Hail and Damaging Wind in Nebraska, July 17 to 18, 2017

Area Forecast Discussion
National Weather Service Hastings NE
624 AM CDT Mon Jul 17 2017

.UPDATE...
Issued at 437 AM CDT Mon Jul 17 2017

Decided to include a mention for the potential of localized
flooding in the HWO for this afternoon and tonight as any
convection that might develop will be very slow moving, and
combined with a moist environment and a slowly moving instability
axis to focus on, this could spell trouble in at least isolated
areas.

&&

.SHORT TERM...(Today and tonight)
Issued at 349 AM CDT Mon Jul 17 2017

Main challenge will be concerning chances of precipitation and to
what extent of any severe weather we may have a shot at. Also, high
temperatures may be challenging thanks to potential added sky cover
in our west, with a sharp gradient of cloudiness progressing east.

The main potential weather maker will be a closed upper low embedded
within a subtropical ridge. This low is coming out of the central
Rockies and into the western Plains, which could give us a shot at
some showers and thunderstorms, especially in our west. A resultant
surface trough to the west will encourage a bit more wind speed from
the south for Monday. With slightly higher, yet still modest bulk
shear along with modest instability, we may be in store for one or
two pulse-type marginal severe storms in our west/northwest, closer
to the trough. We could very well get a localized cluster of storms
to develop in our western CWA for Monday afternoon, with a strong
cold pool potentially shifting the storms perhaps far enough east to
include the tri-cities and beyond, but the strongest wind
aloft/shear will be well north of the area. Topped POPs out at 40
to 50 percent this afternoon/evening, as there is some agreement
of a localized cluster of storms developing, but timing and
placement are not all that predictable with such a small feature.
If anything, the progression east may not be as fast as some short
term models indicate, considering the trends the past couple of
days. However, I did not want to limit POPs to slight, as there is
decent agreement that initiation of convection will begin near
the CWA this afternoon, and gave my best guess of placement and
timing, as inflow is at least somewhat supportive of maintenance
of convection once it gets going.

Highs could be tricky with additional sky cover in our west, and
could be a tough call on perhaps a healthy temperature gradient.
Looks like the thicker clouds will enter late enough to not be all
that much cooler in our west, but perhaps up to 5 degrees cooler
than the rest of the CWA. Currently going with highs near 90 far
west to mid 90s southeast. Lows tonight will be rather warm with
the muggy conditions, bottoming out mostly near 70 to the mid 70s.

.LONG TERM...(Tuesday through Sunday)
Issued at 349 AM CDT Mon Jul 17 2017

The primary weather threat of the upcoming week will be the heat. It
still appears that Wednesday will be the warmest day, with high
temperatures in  the upper 90s and low 100s across the entire area.
In addition, it is looking like Thursday (and possibly even Friday)
will only be a degree or two cooler than Wednesday for most
locations. Heat index values may approach advisory criteria (105
degrees or higher) on Tuesday, but the best opportunity will be
Wednesday and Thursday. Therefore, we've decided to hold off on any
heat headlines for now.

Taking a look at precipitation chances, it looks like today and
Tuesday evening/night will be our best chances for rain/thunderstorms
until at least the upcoming weekend.

Lingering storms should exit the eastern half of the CWA by late
morning Tuesday. By Tuesday evening, a cold front should be located
across northern Nebraska. With increasing convergence along a 850mb
LLJ, I expect scattered storms to develop in this vicinity and
gradually move southward into central and south-central Nebraska.
The NAM shows 2000-3000 J of elevated CAPE and 30 to 40 kts of deep-
layer shear. Therefore, an isolated severe storm or two is certainly
possible.

Wednesday through Friday, the upper level ridge builds moves
overhead, which will severely limit our chances for rain and
thunderstorms in this area. Northern Nebraska, possibly as far south
as Ord, will have off and on thunderstorm chances, but unfortunately
central Nebraska and northern Kansas will likely remain dry.

Friday night into Saturday, a cold front will drop southward into
the area as the upper ridge starts to break down. As this front
stalls in the area, this will bring us multiple opportunities for
rain and thunderstorms, especially across Kansas, through the
weekend and hopefully into early next week.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Tuesday)
Issued at 620 AM CDT Mon Jul 17 2017

The bigger issues concern the potential for convection tonight as
a closed low becomes an open wave within an upper level
subtropical ridge. An attendant surface trough will be the focus
of potential convection to the west afternoon as cold pools could
push convection farther east. We could get enough of a low-level
jet to give us some low-level wind shear, focused to the west,
encompassing perhaps KEAR. Marginal risk of severe storms tonight,
along with the potential for locally heavy rain, which could in
turn reduce visibility, and perhaps ceiling to MVFR or even lower,
especially for visibility. Too early to narrow down specific times
for this.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...None.
KS...None.
&&

UPDATE...Heinlein
SHORT TERM...Heinlein
LONG TERM...Mangels
AVIATION...Heinlein

Hazardous Weather Outlook...CORRECTED
National Weather Service Hastings NE
505 AM CDT Mon Jul 17 2017

Corrected to add spotter activation statement

KSZ005>007-017>019-NEZ039>041-046>049-060>064-072>077-082>087-
181200-
Phillips-Smith-Jewell-Rooks-Osborne-Mitchell-Valley-Greeley-Nance-
Sherman-Howard-Merrick-Polk-Dawson-Buffalo-Hall-Hamilton-York-
Gosper-Phelps-Kearney-Adams-Clay-Fillmore-Furnas-Harlan-Franklin-
Webster-Nuckolls-Thayer-
505 AM CDT Mon Jul 17 2017

This Hazardous Weather Outlook is for south central Nebraska and
portions of north central Kansas.

.DAY ONE...Today and Tonight.

There is a marginal risk of strong to severe thunderstorms for
this afternoon and tonight with hail up to the size of quarters
and wind gusts up to 60 mph possible. Also, local flooding is
may occur with slow moving storms containing heavy rain.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Scattered thunderstorms are expected to develop Tuesday evening into
the overnight. A few of these storms could be strong to severe with
hail to the size of quarters and 50 to 60 mph wind gusts.

Heat index values will climb to between 100 and 108 degrees each
afternoon Tuesday through Friday.

Chances for thunderstorms return to the area late Friday night
through Sunday.

.SPOTTER INFORMATION STATEMENT...

There is a very small chance of spotter activation for this
afternoon and tonight, but in most areas, spotter activation will
not be needed.

&&

More information may be obtained at the following web page:
   https://www.weather.gov/hastings

Heinlein/Mangels