170
ACUS01 KWNS 142001
SWODY1
SPC AC 141959

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0259 PM CDT Sun Jul 14 2024

Valid 142000Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
NORTHERN PLAINS AND THE MIDWEST INTO THE OHIO VALLEY...

...SUMMARY...
Strong to severe thunderstorms are still expected from the northern
Plains into the Upper Midwest and Ohio Valley this afternoon through
tonight.

...20Z Update...
The primary changes made to this outlook were to adjust severe
probabilities in the northern Plains to account for both the latest
guidance consensus, and reflect recent trends in observations and
re-analysis. Visible satellite and surface observations indicate a
northwest-to-southeast oriented baroclinic boundary draped over
extreme northeast MT/northwestern ND, down to central and eastern
SD, extending to the MN border. Though MLCINH remains over the warm
sector, and additional airmass modification is needed for
appreciable airmass recovery after earlier storms, several hours of
surface heating remain. Furthermore, this boundary may serve as a
focal point for deep-moist convection to initiate and anchor on
later this evening. Latest guidance consensus suggests that
supercell structures with mainly a hail threat will materialize
closer to the U.S./Canada by around 00Z (perhaps before).
Thereafter, upscale growth into an MCS is possible along the
baroclinic boundary. Should this occur, steep mid-level lapse rates,
along with adequate vertical wind shear may promote a corridor of
severe gusts, and a 75+ mph gust or two is possible, hence the
addition of a hatched area within the Northern Plains Category
2/Slight Risk.

The Slight Risk in the Midwest was also expanded a bit westward in
IA to account for potential westward convective initiation. This
convection may also form into an MCS and traverse the same areas
impacted by an earlier MCS, hence why changes were not made farther
east despite some convective overturning noted. Otherwise, the
forecast remains on track across the west of the CONUS.

..Squitieri.. 07/14/2024

.PREV DISCUSSION... /ISSUED 1117 AM CDT Sun Jul 14 2024/

...Synopsis...
West-northwesterly flow aloft is in place today across the northern
Plains and Midwest, with several small-scale features noted in
satellite imagery embedded in the flow.  This will result in
multiple MCSs from MT into the upper OH valley during this period.

...IN/OH this afternoon...
A linear MCS is currently ongoing over portions of northwest IN and
northeast IL.  Strong heating ahead of the system across much of
IN/OH, combined with surface dewpoints near 70F will yield a
corridor of moderate CAPE, likely aiding intensification of storms.
Given 20-25 knots of mid-level flow and relatively steep mid-level
lapse rates, a few strong to severe storms are possible through the
afternoon.  Please refer to MCD #1612 for further details.

...Eastern IA/Southern WI/Northern IL/Northern IN...
Strong heating is occurring in wake of aforementioned MCS across
parts of eastern IA/southern WI/northern IL, where ample low-level
moisture remains.  A well-defined remnant MCV from the overnight
severe MCS over SD is currently over northern IA, and will track
into the destabilizing air mass.  A consensus of morning CAM
solutions suggest that thunderstorms will develop ahead of the MCV
and track toward northern IL/IN this evening.  Damaging winds and
some hail would be the main threats.

...Northeast MT/Dakotas/Western MN...
Water vapor imagery shows a strong upper trough digging
southeastward across southern AB.  Large scale lift ahead of this
system will lead to scattered thunderstorm development by early
evening across portions of northeast MT and western ND.  Model
solutions remain diverse in the details of how this convective
scenario unfolds.  However, it appears likely that one or more
clusters of strong/severe storms will track across ND and into
northeast SD/western MN during the night.  Large hail and damaging
winds will be possible with these storms.

...Mid Atlantic...
Widely scattered afternoon thunderstorms are expected today from
parts of eastern VA northeastward into eastern PA and NJ.  Winds
through the low/mid troposphere are rather weak and lapse rates are
poor.  Nevertheless, ample low-level moisture and rather high PWAT
values may result in gusty winds near the strongest storms.

...AZ...
Clear skies early today combined with dewpoints in the mid 60s will
yield a hot and moderately unstable air mass this afternoon with
MLCAPE values of 1000-1500 J/kg.  Thunderstorms are expected to form
over the higher terrain of western NM/eastern AZ and along the rim
later today, with sufficient easterly mid-level flow to aid
propagation off the mountains.  Locally damaging wind gusts may
accompany these storms.

$$