Hail and Damaging Winds in Iowa, August 11 to 12, 2016

Area Forecast Discussion
National Weather Service Des Moines IA
359 AM CDT Thu Aug 11 2016

.SHORT TERM.../Today/
Issued at 359 AM CDT Thu Aug 11 2016

A couple of concerns this morning and through the day.  First,
scattered storms have developed ahead of impending South Dakota MCS
on the nose of the LLJ with additional aide from a weak short wave
and theta-e advection. Coverage will continue to be scattered and
progressively eastward into the morning, with little concern other
than brief heavy rainfall.  Of a bit more concern is the ongoing MCS
that has crossed into northwest Iowa. Heavy, efficient rainfall will
be the main concern with PWats around 2 inches, though with DCAPE in
excess of 1200-1300 J/kg currently, gusty to possible severe winds
may be possible as it continues to translate E/SE across the
northern third/half of the CWA. Local rainfall totals around 1-3
appear likely through the morning, priming areas for possible flash
flooding this evening with the cold front and primary heavy rain
threat.

This afternoon across the southern third of the CWA, heat will be a
concern with temperatures into the low 90s and dew points
approaching 80. In all, heat index values will approach and possibly
exceed 105 degrees at times, warranting a heat advisory this
afternoon. The biggest wild card though will be cloud cover, as it
may limit temperatures should it linger longer into the day than
currently expected.

Lastly, and primarily in the long term period, cold front will enter
northwest Iowa late in the day and make its way across the state
overnight Thursday into Friday. Atmospheric conditions will be
primed for significant rainfall with PWats commonly around 2-2.5
inches, warm cloud layer depths around 14kft, mean winds roughly
parallel to the front causing training, and relatively slow storm
motions and front progression. All of which significantly raise
concerns for long durations of heavy rainfall and possible local
amounts in excess of 4-6 inches.

.LONG TERM.../Tonight through Wednesday/
Issued at 359 AM CDT Thu Aug 11 2016

Big focus of the extended is actually on tonight with the potential
for widespread rainfall and potentially heavy rainfall. Area of
surface low pressure to push into the state by early evening, with
the surface trough axis to move through the CWA tonight and the
associated cold front by early Friday. Upper level trough
responsible for the sfc area of low pressure to dig into the
northern Plains today and shift ESE slowly through the region
tonight into early Saturday. A shortwave trough embedded in the main
upper level trough will eject out of the Rockies and through the
region late tonight into tonight helping ignite storms across the
state. Convection expected to be somewhat ongoing throughout today,
and to become more widespread this evening into the overnight hours
as storms fire along the sfc trough axis by late afternoon/early
evening. Moisture transport oriented right into Iowa tonight, with
PWATS greater than 2 inches expected. NAM overdone advertising
around 2.25 to 2.5 inches or higher, which would put it near or
above the climatological maximum for this time of year. Freezing
levels very high around 15 to 16 kft which will allow for warm rain
processes and efficient rain production. Slightly less moisture
available Wednesday and still had some storms yield 2 to 3 inch
rainfall rates with a very quick 1-3 inches picked up in spots,
therefore expect similar conditions late today with very heavy
rainfall possible. Storms expected to grow upscale quickly into
clusters with storm motions only around 10-20kts and parallel to the
boundary. Therefore training of storms, slow movement and abundant
moisture setting the stage for heavy rainfall and increasing the
flash flood potential.

Many areas with flash flood guidance around 1 to 2 inches in 3
hours, with some sites higher. The area can take some rain with
mature crops in place, but the high rainfall rates may quickly
saturate soils and lead to excessive rainfall and flash flooding.
Therefore will issue a flash flood watch for the entire CWA through
early Friday morning.

Some precip could linger into Friday before the cold front
completely pushes through the CWA and then will see drier and cooler
air in place for the weekend. Max temps to drop back into the low
80s for the weekend, with temps gradually warming back into the mid
80s by the middle of next week. Near zonal to a broad northwesterly
flow pattern to set up toward next week and will see a return to
intermittent precip chances by early to mid week.

&&

.AVIATION.../For the 06Z TAFS through 06Z Thursday night/
Issued at 1142 PM CDT Wed Aug 10 2016

Potential higher impact event during this period due to heavy
rainfall potential/rainfall rates and low visibility. MCS over
South Dakota will move through the area through 14z with possible
redevelopment between 16-19z over the south. Cigs/vsbys will be
variable VFR/MVFR through 19z. As main boundary approaches
increasing training TSRA will move over KFOD/KMCW/KALO between
11/22-12/07z and across the south sites KDSM/KOTM between
12/02-12/12. Some timing differences between HIRES models remain
but slow movement and efficient rainfall may result in water
runoff problems on runways during evening overnight operations
KDSM/KALO. Potential for IFR conditions during heavier storms/rainfall
as well. Will let next two packages further refine that potential.
/rev

&&

.HYDROLOGY...
Issued at 340 AM CDT Thu Aug 11 2016

Some spotty areas have seen some heavier rainfall over the past 24
hours and other areas can handle some rain with higher guidance
values for flash flooding. However the scenario setting up for
today and especially tonight could produce very high rain rates on
the order of 2 to 3 inches per hour in addition to slow moving
storms and potential training of storms. This may lead to the
potential for flash flooding. Fast rises on small streams and
creeks will also be possible. Minor rises on main stem rivers can
be expected, however the potential for flooding on the main stem
rivers is lower.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 1 PM this afternoon to 8 PM CDT this evening
for Adair-Adams-Appanoose-Audubon-Cass-Clarke-Dallas-Decatur-
Guthrie-Jasper-Lucas-Madison-Marion-Monroe-Polk-Ringgold-Taylor-
Union-Warren-Wayne.

