Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 132159
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
359 PM CST Wed Dec 13 2017

.SHORT TERM...(This evening through Thursday)
Issued at 332 PM CST Wed Dec 13 2017

The primary forecast challenges through Thursday afternoon concern
a shortwave crossing the northern Plains and its associated
precip chances. As of Wednesday 21z, Nebraska lies in the wake of
one surface cold front that has moved into Kansas and in the path
of another dropping south through the Dakotas. The main shortwave
was located in Montana with a cirrus shield extending into Wyoming
and SoDak.

This evening and tonight... The gusty winds will subside around
sunset as the pressure gradient relaxes, H85 flow weakens, and
an H5 shortwave currently over the Upper Miss Valley slides east
toward the Great Lakes. Despite the weakening winds and some CAA
overnight, temperatures will remain above normal. Generally split
the guidance due to increasing cloud cover, but lowered min temps
slightly in the Platte River Valley to account for lighter winds
and in case the cigs are slower to drop.

Thursday... The northern Rockies shortwave quickly drops onto the
Plains, crossing the Sandhills by early afternoon. Have adjusted
PoP accordingly, introducing likely across the far north during
the late morning and maintaining chc for most of the forecast area
through the afternoon. The potential exists for a short-lived
deformation band developing in southern SoDak and drifting south,
hence the higher PoP north of Hwy 20. Forecast soundings also
indicate better lift and less dry air in the low levels than
southwest Neb. The precip should turn more showery in nature
during the afternoon as drier air works into the area but weak
lift remains in the low levels. This is suggested by the higher-
res solutions such as SPC HREF, NCAR ensembles, and RAP as well as
folded theta-E in NAM X- sections. Temperature profiles favor
snow for most of the event, although a brief switch to rain is
possible during peak heating as highs approach 40F. Did increase
snow totals slightly north of Hwy 20 up to 0.5 inches for the
morning. Can`t rule out light accumulation as lift and saturation
coincide with the DGZ, but the speed of the system and limited
coverage of the precip will alleviate big impacts. Winds will be
quite gusty once again, especially as a PV anomaly helps mix 50kt
flow at H5 and 35kt at H85. The snow should remain light enough
and spatial extent low enough to limit blowing snow potential.

.LONG TERM...(Thursday night through Wednesday)
Issued at 332 PM CST Wed Dec 13 2017

Low sensible weather concerns in the long term period. Primary
weather highlights include: cooler air filtering in early on with
near-normal highs expected Sunday, increased precipitation
chances late Saturday-Saturday night, and highs rebounding Monday
on.

High temperatures ramp up Friday compared to Thursday`s highs as
winds change from north northwest to westerly Thursday night aloft
in the lower-levels and at the surface. 850 hPa temperatures
increase to near 5-8 C aloft by tomorrow. In addition, modest
downsloping winds are anticipated that should promote drying and
warming. BUFKIT soundings show decent mixing and this with
sufficient insolation/mostly sunny skies should be conducive for
highs mainly in the lower to mid 50s. Meanwhile, afternoon minimum
humidity is expected to lower into the mid-upper teens in the
southeast Panhandle and far southwest NEB. This combined with
light breezes will support elevated fire weather conditions there.

Large scale pattern early Thursday night features an upper level
ridge across the Pacific offshore waters near CA extending across
the Pacific Northwest to the Northwest Territories. The mid-level
ridge aloft will then brake down through Friday as a trough moves
over the top and south into the Pacific Northwest-Northern
Intermountain West by Friday evening. Thereafter deterministic
guidance begins to show more spread with respect to the evolution
and track of this feature Saturday-Sunday. This affecting the
possible impacts across the area, primarily precipitation chances.
Specifically, the GFS in comparison to the ECMWF and CMC wherein
the former has lower QPF and PoP chances across the local
forecast area. The ECMWF appears move progressive moving the
trough eastward steadily during the Sat-Sun timeframe. Of which,
the GFS develops a modest closed low near the Sonoran desert late
Saturday that then tracks into the Southwest US Sunday. As such,
continued slight chances-chances for PoPs given the forecast
envelope and overall confidence with the best chances falling
Saturday night at this time. Highs are expected to trend
downward with near seasonable normal values anticipated Sunday.
Thereafter highs are expected to rebound to above seasonable
normal values Monday and continue through Wednesday. Of which,
a broader upper-level ridge is expected to build and be
positioned across much of the western CONUS by Tuesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1131 AM CST Wed Dec 13 2017

VFR conditions will prevail through this evening across western
Nebraska, although wind is a primary aviation weather concern.
Blustery northwest winds will gust above 30 kts this afternoon,
then taper around sunset. Tonight, cigs begin to drop as a stratus
deck develops ahead of the next storm system. The lowest cigs
(MVFR) and greatest chance of precipitation (morning snow,
afternoon rain) lie across northern Nebraska, mainly affecting
GRN-VTN-ANW-ONL. Northerly winds pick up again mid/late morning
Thursday.


&&

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

$$

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



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