Special Weather Statement, NWS North Platte, NE

Area Forecast Discussion
National Weather Service North Platte NE
121 PM CDT Mon Jul 17 2017

.SHORT TERM...(Today and tonight)
Issued at 419 AM CDT Mon Jul 17 2017

The next 24 hours revolve around shower and thunderstorm chances,
and the potential for locally heavy rainfall. Latest satellite
imagery and surface plot shows predominantly high level clouds
across much of western NEB, except mid-level clouds over portions
of southwest NEB. Local radar display shows a few widely isolated
returns in southwest NEB. The regional radar display showed
convection across west central and northwest KS that has decreased
in intensity and coverage over the last hour.

With respect to convection over western KS, current thinking is
these showers/storms will struggle to get into the area this
morning. Thus the main precip window begins this afternoon. A weak
closed mid-level low now over east central CO will slide
northeastward into eastern NEB today while weakening into an open
wave. Low-level warm air advection will amplify across western NEB
later today as this shortwave trough lifts northward. This will
contribute to increasing shower and thunderstorm chances starting in
the afternoon into the evening across much of the local forecast
area outside of extreme southwest NEB. With these showers, best
chances for locally heavy rainfall will be tonight wherein models
are trending towards a supportive thermodynamic environment. It's
anticipated precipitable water values will be approaching 150% of
normal, modest warm cloud layer (though less than 10 kft), and
storm motion largely on the slower side (10-15 kt) tonight.
However, deterministic guidance continues to show fair/so-so
agreement with respect to location and timing. That said, a group
or cluster of storms is expected to develop with greater
confidence more so towards central NEB compared to elsewhere.
Otherwise, isolated strong or briefly severe thunderstorms will be
possible also in the afternoon to evening given instability and
moisture support in place.

.LONG TERM...(Tuesday through Sunday)
Issued at 419 AM CDT Mon Jul 17 2017

The H3 jet remains quasi zonal along or just south of the
Canadian border through the week while the H5 ridge builds slowly
over the Plains. Closer to the surface, a series of leeside lows
develop off the Rockies and move along a front oscillating across
the central/northern Plains.

Tuesday... Isolated afternoon and evening thunderstorms are
possible ahead of a dryline. Forecast soundings indicate a deep
mixed layer and limited moisture aloft, along with a slight cap
remaining at 00z. However, lift may be sufficient at peak heating
to justify a schc mention. The LLJ will provide extra lift and
better shear at night, so carried the mention of TSRA across
central Neb. Can't rule out a strong or severe storm with elevated
CAPE of 500+ j/kg and 0-6 km shear of 35 kts overnight. Will also
have to watch the heavy rain threat with above normal PWATs and
relatively slow storm motion. Temperature wise, WAA kicks into
high gear across SW Neb with highs around 100F for Chase, Hayes,
Frontier counties and mid 90s for most of the Sandhills. Very
humid air is getting drawn up through the middle of the Great
Plains, as shown by dew points near 70F from BBW to ANW and points
east. Heat indices will locally surpass 100F south of I-80 and
east of Hwy 83.

Wednesday... The ridge axis bisects Nebraska while one of the more
potent surface lows approaches, likely setting up the hottest day of
the week. NAM and GFS suggest H85 temps reaching or exceeding 30C
while ensembles show H5-8 temps greater than the 90th percentile of
climo. This coincides with max temps near or above 100F for
virtually all the Sandhills and SW Neb with the help of sunshine and
breezy south winds. Dew points will reach the mid 60s again in
central Neb, while they drop into the 50s in the panhandle and
western Sandhills. Regardless, heat headline criteria are met for
all areas except Sheridan and western Cherry counties. Any
convection should hold off until sunset as forcing is practically
non-existent until the trough draws nearer and the LLJ kicks in.

Thursday... Southerly flow continues at H85 with temps approaching
30C and highs around 100F again south of I-80. Best chance of heat
index 100+ generally IML to LBF to BBW and southeast. Lift in the
low levels and mid level moisture are slightly better during the
afternoon than Tue and Wed, so kept schc to chc PoP in the panhandle
before 00z and expanded east at night.

Friday through Sunday... The H5 ridge retreats a bit toward the
southeast U.S. and H85 flow transitions to northerly, resulting in
slightly lower temps. TSRA chances continue with the passage of a
couple cool fronts.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 121 PM CDT Mon Jul 17 2017

VFR conditions to prevail the next 24 hrs. Thunderstorms from
southwest into central Nebraska this afternoon and evening should
remain southeast of the KLBF terminal. Low level wind shear also
forecast at KLBF from 08z-11z. At KVTN, no thunderstorm activity
expected in the vicinity through Tuesday morning.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&

SHORT TERM...ET
LONG TERM...Snively
AVIATION...Roberg

Hazardous Weather Outlook...CORRECTED
National Weather Service North Platte NE
936 AM CDT Mon Jul 17 2017

NEZ004>010-022>029-035>038-056>059-069>071-094-181430-
Sheridan-Eastern Cherry-Keya Paha-Boyd-Brown-Rock-Holt-Garden-
Grant-Hooker-Thomas-Blaine-Loup-Garfield-Wheeler-Arthur-McPherson-
Logan-Custer-Deuel-Keith-Perkins-Lincoln-Chase-Hayes-Frontier-
Western Cherry-
936 AM CDT Mon Jul 17 2017 /836 AM MDT Mon Jul 17 2017/

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

.DAY ONE...TODAY AND TONIGHT.

Thunderstorms capable of heavy rainfall are possible this
afternoon and overnight, mainly southeast of a line from Curtis to
North Platte to Broken Bow. Isolated strong to briefly severe
thunderstorms capable of hail and strong wind gusts are also
possible across the entire outlook area.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY.

Isolated strong to briefly severe thunderstorms will be possible
again Tuesday afternoon and evening, mainly along and north of
Interstate 80. A few storms could produce large hail and damaging
winds.

Heat index values should approach or exceed 100 degrees Tuesday
through Thursday across parts of western Nebraska.

While thunderstorm will be possible at times Wednesday and beyond
mainly in the afternoon and evening, the risk of severe
thunderstorms is low at this time.

Thunderstorms will continue to be capable of sparking grass fires
from cloud to ground lightning.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed through tonight.

&&

Get your weather, hydrological, and climate information at
http://www.weather.gov/northplatte

Roberg

Special Weather Statement
National Weather Service North Platte NE
244 PM CDT MON JUL 17 2017

NEZ038-172030-
Custer NE-
244 PM CDT MON JUL 17 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTH CENTRAL CUSTER COUNTY UNTIL
330 PM CDT...

At 244 PM CDT, Doppler radar was tracking a strong thunderstorm 11
miles north of Cozad, or 18 miles northwest of Lexington, moving
northeast at 35 mph.

Dime size hail and winds in excess of 30 mph will be possible with
this storm.

Locations impacted include...
Callaway, Oconto, Buckeye, Lodi and Pressey State Wildlife Management
Area.

LAT...LON 4140 9991 4124 9948 4104 9971 4105 10004
TIME...MOT...LOC 1944Z 207DEG 29KT 4102 9992

Roberg