Special Weather Statement, NWS North Platte, NE

Area Forecast Discussion
National Weather Service North Platte NE
301 PM CDT Sun Jul 30 2017

.SYNOPSIS...
Issued at 300 PM CDT Sun Jul 30 2017

H5 analysis from earlier this morning had high pressure
extending from Texas into California. A low amplitude ridge was
noted over the western CONUS north to Alberta and Saskatchewan. East
of this feature a closed low was located over Labrador Canada with a
trough extending to the southwest along the east coast of the CONUS.
A weak shortwave was noted over western South Dakota with a surface
frontal boundary extending from west of Valentine to just east of
Alliance. As was the case yesterday, the atmosphere is weakly capped
and it has begun to break over the past hour with abundant cu and
some isolated thunderstorms beginning to develop in the western
sandhills. Under mostly cloudy skies this afternoon, 2 PM CDT
readings ranged from 78 at O'Neill to 86 at Valentine.

&&

.SHORT TERM...(This evening through Monday)
Issued at 300 PM CDT Sun Jul 30 2017

Tonight and Monday...Thunderstorm chances are the
main forecasting challenge over the next 24 hours. A similar setup
is in place across western and north central Nebraska compared to
yesterday. A surface boundary located over the northwestern forecast
area will serve as the focal point for thunderstorm initiation. With
a weak cap in place this should be ongoing by late afternoon across
the western sandhills. Deep layer shear remains very weak this
afternoon and a glance at the 12z KLBF RAOB sounding has wind speed
of 10 KTS at 500 MB. With the weak wind shear, the threat for severe
storms is minimal right now. The main hazard from any storms will be
from heavy rain. This notion is supported by decent PWATS, forecast
storm motion of under 15 KTS, and a skinny CAPE sounding from this
morning's KLBF RAOB sounding. Forecast K indexes in the western CWA
are in the lower 40s this afternoon and early evening, lending
further support to the notion of heavy rain. As mentioned earlier,
with weak shear present, storms will be loosely organized and
isolated to scattered in nature. With that in mind, will keep pops
in the 20-30 percent range. Additionally, storms are expected to
dissipate this evening given the degree of weak forcing, limited
shear and a lack of a low level jet tonight. A similar setup is
expected for Monday afternoon with a surface boundary progged across
the northwestern forecast area. A weak cap, abundant moisture and
weak shear, will once again lead to the threat for heavy rain. The
latest NAM12 solution has K indexes in the middle 40s in western
Cherry county Monday afternoon. Will continue to hit this threat for
heavy rain in the HWO.

.LONG TERM...(Monday night through Sunday)
Issued at 300 PM CDT Sun Jul 30 2017

Monday night through Wednesday night...Kind of sounding
like a broken record here but the setup for Monday night to Tuesday
night will be similar to the ongoing setup with the weather pattern
remaining unchanged through Tuesday night. For Tuesday, there will
be plenty of CAPE across western and north central Nebraska, a weak
cap, very limited wind shear...you get the picture. We will see an
increased threat for thunderstorms during the afternoon and evening
hours. With K indexes in the lower 40s Tuesday afternoon, we could
see some heavy rain as well. Highs Tuesday will be in the mid to
upper 80s with lower to middle 80s for Wednesday. By Wednesday
evening, a strong cold front will approach northern Nebraska,
passing through the forecast area overnight. This feature will bring
the best chance for widespread precipitation to the area Wednesday
night.

Thursday through Sunday...The before mentioned cold front will push
well southeast of the forecast area Thursday with drier and much
cooler air pushing into western and north central Nebraska for
Thursday through Saturday. Highs will generally be in the mid to
upper 70s with some lows touching the lower 50s by Friday morning.
The next threat for precipitation will arrive possibly Saturday
night into Sunday as a warm front lifts into the forecast area as
the trough across the Great Lakes moves into eastern Canada.
Temperatures will warm back into the 80s as we approach the second
half of the weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1206 PM CDT Sun Jul 30 2017

Convective development and low cloud potential have made for a
difficult 18z TAF forecast for KLBF and KVTN. With respect to
convection later this afternoon and evening, there is a boundary
off to the west of Valentine and Ogallala Nebraska and believe
this is where convection will fire early this afternoon. With no
cap in place, thunderstorms should fire between 19 and 21z west of
KVTN. However, there are little or no agreement between the short
range model solutions on where and when this convection will fire.
Placing a best guess on this, thunderstorms are expected to impact
the KVTN terminal after 20z and 22z for the KLBF terminal. Will
word this with a VCTS group given the low confidence in the
forecast. Will allow mention of TSRAS to persist through 04z at
the KLBF terminal and 02z at the KVTN terminal. Looking at the
SREF and NAM12 time ht sections for overnight, the KLBF terminal
has the best chance for stratus development and have inserted a
mention of low clouds in the latest 18z forecast.

&&

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

SYNOPSIS...Buttler
SHORT TERM...Buttler
LONG TERM...Buttler
AVIATION...Buttler

Hazardous Weather Outlook
National Weather Service North Platte NE
309 PM CDT Sun Jul 30 2017

NEZ004>010-022>029-035>038-056>059-069>071-094-312030-
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-
309 PM CDT Sun Jul 30 2017 /209 PM MDT Sun Jul 30 2017/

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

.DAY ONE...TONIGHT.

Isolated thunderstorms are possible this evening across western
and north central Nebraska roughly east of a line from cody to
Lisco. Storms that develop are expected to remain below severe
limits, however, they will be capable of producing heavy rain.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

Thunderstorms are possible at times through Thursday across
western and north central Nebraska. At this time, the threat for
severe storms is low, however, heavy rain is possible.

A more organized threat for thunderstorms exists Wednesday
afternoon and Wednesday night across the outlook area. A cold
front will push through the area Wednesday night. At this time,
the threat for severe storms is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed through tonight.

&&

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

CLB

Special Weather Statement
National Weather Service North Platte NE
509 PM CDT SUN JUL 30 2017

NEZ005-094-302300-
Eastern Cherry NE-Western Cherry NE-
509 PM CDT SUN JUL 30 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN CHERRY COUNTY UNTIL
600 PM CDT/500 PM MDT/...

At 508 PM CDT/408 PM MDT/, Doppler radar was tracking strong
thunderstorms along a line extending from near Valentine National
Wildlife Refuge to 17 miles west of Brownlee. Movement was southeast
at 20 mph.

1 to 2 inches of rainfall in an hour and wind gusts of 50 to 55 mph
will be possible with these storms.

Locations impacted include...
Brownlee, Giant Hill and Highway 83 crossing the North Loup River.

This includes Highway 83 between mile markers 168 and 171.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4225 10050 4211 10098 4239 10096 4251 10066
TIME...MOT...LOC 2208Z 337DEG 16KT 4247 10067 4236 10094

CDC

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