High Wind in Nebraska, December 22 to 23, 2020

Area Forecast Discussion
National Weather Service North Platte NE
720 PM CST Tue Dec 22 2020

.UPDATE...
Issued at 720 PM CST Tue Dec 22 2020

Latest model guidance appears to be in good agreement with
regards to current radar trends. With this in mind, have increased
POPs in the 03-06Z timeframe to better reflect the onset of
rain/snow in the far northeastern CWA. Another trend of note in
latest guidance is an increase in QPFs across the northern CWA.
Have trended total QPF up slightly in the northeast but have
stayed on the conservative side of high-res guidance. The current
forecast now paints a narrow area of 2-3" across Keya Paha, Boyd,
and Holt Counties and an areal expansion of 1" amounts to the
southwest. Have expanded the Winter Weather Advisory another tier
southwest to encompass the slight increase in totals. Will defer
to the next shift on any upgrades to ongoing headlines, though
blizzard wording may be warranted if trends continue.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 356 PM CST Tue Dec 22 2020

The primary forecast challenge revolves around the powerful storm
crossing the northern Plains over the next day or so. High winds are
expected across all of western and north central Nebraska, while
snow will accompany the wind in the north and possible blowing dust
in the far southwest. The weather pattern returns to mild and dry
for Christmas Day and the first half of the weekend.

Tonight... A surface low rapidly deepens as it emerges onto the High
Plains and cuts across south Dakota. The attendant cold front
stretches southwest through Nebraska and exits our forecast area by
06z. An accompanying upper trough quickly follows, digging through
the Plains overnight and taking a more neutral orientation. This
combination results in high winds and increased precipitation
potential. Surface pressure changes will be as much as 2mb/hr falls
ahead of the front to 2mb/hr rises behind it, while H85 flow
surpasses 50 kts. Mechanical mixing will bring much of this to the
surface, and forecast soundings indicate at least 60 mph gusts in
the Sandhills. Some guidance suggests 65 to possibly 70 mph in the
panhandle and far southwest Nebraska. Expanded the High Wind Warning
to all counties with this forecast package. Precip chances also
increase overnight with temperatures dropping into the teens and
lower 20s. Guidance has trended stronger with the upper level
component and maxing out frontogenesis over northern Nebraska.
Southerly flow and isentropic upglide have been pulling additional
moisture into the region. Raised PoP accordingly, which is also in
line with morning runs of the CAMs suite. Thermal profiles suggest
any precip starting as rain in the far west shortly after sundown as
CAA lags behind the front a bit. As soon as H85 temps plummet from
around 0C at 06z to -10C at 12z, all locations should be receiving
snow. A couple situations come into play regarding moisture
overnight... one is scattered coverage through 12z and more
rain/snow shower setup, and the other being a broad area of
generally light precip. Either way, not expecting much accumulation
before daybreak, especially with SLR's around 10:1 or lower.

Wednesday and Wed night... The precip situation evolves into a more
organized setup, presenting a greater potential for a swath of
heavier moisture (north central) and continued shower activity
(northwest). Depending on the magnitude and placement of the main
wrap-around band of precip from the low, accumulations are appearing
more likely across north central Neb. Cross sections also suggest
periods of enhanced lift and weakly negative EPV, which will result
in bursts of heavier snow. Increased snow totals slightly across the
far north and into parts of central Neb, roughly using the 1"
contour for a new Winter Weather Advisory. While totals may not be
large with a current max around 2", high winds will definitely
result in winter impacts. Any location with falling snow will
experience significant blowing and reduced visibility. Stayed away
from blizzard wording due to low confidence in any sustained 3-hr
period of whiteout conditions. The most likely scenario right now
appears to be off-and-on snow showers with a one to two hour period
of heavier snow (central Neb). One big caveat... the latest
(afternoon) guidance is trending even stronger across the north
central zones, alluding to double the accumulation in the official
forecast. This trend will need monitored through the evening. Snow
tapers from west to east through the afternoon with all activity
having ended 21-00z. However, patches of blowing snow could continue
through the evening depending on how much has fallen. Farther
southwest near the Colorado border, not much moisture is
anticipated. Due to drought conditions and post-harvest, included
blowing dust wording in the forecast. The wind should relax somewhat
after sunset as the surface low pulls away, but sustained strong
flow aloft.

