Mesoscale Discussion 2180
NWS Storm Prediction Center Norman OK
1238 PM CDT Mon Aug 31 2026

Areas affected...Southwest Utah into northwest Arizona and far
eastern Nevada

Concerning...Severe potential...Watch unlikely 

Valid 311738Z - 312015Z

Probability of Watch Issuance...20 percent

SUMMARY...Thunderstorms will increase in coverage across portions of
the Great Basin through early evening, and may pose a localized
threat of large hail and severe winds. This threat should remain
sufficiently isolated to preclude watch issuance.

DISCUSSION...Thunderstorm development is evident across western UT,
northwest AZ, and far eastern NV based on recent GOES imagery and
lighting trends. This comes as daytime heating of a seasonally moist
air mass erodes residual inhibition and ascent ahead of an
approaching low-amplitude upper wave overspreads the region. Based
on latest forecast soundings and RAP mesoanalysis estimates, MUCAPE
values are likely increasing into the 1000-2000 J/kg range through
the lower CO River Valley under a pocket of colder mid-level
temperatures. Although buoyancy generally decreases with northward
extent, a combination of mid-level cold advection and continued
daytime heating should augment buoyancy region-wide through late
afternoon and support a steady increase in thunderstorm coverage. 

Recent VWP observations from KICX recently sampled 50-55 knot flow
near 6 km AGL atop weaker low-level winds. While hodograph structure
is somewhat poor, sufficient deep-layer wind shear is in place to
promote organized convection - including a few transient supercells
- capable of producing large hail. With time, storm mode will likely
become a modulating factor to large hail production as storm
coverage increases and clustered modes become more probable.
However, this may promote cold pool consolidation through late
afternoon when low-level lapse rates will be maximized.
Consequently, the potential for severe wind gusts may increase
through late afternoon/early evening as convection spreads
north/northeast across western UT. 

Regardless, latest time-lagged CAM ensembles appear to be capturing
recent convection trends will and generally suggest that the overall
severe hail/wind threat should remain too widely spaced/isolated to
warrant watch issuance.

..Moore/Gleason.. 08/31/2026

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...FGZ...SLC...VEF...LKN...

LAT...LON   35861380 36261388 36841410 37591451 38021462 38721461
            39721416 40071351 40161283 39931211 39521161 39181137
            38481138 37751144 37261159 36751179 36081197 35151259
            34941296 34931346 34931368 35031387 35181400 35481397
            35861380 

MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1126 AM CDT Mon Aug 31 2026

Valid 311630Z - 011200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER MIDWEST/GREAT LAKES INTO WESTERN NEW YORK...THE CENTRAL
PLAINS...AND LOWER COLORADO RIVER VALLEY INTO THE GREAT BASIN...

...SUMMARY...
Isolated strong to severe thunderstorms may occur this afternoon
into tonight across parts of the Upper Midwest/Great Lakes into
western New York, the central Plains, and lower Colorado River
Valley into the Great Basin. Severe hail and strong/damaging winds
should be the main threats.

...Upper Midwest/Great Lakes into Western New York...
A closed mid/upper-level low over the northern Plains and
Saskatchewan/Manitoba will move generally eastward today, with a
mid-level anticyclone remaining centered over the mid MS
Valley/Mid-South through the period. Between these two features, a
belt of enhanced westerly mid-level winds will overspread parts of
the Upper Midwest and Great Lakes. A rather moist and strongly
unstable airmass is expected to be in place this afternoon across
portions of WI/MI ahead of a weak front. While there are still some
concerns about convective initiation and overall thunderstorm
coverage, it appears that a weak mid-level perturbation over eastern
NE/western IA late this morning will track northeastward towards WI
by late afternoon/early evening. This feature may aid the
development of isolated to widely scattered thunderstorms across
parts of WI into the U.P. of MI.

Given strong to very strong instability and moderate to strong
deep-layer shear forecast, widely spaced supercells capable of
producing large hail appear possible late this afternoon into the
evening across these areas, if convection develops. Considered
greater hail probabilities to account for this scenario, but warm
low-level temperatures (around 850 mb) and mixed signals in
high-resolution guidance cast enough uncertainty on coverage to
defer upgrading with this update. Thunderstorms may also spread from
Lower MI into western NY tonight into early Tuesday morning.
Increasing low-level moisture and related instability may support an
isolated threat for damaging winds with this activity, even though
lapse rates aloft should remain modest.

