Hail and Heavy Rain in Iowa, August 16, 2016

Area Forecast Discussion
National Weather Service Sioux Falls SD
257 PM CDT TUE AUG 16 2016

.SHORT TERM...(This evening through Wednesday)
Issued at 257 PM CDT Tue Aug 16 2016

Another night with disorganized and not easily forecast thunderstorm
potential. At 19z it appears that the surface front extended from
Just north of Storm lake and Sioux City west along the Missouri
River into south central SD. Shear along this boundary and in the
surrounding environment pretty weak with CAPE values likely to be
around 1500-2000 J/kg. All of this spells a similar outcome, which
is a few stronger updrafts, likely fairly short lived with fairly
disorganized convection. Upper level support and fairly weak mid
level convergence suggest that east of the James River will be the
best chance for thunderstorms with the slightly better chance in
southwest Minnesota and parts of northwest Iowa. The main threat
should end by about 10 pm. Temperatures will be seasonal with lows
from the upper 50s to lower 60s and highs Wednesday from 80 to 85 in
southwest Minnesota to the lower 90s in south central SD.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 257 PM CDT Tue Aug 16 2016

Warm front lifts toward the Missouri River Valley Wednesday night,
accompanied by a ribbon of elevated instability and modest warm
advection into the James River Valley after midnight. Could see
spotty elevated storms develop during the pre-dawn hours, though
severe threat continues to look low given limited effective shear.
Any early morning activity should lift north of the area by mid to
late morning, with attention then turning to approaching mid-upper
level wave and cold front. 12Z model runs showing a little better
agreement on timing the front into the northwest portion of our
forecast area near Chamberlain to De Smet line by 19/00Z. Strong
thermal ridge works into the forecast area ahead of the front, which
should aid in warming temperatures into the lower-mid 90s throughout
much of the forecast area. Some raw models mix temperatures into the
triple digits in areas west of I-29, but this seems little overdone
and will stick with somewhat more conservative numbers for now.

Primary upper trough lags back over the northern Rockies through
Friday, though a couple of waves in the southwest flow ahead of the
trough should provide sufficient upper level support for storm
development, primarily along/north of the boundary Thursday night
through Friday. Shear profiles appear marginal for severe weather
threat through Thursday night, as mid-upper level winds remain on
the weaker side and increasing low level jet may not be utilized by
potentially elevated storms. Expect to see increasing deep layer
shear and associated severe threat on Friday, with the approaching
boundary adding directional component and an increase in the mid-
upper level flow adding to speed shear. Temperatures a little tricky
as gradient location will depend on frontal boundary position and
associated precip, but generally looks like mid 70s northwest to
lower-mid 80s southeast.

Cooler air settles into the region for the weekend, with highs in
the upper 60s-mid 70s and lows largely in the lower 50s. Main upper
trough swings through Saturday, so will linger some low chances for
showers/isolated thunder across the area for the first half of the
weekend. Gradual warming expected through the early part of the
week, with generally dry conditions through Tuesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1217 PM CDT Tue Aug 16 2016

The main threat for thunderstorms should be from about 21z through
3z with the better chances east of the James River and especially
over parts of southwest Minnesota and northwest Iowa. Outside of
the thunderstorms, VFR conditions are expected.

&&

.FSD Watches/Warnings/Advisories...
SD...None.
MN...None.
IA...None.
NE...None.
&&

SHORT TERM...08
LONG TERM...JH
AVIATION...08

HAZARDOUS WEATHER OUTLOOK...CORRECTED TYPO
NATIONAL WEATHER SERVICE SIOUX FALLS SD
515 AM CDT TUE AUG 16 2016

SDZ050-052-057>059-063>066-068-069-171015-
GREGORY-JERAULD-BRULE-AURORA-DAVISON-CHARLES MIX-DOUGLAS-
HUTCHINSON-TURNER-BON HOMME-YANKTON-
515 AM CDT TUE AUG 16 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL SOUTH
DAKOTA...SOUTH CENTRAL SOUTH DAKOTA AND SOUTHEAST SOUTH DAKOTA.

.DAY ONE...TODAY AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

THUNDERSTORMS WILL BE POSSIBLE THURSDAY EVENING INTO THE
OVERNIGHT. THE GREATEST LIKELIHOOD OF STORMS WILL BE NORTH OF
INTERSTATE 90 NEAR HIGHWAY 14. SOME OF THE STORMS MAY BE
SEVERE...WITH LARGE HAIL AND DAMAGING WINDS AS THE GREATEST
THREATS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL BE POSSIBLE AFTER 4 PM TODAY.

IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097-
098-NEZ013-014-SDZ038>040-053>056-060>062-067-070-071-171015-
LYON IA-OSCEOLA-DICKINSON-SIOUX-O'BRIEN-CLAY IA-PLYMOUTH-CHEROKEE-
BUENA VISTA-WOODBURY-IDA-LINCOLN MN-LYON MN-MURRAY-COTTONWOOD-
NOBLES-JACKSON-PIPESTONE-ROCK-DIXON-DAKOTA-BEADLE-KINGSBURY-
BROOKINGS-SANBORN-MINER-LAKE-MOODY-HANSON-MCCOOK-MINNEHAHA-
LINCOLN SD-CLAY SD-UNION-
515 AM CDT TUE AUG 16 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHWEST
IOWA...WEST CENTRAL IOWA...SOUTHWEST MINNESOTA...NORTHEAST
NEBRASKA...EAST CENTRAL SOUTH DAKOTA AND SOUTHEAST SOUTH DAKOTA.

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORMS WILL BE POSSIBLE THIS AFTERNOON INTO THIS EVENING.
A FEW OF THESE STORMS MAY APPROACH SEVERE LIMITS PRODUCING HAIL TO
THE SIZE OF QUARTERS AND WIND GUSTS TO 60 MPH.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

THUNDERSTORMS WILL BE POSSIBLE THURSDAY EVENING INTO THE
OVERNIGHT. THE GREATEST LIKELIHOOD OF STORMS WILL BE NORTH OF
INTERSTATE 90 NEAR HIGHWAY 14. SOME OF THE STORMS MAY BE
SEVERE...WITH LARGE HAIL AND DAMAGING WINDS AS THE GREATEST
THREATS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE AFTER 3 PM TODAY.