Severe Thunderstorm Warning 203, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
624 PM CDT Mon Sep 9 2019

...Updated Aviation Discussion...

.DISCUSSION.../Tonight through Monday/
Issued at 314 PM CDT Mon Sep 9 2019

Surface boundary has made slow progress north into central Iowa
this afternoon with isolated to scattered convection. Instability
has increased rapidly in the warm sector with 100MB Mixed-Layer
CAPE of around 2000 J/KG in southwest Iowa. There is a very tight
gradient of CAPE along the boundary and this will be the focus
area late this afternoon into the evening of any potential severe
storms. Shear along this boundary is quite robust with bulk
parameters of 30-40kts in the first kilometer. While the low level
shear is quite good along with the 0-3km CAPE of 100-150 J/KG,
mid level lapse rates are somewhat weak. This would suggest an
overall limit on hail size without stronger mid level
accelerations. However, the tornado threat will still remain given
the low LCL, decent low level CAPE and the strong near low level
shear. The main concern will be as storms approach/intersect the
boundary where the increased helicity would support quick spin-
ups.

All the activity will lift northeast this evening and will pass
into MN later in the evening. However, additional forcing is
forecast along the low level moisture transport axis overnight
with additional convection. This will produce an axis of storms
from southwest to northeast across the forecast area during the
night which will shift slightly south as a the front heads back
south toward daybreak. Locally heavy rainfall is expected with
the storms as the train over the same areas, although most areas
can handle some decent rainfall. The convection will gradually
subside Tuesday morning with a break from storms for much of the
day as forcing will remain negligible.

Additional convection is expected in Tuesday night/early
Wednesday, primarily across the northern half of the state where
near the location of a warm front. Strong moisture transport into
the boundary overnight will support convection which is expected
to be moving east into Iowa from Nebraska and South Dakota. The
main threat will be from heavy rainfall but some gusty winds are
also expected. With the boundary lifting northward into later
Wednesday/early Thursday, the threat of storms will be relegated
to northern Iowa with warm and humid conditions in central and
southern Iowa. The main western trof approaches on Thursday with a
stronger synoptic boundary crossing the state during the day.
Convection, possibly severe, is expected to cross central into
eastern Iowa by midday into the evening before cooler and drier
air arrives in the wake of the front. Thereafter, much of the
weather will be quiet Thursday night into early next week except
for some threat of storm Saturday night into early Sunday with a
surge of theta-e advection.

&&

.AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/
Issued at 620 PM CDT Mon Sep 9 2019

Storms to impact ALO and possibly DSM and MCW this evening. Strong
winds likely at the ALO airport through 01z. Otherwise,
intermittent MVFR to IFR ceilings this evening and then another
round of rain is forecast to develop past 06z tonight. This round
likely to bring some MVFR visibility at times.

&&

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

&&

DISCUSSION...Cogil
AVIATION...Podrazik

Hazardous Weather Outlook
National Weather Service Des Moines IA
424 PM CDT Mon Sep 9 2019

IAZ074-075-081>086-092>097-101100-
Marion-Mahaska-Adams-Union-Clarke-Lucas-Monroe-Wapello-Taylor-
Ringgold-Decatur-Wayne-Appanoose-Davis-
424 PM CDT Mon Sep 9 2019

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

Thunderstorms are possible this afternoon and evening. At this
time, the threat for severe weather is marginal.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Thunderstorms are possible Wednesday and Thursday afternoon and
evenings. A few of these storms could be strong to
severe...especially Thursday afternoon and evening.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time, but cannot be
ruled out later in the week.

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>073-101100-
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-
424 PM CDT Mon Sep 9 2019

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

Strong to severe thunderstorms are expected into the evening.
Tornadoes and damaging winds are the primary threats, with large
hail a secondary threat.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Thunderstorms are possible Tuesday... Wednesday... and Thursday
afternoon and evenings. A few of these storms could be strong to
severe...especially on Thursday afternoon and evening.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon and evening... and
also again later this week.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
547 PM CDT MON SEP 9 2019

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

0448 PM     TSTM WND DMG     1 SE SHELDAHL           41.85N 93.68W
09/09/2019                   POLK               IA   TRAINED SPOTTER

            TELEPHONE POLE LEANED OVER. NO PASSING SIGN
            LEANED OVER. DELAYED REPORT. TIME ESTIMATED
            FROM RADAR.

&&

JAZ

Special Weather Statement
National Weather Service Des Moines IA
548 PM CDT Mon Sep 9 2019

IAZ047-058>061-072-092345-
Guthrie IA-Boone IA-Jasper IA-Polk IA-Madison IA-Dallas IA-
548 PM CDT Mon Sep 9 2019

...THUNDERSTORMS WITH GUSTY WINDS APPROACHING THE DES MOINES
METRO...

At 546 PM CDT, Doppler radar was tracking a strong thunderstorm near
Stuart, or 12 miles southwest of Adel, moving northeast at 55 mph.

Wind gusts of 50 to 55 mph will be possible with this storm.

Rainfall amounts up to one inch will be possible with this storm.

Locations impacted include...
Des Moines, West Des Moines, Ankeny, Urbandale, Johnston, Clive,
Altoona, Waukee, Norwalk, Pleasant Hill, Grimes, Perry, Adel, Windsor
Heights, Bondurant, Polk City, Saylorville, Madrid, Mitchellville and
Dallas Center.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

A Tornado Watch remains in effect until 1000 PM CDT for central,
south central and west central Iowa.

LAT...LON 4164 9447 4203 9394 4190 9370 4186 9370
      4186 9363 4166 9326 4151 9368 4151 9379
      4147 9379 4139 9402
TIME...MOT...LOC 2246Z 227DEG 49KT 4153 9422

Fowle

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
551 PM CDT MON SEP 9 2019

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

0543 PM     TSTM WND GST     2 N COLLINS             41.93N 93.31W
09/09/2019  M61 MPH          STORY              IA   STORM CHASER

            REPORT VIA SOCIAL MEDIA.

&&

KLP

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