Mesoscale Discussion 2272
NWS Storm Prediction Center Norman OK
0733 PM CDT Tue Sep 08 2026

Areas affected...parts of south central and southeastern Iowa

Concerning...Severe potential...Watch unlikely 

Valid 090033Z - 090230Z

Probability of Watch Issuance...20 percent

SUMMARY...A loosely organized cluster of storms may continue to pose
a risk for severe wind and hail another hour or two, but seems
likely to weaken as it approaches the southeastern Iowa Mississippi
River vicinity toward 10-11 PM CDT.  At this point a severe weather
watch is not anticipated, but trends will continue to be monitored.

DISCUSSION...A strong downburst, and perhaps an associated
developing meso-beta scale cyclonic circulation, associated with
intensifying convection initially above/to the cool side of a fairly
sharp low-level baroclinic zone, overtook the boundary across and
east of the Des Moines area 1-2 hours ago.  This remains the case as
activity propagates east-southeastward near and to the northeast of
the Knoxville IA vicinity.  

Probably initially supported by an influx of seasonably moist
boundary-layer air characterized by CAPE on the order of 2000-3000
J/kg, it remains unclear how long this will be maintained into this
evening.  There has been some recent increase in surface dew points
along/just ahead of the convection and wave along the boundary,
accompanied by an increase in initially more modest CAPE toward the
Mississippi River.  However, with little in the way of cooling
aloft, and at least gradually surface cooling underway, it remains
unclear how long large-scale and mesoscale ascent will overcome
increasing inhibition.

..Kerr/Gleason.. 09/09/2026

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

ATTN...WFO...DVN...DMX...

LAT...LON   41519351 41749253 41909240 41889172 41809094 41449030
            40899087 40809202 40869243 41139333 41519351 

MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0736 PM CDT Tue Sep 08 2026

Valid 090100Z - 091200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS EVENING
ACROSS PORTIONS OF IOWA...

...SUMMARY...
A few severe storms capable of mainly severe wind gusts appear
possible across portions of Iowa this evening.

...Discussion...
Widely scattered thunderstorm activity continues across the surface
boundary extending from portions of central/southern Iowa into
southern Nebraska and northern/western Kansas. A more organized
cluster is ongoing across portions of south-central Iowa. This
cluster will continue to pose a wind threat for the next couple of
hours before eventually moving southeast into less favorable air
across southeastern Iowa/western Illinois. Additional convection
will evolve overnight with the increasing low-level jet across
central Kansas into southeastern Nebraska and southern Iowa. This
will pose at least some potential for small hail and strong to
severe wind.

Across Colorado, scattered convection is ongoing near the foothills
of the Front Range. Time lagged HRRR/RRFS guidance continues to
suggest that this evolves into a cluster with potential for strong
to severe wind to continue downstream this evening. Though moisture
is limited, very warm surface temperatures and steep low to
mid-level lapse rates are supporting at least marginally unstable
conditions downstream.

..Thornton.. 09/09/2026

Day 3-8 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0456 PM CDT Tue Sep 08 2026

Valid 101200Z - 161200Z

...Synopsis...
A mid-level shortwave trough will descend into the northwestern U.S.
as a surface cyclone traverses the Canadian Prairies on Day
3/Thursday. Strong flow aloft and a tightening surface pressure
gradient will promote widespread dry and breezy conditions across
the northern Great Basin into the northern Plains. A strong cold
front will then navigate the north-central states as the shortwave
trough departs on Day 4/Friday; meanwhile, dry west-southwesterly
flow will overspread the northwestern CONUS. Ensembles are in
general agreement for an upper-level low to invade the Pacific
Northwest and Northern Rockies this weekend. This pattern may
provide broader precipitation chances and much cooler temperatures,
thus subduing fire weather concerns across most of the
northwestern/northern CONUS into early next week.  

...Central Rockies into the Northern High Plains...
A dry airmass and strong winds will expand across the northern Great
Basin into the northern Plains on Day 3/Thursday. Westerly sustained
winds of 15-25 mph and 10-20% RH values will increase fire weather
concerns from far eastern ID/southwestern MT into the northern
Plains where 80-95th percentile ERCs exist. Poor overnight humidity
recoveries are forecast across eastern WY, western SD, and the NE
Panhandle leading into a second consecutive day of concern; on Day
4/Friday, RH values will quickly decline to 10-20% as winds
accelerate ahead of an advancing cold front. Sustained westerly
winds may approach 25 mph across the terrain-favored plains, then
shift to northerly as the front passes. Notably, guidance indicates
a 50-80% probability of wind gusts exceeding 35 mph through the
afternoon. 40% Critical probabilities have been introduced on Day
4/Friday across southeastern WY, northwestern NE Panhandle, and
southwestern SD to account for this threat. 

...Northeastern California and western Great Basin...
An Eastern Pacific upper low will impinge upon the northwestern U.S.
on Day 5/Saturday, amplifying west-southwesterly flow over northern
CA and the western Great Basin. Ensemble guidance depicts 70-90%
probabilities of wind speeds exceeding 20 mph amid critically low RH
in northeastern CA and northern NV, which would typically enhance
fire weather concerns. However, forecast ERCs at the 50-70th
percentile should mitigate a broader threat.

..Elizalde-Garcia.. 09/08/2026

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