Severe Thunderstorm Warning 52, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
631 PM CDT Wed Apr 19 2023

...Updated for the 00z Aviation Discussion...

.DISCUSSION.../Tonight through Wednesday/
Issued at 225 PM CDT Wed Apr 19 2023

Key Messages:

- Multiple rounds of convection likely by later this evening and
overnight. Severe storms and locally heavy rainfall possible.
- Cool and blustery Friday through the weekend.

The potential for multiple rounds of thunderstorms over the next 18-
24 hours remains the primary forecast challenge. As of 19z GOES
water vapor imagery depicts mean troughing with several embedded
waves over the western conus. At the surface a warm front is draped
across central Iowa, noted on radar just between Hwy 30 and I80.
Warm, south winds below the front have pushed temps into the 70s and
dewpoints into the 50s to low 60s. Cooler conditions and more cloud
cover is evident north of the front with easterly winds and temps in
the 50s and 60s. The warm front extends westward toward an analyzed
sfc low center in southeast Nebraska, and an attendant dry line
stretching south through KS into OK.

First window for potential thunderstorm activity opens this
afternoon as hi-res models try to develop elevated convection in
northwest Iowa near the vicinity of a mid-level baroclinic zone.
Satellite imagery shows some agitated cu in the general vicinity,
but no robust updrafts to this point. Some small hail is possible
with any of this activity if/when it develops and moves north
into MN. Next opportunity has the potential to be more robust as
surface based convection activates along the dry line north and
east toward the sfc low triple point, likely near or into
southwest to west central Iowa. Model trends continue to favor
23-01z for CI as the LLJ cranks up. The shear/instability
parameter space will be conducive for strong, organized updrafts
capable of large hail and damaging wind gusts as the activity
pushes north and east. A few tornadoes cannot be ruled out,
particularly near the triple point where low level SRH will be
maximized. Hires models show storm modes eventually becoming more
clustered or linear with a deep cold pool. This could stall out
progression if it becomes perpendicular to the mean southerly low
level flow, however intensity is expected to wane a bit as this
occurs.

Convection becomes reinvigorated overnight as a shortwave trough
axis sweeps through the region. LLJ remains strong and actually
intensifies northward moisture transport into the state.
RAP/HRRR/ARW camp suggests there is some potential for this
convection to remain surface based and pose a QLCS tornado threat
given 0-3km bulk shear of 40-50 kts and storm motion relatively
parallel to the mean vector. However, it is unknown how the
boundary layer recovers after the initial round of storms.
Regardless, strong wind gusts and large hail will also remain a
concern even if updrafts are rooted off the surface. Locally heavy
rainfall of 1-2"+ may be realized in areas that see repeat rounds
of convection, although the threat for flash flooding looks low
at this time especially outside of urban areas.

Showers and storms linger into Thursday morning before dry air
advection and increasing deep layer subsidence clears it out by the
afternoon. This will give way to a blustery period with below normal
temps into the weekend as an upper low nearly stalls out over Lake
Superior and shoves cooler air southward into the region. Guidance
suggests highs only in the 40s and 50s. Some light shower activity
may develop as weak waves rotating around the parent upper low
interact with steep low level lapse rates within the caa regime. Dry
air will be a mitigating factor, but did go ahead and add PoPs into
northern Iowa where moisture is a bit deeper in model soundings.
Some or all of this precip may fall as snow. Little to no
accumulation is expected. Temperatures try to moderate early next
week, but models are becoming more stubborn to erode the cold air
mass. In addition, chances for showers and perhaps some storms
return as another upper low digs into the Rockies. Large model
variability grows considerably at this time range makes it
difficult to discuss any specifics.

&&

.AVIATION.../For the 00Z TAFS through 00Z Thursday evening/
Issued at 631 PM CDT Wed Apr 19 2023

Main concern will be 2 rounds of convection; one prior to 06z west
half with another round of storms expected from 08 to 14z as main
system tracks through the area. Cigs will also lower to IFR aft
12z as cooler air and lingering showers/iso storms track east.
Winds turn WNW and increase aft 12z and remain gusty through end
of period. /rev

&&

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

DISCUSSION...Martin
AVIATION...REV

Hazardous Weather Outlook
National Weather Service Des Moines IA
239 PM CDT Wed Apr 19 2023

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-201945-
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 PM CDT Wed Apr 19 2023

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

Thunderstorms will develop late this afternoon or early this
evening and continue this evening. A second round of storms will
arrive after midnight into Thursday morning. Both rounds will have
the threats of a few tornadoes, large hail, and damaging wind
gusts. Locally heavy rainfall is also possible.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

A few stronger thunderstorms may linger into the daylight
Thursday morning hours, but the severe threat will be diminishing.

.SPOTTER INFORMATION STATEMENT...

Spotter reports will be needed tonight into Thursday morning.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
723 PM CDT WED APR 19 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0722 PM     HAIL             CHARTER OAK             42.07N 95.59W
04/19/2023  E2.75 INCH       CRAWFORD           IA   EMERGENCY MNGR

            SIGNIFICANT CAR DAMAGE REPORTED.

&&

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
821 PM CDT WED APR 19 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0819 PM     FUNNEL CLOUD     5 E KIRON               42.20N 95.23W
04/19/2023                   CRAWFORD           IA   FIRE DEPT/RESCUE

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
828 PM CDT WED APR 19 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0823 PM     HAIL             1 ENE ODEBOLT           42.31N 95.24W
04/19/2023  M1.00 INCH       SAC                IA   FIRE DEPT/RESCUE

            PENNY TO QUARTER SIZED WITH PONDING OF WATER
            ON ROADS IN TOWN.

&&