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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1252 AM CDT Wed Aug 21 2024

Valid 211200Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
EASTERN MONTANA AND WESTERN NORTH DAKOTA....

...SUMMARY...
Scattered thunderstorms, some with severe hail and damaging gusts, 
are expected to develop today over parts of far eastern Montana and
western North Dakota.

...Synopsis...
A mid-level shortwave trough over north-central California early
this morning will move across the Great Basin and emerge across
eastern Montana this afternoon. This shortwave trough will be the
focus for a severe weather threat this afternoon/evening across
eastern Montana and western North Dakota. Farther east, a mid-level
trough centered over the Plains will start to break down during the
day today. As this occurs, surface troughing is forecast to develop
from the northern Plains to the central High Plains. Scattered
strong to potentially severe storms are expected along the extent of
this surface trough from western South Dakota to eastern Colorado. 

...Eastern Montana and western North Dakota...
Significant heating is forecast across eastern Montana this
afternoon with temperatures forecast to warm into the mid to upper
90s (depending on the degree of mixing). This will result in
moderate instability and a mostly uncapped atmosphere by mid to late
afternoon. DCVA ahead of the approaching mid-level trough will
result in sufficient deep-layer ascent for thunderstorm development
by mid to late afternoon. These storms will likely be supercellular
in nature as mid-level flow strengthens to near 50 knots while the
associated mid-level jet streak overspreads the region. The
long-straight hodograph may also support some splitting storms.
Large hail (up to golf ball size) and severe wind gusts of 60 to 80
mph will be the primary threats associated with this activity. 

...Western South Dakota to eastern Colorado...
Scattered thunderstorm activity is expected within a broad surface
trough from western South Dakota to eastern Colorado where moderate
to strong instability will be in place by mid-afternoon. Mid-level
flow will be mostly weak across this region (15 to 20 knots) which
will limit the overall shear magnitude. However, moderate
southeasterly flow ahead of this surface trough, coupled with the
westerly mid-level flow may result in adequate shear for storm
organization and perhaps a few slow-moving supercells. The deeply
mixed boundary layer across this zone will support a threat for
severe wind gusts with isolated hail as a lesser threat
(predominantly associated with any more robust supercell development
which may occur). A few regions within the marginal risk may have a
greater threat (southwest South Dakota/northern Nebraska and
northeast Colorado), but it is not clear at this time whether
coverage/intensity will be sufficient for a slight risk.

...Southeast Arizona...
A surge of monsoon moisture across southern Arizona will result in
moderate (1500-2000 J/kg MLCAPE) instability and scattered to
widespread thunderstorm development this afternoon. Storm
organization will likely be somewhat weak given the weak shear (~15
knots). However, the moderate instability in a deeply mixed boundary
layer will support an isolated severe-wind threat. In addition, the
widespread nature of the convection will likely result in numerous
outflow boundary collisions which may locally enhance updraft
intensity and support a few stronger cells.

..Bentley.. 08/21/2024