Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 150537
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
1237 AM CDT Tue Aug 15 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 314 PM CDT Mon Aug 14 2017

The HRRR, HRRR EXP and GFS were the basis for rain chances tonight
and Tuesday. Two or more MCS`s should form. One tonight and a second
or third Tuesday.

The system tonight is spawned off the Big Horns and Laramie range
this afternoon. This storm activity is expected to grow upscale,
mainly affecting SD this evening. Some of the HRRR solns show
isolated activity over the Sandhills late this afternoon ahead of
the WY storms. There is considerable variability in the extent of
upscale growth across Wrn Neb this evening with some solns showing
more storm coverage than others. POPS are limited to 30 percent for
this reason.

Isolated showers and thunderstorms are possible in many areas
Tuesday morning. The extent of upscale growth tonight could deeply
influence the sfc focus Tuesday across Neb. The consensus of the
HRRR EXP, NAM and GFS suggested storms firing on a frontal boundary
laying somewhere across the cntl Sandhills...perhaps near or
along highway 2.

The NAM nest and HRRR EXP show upscale storm growth across the ern
Sandhills which drops south into Custer Co. where a flash flood
watch will be posted.

Rain activity should continue well into Tuesday night, generally
along and east of highway 83. The model consensus shows sfc dew
points in the upper 60s to around 70 with deep moisture aloft
supporting storms capable of heavy rainfall. WPC suggested the
increasing low level jet could support back building or train storm
behavior.

.LONG TERM...(Tuesday night through Monday)
Issued at 314 PM CDT Mon Aug 14 2017

Rain activity should continue well into Tuesday night, generally
along and east of highway 83. The model consensus shows sfc dew
points in the upper 60s to around 70 with deep moisture aloft
supporting storms capable of heavy rainfall. WPC suggested the
increasing low level jet could support back building or training
storm behavior.

The models then show a second, post-frontal, disturbance moving
through Wednesday morning. Dry weather is expected Wednesday evening
and Thursday with cool temperatures. A northwest flow disturbance may
produces showers and thunderstorms Thursday night.

Dry weather is in place Friday through Monday with just an isolated
rain chance. This is the result of a warming trend as H700mb
temperatures rise toward 14C by Monday which should cap most
opportunities for thunderstorm development. Still, a blend of bias
corrected model temperatures and the National blend of model
data produces highs in the upper 80s to around 90.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1238 AM CDT Tue Aug 15 2017

Thunderstorms will continue in the vicinity of the KVTN terminal
through 08z tonight. Thunderstorms are also possible in the
vicinity of the KLBF terminal after 08z through 12z this morning.
Expect partly to mostly cloudy skies to persist on Tuesday with an
increasing threat for thunderstorms after 23z at the KVTN terminal
and after 00z at the KLBF terminal. Heavy rain, reduced
visibilities and small hail are possible at both terminals Tuesday
evening.

&&

.HYDROLOGY...
Issued at 314 PM CDT Mon Aug 14 2017

3-hour flash flood guidance has fallen to around 2 inches across
parts of Southwest and Ncntl Neb. The key feature could be the 7-day
rain totals across parts of Custer and Frontier Counties of 3 to 7
inches.

Conditions will become favorable for thunderstorms and heavy
rainfall Tuesday afternoon-Tuesday night. Ambient precipitable water
increases to over 1.5 inches and winds aloft are fairly weak and
unidirectional.

The models show a frontal boundary dropping into Ncntl Nebraska
Tuesday night which could be the focus to storm development. The
forecast places Custer County in a flash flood watch Tuesday
afternoon through early Wednesday morning.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from noon CDT today through Wednesday morning
for NEZ038.

&&

$$

SHORT TERM...CDC
LONG TERM...CDC
AVIATION...Buttler
HYDROLOGY...CDC



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