...Central Plains...
High-based thunderstorms should develop this afternoon across the
higher terrain of the central Rockies/Front Range, and spread
east-northeastward across the adjacent High Plains through the
evening. While low-level moisture/instability will remain limited
across eastern CO and vicinity, steepened low/mid-level lapse rates
amid a very well-mixed boundary layer may still support isolated
strong to severe downdraft winds with this activity. Occasional hail
may also occur with the strongest cores. Thunderstorm coverage
farther east across NE along/near a weak front remains uncertain.
But, any convection which can develop and be sustained across this
area may also pose an isolated severe threat.

...Lower Colorado River Valley into the Great Basin...
A mid-level shortwave trough over CA will move northeastward across
NV today and aid thunderstorm development as the boundary layer
warms into this afternoon across parts of the lower CO River Valley
and Great Basin. Some enhancement to the mid-level flow is forecast,
which should support sustained updrafts and possibly a few transient
supercells, primarily across far eastern NV, southwest UT, and
northwest AZ. Isolated severe hail could occur with these cells.
But, strong to severe wind gusts will probably become the primary
risk with time given steep low-level lapse rates and tendency for
convection to cluster through the late afternoon/early evening.

...Coastal/Southeast Texas into Southern Louisiana...
Reference NHC forecasts/advisories for the latest information on PTC
Five over the northern Gulf. Latest model guidance continues to
suggest that low-level easterly flow on the northern side of this
system will only modestly strengthen before landfall tomorrow. As
such, the degree of low-level shear appears too limited to warrant
low severe wind or tornado probabilities at this time.

..Gleason/Moore.. 08/31/2026

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1230 PM CDT Mon Aug 31 2026

Valid 011200Z - 021200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF
PENNSYLVANIA...NEW JERSEY...AND FROM WESTERN NEW YORK TO THE LOWER
HUDSON VALLEY...

...SUMMARY...
Scattered strong to severe storms are possible Tuesday over parts of
New York, Pennsylvania and New Jersey. Isolated severe storms may
also extend westward into Nebraska.

...Much of Southern NY and PA...NJ...Lower Hudson Valley...
Scattered morning thunderstorms are expected over parts of the
region Tuesday morning, as westerly low-level winds maintain a
theta-e plume. This activity is likely to wane throughout the day as
low pressure redevelops over NY. Destabilization will occur
generally near and west of the Hudson River, with MLCAPE averaging
3000 J/kg. This will also occur beneath midlevel northwesterly winds
near 40 kt.

Storms are expected to redevelop along the effective warm front,
perhaps over the lower Hudson Valley, and these would likely move
southeast/to south with hail and localized damaging wind potential.
Other activity may develop over northeast PA/NJ near the surface
low, and, farther upstream near the Lower Great Lakes. Low-level
shear will be greatest near the Hudson Valley and the instability
gradient, and this increased shear could support a brief tornado.

...NE into southern MN & WI...
A lead wave is forecast to move out of CO and across NE, SD, and MN
Tuesday. Midlevel winds are forecast to strengthen into the 40-50 kt
range, though temperatures aloft will not cool much. Meanwhile, a
stalled font will extend roughly from central NE into IA. Strong
heating and boundary layer mixing will occur south of this front,
where dewpoints should hold in the 60s F. The result will be a zone
of moderate instability and shear, conditionally favoring supercells
with large hail and locally damaging gusts.

Storms may develop during near the boundary and farther south near a
surface low over NE as strongly heated air mass develops. Due to
uncertainty in storm coverage, will maintain 5% severe
probabilities. 

...Upper TX Coast...
Potential Tropical Cyclone 5 is forecast to move toward the Upper TX
Coast on Tuesday. Wind fields are forecast to remain relatively
concentrated, and not particularly strong. As such, tornado
potential appears low at this time. Subsequent forecasts cycles will
continue to monitor the potential for stronger-than-forecast shear
and possible introduction of 2% tornado probabilities.

..Jewell.. 08/31/2026

Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1150 AM CDT Mon Aug 31 2026

Valid 311700Z - 011200Z

The forecast remains on track with no changes made to the Day 1 Fire
Weather Outlook. Please see previous discussion for more details.

..Williams.. 08/31/2026

.PREV DISCUSSION... /ISSUED 1203 AM CDT Mon Aug 31 2026/

...Synopsis...
A modest increase in southwesterly flow across the northern Sierra
will promote a weak surface trough within the Northwest into
northwestern Nevada. Modestly dry and breezy conditions will develop
during the afternoon as downslope winds increase to 15-20 mph.
Afternoon RH of 15-20% can be expected. While meteorological
conditions will be somewhat marginal, very dry fuels will support an
elevated fire weather threat today.

...Please see www.spc.noaa.gov/fire for graphic product...