Hail and Damaging Winds in Iowa, August 30 to 31, 2021

Area Forecast Discussion
National Weather Service Des Moines IA
628 AM CDT Mon Aug 30 2021

...Updated for 12z Aviation Discussion...

.DISCUSSION.../Today through Sunday/
Issued at 354 AM CDT Mon Aug 30 2021

Forecast Highlights:
-- Seasonable temperatures much of this week
-- Storm chances tonight into Tuesday morning
-- Additional storm chances late in the week

Details: The cold front that pushed through the state settled
farther south over central Missouri and have seen recent
thunderstorm development northwest of St. Louis, MO this morning.
GOES-East Nighttime Microphysics RGB shows an expansive area of
stratus clouds over Nebraska lifting northward in the warm air
advection over that area. There are also indications of patchy fog
in some river valleys, notably over southwestern Iowa/northwestern
Missouri and southwestern Wisconsin on the GOES-East Night Fog
imagery. Surface observations in central Iowa largely have
visibility above 6 miles. GOES-East upper level water vapor
imagery shows the fast westerly flow moving over the northern
states. For today, have removed any lingering PoPs until late this
afternoon leaving much of the daylight hours dry with
temperatures and humidity comparable to yesterday. Thunderstorm
chances will increase through the evening and overnight hours as a
mid-level shortwave trough, which the RAP analyzes approaching
the Oregon coast early this morning, moves into the region. This
trough interacting with the stalled boundary stretching through
Nebraska will be the focus for initial storm development over
parts of Nebraska and South Dakota later this afternoon. These
storms will likely move southeastward along this boundary and the
instability gradient. As these storms move into Iowa tonight,
their severity is expected to be waning with forecast soundings at
CRL and CSQ showing 25 to 30 knots of deep layer shear and a
shallow inversion meaning likely elevated storms. However, 6z HRRR
and 0z WRF ARW show a bowing segment moving into Iowa with
potential for strong wind gusts. If this bowing segment were to
materialize, the 06z HRRR and 00z HREF wind gusts look to be
largely below 50 knots as they move into our forecast area. If the
bowing segment does not materialize, then the elevated storms
would pose a hail risk. Overall, the severe risk is low with the
most likely location of a severe report in our west central or
southwestern counties if at all.

Conditions will turn drier and brighter through the day Tuesday as
the storms push out of the state. The mid-level shortwave will dive
southeastward as the remnants of Hurricane Ida move over Tennessee.
Ridging to the west of Iowa will develop with a warm front moving
across the state on Thursday and this may promote scattered storms
over northern Iowa into Minnesota. The ridge will be pushed eastward
on Friday as a lead shortwave trough rotates around a sprawling
closed low over central Canada. This will help to bring a cold front
into the state with scattered storms. While deep layer shear would
support strong storms, the instability is quite weak and not
supportive of stronger storms at this time, but will monitor trends
in the coming days. Another shortwave trough rounding the base of
the central Canadian closed low will help to finally push the cold
front through the state on Saturday and bring an end to the storm
chances.

&&

.AVIATION.../For the 12Z TAFS through 12Z Tuesday morning/
Issued at 628 AM CDT Mon Aug 30 2021

Primary concern this period is initial fog and then storm chances
toward the end of the period with much of the TAF period being VFR.
Patchy, locally dense fog at MCW and FOD will dissipate a little
after sunrise this morning. Winds will be light and where a
prevailing direction could not be ascertain, left VRB03KT.
Scattered storms are expected to develop with most likely timing
after midnight. With low confidence in timing, have just
introduced VCSH at FOD and DSM.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

DISCUSSION...Ansorge
AVIATION...Ansorge

Hazardous Weather Outlook
National Weather Service Des Moines IA
239 AM CDT Mon Aug 30 2021

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-310745-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-Carroll-Greene-
Boone-Story-Marshall-Tama-Audubon-Guthrie-Dallas-Polk-Jasper-
Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union-
Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-
Appanoose-Davis-
239 AM CDT Mon Aug 30 2021

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and Tonight

Thunderstorm chances return later today into tonight. The threat
of severe weather is low.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Storm acidified continues into early Tuesday, but severe weather
is not expected. Additional storms are possible Thursday and into
the weekend. The severe weather threat is more uncertain late in
the week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation in not likely