Tornado and Hail in Iowa, April 19 to 20, 2023

Area Forecast Discussion
National Weather Service Des Moines IA
416 AM CDT Wed Apr 19 2023

.DISCUSSION.../Today through Tuesday/
Issued at 415 AM CDT Wed Apr 19 2023

Key Messages:

- Precipitation shifting into northern Iowa this morning.
- Strong to severe storms possible later this afternoon and
  overnight.
- Overall cooler weather for the remainder of the forecast period.

Surface low pressure has moved into south central Nebraska with the
warm front now into far southwest Iowa where temperatures have
warmed into the 60s. Thunderstorms are ongoing in the mid-level
theta-e advection and in advance of the first passing short wave. A
few storms have been producing small hail but overall individual
updrafts are not persisting long with the lack of deep layer shear.
That said, localized quarter sized hail remains possible yet over
the next few hour. Parts of northwest Iowa are having strong
northeast winds with gusts in the 50-65 mph range in the area along
the back edge of the precipitation where stronger subsidence and
precipitation erosion is occurring. Will continue to monitor this as
that back edge moves towards Emmet and Palo Alto counties.

For today, the area of low pressure will lift east/northeast today
into west central Iowa and will pull the warm front northward as
well. While this occurs, a stronger low pressure will develop into
Kansas in advance of a stronger short wave and this will gradually
lead to the western Iowa low to diminish some tough the triple point
and surface circulation will remain. Any precipitation by mid
morning and into the early afternoon should be relegated to north of
the warm front. South of the warm front, the amount of stratus to
fill into the warm sector remains in question. There currently is a
vast area of stratus from southeast Nebraska and into the eastern
half of Kansas. The stratus is expected to fill into central and
southern Iowa though confidence is not high that it will remain into
the afternoon and how much impact it will have on temperatures. Have
maintained highs in the 70s in the warm sector today and worst case
would be the 60s with dew points in the upper 50s and low 60s
inbound. An elevated mixed layer aloft should keep the area capped
for much much of the day. The area to watch later this afternoon is
near the triple point into west central Iowa and the tailing
boundary to the south where forcing will be strongest and the cin
with the EML will be weakest. The CAMs continue to suggest the cap
will break in this area late this afternoon with strong storm
development. The deterministics regional and global models are
holding the EML and don't break out widespread storms until the low
level jet increases this evening along with the arrival of the
stronger kinematics with the upper short wave.

Overall have maintained the potential for surface based convection
for late this afternoon over the far west with the greater chances
later this evening and overnight. A few supercells are possible
early with large hail and damaging winds the main threat though
there is a non-zero tornado potential, especially in vicinity of the
triple point. Concern overnight is for a QLCS development that will
lift northeast across the southern half of the forecast area. The
QLCS tornadic threat is certainly there. Finally, locally heavy
rainfall remains possible as PWATs increase to 1.25-1.50 inches
which is approaching 250% of climatology for this date. There should
not be much of a flooding threat but will watch. Convective chances
will persist into Thursday morning before moving east of the area.
Currently have much of Thursday afternoon and evening dry though
sounding profiles and CAM solutions do suggest that a few showers
and isolated thunderstorms could redevelop during this period.

The large upper low moving over the Upper Midwest will hamper the
weather across Iowa for Friday and into the weekend leading
cool/cold cyclonic flow that will persist until Sunday night.
Freezing overnight low temperatures are likely for many areas. Early
next week will be a little warmer but the large scale flow suggests
cooler than normal weather and may have another cold intrusion by
mid next week.

&&

.AVIATION.../For the 06Z TAFS through 06Z Wednesday night/
Issued at 1139 PM CDT Tue Apr 18 2023

Storms beginning to develop in northern Iowa with MCS over eastern
NE heading ENE with time. Expecting the MCS to track toward DSM
and FOD, ALO through 10z with another area of storms over northern
NE to track along IA-MN border through 13z. Cigs lower to IFR
while winds remain brisk from ESE until 15-16z when winds turn
south. South sites return to VFR aft 20z. More storms expected
aft 21z through end of period. More details on those in next
package. /rev

&&

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

DISCUSSION...Donavon
AVIATION...REV

Hazardous Weather Outlook
National Weather Service Des Moines IA
515 AM CDT Wed Apr 19 2023

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-201015-
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-
515 AM CDT Wed Apr 19 2023

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Thunderstorms will impact the area again tonight through early
Thursday morning. The primary threats will be strong winds and
large hail, however, a few tornadoes are possible. Severe weather
is expected through much of the night. Locally heavy rainfall is
also possible.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

A few storms may linger through Thursday morning, but the severe
threat will be diminishing.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed tonight into Thursday morning.

Dodson