Hail and Damaging Wind in Iowa, July 30 to 31, 2021

Area Forecast Discussion
National Weather Service Des Moines IA
405 AM CDT Fri Jul 30 2021

.DISCUSSION.../Today through Thursday/
Issued at 401 AM CDT Fri Jul 30 2021

Forecast Highlights
-Smokey skies today into Saturday
-Severe Storms and Heavy Rain Potential today into Saturday
-Cool and dry Sunday into next week

Today into Saturday...The majority of the forecast concerns
resided within this period as the focus was on the wildfire
smoke and convection potential. The latest runs of the HRRR
(vertically integrated smoke) continue to hamper the skies
through Saturday. With the convection likely over the central to
southern parts of the state tonight, the smoke looks to be densest
across the northern half by Saturday morning. Visibility
continues to be a problem however through the morning hours today
with weak surface flow and little mixing to help dissipate the
smoke. CAA is anticipated to develop by Saturday afternoon, but
with the northerly flow, this will likely bring additional smoke
into the state and have smoke mentioned through 00z Sunday but
there's a good chance it'll linger past this time.

WRT to thunderstorm potential, there appears to be two main rounds
through Saturday morning. The first round will be across northern
Iowa later this afternoon into the evening, while the second and
more robust convection is likely to occur late this evening into
Saturday morning. Albeit, a couple of the hires models suggest one
continuous round of convection this afternoon into Saturday
morning. Some isolated storms are possible this morning over the
southwest but cap remains strong and instability and shear remain
very weak or non-existent. Thus, don't expect to see anything
widespread or lengthy this morning.

Surface low over the High Plains and front range of the Rockies
remains stalled in this location for the next 24-30 hours with a
boundary draped across southwest Iowa. A quick moving shortwave
spawns some convection across southern MN into northern Iowa this
afternoon. The latest HRRR has convection by around 21z and
transition it southward with another shortwave and the LLJ
increasing late tonight. The NAM nest is a bit faster with the
convection this afternoon and then slower to move it south by
Saturday morning. The shortwave late tonight in conjunction with
the LLJ remains the focus for severe development and heavy rain
potential. First with the heavy rain, warm layer cloud depths of
4000-4500 meters by 06z Saturday and precipitable water values of
1.5 to 2.5 inches, and weak storm motion matching up with Corfidi
vectors should be a great setup for training convection and thus
heavy rain over central to southwest portions of the forecast
area.

WRT to severe weather potential, the best chance looks to be later
this afternoon with the second shortwave near the warm front in
southwest Iowa.  Deep layer shear is sufficient for thunderstorm
sustainability and instability should be enough for robust
updrafts. LCLs are near 5kft, so low confidence with the tornado
threat and with the deep warm layer cloud depths, hail is not as
likely as well. Thus leading to the main concern of damaging winds
this evening into Saturday morning.

Sunday into Thursday...Surface high pressure builds into the state
by Sunday and dominates the weather pattern into the middle of
next week. After Saturday, plenty of pleasant temperatures and
dry weather. Some hints on the upper ridge breaking down late next
week, but any threat appears to be minimum attm.

&&

.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1144 PM CDT Thu Jul 29 2021

Main aviation impacts are going to be visibility restrictions due
to the wildfire smoke moving south behind frontal passage earlier
today. MVFR visibilities will be most likely, but there may be
periods dipping into IFR. Most likely impacting central and
northern airports. Less confidence at KOTM, so have left out for
now. Conditions should improve somewhat as the air mass mixes
after 13-15z tomorrow. Scattered afternoon convection to impact
all but KALO and KMCW after 20z.

&&

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

&&

DISCUSSION...Podrazik
AVIATION...Hahn

Hazardous Weather Outlook
National Weather Service Des Moines IA
255 AM CDT Fri Jul 30 2021

IAZ004>007-015>017-023>028-033>039-047>050-061-062-075-086-310800-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-Boone-Story-Marshall-
Tama-Jasper-Poweshiek-Mahaska-Wapello-
255 AM CDT Fri Jul 30 2021

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and Tonight

Thunderstorm chances return today into tonight. The threat of
severe weather is low.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotters will not be needed.

IAZ044>046-057>060-070>074-081>085-092>097-310800-
Crawford-Carroll-Greene-Audubon-Guthrie-Dallas-Polk-Cass-Adair-
Madison-Warren-Marion-Adams-Union-Clarke-Lucas-Monroe-Taylor-
Ringgold-Decatur-Wayne-Appanoose-Davis-
255 AM CDT Fri Jul 30 2021

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and Tonight

Thunderstorm chances increase today, followed by widespread
thunderstorms likely later this evening into tonight. A few
storms may be strong to severe with strong wind gusts the primary
threat.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

A few thunderstorms may linger into early Saturday, but severe
weather is not expected. No hazardous weather is expected through
the rest of the forecast period.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed later today into tonight.