Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 181751
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
1151 AM CST Sun Feb 18 2018

.SYNOPSIS...
Issued at 354 AM CST Sun Feb 18 2018

H5 analysis from earlier this evening had a closed low over
western Hudson Bay with a shortwave trough of low pressure noted
over the southern Great Lakes. Further west, a low amplitude
pattern extended to the west coast of the CONUS where a strong
shortwave was located over southwestern British Columbia. At the
surface, Low pressure was located over northeastern Wyoming. A
warm front extended east of this feature into southern South
Dakota. South of the low, a surface trough of low pressure
extended south into eastern Colorado. With a tight pressure
gradient noted across western and north central Nebraska this
morning, gusty southerly winds were present across the area. The
gusty winds have resulted in mild temperatures overnight with
readings in the middle to upper 30s across western and north
central Nebraska.

&&

.SHORT TERM...(Today and tonight)
Issued at 354 AM CST Sun Feb 18 2018

Low pressure will track east along the warm front today, ushering
in an arctic cold front late this afternoon into the early
evening hours. Temperatures south of the approaching front, will
be very mild today with forecast highs in the 50s to around 50,
generally south of a line from Antioch to O`Neill. North of this
line to the South Dakota/Nebraska border, highs will be in the
40s, with lower 40s in the Pine Ridge. The arctic front will track
into northern Nebraska late this afternoon, clearing the forecast
area by late evening. The boundary layer will saturate quickly
with passage of the arctic front this evening. Thermal profiles,
especially in the far southeastern and southern forecast area are
supportive of a brief period of light freezing drizzle overnight
tonight. Looking at Bufkit soundings, qpf`s where freezing drizzle
is possible, will be very light, with qpf`s under 0.01 inches.
That being said, given the limited qpf and a very tight window for
freezing drizzle, will forgo any headlines as better chances for
icing are off to the east and southeast of the forecast. Across
the northwest, where mid level moisture is prevalent, light snow
will develop this evening and continue into the overnight hours.
By Monday morning, snow accumulations of 1 to 3 inches are
expected across the Pine Ridge into northwestern Cherry county.
Decided to upgrade Sheridan and Western Cherry county to a winter
storm warning and add Eastern Cherry county to a winter storm
watch. Realize this will be a long duration event with piece one
tonight and the much stronger piece two expected Monday night.

.LONG TERM...(Monday through Saturday)
Issued at 354 AM CST Sun Feb 18 2018

With an amplified trough across the Intermountain West and a low
stalled over the Hudson Bay, southwest flow aloft dominates the
pattern for Nebraska the next several days. At the surface, the
state is stuck between a strengthening Arctic high sliding south
along the Rockies and lows ejecting across the central Plains.

The primary forecast challenges continue to revolve around precip
and temperatures with the storm system through Tuesday morning.
Strong CAA (H85 temps dropping to -15C by 18z Monday), blustery
north winds, and overcast conditions will limit highs to the single
digits far NW Neb to lower 20s SW Neb Monday. Confidence is
increasing with a potentially powerful storm (mainly northern Neb),
so introduced definite PoPs along the Pine Ridge for Monday morning
and expanded likely PoPs through Tuesday.

Trends continue to point toward a long duration event, especially
for northwest Neb along the Pine Ridge. The greatest potential for
heaviest/most widespread snow comes Monday evening into Tuesday
morning. The combination of deep moisture/saturation, maximized mid-
level fgen, a coupled 130kt+ H3 jet, and persistent isentropic
upglide will result in a band(s?) of moderate to possibly heavy
snow. The lift and moisture also coincide with the DGZ for much of
the event, supporting enhanced snowfall rates and higher SLR`s. X-
sections indicate negative EPV and Theta-E folding, which also point
toward bursts of heavy snow of 1"+/hr accum. Trended QPF and blended
toward WPC guidance, resulting in storm total 0.5" liquid equiv near
the Pine Ridge and up to 0.25" central Sandhills. Accounting for
SLR`s of at least 20:1, forecast snowfall surpasses 10" northern
Sheridan and far NW Cherry counties. Upgraded to Winter Storm
Warning there. Totals have also increased across much of the
forecast area, now 1-2" along the I-80 corridor and 3-6" in the
heart of the Sandhills. Locally higher amounts are possible in
northeast Cherry Co, so issued Winter Storm Watch there. Held off on
any further expansions as there`s still some uncertainty in
placement of higher totals across SW Neb, along with the main event
still 48 hours away. Blowing snow does not appear to be a primary
concern attm as wind gusts remain generally 25mph and less, but with
the snow probably on the drier side, can`t rule it out completely.

Lowered temps Tuesday and Wednesday mornings to account for
continued CAA (model suite now approaching -20C at H85) and then
clear skies/light wind Wed AM. With a fresh deep snow pack, lows
cooler than -10F are likely for NW Neb and below 0F north of I-80.
Will likely need a Wind Chill headline for northern Neb. Wed AM.

The next shot of precip arrives late Thursday as a shortwave
traverses the northern Plains and a warm front tries to push into SW
Neb. Regardless, temps remain near or below normal, so main ptype
will probably be of the frozen variety.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1149 AM CST Sun Feb 18 2018

For KLBF, minimal aviation concerns are expected as a cold front
approaches the region. At KLBF, the only major impact will be a
lowering and thickening of ceilings over the next 24 hours. By 14Z
Monday, broken clouds are expected to drop to near 1500 feet. Gusty
northerly winds are also expected Monday as gusts rise to near 25 to
30 knots.

For KVTN, aviation concerns start tonight as a frontal system moves
into northern Nebraska. Snow chances arrive by 04Z Sunday. Visibility
restrictions are possible, but should remain above 4SM as the
heaviest snow will stay west of KVTN. Clouds remain broken to
overcast through the next day with ceilings dropping to near 1500
feet by late Sunday night.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 6 PM CST /5 PM MST/ this evening to
noon CST /11 AM MST/ Tuesday for NEZ004-094.

Winter Storm Watch from 6 PM CST /5 PM MST/ this evening through
Tuesday morning for NEZ005.

&&

$$

SYNOPSIS...Buttler
SHORT TERM...Buttler
LONG TERM...Snively
AVIATION...Kulik



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