Special Weather Statement, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
641 AM CDT Tue Aug 24 2021

.DISCUSSION.../Today through Monday/
Issued at 426 AM CDT Tue Aug 24 2021

Forecast highlights:

-Heat and humidity producing headlines today with an ongoing heat
threat in place much of the week across southern Iowa.
-Chances for thunderstorms remain in the forecast almost daily for
the next several days.  Highest threat in the north this week.

A warm and humid airmass has become established across much of Iowa
early this morning with temperatures holding in the mid to upper
70s.  A few stay showers passed through far northern Iowa early this
morning but the main activity is organizing across Minnesota with a
strengthening progressive system.  The bulk of this activity is
expected to remain north of the forecast area over the next several
hours, however a few storms may develop within the low level inflow
across far northern Iowa this morning. Otherwise, hot and humid
conditions are expected for much of southern into central Iowa
today. Evapotranspiration continues to add moisture into the low
levels with dewpoints in the mid to upper 70s expected.  Therefore,
heat index values of 100-110 are expected this afternoon across much
of the forecast area with the southern half reaching advisory
criteria.  Some expansion was needed in west central Iowa and added
counties in this area with 105 heat index values likely in Denison
and Carroll.

The tail end of the convective system in Minnesota may still edge
into the far north per a few CAMs although output remains
inconsistent.  It appears much of the area is capped into this
afternoon with little forcing, therefore much of today is expected
to be dry.  However, a weak shortwave arrives by this evening with
some minor forcing which is likely to be sufficient for some
convective development this evening in western Iowa.  Despite
impressive instability values, mid level flow remains around 15-
20kts limiting deeper convective shear and widespread
organization. However, given the instability some limited threat
still exists for a downburst or hail development with the initial
strong updrafts.

Boundary sinks into the north on Wednesday with movement back north
by the end of the week.  There remains decent uncertainty in the
outcome of the forecast during the week given the daily convection
producing outflow boundaries which impact subsequent convection-
therefore confidence in any given solution is low. The heat and
humidity appear likely to continue in at least the southern third
of Iowa through much of the work week and into the weekend before
some relief and additional heat headlines may be needed.

&&

.AVIATION.../For the 12Z TAFS through 12Z Wednesday morning/
Issued at 640 AM CDT Tue Aug 24 2021

Generally VFR conditions across much of central Iowa for the
duration of the forecast. There will be isolated to scattered
thunderstorms in the north today and across much of central Iowa
tonight. MVFR to IFR conditions are expected in and around
thunderstorms but the majority of the area will remain VFR. Winds
increase from the south to southwest today becoming lighter with
sunset this evening.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon today to 7 PM CDT this evening for
IAZ044>050-057>062-070>075-081>086-092>097.

&&

DISCUSSION...Cogil
AVIATION...Cogil

Hazardous Weather Outlook
National Weather Service Des Moines IA
310 AM CDT Tue Aug 24 2021

IAZ044>050-057>062-070>075-081>086-092>097-250815-
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-
310 AM CDT Tue Aug 24 2021

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

A Heat Advisory is in effect for the area today. Please visit
weather.gov/desmoines for more information.

Chances for storms will move through the state tonight. A few
strong to severe storms cannot be ruled out, with hail and wind
the main threats.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Periodic chances for storms continue through the week and into the
weekend. A few strong to severe storms may be possible along with
locally heavy rainfall.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed in a few instances through the week.

IAZ004>007-015>017-023>028-033>039-250815-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-
310 AM CDT Tue Aug 24 2021

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Chances for storms will move through the state tonight. A few
strong to severe storms cannot be ruled out, with hail and wind
the main threats.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Periodic chances for storms continue through the week and into the
weekend. A few strong to severe storms may be possible along with
locally heavy rainfall.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed in a few instances through the week.

CURTIS

Special Weather Statement
National Weather Service Des Moines IA
1106 AM CDT Tue Aug 24 2021

IAZ004-005-015-241630-
Palo Alto IA-Kossuth IA-Emmet IA-
1106 AM CDT Tue Aug 24 2021

...Strong thunderstorms will impact portions of Emmet, western
Kossuth and northern Palo Alto Counties through 1130 AM CDT...

At 1106 AM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Iowa Lake to near Emmetsburg. Movement was
east at 45 mph.

HAZARD...Wind gusts up to 50 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Strong thunderstorms will be near...
  Iowa Lake around 1110 AM CDT.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4350 9419 4302 9424 4313 9491 4350 9491
TIME...MOT...LOC 1606Z 273DEG 39KT 4353 9446 4314 9478

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...50 MPH

Krull

Special Weather Statement
National Weather Service Des Moines IA
1130 AM CDT Tue Aug 24 2021

IAZ005-006-016-241715-
Kossuth IA-Winnebago IA-Hancock IA-
1130 AM CDT Tue Aug 24 2021

...A strong thunderstorm will impact portions of Kossuth, northern
Hancock and Winnebago Counties through 1215 PM CDT...

At 1129 AM CDT, Doppler radar was tracking a strong thunderstorm near
Union Slogh, or 15 miles north of Algona, moving east at 55 mph.

HAZARD...Winds in excess of 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
  Forest City.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4350 9350 4307 9351 4310 9441 4350 9439
TIME...MOT...LOC 1629Z 272DEG 49KT 4330 9419

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

Krull

Special Weather Statement
National Weather Service Des Moines IA
1207 PM CDT Tue Aug 24 2021

IAZ006-007-016-017-241815-
Cerro Gordo IA-Winnebago IA-Worth IA-Hancock IA-
1207 PM CDT Tue Aug 24 2021

...A strong thunderstorm will impact portions of Worth, Hancock,
Cerro Gordo and eastern Winnebago Counties through 115 PM CDT...

At 1207 PM CDT, Doppler radar was tracking a strong thunderstorm near
Eagle Lake, or 7 miles southwest of Forest City, moving east at 55
mph.

HAZARD...Wind gusts up to 50 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

This strong thunderstorm will be near...
  Garner around 1215 PM CDT.
  Clear Lake around 1225 PM CDT.

Other locations in the path of this storm include Mason City
Municipal Airport, Mason City and Nora Springs.

This includes Interstate 35 between mile markers 179 and 218.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4291 9303 4291 9397 4311 9397 4350 9364
      4350 9302
TIME...MOT...LOC 1707Z 270DEG 47KT 4318 9374

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...50 MPH

Krull