Flash Flood Watch from this evening through Friday morning for
Adair-Adams-Appanoose-Audubon-Boone-Carroll-Cass-Clarke-Crawford-
Dallas-Davis-Decatur-Greene-Guthrie-Jasper-Lucas-Madison-Mahaska-
Marion-Marshall-Monroe-Polk-Poweshiek-Ringgold-Story-Tama-Taylor-
Union-Wapello-Warren-Wayne.

Flash Flood Watch from 7 AM CDT this morning through Friday
morning for Black Hawk-Bremer-Butler-Calhoun-Cerro Gordo-Emmet-
Franklin-Grundy-Hamilton-Hancock-Hardin-Humboldt-Kossuth-Palo
Alto-Pocahontas-Sac-Webster-Winnebago-Worth-Wright.

&&

SHORT TERM...Curtis
LONG TERM...Beerends
AVIATION...REV
HYDROLOGY...Beerends

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
404 PM CDT WED AUG 10 2016

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-112115-
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-
404 PM CDT WED AUG 10 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

ISOLATED TO SCATTERED THUNDERSTORMS WILL OCCUR INTO THIS EVENING.
LOCALIZED DAMAGING WIND GUSTS ARE POSSIBLE WITH THESE STORMS.
ADDITIONAL STORMS ARE EXPECTED TO ARRIVE AFTER MIDNIGHT TONIGHT
OVER PORTIONS OF CENTRAL AND NORTHERN IOWA. LOCALIZED HEAVY
RAINFALL AND DAMAGING WIND GUST WILL AGAIN BE POSSIBLE.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

HEAT INDEX VALUES MAY REACH INTO THE 100 TO 105 DEGREE RANGE
THURSDAY AHEAD OF IMPENDING COLD FRONT.

WIDESPREAD THUNDERSTORMS WILL BE LIKELY ACROSS THE STATE BEGINNINGOVER
NORTHERN IOWA THURSDAY AND THE REMAINDER OF THE AREA THURSDAY
NIGHT AND FRIDAY. VERY HEAVY RAINFALL WITH LOCALIZED AMOUNTS IN
EXCESS OF 5 INCHES IS POSSIBLE. THIS MAY RESULT IN FLASH FLOODING
AND SIGNIFICANT RISES ON STREAMS. ISOLATED STRONG TO SEVERE
THUNDERSTORMS ARE ALSO POSSIBLE WITH DAMAGING WINDS THE PRIMARY
THREATS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED AT THIS TIME HOWEVER
RAINFALL AND FLOODING REPORTS ARE ENCOURAGED AND HELPFUL.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
429 AM CDT THU AUG 11 2016

IAZ005>007-015>017-023>025-033>035-111030-
WORTH IA-WEBSTER IA-WRIGHT IA-CERRO GORDO IA-WINNEBAGO IA-
PALO ALTO IA-HUMBOLDT IA-SAC IA-CALHOUN IA-POCAHONTAS IA-KOSSUTH IA-
HANCOCK IA-
429 AM CDT THU AUG 11 2016

...LINE OF STORMS PRODUCING GUSTY WINDS AND HEAVY RAINFALL...

AT 428 AM CDT...DOPPLER RADAR WAS TRACKING STRONG THUNDERSTORMS ALONG
A LINE EXTENDING FROM 7 MILES SOUTHWEST OF ELMORE TO NEAR ALBERT CITY
TO NEAR KINGSLEY. MOVEMENT WAS EAST AT 55 MPH.

WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH THESE STORMS.

LOCATIONS IMPACTED INCLUDE...
MASON CITY...FORT DODGE...ALGONA...FOREST CITY...EMMETSBURG...
GARNER...CLARION...SAC CITY...POCAHONTAS...ROCKWELL CITY...DAKOTA
CITY...HUMBOLDT...EAGLE GROVE...BELMOND...BRITT...MANSON...NORA
SPRINGS...MANLY...LAURENS AND LAKE VIEW.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THESE STORMS...AND MAY
LEAD TO LOCALIZED FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH
FLOODED ROADWAYS.

&&

LAT...LON 4333 9302 4315 9302 4291 9339 4291 9350
      4283 9350 4258 9387 4227 9498 4234 9532
      4247 9532 4248 9539 4256 9539 4256 9492
      4297 9491 4326 9449 4325 9445 4329 9444
      4346 9418
TIME...MOT...LOC 0928Z 282DEG 46KT 4340 9415 4279 9506 4252 9598

CURTIS