Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 201022
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
422 AM CST Sat Jan 20 2018

.SHORT TERM...(Today and tonight)
Issued at 420 AM CST Sat Jan 20 2018

Storm system poised to intensify today across the southern Rockies,
is currently moving inland across the west coast. High level
cloudiness continues to stream northeast across the region ahead of
the system, and will continue to do so through the day today. Expect
partly to mostly cloudy skies as a result, and will go a little
under guidance on highs due to the cloud cover. Highs should range
from the mid and upper 30s across the panhandle, with 40s elsewhere.
By late afternoon the column begins to saturate across far northwest
Nebraska, where a mix of light rain and snow is possible.

System really begins to intensify tonight with considerable height
falls across southern Colorado into western Kansas. South to
southwest flow aloft increases across our area just ahead of the
system. Warm air advection and isentropic upglide increase through
the night, with precipitation gradually expanding across western
Nebraska. Sounding profiles support a mention of patchy freezing
drizzle mainly across southwest Nebraska. Should be all snow across
northwest Nebraska, where a couple of inches should fall by dawn
Sunday.

.LONG TERM...(Sunday through Friday)
Issued at 420 AM CST Sat Jan 20 2018

The primary forecast challenge over the mid and long range revolves
around the winter storm slated for the weekend. The big change is
upgrading the Winter Storm Watch to a Warning for the entire CWA.

Winter storm summary... Snow should be well underway across the
northwest at 12z Sunday and overspread the rest of the area by 18z.
Reintroduced a period of patchy freezing drizzle in central Neb.,
mainly Curtis to Arnold to Bartlett and points southeast. Forecast
soundings indicate a higher chance in WFO Hastings area, but given
the amount of low level moisture and some lift before total column
saturation occurs, couldn`t rule it out. The deformation/fgen band
really takes shape Sunday afternoon and slowly (key word) lifts
northeast into Monday morning. The expanse of the system along with
the speed will result in a prolonged period of accumulating snow,
especially the eastern half of the CWA. Overall, increased snow
totals about two inches and brought the axis of highest totals west
to the Hwy 83 corridor, resulting in widespread 8-10".

Factors favoring heavy snow... NAM, GFS, and ECM place the forecast
area in the TROWAL region for much of Sunday, allowing a constant
stream of warm/moist advection for a broad swath of accumulating
snow. Latest guidance has increased QPF to over a half inch
along/east of Hwy 83. This is seen in soundings with the temperature
and wind profiles, along with strong consistent lift in the low/mid
levels (collocated with the DGZ). The pattern is also shown using
isentropic analysis with lift and saturation (mostly at 285 to
290K). On the smaller scale, negative EPV and strong lift owe to
increased rates, possibly brief periods of convective snowfall in
bands.

Storm concerns... One main factor to consider is convection across
the southern Plains/Miss Valley, especially with a neutral tilt of
the trough. This would decrease moisture advection into Nebraska and
possibly pull the sfc low away from the area. Temperatures will
hover around freezing for much of Sunday with the lack of very cold
air aloft (H85 temps around -5C) and no Arctic air upstream. Did put
in RASN Sunday afternoon across north central where highs reach the
mid 30s. However, if precip rates increase and dynamic cooling takes
over, snow totals could be higher near OAX/FSD borders. Warmer temps
and strong winds will result in slightly lower SLR`s, but high rates
could easily overcome.

Impacts... Wind is the driving factor beside the accumulating snow.
H85 winds approach 50 kts as the center of the low and the PV
anomaly pass by. Momentum will carry a lot of that toward the
surface, so used stronger solutions like ConsMos to increase wind
speeds. Gusts will approach 40 to 45mph, which will create serious
blowing and drifting snow. Depending on the snowfall intensity,
may approach whiteout conditions in spots.

Beyond Monday... Northwest flow resumes with a building ridge to the
west. Fair conditions and slowly modifying temps are in store with
downsloping winds, but tempered highs through Wed due to projected
snow cover. The next precip maker moves in at the end of the week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1131 PM CST Fri Jan 19 2018

For the KLBF terminal: Expect broken high clouds to continue over
the next 24 hours at the KLBF terminal. Some lower CIGS may push
into the area Saturday evening. At this time, the lower ceilings
are expected after 06z Sunday. For the KVTN terminal: Broken high
clouds will gradually lower Saturday evening with MVFR cigs
possible toward 06z Sunday.


&&

.LBF WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 6 PM CST /5 PM MST/ this evening to 6
AM CST /5 AM MST/ Monday for NEZ004-005-022>024-035-036-056>058-
069-094.

Winter Storm Warning from 6 AM Sunday to noon CST Monday for
NEZ006>010-025>029-037-038-059-070-071.

&&

$$

SHORT TERM...Taylor
LONG TERM...Snively
AVIATION...Buttler



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