Area Forecast Discussion
Issued by NWS North Platte, NE

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167
FXUS63 KLBF 201125 AAA
AFDLBF

Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
625 AM CDT Sun Aug 20 2017

.SHORT TERM...(Today and tonight)
Issued at 358 AM CDT Sun Aug 20 2017

Forecast challenge with the impending eclipse on Monday will be
precipitation forecast and associated cloud cover associated with
it. Today will see clear skies this morning with convective cloud
development this afternoon as temperatures rise into the mid to
upper 80s and weak cool front drops southeast across the forecast
area and stalls out along the Kansas border. Northeast flow today.
Lee side low develops over northwest Kansas with stronger upper wave
digging across the northern plains. Warm frontal boundary will lift
into north central Nebraska over night with winds becoming southeast
to the south of the frontal boundary. Temperatures and dew points
indicative of fog development and have included patchy fog in the
forecast to the south of the boundary. As the upper wave moves
across the Dakotas chances will increase for precipitation over the
north increasing cloud cover through the evening and into the early
morning with a partly cloudy to mostly cloudy forecast going around
sunrise.

.LONG TERM...(Monday through Saturday)
Issued at 358 AM CDT Sun Aug 20 2017

The main forecast challenge over the next week deals with cloud
cover and precip potential Monday, primarily during the eclipse.

Synopsis... In the mid/upper levels, Nebraska is predominately in
northwest flow as a closed low over northern Ontario digs a trough
into the Great Lakes and a ridge builds over the Desert Southwest.
The ridge broadens as it progresses east onto the Plains late week.
At the surface, a low pressure center near the KS/CO/NE border
stretches a quasi stationary front across Nebraska on Monday. The
system gets pushed out by a 1022mb high settling onto the northern
Plains early Tuesday. The high meanders toward the Great Lakes
throughout the week as another trough emerges from the Rockies on
Thursday. A low over the Dakotas drags the boundary through the
Sandhills by Saturday.

Monday... Feel like the bearer of bad news. Stationary/warm fronts
in the vicinity do not bode well for clear skies. A stronger signal
is showing up in SREF guidance for stratus over the northern half of
the area and fog elsewhere during the morning. Even if widespread
measureable precip is absent late Sunday night, the air remains
juicy with dew points in the mid/upper 60s. Add in light
east/southeast winds, and conditions are ripe for fog development.
Introduced patchy fog generally between I-80 and Hwy 20, although
some guidance is pushing locally dense visby. Have the fog and some
stratus mixing out by 15z. Differences remain in the models
regarding overall cloud coverage and precip chances at 18z, but sct-
bkn sky is looking likely. NAM is most aggressive with low level
clouds, GFS and ECM suggest more mid-high level cover. Isentropic
lift, most evident at 305 and 315K, and the moisture suggest some
mid-level cloudiness over the area. The strongest lift occurs
generally north of Hwy 2, so kept schc PoP during the morning hours.
Better forcing across the south arrives later in the day, especially
with the approaching shortwave. With all that said, there will
probably be some breaks in the clouds, and the eclipse viewing won`t
be ruined everywhere, but it`s still too difficult to pin down
exactly when and where. Regarding P.M. storms, sufficient MUCAPE and
fairly steep low/mid level lapse rates will support stronger
convection capable of hail and wind. Deep layer shear continues to
be the limiting factor for widespread organized severe weather.
Heavy rain will also be a concern, mainly east of Hwy 83, where
PWATs are forecast well above climo levels and storm motion is <15
kts.

Tuesday and beyond... Schc PoP Thursday evening across the panhandle
with the trough approaching and a weak shortwave over the Rockies.
The better shot of widespread precip comes Fri-Sat with
strengthening moisture advection and the actual sfc front/shortwave
passages. Despite nearly persistent southerly flow at H85, temps
remain near normal. No significant WAA takes place with the sfc
high recycling cool air from the Great Lakes.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 619 AM CDT Sun Aug 20 2017

Some isolated stratus in a small area over northern Nebraska near
KVTN. This is associated with a cool front dropping south over the
area. Some convective cloud development over western Nebraska this
afternoon and then chance thunderstorms through most of western
Nebraska through the late evening and early morning with patchy
fog developing around sunrise.


&&

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

$$

SHORT TERM...Power
LONG TERM...Snively
AVIATION...Power



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