445
ACUS01 KWNS 160557
SWODY1
SPC AC 160556

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1256 AM CDT Mon Sep 16 2024

Valid 161200Z - 171200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN PLAINS...

...SUMMARY...
Thunderstorms capable of severe gusts and large hail are expected
today in parts of the northern Plains. An isolated tornado threat is
expected in the Carolinas. Marginally severe wind and hail may occur
in parts of the Four Corners and Intermountain West.

...Northern Plains...
Southwest mid-level flow will be in place across the north-central
U.S. today. A shortwave trough is forecast to move across North
Dakota this afternoon. At the surface, a low will deepen across
southeast Montana as a warm front moves northward across central and
eastern North Dakota. Surface dewpoints near the front will be in
the mid to upper 60s F and moderate instability is expected to
develop by afternoon. The front will be a focus for convective
initiation from late this morning into the afternoon. RAP forecast
soundings near the front in east-central North Dakota have 0-6 km
shear in the 30 to 35 knot range with some directional shear in the
boundary layer. Mid-level lapse rates are forecast to be between 7.5
and 8 C/km. This environment should support supercells with severe
gusts and large hail. The event will be driven by mesoscale
processes, and the greatest severe threat coverage will likely be
located in areas where the maxima in low-level convergence,
instability and deep-layer shear become juxtaposed. The severe
threat may ramp up during the early evening as a 40 to 50 knot
low-level jet strengthens across the northern Plains.

...Eastern North Carolina/Far Eastern South Carolina...
A low pressure area off the coast of the Carolinas is forecast to
become a tropical storm by the National Hurricane Center and move
northwestward into far eastern South Carolina this evening. RAP
forecast soundings to the right of the expected landfall at
Wilmington, North Carolina have 0-3 km storm-relative helicity
increasing to around 150 m2/s2 by early evening with 0-1 km shear
reaching the 20 to 25 knot range. This should support an isolated
tornado threat as the tropical storm moves inland this evening. This
threat may continue into the late evening and overnight along the
coast of North Carolina, where moderate instability is forecast.

...Four Corners/Intermountain West...
An mid-level low will move northeastward across the Intermountain
West today. Ahead of the system, a band of strong large-scale ascent
will aid thunderstorm development from the Four Corners region
northwestward across parts of Utah. Scattered storms will likely
develop and move northeastward across the region during the
afternoon. Although instability will remain weak, very steep lapse
rates and strong deep-layer shear may support an isolated severe
threat. Marginally severe wind and hail will be possible with the
stronger cells.

..Broyles/Weinman.. 09/16/2024

$$