Tornadoes and Damaging Winds in Iowa, August 5, 2023

Area Forecast Discussion
National Weather Service Des Moines IA
231 PM CDT Sat Aug 5 2023

.DISCUSSION.../Tonight through Saturday/
Issued at 231 PM CDT Sat Aug 5 2023

Key Messages:

- Showers and storms move slowly west to east across the area
  this evening and overnight. Severe Risk is low, but gusty winds
  and locally heavy rain are possible.
- Rain continues through much of Sunday, finally tapering off
  into Monday morning

Discussion:

Showers and thunderstorms have percolated across parts of
northwestern Iowa through much of the day on a nearly stationary
boundary. Zooming out, the impending shortwave is currently situated
across parts of South Dakota and Nebraska. As this pivots into the
state later today this will help to finally get those NW Iowa storms
moving. Initial storms this afternoon carry a severe risk, though as
they move into western Iowa this evening shear diminishes to around
30 kts or less. While shear is weak, MLCAPE remains around 1500-2000
J/kg into the overnight and is aided by deep mechanical forcing from
the shortwave. As such, and severe risk is expected as gusty winds
with early storms. The main hazard will then be locally heavy rain
as we move through the overnight, more on that in a moment. With
these slow moving storms, expect convection to reach the I-35
corridor around 10pm - midnight, approaching Waterloo through the
early morning to around sunrise time frame.

Rain continues through much of the day on Sunday as the surface low
passes across the area. As this occurs, there is a risk of funnels
clouds or perhaps tornadoes within the vicinity of the surface low
towards southeast Iowa as enhanced vorticity there is coincident
with peak afternoon heating and enhanced stretching. This is where
HREF updraft helicity tracks are in greatest concentration. Rain
will finally begin tapering off overnight into Monday morning. Rain
totals across the state look to exceed half an inch in most places,
with amounts over an inch north of I-80 based on HREF guidance and
PWAT values exceeding 1.5 inches. Expect to see pockets of totals
around 2+ inches across northern Iowa wherever stronger cores
develop.

The pattern remain active into next week with chances for widespread
rain expected again on Tuesday into Wednesday and Thursday into
Friday. While details on severe potential are uncertain at this time
range, it does appear that a few stronger storms may be possible with
the slightly more robust Wednesday system, though this may occur
south of the area as noted in the SPC Day 5 outlook.

&&

.AVIATION.../For the 18Z TAFS through 18Z Sunday afternoon/
Issued at 1241 PM CDT Sat Aug 5 2023

VFR conditions will continue across most sites through this
evening. Tonight expect showers and thunderstorms to move into the
area from the west impacting sites KFOD/KDSM shortly after 00z and
expanding to eastern sites KALO/KOTM towards 12z. Convection will
linger across the area through much of Sunday, resulting in
reduced ceilings and visibility to MVFR to IFR at times. Expect to
see precipitation begin tapering off beyond the current period
into Monday morning.

&&

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

DISCUSSION...Hagenhoff
AVIATION...Hagenhoff

Hazardous Weather Outlook
National Weather Service Des Moines IA
246 PM CDT Sat Aug 5 2023

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-062000-
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-
246 PM CDT Sat Aug 5 2023

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

Showers and thunderstorms will move over western Iowa by this
evening and overspread central Iowa tonight. A few of the storms
west of Interstate 35 may be strong to severe during the evening
with strong thunderstorm winds and locally heavy rainfall.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

Periods of showers and thunderstorms are expected Sunday into
Sunday night. There is a low risk of severe storms east of
Interstate 35 and south of Highway 30 Sunday afternoon and
early evening. Locally heavy rainfall will also be possible.

Additional showers and thunderstorms will return to the region
late Tuesday night into early Thursday and again late week around
Friday. Any threat for severe storms will be better determined
early next week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this evening, especially in
western Iowa and again over southeast Iowa Sunday afternoon.

Ansorge