Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 220517
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
1117 PM CST Wed Feb 21 2018

.SHORT TERM...(This evening through Thursday)
Issued at 338 PM CST Wed Feb 21 2018

The primary forecast challenge through Thursday concerns a
shortwave passing through the northern Plains. With the wave
comes a shot of accumulating snow and continued cold temperatures.

This evening and tonight... Sky cover slowly fills in as mid level
moisture increases ahead of the shortwave. Combined with
strengthening fgen and isentropic upglide (best shown 285-290K),
flurries or light snow showers should begin to develop across SW
and central Neb after 06z. With weak CAA at H85 overnight and
generally clear skies/light winds right after dark, opted for the
cool end of guidance for lows. Lows range from single digits
panhandle (most clearing) to lower teens.

Thursday...The column saturates and lift increases through the
morning and into the afternoon. With the bulk of the saturation
outside the DGZ (-5 to -10C) and max temps in the mid/upper 20s,
SLR`s will likely stay close to climo (13-14:1). NAM/GFS soundings
and some higher resolution guidance (HREF/RAP) indicate a
prolonged period of light snow and possibly a couple bands
developing late morning/early afternoon. Cross sections also show
weakly negative EPV and some theta-E folding, supporting banded
snowfall with higher rates. The GFS tries to close a low at H7,
which could also add to forcing and lift. Due to uncertainty in
where exactly the locally heavier snow sets up, went with a more
blended QPF approach, resulting in 1-2" across the Sandhills and
up to 1" south of I-80. Kept icing potential out of this forecast
as saturation runs rather deep and stays cold enough for most of
the area, however the warm nose approaches -1 to -2C across
central Neb (BBW and ONL). This will need to be watched for the
introduction of mixed precip if later model runs trend warmer.

.LONG TERM...(Thursday night through Wednesday)
Issued at 338 PM CST Wed Feb 21 2018

The main sensible weather concern revolves around a weather system
impacting NEB Friday night-Saturday. Weather highlights in the
long term include: potential for banded snowfall late Friday-
Saturday, low-end chances for precip at the end of the month, and
below-normal highs persisting through the long term period.

An amplified large scale pattern will be in place early Thursday
night wherein there will be a positive tilted long wave trough
over the western CONUS while a weakening shortwave trough lifts
northeast through NEB. The upper level trough will evolve eastward
through Friday night becoming neutrally tilted. Meanwhile, the
primary shortwave will be moving through the Four Corners region
and entering the Central High Plains. Thereafter the upper wave
will become negatively tilted while deepening Saturday as the
shortwave moves into the lower-half of the Missouri Valley.

Otherwise, fair agreement exists with respect to surface
cyclogenesis Friday night. The surface low is expected to develop
in far eastern CO/western KS/OK Panhandle then evolve east to
northeast KS/extreme southeast NEB Saturday afternoon. Current
thinking is there is increasing potential for light to moderate
banded snowfall over the southeast to east portion of the local
forecast area. Of which, an enhanced zone of lower-mid
tropospheric deformation and frontogenesis is expected to set up.
Further, an area of potential instability is anticipated to form
based on the evolution and position of the WCB, DCB, and overall
track of the negative PV anomaly with an area of near zero to
negative EPV noted. Thus there is concern for enhanced snowfall
rates Saturday. Furthermore, thermodynamic profiles suggest low-
end chances for freezing precip prior to changeover to all snow.
However, confidence is low at this point regarding any ice accums.
Regarding the location of heaviest snowfall, there is still some
uncertainty. The risk for heaviest snow accumulations presently
lie across southwest NEB into north central/towards northeast
NEB.

Looking beyond Saturday, fair weather is expected Saturday night
through Tuesday under a progressive large scale pattern.
Generally, below-normal highs will prevail also, albeit not as
cold compared to earlier this week. Chances for snow then return
Tuesday night-Wednesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1117 PM CST Wed Feb 21 2018

Areas of flurries occurring from southwest into central Nebraska
late this evening with VFR ceilings. Overcast skies will expand
northward across north central Nebraska overnight as cigs drop to
MVFR from 09z- 12z overnight across southwest into central
Nebraska as the next storm system approaches. Light snow will
develop across much of western Nebraska Thursday morning
(affecting KLBF and KVTN) and continue into the afternoon. MVFR
cigs and vsbys are possible after 22/12z southwest and 22/18z
north central. Any lingering snow should end across western
Nebraska by 00z/23rd as IFR ceilings improve to MVFR in some
areas.

&&

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

$$

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


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