Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 121745

Area Forecast Discussion
National Weather Service North Platte NE
1245 PM CDT Thu Oct 12 2017

Issued at 332 AM CDT Thu Oct 12 2017

At 08z...A cold front had moved into far western North Dakota and
far northern Wyoming. Mild temperatures from 45 to 50 continued
across western Nebraska.


.SHORT TERM...(Today and tonight)
Issued at 332 AM CDT Thu Oct 12 2017

An upper trough currently located from western Montana into eastern
Idaho will track east-northeast into the Dakotas this afternoon.
This will push a cold front southeastward to near an Ainsworth
through Ogallala line by late afternoon. With 850mb temperatures
from 16-20C in place along and ahead of the front, highs today will
reach the mid to upper 70s. Used the warmer CONSMOS guidance. Skies
will remain mostly sunny today, except becoming partly cloudy in the
eastern panhandle late afternoon.

For tonight, the upper trough will advance across Minnesota into the
western Great Lakes. On the trailing end of the trough from
southeast Wyoming into southwest South Dakota, an area of 700mb
frontogenesis will develop to include Sheridan, Cherry, and northern
Garden county. The 700-500mb layer will become fairly saturated.
while the lower level remains fairly dry. Will keep near the
previous forecast for a slight chance of showers late evening in the
far northwest zones, then a 20-30 percent chance after midnight in
Sheridan, Cherry, and northern Garden county. Overnight, the cold
front will advance into northwest Kansas and southeast Nebraska.
850mb temps will cool to 5-10C overnight, with lows from the upper
30s to lower 40s northwest, and near 45 far southeast.

.LONG TERM...(Friday through Wednesday)
Issued at 332 AM CDT Thu Oct 12 2017

Aloft, a trough quickly digs across the northern Rockies, crossing
the Plains over the weekend. A ridge tries to build across the
Southwest U.S. early week, placing Nebraska in northwest to quasi-
zonal flow. At the surface, a cold front pushes through western
Nebraska early Saturday and is replaced by a high pressure for the
remainder of the weekend. Next week, a series of weak troughs
traverse the northern/central Plains.

The main forecast challenge over the long term pertains to the
weekend system (sfc front and upper level trough). Forcing and
moisture content in the low levels is greatest Sat AM ahead of the
front as southerly flow pushes dew points up overnight and
corresponds to isentropic upglide at 295-305K. Behind the front,
drier air works in. However, fgen intensifies and humidity briefly
increases in the H5-7 layer during the evening with the trough axis.
Overall, limited PoP primarily to schc and Sat 06z to Sun 06z as
moisture content is relatively limited. Increased winds slightly Sat
PM - Sun AM in the wake of the front to account for some transfer of
35+ kts at H85 to the sfc. The GFS now brings the 1.5 PVU surface to
as low as 550mb across the Sandhills, and MSL pressure change
approaches 2mb/hr. Dropped highs slightly Saturday as models agree
with strong CAA behind the front and H85 temps falling to near 3C at
00z Sun.

Early to mid week, an amplified H8 high over the Eastern U.S. puts
Nebraska in a return flow regime with some downsloping winds at
times, translating to warming and drying. Current forecast highs in
the lower 70s may not be warm enough Mon and Tue, considering the
synoptic pattern and MEX/ECM ensemble max Ts in the upper 70s.
Precip chances after Saturday are scant, and NAEFS ensembles suggest
PWAT values near 10%ile of climo.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1245 PM CDT Thu Oct 12 2017

VFR conditions continue through the period.

A cold front just entering the northwest portion of NE will
progress southeast through the day and exit the area this evening.
Cross sections through the frontal zone show a decent mid level
circulation developing on the cold side of the front with the
responding upward vertical motion on the warm side of the
circulation, typical of a direct thermal circulation associated
with the right entrance region of the upper jet which will be
located across the Dakotas but sagging southward as the trough
broadens. However, the mid level circulation is not juxaposed with
either the larger scale upper cirtculation nor lower frontal lift
until after it moves south and east of this area. This results in
decent cloud development in the mid levels as mid level
saturation takes place, especially in the northwestern portion of
the area. However low levels remain fairly dry so QPF will be
light if any and not wide spread enough to include in either TAF

Otherwise winds behind the front will change to northwest then




LONG TERM...Snively
AVIATION...Stoppkotte is the U.S. government's official web portal to all federal, state and local government web resources and services.