Severe Thunderstorm Warning 196, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
624 PM CDT Sat Sep 17 2022

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

.DISCUSSION.../Tonight through Saturday/
Issued at 337 PM CDT Sat Sep 17 2022

Key Messages:

-Strong to Severe Storms This Evening
-Additional Scattered Storm Chances Sunday
-Hot Beginning Of The Week Then Cool To End It

Shortwaves ejecting through weak upper level flow will be the
primary driver for weather this weekend with multiple chances for
showers and storms. The first wave of this weekends showers and
storms moved through earlier this morning and has stuck around
much of the day. These storms should wrap up this afternoon before
another wave of storms develops across the state later this
evening, bringing with it the potential for a few strong to severe
storms. Finally, one more system will pass through on Sunday, but
is expected to focus more in southeast Iowa.

Showers and storms tonight were the primary focus for today's
forecast. The instability within the atmosphere will be marginal,
with CAPE values in the 1000 to 2000 J/kg range and mid-level lapse
rates of 7-8 C/km. This should be sufficient for creating strong
updrafts with any lifted parcels. The shear within the atmosphere
also looks favorable, with 40kts+ of effective bulk shear and curved
hodographs with helicity values over 300 m2/s2. However, the
limiting factor for severe weather this evening will be the strength
of the EML. Due to this morning's MCS and it's residual clouds and
convection, temperatures have underachieved, which has slowed the
erosion of this convective inhibition and pushed back the timing of
organized storm initiation. Storms tonight will line up more with
the strengthening LLJ and likely struggle to become surface based.
This will limit how much of the low level shear that updrafts can
tap into and further reduce the chance for tornadic development. All
of this implies that tonight's storms should remain elevated with
large hail and strong winds being the primary concerns, while the
threat for tornadoes is diminishing. This trend is represented well
in SPCs most recent Day 1 convective outlook, with a reduction of
the tornado probabilities and the slight risk. However, a slight
risk for severe weather still resides in southwest IA and a marginal
across the rest of the area.

Storms tonight will wrap up early tomorrow morning and could be
followed by some patchy fog development in areas across northern and
western Iowa. Fog will likely only last a few hours and would be
followed by isolated shower chances throughout the day. The shower
and storm chances Sunday afternoon and evening have decreased
drastically with only the far southeast portions of the area being
at risk for a few potentially strong storms.

Following Sunday, thermal ridging will build to our south and result
in warm temperatures to kick off the week. By Tuesday, high
temperatures could reach into the low 90s for a good portion of the
state before a cold front pushes through the midwest, dropping
temperatures into the 70s by Wednesday and 60s by Thursday. Longer
range models suggest there could be some precipitation along this
cold front as it passes early Wednesday, but exact location and
timing varies. Similarly, the GFS also develops some precipitation
across us on Thursday night into Friday. However, it still remains
much too early to say anything for certain so will continue to
monitor over the coming days.

&&

.AVIATION.../For the 00Z TAFS through 00Z Sunday evening/
Issued at 625 PM CDT Sat Sep 17 2022

Primary aviation concerns this period will be storm trends at the
terminals as well as fog setup toward Sunday morning. Have focused
any TS/VCTS mention on period of most likely storms as they are
just beginning to develop early this evening. This is in addition
to storms that have festered between DSM and OTM the last few
hours. As the storms move southeastward, calm winds and a moist
near surface layer should allow for fog development over parts of
northern Iowa toward 12z Sunday and have held visibility
restrictions at IFR. Fog will dissipate in the morning and future
TAF issuances will then focus on any additional storm development
over southern Iowa later Sunday.

&&

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

DISCUSSION...Dodson/Hahn
AVIATION...Ansorge

Hazardous Weather Outlook
National Weather Service Des Moines IA
631 PM CDT Sat Sep 17 2022

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-182345-
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-
631 PM CDT Sat Sep 17 2022

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

Thunderstorm chances continue this evening, especially in central
and southern Iowa. Thunderstorms this evening may become severe
containing large hail, damaging winds, and heavy rains. A tornado
or two cannot be ruled out across southwestern Iowa.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

Thunderstorms will again be possible across southern Iowa on
Sunday. A few storms across far southeast areas may become strong
on Sunday evening.

It will be hot Tuesday when record or near record highs are
possible. Peak heat indices are expected to reach the upper 80s
and 90s.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed this evening.

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