Hail in Nebraska, August 24, 2017

Area Forecast Discussion
National Weather Service Sioux Falls SD
330 PM CDT Thu Aug 24 2017

.SHORT TERM...(This evening through Friday)
Issued at 328 PM CDT Thu Aug 24 2017

A very large area of high pressure will be situated east of the area
tonight, sprawling from the Great Lakes Region southward to the Ohio
Valley. Aloft, a very weak 700mb short wave is trying to move from
west to east, primarily across our southern zones while mid level
QG forcing persists across areas from I 29 and points eastward all
night. With a weak low level jet aiding ascent, coupled with
persistent thetae advection and moisture trapped in the 850-700mb
layer, there will be a small threat for showers and a few
thunderstorms tonight, generally east of the James River valley.
There is really not a focusing mechanism, so timing any individual
storms is extremely problematic, with just a developmental situation
involving the warm air advection regime. With 700mb temperatures
only +6 to +8C across the eastern half of our forecast area, the
profiles are just not capped so a shower or TSRA could develop
rapidly at about any time.

On Friday, there could be some stratus developing across our
northern zones and parts of our east late tonight, lingering through
Friday morning. However, indications for fog were not overly strong
which stands to reason if the stratus develops first. Otherwise,
there should also be plenty of mid and high level clouds, so sky
cover will not be very pristine Friday morning, perhaps improving
during the afternoon hours. A stripe of thetae advection lingers
across northwest Iowa and the eastern sections of southwest MN
Friday morning which may help produce a few showers and storms. A
stronger mid level short wave then encroaches into central SD by
Friday afternoon, but it looks too far west to largely affect our
forecast area. Therefore only air mass type showers and storms are
possible Friday afternoon with chilly air aloft and an uncapped
atmosphere responsible for this. 850mb temperatures are actually
quite warm Friday afternoon, therefore trended toward the warmer
bias corrected readings for highs.

.LONG TERM...(Friday night through Thursday)
Issued at 328 PM CDT Thu Aug 24 2017

Expecting elevated storms ahead of strong but slow moving shortwave
working east across the area on Friday night into Saturday.  With
the 12Z models, slowed the progression of rain slightly from west
to east. Storms appear to be elevated, limiting the effective shear
for storms. 2-8 km bulk shear values are generally in the 20-25 knot
range.  With elevated CAPE values of 1500-2000 J/kg could see storms
briefly spike up towards severe but think it would be difficult to
sustain with weak shear.  As for heavy rain potential, precipitable
water values are around 1.5 inches, which is 0.2 or so above the
median moving average.

Rain should gradually come to an end across the area Saturday
afternoon into Saturday night as short wave works east.  Second
shortwave moves through the area on Sunday, but limited amounts of
low level moisture will limit precipitation chances with this
disturbance.

Thereafter, ridge of high pressure dominates across the region
through the first half of next week.  Will see a gradual increase in
temperatures Monday-Thursday, but should only be an increase of a
degree or two each day.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1225 PM CDT Thu Aug 24 2017

Upper end MVFR ceilings will be a threat for the next couple of
hours at the TAF sites. The culprit for KFSD and KHON is fair
weather cumulus clouds, and they will raise along with the mixing
potential height through the afternoon hours into the VFR
category. At KSUX, the MVFR ceilings could develop due to rain
cooled air to their south due to the TSRA passing through the
region. So far, only have a scattered deck for KSUX in the MVFR
range, but will monitor.

Otherwise, left TSRA chances out of the TAF sites after 20Z today
as the chances look too skittish to mention at this time for the
remainder of the TAF period. One thing to keep an eye on late
tonight and Friday morning are MVFR ceilings that could develop
at KHON and KFSD under moist air aloft when a warm front lifts
slowly northward. In fact, there are some indications that the
ceilings could lower into the IFR category if they develop.
However at this time, not a hundred percent confident of this
scenario occurring, therefore did want to include the mention of
IFR at this time, but did mention MVFR as a heads up.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

SHORT TERM...MJ
LONG TERM...BT
AVIATION...MJ

Hazardous Weather Outlook
National Weather Service Sioux Falls SD
354 PM CDT Thu Aug 24 2017

IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097-
098-NEZ013-014-SDZ038>040-050-052>071-252100-
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-Gregory-Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora-
Davison-Hanson-McCook-Minnehaha-Charles Mix-Douglas-Hutchinson-
Turner-Lincoln SD-Bon Homme-Yankton-Clay SD-Union-
354 PM CDT Thu Aug 24 2017

This Hazardous Weather Outlook is for portions of northwest Iowa,
west central Iowa, southwest Minnesota, northeast Nebraska,
central South Dakota, east central South Dakota, south central
South Dakota, and southeast South Dakota.

.DAY ONE...This Afternoon and Tonight

Scattered showers and a few thunderstorms may be possible
this evening and tonight focused primarily along or east of
Interstate 29. While the risk of severe storms is low, an isolated
strong storm may be possible over northeast Nebraska and adjacent
areas of South Dakota and Iowa this evening.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Scattered showers may linger over portions of Northwest Iowa and
surrounding areas in the morning. After a break, scattered
thunderstorms are expected to form over western and central South
Dakota and Nebraska late in the afternoon and evening.

As these storms move eastward, a few strong to even severe storms
area possible. The primary risks will be large hail and locally
damaging winds. Several clusters of storms will move across the
outlook area into Saturday morning, and may bring a risk of
locally heavy rainfall.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.