Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 150512

Area Forecast Discussion
National Weather Service North Platte NE
1112 PM CST Thu Dec 14 2017

.SHORT TERM...(This evening through Friday)
Issued at 347 PM CST Thu Dec 14 2017

The main forecast challenges through Friday concern a shortwave
passage this afternoon and the breakdown phase of the Western
U.S. ridge aloft. As of 21z, scattered rain/snow showers continue
across the Sandhills with blustery northwest winds gusting above
30 mph. A surface cold front is draped across the Upper
Mississippi Valley with the mid level shortwave currently working
through Nebraska.

This afternoon/evening... Gradually taper PoP west to east,
cutting off all chances by 00z as drier air works into the lower
levels and lift weakens. Dew point spreads range from 10-15F in
the southern panhandle to 1F north central. Winds will also taper
toward sunset with the shortwave and PV anomaly clearing the area.
Models are in general agreement with the H85 flow weakening from
35 to 20 kts by 06z. Cloud cover will begin to break up across
southwest Neb. this evening, but better moisture in the mid levels
will help retain a alto deck across the north.

Tonight: Min temps will range from the mid teens SW to lower 20s
north central, mainly dependent on cloud cover. Did drop an extra
degree or so in the Platte River Valley, but it may not be enough
especially if winds lighten even further. Winds switch from north
to west overnight, which still allows cold air drainage.

Friday: Mainly fair conditions are expected for western Nebraska
as the region lies on the periphery of the ridge (northwest flow
aloft). At H85, a notable downslope pattern sets up, adding to the
warmth and dryness. A thermal ridge pushes temps to near 10C, and
given efficient mixing, sfc temps should reach the lower to mid
50s region wide (about 15 degrees above normal). This pattern also
supports elevated to near critical fire weather conditions,
mainly across SW Neb. The limiting factor is wind, which should
remain below 25 mph, as RH drops below 20 percent.

.LONG TERM...(Friday night through Thursday)
Issued at 347 PM CST Thu Dec 14 2017

The main sensible weather highlights are precipitation chances
late Saturday-Sunday morning across western NEB and the indication
of a pattern change at the end of the long term period. The latter
will be conducive for cooler than seasonable normal temperatures.
Confidence is increasing for a highly amplified pattern setting up
wherein there is an increased likelihood for below-normal
temperatures. Further, these enhanced probabilities continue
beyond Thursday and are noted in the CPC 8-14 day outlook.

Large scale pattern early Friday night features a shortwave trough
moving onshore the Pacific Northwest with northwest flow overhead
western NEB. This feature is expected to continue moving
southeastward while undergoing amplification and will be
positioned from the Northern Rockies to Baja California Sunday.
Guidance has trended slower with general agreement towards a
modest closed low developing near the Sonoran desert. Thereafter
the trough will weaken through Sunday with little movement and a
weak closed low positioned near the far southwest US. Overall,
deterministic guidance generally in better agreement through
Saturday night compared to previous forecast packages. Current
thinking is enough large scale forcing and support for increased
chances across the eastern Panhandle and northwest NEB with
decreased chances farther east into the central Sandhills and far
southwest NEB. Confidence with respect to eastward extent of
precipitation remains low at this point, and currently are not
forecasting precip at North Platte presently. Current forecast
snow amounts are up to 1 inch in portions of the northeast
Panhandle. There is some concern for freezing precipitation
Saturday night as it relates to ice crystal initiation/saturation
in the cloud given BUFKIT soundings. However, confidence is low at
this point. As such, will continue to monitor this possibility.
Precipitation chances then continue through Saturday morning than
taper off. Thereafter quiet weather is expected Sunday afternoon
through Wednesday.

Attention turns to late Wednesday-Thursday, the tail end of the
long term period. Guidance continues to support a change in the
large scale pattern, though uncertainty remains in the details. Of
note, this change is expected to impact primarily temperatures
Thursday. Ensemble guidance, NAEFS, support the development of a
strong upper-level ridge in the Pacific off the west coast with
subsequent downstream amplification of an upper-level trough in
the western CONUS Wednesday-Thursday. Wherein colder air is
expected to be advected southward in this pattern Thursday
affecting western and north central NEB. Further, a decent signal
is noted in GEFS plumes at KLBF and KVTN. While there is
uncertainty with respect to highs, there is confidence for highs
to read below-normal and this is forecast presently.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1112 PM CST Thu Dec 14 2017

VFR conditions across western Nebraska the next 24 hours. Westerly
winds to remain light, except increasing to near 12 kts 18z-00z.




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