Flash Flooding and Hail in Iowa, August 19, 2022

Area Forecast Discussion
National Weather Service Des Moines IA
108 PM CDT Fri Aug 19 2022

...Updated for the 18z Aviation Discussion...

.DISCUSSION...

Key Messages:

- Strong to severe thunderstorms possible today with large hail
  and damaging winds the main threats.

Discussion:

The much anticipated late week system arrived on our doorstep last
night as a surface front associated with the leading edge of the
shortwave trough pushed across the area. By 2am this was east of the
I-35 corridor and much of the convective activity has diminished.
Skies have cleared rapidly behind the convection and temperatures in
those areas have dropped off. This, combined with calm wind behind
the boundary has allowed for a few pockets of fog to develop in
northwest iowa. It is possible that this will expand across
northern, and perhaps into central, Iowa through the morning so
we'll continue to monitor for possible impacts to the morning
commute.

The first part of the day will be a dry period between the exiting
surface boundary and the next round thunderstorms associated with
the primary cold front. Thunderstorms will develop this afternoon as
daytime heating helps to erode the cap. Steep lapse rates with cool
mid levels will aid in the development with deeper updrafts while
deep layer shear of 30-40kts (particularly towards southern Iowa)
will help to organize storms. As such, the primary hazard looks
to be large hail with damaging winds possible as well, especially
towards southern Iowa with drier low levels in model soundings.
We've talked about the funnel cloud potential the past several
days and this remains a possibility with updrafts today as CAMs
indicate areas of 100-200+ J/kg 0-3km CAPE. Some of the higher
cloud bases could thwart this, as mentioned in the previous AFD,
but still worth monitoring.

The severe threat will come to an end Friday night but showers and
thunderstorms will linger over central and eastern Iowa into
Saturday as the slow moving low continues to rotate through the
area. Though thunderstorms are not expected to become severe, the
possibility for funnel clouds remains with the same low level
instability in place, enhanced as the the surface low cuts across
the area. In addition to the precipitation, Saturday will be on
the cool side with highs in the 70s thanks to lingering
clouds/rain and northerly flow.

Recent guidance form both CAMs and synoptic models have trended
drier for Saturday night with a quicker exit as the system lifts
into the Great Lakes region. Sunday will see temperature in the
80s to low 80s with dry conditions. Similar weather is forecast
into next week with temperatures gradually warming.

&&

.AVIATION.../For the 18Z TAFS through 18Z Saturday afternoon/
Issued at 100 PM CDT Fri Aug 19 2022

Ceilings should be mostly VFR this afternoon with some scattered
clouds at MVFR heights. Showers and storms moving in from the
north could also lead to lower ceilings for sites impacted.
Confidence is fairly low on exact location of showers and storms,
but all sites in the area could potentially see some vicinity
lightning or showers through the evening. Tomorrow morning,
ceilings and visibility could drop into IFR, but have kept TAFs
MVFR for now and will re-assess at next issuance. Patchy fog is
also possible in the northwest, but is also not yet reflected in
the TAFs.

&&

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

DISCUSSION...Hagenhoff
AVIATION...Dodson/Donavon

Hazardous Weather Outlook
National Weather Service Des Moines IA
1113 AM CDT Fri Aug 19 2022

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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-
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Appanoose-Davis-
1113 AM CDT Fri Aug 19 2022

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

Scattered thunderstorms are expected again today. A few strong to
severe storms will be possible this afternoon into the evening
with large hail and damaging wind gusts the primary threats.
There may also be some funnel clouds with a few of the storms
today.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Scattered, mainly non-severe, thunderstorms will continue into
Saturday. Gusty winds and perhaps a few funnel clouds may also
occur.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed this afternoon and evening.