Hail and Damaging Wind in Iowa, August 23 to 24, 2018

Area Forecast Discussion
National Weather Service Des Moines IA
639 AM CDT Thu Aug 23 2018

.SHORT TERM.../Today through Tonight/
Issued at 401 AM CDT Thu Aug 23 2018

Surface ridge across the state providing for light winds and
generally clear skies and cool temperatures.  This ridge will slide
east this morning and will immediately be replaced by increasing
warm advection and theta-e advection.  Already have showers and
thunderstorms expanding across south central Nebraska into northern
Kansas on nose of low level jet and moisture transport and
anticipate this area moving east today into Iowa. Most recent CAMs
output has convection approaching the SW by late morning.
However, as the convection nears, it will encounter a much drier
low level airmass and some diminishing of the precipitation is
expected also aided by the weakening low level jet. There will be
limited progress east through the day until strengthening flow and
moisture transport increase by late afternoon/evening.
Instability during this time will remain quite elevated and the
threat for severe weather is expected to be marginal with hail and
a strong wind gust the main concern from this evening into the
overnight. Temperatures today will remain cool, especially in
western Iowa where clouds and a few showers will limit heating the
most.

Showers and scattered convection will overspread much of the state
overnight as low level jet increases and theta-e advection spread
north and east.  Have maintain the likely pops in the east and north
but forcing will be waning in the southwest with lower pops there.
Overnight lows will be warmer tonight with more cloud cover and
higher dewpoints allowing temperatures remain higher during the
night.

.LONG TERM.../Friday through Wednesday/
Issued at 401 AM CDT Thu Aug 23 2018

Storm chances Friday shift to the eastern portion of the cwa as
shortwave trough lifts east. Diurnal heating will help increase
instability and erode decent cap across the area. With CAPE values
exceeding 2000 J/kg and bulk shear around 40 kts, severe storms
are expected. The main threats are hail and winds, however with
low-level helicity around 150 m^2/s^2 and 0-3 km CAPE of 200+
J/kg, the chance of a tornado cannot be ruled out. Although
slightly mitigated by cloud cover, WAA Friday will help
temperatures across the south to warm into the mid 80s. GFS/NAM
are several degrees cooler (low 80s) than the Euro/Canadian (mid
80s), and with precip chances and increased cloud cover Friday
opted to nudge high down a degree or two.

As the shortwave trough pushes east Friday night, slight ridging
will build into the state through Saturday. This will help high
temperatures Saturday afternoon to climb into the mid to upper 80s
north and low 90s across the south. A shortwave moving across
south central Canada with a trailing boundary will bring another
chance for storms on Sunday into Monday morning.

Through mid-week the area will be influenced by westerly to
southwesterly flow, allowing temperatures to remain the mid 80s
to around 90. The pattern will remain relatively active, with
several embedded shortwaves bringing multiple round of
precipitation throughout the upcoming week.

&&

.AVIATION.../For the 12Z TAFS through 12Z Friday morning/
Issued at 639 AM CDT Thu Aug 23 2018

There will be increasing warm advection and theta-e advection
today into tonight across Iowa. Ceilings will spread across the
state today remaining mostly VFR. However, the ceilings are
forecast to lower later tonight to MVFR and eventually IFR across
much of central Iowa. There will be the threat of a few showers
and storms in southwest Iowa today and much of the area tonight,
especially east of the KMCW-KDSM-KLWD corridor.

&&

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

&&

SHORT TERM...Cogil
LONG TERM...Hagenhoff
AVIATION...Cogil

Hazardous Weather Outlook
National Weather Service Des Moines IA
432 AM CDT Thu Aug 23 2018

IAZ004>007-015>017-023>026-033>037-044>048-057>060-070>073-
081>084-092>095-240945-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Sac-Calhoun-Webster-Hamilton-
Hardin-Crawford-Carroll-Greene-Boone-Story-Audubon-Guthrie-Dallas-
Polk-Cass-Adair-Madison-Warren-Adams-Union-Clarke-Lucas-Taylor-
Ringgold-Decatur-Wayne-
432 AM CDT Thu Aug 23 2018

This Hazardous Weather Outlook is for portions of central Iowa,
north central Iowa, northwest Iowa, south central Iowa, southwest
Iowa, and west central Iowa.

.DAY ONE...Today and Tonight

Thunderstorms are expected today and tonight. The Storm
Prediction Center has issued a marginal risk for severe storms,
as a few strong to severe storms are possible with the main
threats being large hail and damaging winds.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Thunderstorms are expected to linger through Friday, with a few
strong to severe storms possible. Additional thunderstorms are
forecasted for Sunday into Monday. The severe potential appears
low at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated at this time.

IAZ027-028-038-039-049-050-061-062-074-075-085-086-096-097-240945-
Butler-Bremer-Grundy-Black Hawk-Marshall-Tama-Jasper-Poweshiek-
Marion-Mahaska-Monroe-Wapello-Appanoose-Davis-
432 AM CDT Thu Aug 23 2018

This Hazardous Weather Outlook is for portions of central Iowa,
north central Iowa, northeast Iowa, south central Iowa, and
southeast Iowa.

.DAY ONE...Today and Tonight

Thunderstorms are expected today and tonight. A few strong to
severe storms are possible with the main threats being large hail
and damaging winds.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

The Storm Prediction Center has issued a slight risk for severe
storms on Friday. The main threats are large hail and damaging
winds, although a tornado cannot be ruled out. Additional
thunderstorms are forecasted for Sunday into Monday. The severe
potential appears low at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be necessary Friday.