Hail and Damaging Winds in Iowa, August 27 to 28, 2022

Area Forecast Discussion
National Weather Service Des Moines IA
406 AM CDT Sat Aug 27 2022

.DISCUSSION.../Today through Friday/
Issued at 404 AM CDT Sat Aug 27 2022

Key Messages:

- Thunderstorms becoming widespread late today and tonight
- A few severe storms and heavy rain are possible.
- Pleasant and mostly dry next week.

A 50+ kt low level jet has developed this morning from eastern
Nebraska through nw Iowa and into Minnesota. Strong theta-e
advection is ongoing through much of eastern Iowa though the primary
focus is to the north into Minnesota. Some elevated radar returns
are showing up over north central Iowa though cloud bases remain
near 20 kft thus little to no precipitation is reaching the ground.
The thunderstorm activity is to the north with the stronger forcing
in Minnesota.

To the west, a short wave is moving into western Nebraska and
Kansas. That system will arrive later this afternoon and overnight
while another round of theta-e advection will commence across the
state ahead of the short wave. Ahead of this, conditions are
expected to destabilize across central Iowa though there remains
some uncertainty due to the potential for upper level cirrus to
limit surface heating which could delay thunderstorm initiation. The
CAMs and even the courser NAM are trending slower with thunderstorm
initiation until the upper level kinematic forcing arrives and a bit
further west. The initial thunderstorms will have a large hail and
damaging wind threat. The large hail threat should not last as long
as profiles saturate but descent lapse rates and relatively fat CAPE
does exist through around 500 mb for good updraft acceleration
before lapse rates weaken above that level. The 0-3 km theta-e
differences are around 25k which will promote sustained cold pools
which will aid the damaging wind threat.

Heavy rainfall is certainly possible with PWAT values in excess of 2
inches and profiles do eventually saturate with warm cloud depths
AOA 13 kft, all of which support efficient rain producing storms. In
addition, the 850-300 mb steering flow to the north/northeast
will also promote the training of storms over the same areas. A
widespread 1-2 inches of rain could occur with a localized area of
3 to 5 inches by Sunday morning. The agricultural land will be
able to absorb much of any heavy rainfall but as has occurred with
recent events, significant ponding or localized flooding can
occur in urban areas with these types of rainfall, especially if
it occurs over short periods.

A break in the rain should occur much of Sunday in what will be a
warm and humid day. Another system will drop out of the northwest
and drag a cold front through the state late in the day and
overnight and will bring another chance for storms. A few strong
storms may occur with this system. Generally pleasant and dry
conditions will follow for much of next week as high pressure ridge
at the surface and northwest flow aloft dominate the weather. High
temperatures in the 70s to low 80s with overnight lows in the 50s
will be common.

&&

.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1120 PM CDT Fri Aug 26 2022

VFR conditions currently prevail across the area. Isolated TSRA
activity is forecast after 07z, affecting mainly north central
Iowa. Mentioned TEMPO TSRA and KMCW to cover potential threat.
More widespread shower and thunderstorm activity is expected after
20z. Brief drops to IFR/MVFR conditions are possible at times as
bouts of heavier precipitation move through, although these
periods are difficult to pin down for the terminal forecast at
this time.

&&

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

DISCUSSION...Donavon
AVIATION...Martin

Hazardous Weather Outlook
National Weather Service Des Moines IA
316 AM CDT Sat Aug 27 2022

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-280830-
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-
316 AM CDT Sat Aug 27 2022

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Thunderstorms are expected later this afternoon. Locally heavy
rainfall will be the primary concern today. A few stronger storms
may also produce gusty winds and hail.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

Thunderstorms are forecast to continue into Sunday with additional
redevelopment Sunday night into Monday. A few stronger storms are
possible again Sunday night, mainly across northern Iowa.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed, but rainfall reports are
always appreciated.

Dodson