Special Weather Statement, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
207 PM CDT Wed Apr 7 2021

.DISCUSSION.../Tonight through Wednesday/
Issued at 207 PM CDT Wed Apr 7 2021

After the initial rain band moved across the state this evening,
much of central Iowa saw rapid clearing, as evidenced by GOES east
day-cloud phase. In this area between the outer rain band and the
inner low stratus near the low center, temperatures soared in the
mid 70s while surrounding areas remained in the mid 60s. By 1 pm the
surface cold front was across western Iowa, where Denison dropped to
52 degrees with the next county over remaining in the upper 60s.
Meanwhile, thunderstorm activity has increased across southern Iowa
as a diffuse surface boundary lifts out of Missouri. With a lack of
focused forcing mechanism, convective development has been rather
messy and is expected to continue as such through the evening.
Instability is also rather marginal, generally around 1000+ J/kg.
While clearing this afternoon has helped to boost values, clouds
ahead of the convection will limit the impact. Model soundings
depict tall, skinny CAPE profiles supporting more wind than hail
with the severe threat. Low level storm-relative helicity values
increase along the diffuse front and within the vicinity of the
surface low, where a narrow window for a brief tornado exists.
Overall with weak forcing and fairly low instability, the
environment is not overly supportive of severe weather this
afternoon and evening. While a weak tornado or stronger thunderstorm
is certainly possible, the threat is marginal.

A the surface low lifts slowly to the northeast, wrap around
precipitation on the back of the low will linger through Thursday
and into Friday. Northwest flow will increase cold air advection
into the area, putting a damper on high temperatures as readings
remain in the 50s or low 60s. A quick moving upper level low will
eject out of the northern plains and undercut the present system on
Friday into Saturday, increasing shower activity through the first
half of the weekend.

By Sunday upper level ridging will help to clear out the area and
low temperatures to rise back into the mid 60s. This will be fairly
short lived with another system set to impact the area by the first
half of next week.

&&

.AVIATION.../For the 12Z TAFS through 12Z Thursday morning/
Issued at 1241 PM CDT Wed Apr 7 2021

Thunderstorm activity will increase across the area this afternoon
and evening from south to north. More vigorous convection will
transition over to showers overnight, with cigs diminishing to MVFR
and IFR conditions my Thursday morning. While precipitation will
come to an end overnight low cigs will remain in place much of
Thursday.

&&

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

DISCUSSION...Hagenhoff
AVIATION...Hagenhoff

Hazardous Weather Outlook
National Weather Service Des Moines IA
233 PM CDT Wed Apr 7 2021

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-081945-
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-
233 PM CDT Wed Apr 7 2021

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

Showers and thunderstorms will expand across the area this
afternoon and evening. A few strong to severe storms are possible,
especially for southern and central Iowa. Wind and hail are the
main threat, however a brief tornado may be possible.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

Rain showers and perhaps a few isolated thunderstorms are possible
Thursday and will continue into Friday. Some showers may produce
heavier rainfall.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon and evening.

Hagenhoff

Special Weather Statement
National Weather Service Des Moines IA
155 PM CDT Wed Apr 7 2021

IAZ093-094-071930-
Ringgold IA-Decatur IA-
155 PM CDT Wed Apr 7 2021

...Small Hail Possible in Eastern Ringgold County...

At 154 PM CDT, Doppler radar was tracking a strong thunderstorm 8
miles southeast of Mount Ayr, moving north at 40 mph.

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

Locations impacted include...
Sun Valley Lake, Kellerton, Grand River, Tingley, Ellston and
Beaconsfield.

LAT...LON 4090 9422 4089 9391 4057 9399 4057 9421
TIME...MOT...LOC 1854Z 187DEG 37KT 4061 9414

Martin

Special Weather Statement
National Weather Service Des Moines IA
226 PM CDT Wed Apr 7 2021

IAZ082-083-093-094-072000-
Clarke IA-Ringgold IA-Union IA-Decatur IA-
226 PM CDT Wed Apr 7 2021

...SPECIAL WEATHER STATEMENT...

At 225 PM CDT, Doppler radar was tracking an area of strong
thunderstorms from near Beaconsfield to Leon, moving northeast at 40
mph.

Half inch hail and winds in excess of 30 mph will be possible with
this storm.

Locations impacted include...
Osceola, Leon, Sun Valley Lake, Lakeside Casino, Murray, Lorimor,
Grand River, Van Wert, Woodburn, Decatur City, Weldon, Thayer,
Ellston, Beaconsfield and Murray Roadside Rest Area.

LAT...LON 4081 9416 4116 9404 4116 9356 4108 9355
      4067 9371 4067 9395
TIME...MOT...LOC 1925Z 203DEG 33KT 4086 9400

Martin

Special Weather Statement
National Weather Service Des Moines IA
252 PM CDT Wed Apr 7 2021

IAZ072-073-072015-
Madison IA-Warren IA-
252 PM CDT Wed Apr 7 2021

...Special Weather Statement...

At 251 PM CDT, Doppler radar was tracking a strong thunderstorm 9
miles south of Winterset, moving north at 30 mph.

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

Locations impacted include...
Winterset, Avenue Of The Saints Event Center, St. Charles, Truro,
Martensdale, Patterson, St. Marys, East Peru, Bevington and Spring
Hill.

LAT...LON 4146 9398 4145 9363 4116 9379 4116 9405
TIME...MOT...LOC 1951Z 196DEG 27KT 4121 9395

Martin

Special Weather Statement
National Weather Service Des Moines IA
323 PM CDT Wed Apr 7 2021

IAZ059-060-072-073-072045-
Polk IA-Madison IA-Dallas IA-Warren IA-
323 PM CDT Wed Apr 7 2021

...Small Hail Possible in the Des Moines Metro...

At 322 PM CDT, Doppler radar was tracking a strong thunderstorm 7
miles southwest of Norwalk, moving northeast at 30 mph.

Pea size to half inch hail and winds in excess of 30 mph will be
possible with this storm.

Locations impacted include...
Des Moines, West Des Moines, Ankeny, Urbandale, Johnston, Clive,
Altoona, Waukee, Norwalk, Pleasant Hill, Grimes, Windsor Heights,
Saylorville, Southridge Mall, Jordan Creek Town Center, Adventureland
Amusement Park, Merle Hay Mall, Iowa Events Center, Prairie Meadows
and Iowa State Fairgrounds.

LAT...LON 4130 9369 4136 9391 4174 9378 4164 9344
TIME...MOT...LOC 2022Z 203DEG 26KT 4141 9377

Martin