
J/kg MLCAPE by peak heating. Thunderstorm development ahead of the
MCV appears likely based on latest CAM guidance, and slightly
augmented flow in the vicinity of the vorticity maximum should
result in around 25-30 knots of effective bulk shear. These
environmental conditions will likely be sufficient to support
organized convective clusters within a somewhat focused corridor
across parts of PA and NY.

...Central High Plains...
Steep mid-level lapse rates and mid-level moisture across the
central Rockies will foster another day of widely scattered
thunderstorms across CO and WY. Storms will migrate into the central
High Plains by late afternoon amid a mean easterly flow regime. Weak
low-level storm-relative winds and a deeply mixed boundary layer
should yield outflow-dominant storms, but stronger mid-level flow
compared to previous days may favor some thunderstorm
clustering/cold pool amalgamation. Consequently, a more focused
corridor of severe-wind potential may emerge across the central High
Plains. While the exact location of where such clusters may emerge
remains uncertain, ensemble guidance suggests this is most probable
across the NE Panhandle into northeast CO/northwest KS.

...Southeast Arizona...
Thunderstorm development is expected again along the eastern
portions of the Mongollon Rim and out of the Gila region of
southwest NM. Southwesterly flow out of Gulf of California will
maintain dewpoints in the upper 50s to low 60s that should support
MLCAPE values above 1000 J/kg. Warm temperatures in the upper 90s to
low 100s should support another day of 40-50 F dewpoint depressions
amid deep boundary-layer mixing. Storms moving off the terrain will
be capable of strong to severe downburst winds as they migrate into
the buoyant, but deeply mixed environment at lower elevations.

..Moore/Darrow.. 07/15/2024

$$