.LONG TERM...(Thursday through Tuesday)
Issued at 356 PM CST Tue Dec 22 2020

Thursday and beyond... The upper trough digs further on Thursday and
spins off a closed low over the Upper Midwest, while the next ridge
builds over the Desert Southwest. A stark temperature gradient is
still looking good for Nebraska with H85 temps range from around 2C
in the panhandle to -10C north central, roughly translating to mid
20s vs mid 40s for highs. Potential also exists for some flurries
across the north as a weak impulse rides along the trough. The upper
ridge centers over the High Plains for Christmas Day while a surface
high pressure also takes over. H85 winds become consistent out of
the west, aiding in the milder conditions. Guidance has trended
warmer slightly with highs ranging from upper 40s north central to
mid 50s southwest. The next cold front arrives late Saturday, which
may present another chance of moisture, although major impacts
appear unlikely at the moment.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 618 PM CST Tue Dec 22 2020

A strong storm system and cold front will cross the area tonight
into Wednesday. Gusts from the northwest late tonight through
midday Wednesday could approach 50 kt. Otherwise look for
conditions to rapidly deteriorate across the Sandhills and north
central Nebraska as snow increases late tonight then tapers
Wednesday afternoon. Look for MVFR in those areas through
Wednesday afternoon.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from midnight CST /11 PM MST/ tonight to 6 PM
CST /5 PM MST/ Wednesday for NEZ004>010-022>029-035>038-056>059-
069>071-094.

Winter Weather Advisory from midnight CST /11 PM MST/ tonight to
6 PM CST /5 PM MST/ Wednesday for NEZ005>010-025>029-037-038-094.

&&

UPDATE...Brown
SHORT TERM...Snively
LONG TERM...Snively
AVIATION...Taylor

Hazardous Weather Outlook
National Weather Service North Platte NE
323 PM CST Tue Dec 22 2020

NEZ004>010-022>029-035>038-056>059-069>071-094-232130-
Sheridan-Eastern Cherry-Keya Paha-Boyd-Brown-Rock-Holt-Garden-
Grant-Hooker-Thomas-Blaine-Loup-Garfield-Wheeler-Arthur-McPherson-
Logan-Custer-Deuel-Keith-Perkins-Lincoln-Chase-Hayes-Frontier-
Western Cherry-
323 PM CST Tue Dec 22 2020 /223 PM MST Tue Dec 22 2020/

This Hazardous Weather Outlook is for portions of western and
north central Nebraska.

.DAY ONE...TONIGHT.

A strong arctic cold front will push through the area tonight.
Strong northwest winds with gusts to around 60 mph are expected.
Light snow is also possible tonight, mainly after midnight across
northern Nebraska. A Winter Weather Advisory goes into effect
at midnight for snow and blowing snow across northern Nebraska.
Slippery road conditions and significantly reduced visibilities
can be expected with blowing snow.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

On Wednesday, strong northwest winds are expected to gust to
around 60 mph at times. This will create hazardous travel
conditions, especially for high profile and lightweight vehicles.
Blowing dust is possible across portions of southwest Nebraska,
leading to reductions in visibility. A High Wind Warning is now
in effect across most of western and north central Nebraska.

Snow will continue into Wednesday evening, with slippery road
conditions and blowing snow reducing visiblity expected. Wind
chill values will be near or below zero Wednesday morning, and
again on Wednesday night.

After Wednesday, no hazardous weather is expected.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed through tonight.

&&

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