Severe Thunderstorm Warning 136, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
1245 PM CDT Thu Aug 6 2020

.DISCUSSION.../Today through Wednesday/
Issued at 423 AM CDT Thu Aug 6 2020

Surface high pressure continues to shift east towards the Great
Lakes. Southerly flow aloft has returned to Iowa overnight with
several fragments of theta-e advection lifting through the state.
Modest MUCAPEs have arrived as well at 500 J/kg or less though
greater instability is just to the west in the Missouri Valley.
Showers and a few thunderstorms have developed to the increased
forcing and instability over southeast Iowa and over the northwest.
Of course the areas that really need the rainfall are currently
devoid of precipitation. The showers and thunderstorms will likely
continue to bubble into central Iowa this morning and into the early
afternoon as repeated rounds of theta-e advection lift northward.
The focus for precipitation should eventually lift northward as well
this afternoon. The slow movement and potential for repeated small
cells over some areas could lead to some beneficial rainfall for
some lucky areas. High temperatures today will again likely be
impacted by cloud cover and have again tempered high temperatures
down north of Highway 30. South of there, temperatures may receive
some sun during the afternoon to allow temperatures to rebound.

The low level jet will develop tonight and be focused over Kansas
and Missouri with the speed convergence zone over the northern
portion of those states. That will be the most favored region for
thunderstorm development tonight though some of the activity may
reach far southern Iowa and linger into Friday morning. The
remainder of Friday should be mostly dry and warmer with highs in
the 80s. The upper flow by later Friday and into the weekend
transitions to more zonal/westerly flow as the region is sandwiched
between an upper low over western Canada and upper high over the
south central CONUS. Numerous short waves will be passing through
this flow and there still remains a fair amount of uncertainty where
and when these will arrive and areal coverage of any thunderstorms.
This has resulted in an extended forecast filled with low chances
for thunderstorms throughout with a couple more focused areas.
Another strong low level jet will develop Friday night and the setup
is favorable for an MCS to develop somewhere in the vicinity of
southeast South Dakota/northwest Iowa. The deterministic ECMWF
continues to be aggressive with the MCS to track southeast into
central Iowa while other solutions remain less optimistic. Should an
MCS develop, corfedi vectors would suggest any rooted system should
settle southeast. Some challenges though showing up in sounding
profiles with dry air still lingering in the favored lift zone that
would inhibit convective development. Another storm complex looks
favorable Sunday night into Monday morning as the upper flow bows a
bit as the Canadian upper low moves east, which will allow a frontal
boundary to drop into Iowa. As of now, northern Iowa is the most
favored area for precipitation though scattered storms should also
reach central Iowa. Periodic thunderstorm chances into next week as
mentioned previously which will be dependent on the surface boundary
placement and short wave timing. There will be some severe weather
potential this weekend with damaging winds the greatest threat.

The weekend will be warmer and more humid with highs in the upper
80s to low 90s into Monday then slightly cooler the remainder of the
period. Afternoon heat index values Saturday and Sunday will be in
the 90s to near 100.

&&

.AVIATION.../For the 18Z TAFS through 18Z Friday afternoon/
Issued at 1245 PM CDT Thu Aug 6 2020

Scattered thunderstorms will move gradually north through the
forecast area this afternoon. Ceilings and visibilities will
mainly be VFR but MVFR to IFR in and around the thunderstorms. By
tonight, much of the area will be dry with VFR conditions in most
locations continuing into Friday morning. Surface winds are
expected to be south to southeast for the entire period.

&&

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

&&

DISCUSSION...Donavon
AVIATION...Cogil

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
1134 AM CDT THU AUG 6 2020

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

1130 AM     HAIL             3 W BAGLEY              41.85N 94.49W
08/06/2020  E0.88 INCH       GUTHRIE            IA   EMERGENCY MNGR

            A LOT OF PEA SIZED HAIL AND SOME NICKLE
            SIZED HAIL MIXED IN PERIODICALLY.

&&

ANSORGE

Special Weather Statement
National Weather Service Des Moines IA
1200 PM CDT Thu Aug 6 2020

IAZ046-047-059-061745-
Boone IA-Greene IA-Dallas IA-
1200 PM CDT Thu Aug 6 2020

...Dime to Penny Hail and Winds to 40 mph Possible...

At 1159 AM CDT, Doppler radar was tracking a strong thunderstorm near
Perry, moving east at 25 mph.

Penny size hail and winds in excess of 30 mph will be possible with
this storm.

Locations impacted include...
Perry, Woodward, Minburn, Rippey, Dawson, Bouton, Berkley, Perry
Municipal Airport and Ledges State Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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.

&&

LAT...LON 4201 9389 4171 9385 4178 9428 4195 9429
TIME...MOT...LOC 1659Z 261DEG 23KT 4189 9420

Kotenberg

Special Weather Statement
National Weather Service Des Moines IA
101 PM CDT Thu Aug 6 2020

IAZ072-061830-
Madison IA-
101 PM CDT Thu Aug 6 2020

...Dime to Penny Size Hail Possible...

At 101 PM CDT, Doppler radar was tracking a strong thunderstorm near
Winterset, moving east at 15 mph.

Penny size hail and winds in excess of 30 mph will be possible with
this storm.

Locations impacted include...
Avenue Of The Saints Event Center, St. Charles, Patterson, Bevington
and Badger Creek State Park.

LAT...LON 4136 9398 4149 9397 4146 9379 4128 9379
TIME...MOT...LOC 1801Z 282DEG 12KT 4137 9392

Kotenberg

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