Damaging Winds and Heavy Rain in Iowa, July 8 to 9, 2020

Area Forecast Discussion
National Weather Service Des Moines IA
327 PM CDT Wed Jul 8 2020

.DISCUSSION.../Tonight through Wednesday/
Issued at 326 PM CDT Wed Jul 8 2020

Warm and humid conditions this afternoon with temperatures in the
low to mid 90s common with dew points in the low 70s. A cumulus
field has develop around 5 kft. A wave dropping south from early
morning Minnesota MCS has led to some agitated cumulus and even a
few showers as it passes by to overcome weak capping but these cells
have been short lived. The wave is now approaching the Highway
30/Interstate 80 corridor and into an area where weaker inhibition
will be as stronger daytime heating continues. That said, while an
isolated strong storm could develop and there remains a low chance
for a cell to become severe, though it should be short lived with
deep layer less than 20 kts. The main threat is microburst with any
of the stronger cells. Subsidence behind the wave should keep the
remainder of the evening relatively quiet.

Storms will develop today along a boundary across South Dakota into
Nebraska. The trends continue to suggest the activity will congeal
into an MCS across Nebraska and dive southeast along the ribbon of
higher instability through eastern Kansas into nw Missouri while the
northern activity dissipates prior to reaching the forecast area.
This scenario would leave much of central Iowa devoid of
precipitation through the night. The HRRR and other CAM solutions
continue to suggest a remnant MCV arriving Thursday morning and
moving slowly east across the state with thunderstorms igniting by
mid to late morning mainly along and north of Interstate 80 as
strong instability develops in that area. Deep layer shear will be
much more favorable for organized storms even an isolated supercell
or two. These type of situations can end up having an isolated
tornado threat with more shear and vorticity around than progged in
addition to a large hail and damaging wind threat.

Thursday night into Friday will be mostly quiet with thunderstorm
chances ending. Friday will be cooler and less humid with high
temperatures in the mid to upper 80s. Another MCS is expected to
develop Friday night into Saturday morning though the projected path
is currently lining up along the Missouri valley and will miss much
of the area. Will continue to monitor further once the current
system passes.

Next week is trending warmer again as the thermal trough leans into
Iowa by around Tuesday and Wednesday. A boundary does lean into Iowa
during this time but 850 mb temperatures in the mid 20s and 700 mb
temperatures in the mid teens would likely suppress any convective
chances. These temperatures are also much warmer than what was over
the area today. Should the area miss much of the rain this week, the
dry ground combined with very warm temperatures aloft could allow
surface temperatures to push into the upper 90s to near 100 next
week. That will be the forecast challenge following the convective
chances early this weekend.

&&

.AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/
Issued at 1242 PM CDT Wed Jul 8 2020

VFR conditions through much of today and tonight. Scattered
cumulus this afternoon around 4 kft then will dissipate overnight.
A few thunderstorms will be possible late tonight into Thursday
morning with best potential near KMCW/KALO. Breezy south winds
today will diminish tonight.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT this evening for IAZ004>007-015>017-
024>028-035>039-047>050-059>062-072>075-083>086-095>097.

&&

DISCUSSION...Donavon
AVIATION...Donavon

Hazardous Weather Outlook
National Weather Service Des Moines IA
347 PM CDT Wed Jul 8 2020

IAZ004>007-015>017-024>028-035>039-047>050-059>062-072>075-
083>086-095>097-092100-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Humboldt-Wright-Franklin-Butler-Bremer-Webster-Hamilton-Hardin-
Grundy-Black Hawk-Boone-Story-Marshall-Tama-Dallas-Polk-Jasper-
Poweshiek-Madison-Warren-Marion-Mahaska-Clarke-Lucas-Monroe-
Wapello-Wayne-Appanoose-Davis-
347 PM CDT Wed Jul 8 2020

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

A Heat Advisory is in effect for the area through tonight. Please
refer to the National Weather Service website at
weather.gov/desmoines for further details.

A few isolated storms are possible east of Interstate 35 through
sunset.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

There is a chance for strong to severe storms across central to
eastern Iowa Thursday. Hail and damaging winds look to be the main
threats.

There is a marginal risk for severe thunderstorms Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not likely at this time.

IAZ023-033-034-044>046-057-058-070-071-081-082-092>094-092100-
Pocahontas-Sac-Calhoun-Crawford-Carroll-Greene-Audubon-Guthrie-
Cass-Adair-Adams-Union-Taylor-Ringgold-Decatur-
347 PM CDT Wed Jul 8 2020

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

Hot and humid conditions will combine to push indicies to around
100 to 105 degrees today.

Non-severe thunderstorms are possible west tonight.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

There is a marginal risk for severe thunderstorms Thursday night
into Friday morning and again Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not likely at this time.

KLP