Severe Thunderstorm Warning 216, NWS Hastings, NE

Area Forecast Discussion
National Weather Service Hastings NE
110 AM CDT Thu Aug 16 2018

.SHORT TERM...(This evening through Thursday)
Issued at 236 PM CDT Wed Aug 15 2018

The first short term forecast concern is the chance for
thunderstorms this evening and overnight. The second concern is
continued thunderstorms, timing, location and severity tomorrow.

First off today, an upper disturbance is moving southeast across
the northern Plains, currently located over the southwestern
corner of South Dakota. This disturbance is expected to slowly
track southeast across northern/eastern Nebraska over the next 24
hours. At the surface this afternoon surface high pressure is
dominant with mostly clear/partly cloudy skies, light winds and
below normal temperatures.

The disturbance is supporting thunderstorms that have been ongoing
throughout much of the day across southern South Dakota and
northern Nebraska. These thunderstorms are tracking east across
northern Nebraska, but they have kicked an outflow boundary
southeast as is apparent on radar data this afternoon. This
outflow boundary may impact when/where thunderstorms may develop
this evening across the High Plains. The high-res guidance has
been indicating that these thunderstorms will fire in the
sandhills and take a while until they make it into central
Nebraska. The mesoscale boundary could change this location,
pushing storm development further south which could cause an
earlier initiation across central Nebraska. Did tweak my pops at
the last minute to include small chances for thunderstorms in
central Kansas into the late afternoon hours. Moderate instability
and plentiful shear will help any thunderstorm that develops to
become severe. With earlier models, thought that the best chance
for severe activity was north and west of the area, but with this
outflow boundary, some of that severe activity may reach into
central Nebraska. The Marginal Risk looks good with the main
threat across the northwestern half of the forecast area.

As this upper low tracks southeast, thunderstorms are expected to
continue to re-develop and impact central and eventually eastern
portions of the area tonight and into Thursday. While constant
widespread activity is not anticipated, scattered off and on
thunderstorms are possible overnight and early Thursday. The upper
low will be pushing southeast by the afternoon with additional
re-development expected Thursday afternoon across northern Kansas.
Much of the forecast area is in a Marginal Risk on Thursday with a
Slight Risk for the southeast portion. Think the best chance for
strong to severe thunderstorms will be later in the afternoon in
the area aligned with the Slight Risk.

.LONG TERM...(Friday through Wednesday)
Issued at 236 PM CDT Wed Aug 15 2018

After the upper low exits to the southeast late Thursday, Surface
high pressure will build in across the area. The end of the work
week will remain relatively quiet with highs in the low to mid 80s
for much of the area and dry.

The next disturbance will approach the Central Plains late
Saturday. This disturbance is fairly strong and will help to
develop thunderstorms late Saturday with the chance persisting
through Sunday and into Monday as the system slowly moves across
the area. Temperatures will continue to be below normal, with
highs in the 70s possible Sunday and Monday. It is expected to dry
out late Monday through mid-week and continue to be cooler than
normal through Wednesday.

&&

.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Friday)
Issued at 110 AM CDT Thu Aug 16 2018

General overview:
This is a somewhat tricky period, with the main
concerns/challenges consisting of: 1) Will thunderstorms affect
either/both sites this morning?...2) Will ceiling through much of
the period (especially 12-00Z) remains in VFR range, or instead
drops into MVFR for at least a few hours? A possible third concern
is some possibility of light fog development/reduced visibility
this morning, but overall conditions do not seem very supportive
so have kept visibility at least low-end VFR throughout. Wind-
wise, while there is high confidence that sustained speeds
(outside of thunderstorm activity, of course) will average solidly
under 10KT throughout, there is below average confidence in
direction (especially during the daylight hours) so have gone with
a variable mention until Thursday evening, when there is slightly
higher confidence in prevailing north-northeasterly. Read on for
more element-specific detail...

Ceiling:
As mentioned, this is a potentially big question mark, as various
models/guidance show it could be a fairly "close call" between
low-end VFR and middle-high end MVFR ceiling through much of the
period. Will officially stick with VFR for now, but will at least
"hint" at the MVFR with a SCT015 mention much of the time.

Thunderstorm potential:
It's looking as though the main window of opportunity for
thunderstorms at both sites will focus during these first 7 hours
or so, and this has been mainly handled with a "vicinity" (VCTS)
mention for now. Cannot rule out a stronger storm with gusty
winds/small hail. Beyond 13Z, chances of convection are not "zero"
for several more hours (at least until closer to 00Z), but the
better chances should focus farther south-southeast with time, and
don't have the confidence any convective mention beyond 13Z at
this time.

&&

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

SHORT TERM...Billings Wright
LONG TERM...Billings Wright
AVIATION...Pfannkuch

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Special Weather Statement
National Weather Service Hastings NE
335 AM CDT THU AUG 16 2018

NEZ039-040-046-047-160915-
Valley NE-Howard NE-Greeley NE-Sherman NE-
335 AM CDT THU AUG 16 2018

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHERN GREELEY...SOUTHEASTERN
VALLEY...NORTHEASTERN SHERMAN AND NORTHWESTERN HOWARD COUNTIES UNTIL
415 AM CDT...

At 335 AM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near North Loup to near Sherman Reservoir Dam.
Movement was southeast at 30 mph.

Penny size hail and winds in excess of 40 mph will be possible with
these storms.

Locations impacted include...
Loup City, Scotia, North Loup, Wolbach, Elba, Ashton, Farwell,
Cotesfield and Sherman Reservoir Dam.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 4145 9830 4109 9871 4131 9904 4158 9877
TIME...MOT...LOC 0835Z 296DEG 24KT 4149 9873 4132 9891

Pfannkuch