Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 170532

Area Forecast Discussion
National Weather Service North Platte NE
1132 PM CST Sun Feb 16 2020

.DISCUSSION...(This evening through Sunday)
Issued at 251 PM CST Sun Feb 16 2020

Highlights and Confidence: Sensible weather impacts revolve
around three rounds of light precip early on in the forecast
package. Specifically tonight-tomorrow, Tuesday afternoon-Tuesday
night, and Wednesday. Of which, the first and third rounds look to
affect the most in terms of areal coverage, albeit light snowfall
is expected with them all. 1-3 inches is possible in the Pine
Ridge region and Sheridan county tonight and Monday. Light
measureable snowfall is then possible across parts of southwest
NEB and the Sandhills Wednesday. Moderate-high confidence in
amounts the next 24 hours with low-moderate confidence Tuesday-
Wednesday. Otherwise, colder air arrives Wednesday with highs
upper teens to around 30, about 15-20 degrees below normal.
Western and north central NEB is anticipated to then see a warming
trend begin Thursday that will peak this weekend with Saturday
highs in the upper 40s to mid 50s.

Discussion: Latest water vapor imagery and 500 VWP shows quasi-
zonal flow overhead with a shortwave trough embedded in the flow
upstream in eastern OR and WA. Otherwise, latest day cloud phase
distinction satellite imagery and surface obs depict what appears
as stratocu to maybe altocu across parts of southwest NEB and the
Sandhills with high-level clouds streaming eastward above. Latest
surface analysis showed a weak surface low in southwest SD with a
surface trough extending south across eastern CO. Current thinking
is this shortwave trough and associated vort max will move into
the Central High Plains by late tonight. Meanwhile, the weak lee-
side low over the northern NEB Panhandle will evolve off to the
east into eastern NEB tonight with a weak cold front moving
through tonight.

Low-end chances start increasing late this evening peaking
overnight across Pine Ridge and northwestern NE. Current thinking
is there will be a delay in onset associated with a slow top-down
saturation as mentioned in the previous forecast. Current thinking
is precip type will be snow, except sprinkles/rain possible
outside the northeast Panhandle/far northwest NEB. There will then
be a window for a wintry mix late evening/early small hours prior
to changeover to all snow. Current thinking is the risk for
freezing precip is low given column saturation and ice in the
cloud based on BUFKIT soundings. Furthermore, NBM V3.2
conditional precip type probs leaned strongly towards a higher
likelihood of snow compared to rain or freezing rain tonight.
There was a small signal for freezing rain though noted across
west central NEB and parts of the Sandhills tonight so cant be
ruled out completely. Otherwise, highest snowfall is forecast
along the Pine Ridge and Sheridan county with 1-3. A dusting
possible across remainder of northern NEB and west central NEB.
Cooler air then in place tomorrow with highs 10-15 degrees colder
compared to today, generally mid 30s to mid 40s, warmest towards
south central NEB.

By early Tuesday, a broad mid-level trough will encompass much of
the northern and central CONUS with apparent embedded shortwave
troughs over southern WY/northern CO, Lake Michigan, and near Lake
Winnipeg that will be rotating eastward in time. The positive PV
anomaly over southern WY/northern CO is expected to move through
the forecast area Tuesday. While there is increasing large scale
forcing for ascent briefly early Tuesday, the drier air working in
is a limiting factor. Though by late Tuesday-Tuesday night, a
piece of lower-level tropospheric (~950-850 hPa) frontogenesis
develop across the area with increasing saturation in the column
Tuesday night. Of which, any precip that is realized looks to be
predominantly snow. Meanwhile, upstream, the next shortwave trough
will be positioned from the Northern Intermountain West to
northern CA by late Tuesday, this upper trough will move into the
region Wednesday. Guidance is more in agreement in terms of
potential and greater areal coverage seeing precip/light snow. Of
which, a decent W-E zone of increasing mid-level deformation
develops along with associated frontogenesis (850-700 hPa) across
the area over the Sandhills and sags south in time with greatest
large scale forcing for ascent. Snow will wind down late
Wednesday-Wednesday night. That said, there is still some
uncertainty with the placement of snow across the area. Overall,
while light snowfall is possible both time frames (Tue-Tue night
and Wed), this latter round of precip looks the best in terms of
forcing and possible impacts. The first round of slight
chances/chances appears more as a trace/dusting event with lower
areal coverage of the area seeing any impacts given the current

Otherwise, a surge of colder air will be moving from southern
Saskatchewan and Manitoba through the Dakotas Tue that will be
reaching the area Tuesday night. ECMWF ensemble system is notably
colder than the NAEFS with mean 850 hPa temperatures -14 to -8 C
compared to -10 to -6 C, respectively with the ECMWF system
reaching the 10th percentile by Thu 00Z. This will be something to
monitor. Nonetheless the cold shot looks to be more of a glancing
blowing compared to areas north. Highs Wednesday are forecast
15-20 degrees below normal, upper teens to around 30, warmest over
southwest NEB. Wednesday should be the coldest day this week.

Thursday and beyond, a upper-level ridge will be in place over the
Central Great Basin to Alberta early Thursday. This ridge will
break down through Thursday night as the next upper trough moves
across the Canadian Prairies. That said, prior will see modest 500
ht rises spread in Thursday with a low amplified large scale
pattern then in place by Friday. Northwest flow looks to then
prevail Friday-Saturday with a weak ridge across the Southern
Rockies shifting east to the Southern Plains. While there are some
differences in phase and amplitude, looks like fair weather/dry
conditions will prevail Thursday-Saturday. Western and north
central NEB is anticipated to see a warming trend begin Thursday
peaking this weekend. Of which Thursdays southerly flow turns
westerly with downsloping winds on Friday. Highs Saturday are
forecast to read above-normal near 10-15 degrees across the area
with upper 40s to mid 50s.

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1131 PM CST Sun Feb 16 2020

For aviation concerns are expected as ceilings remain
above 5000 feet through Monday morning. Ceilings will eventually
lower Monday afternoon in advance of the next weather system
arriving Monday night.

For KVTN...aviation concerns will be low through the evening. Some
light snow is possible at the terminal after 06Z lasting through
much of Monday morning. Snow will gradually diminish Monday
afternoon; however, ceilings will remain below 3000 feet through the
remainder of the TAF period.




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