Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 142125
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
325 PM CST Sat Jan 14 2017

.SHORT TERM...(This evening through Sunday)
Issued at 324 PM CST Sat Jan 14 2017

Primary challenge of the short term period will be pinning down
wintry precipitation chances and timing as our long talked about
winter storm finally begins to impact the forecast area. As of 21z
the main upper level low was slowly tracking east across the Baja of
California and into northern Mexico. Widespread moisture continues
to stream north out ahead of this system, which has pushed PWAT
values over the southern High Plains to near climatological maxes
for this time of year.

The upper level low will pivot northeast into New Mexico overnight
and take on a negative tilt as a ridge continues to build
downstream. The HRRR/RAP are beginning to capture the onset of light
precipitation in southwest Nebraska during the early morning hours
as the subtropical airmass is advected northward and lifted
isentropically over the cool, dry air already in place.
Slight/chance POPs steadily spread north through morning and
afternoon hours, which is supported by the latest runs of the
NAM/SREF/EC. The GFS has consistently been a dry outlier, but it
is also on the dry side of the GEFS envelope.

Light freezing rain is the favored p-type Sunday as dry mid-level
air will limit both precip amounts and the potential for ice to be
introduced into the cloud layer. Observations from the Nebraska
Mesonet also show sub-freezing ground temperatures, so it will not
take much freezing rain to create a thin glaze of ice on local
roadways. For this reason the Winter Storm Warning will go ahead and
start at 18z over southwest and central Nebraska.

.LONG TERM...(Sunday night through Saturday)
Issued at 324 PM CST Sat Jan 14 2017

A strong low pressure system will continue to track across the
central plains on Sunday night and Monday. This system will bring
some messy conditions to central Nebraska for Sunday night through
Monday evening. While confidence in occurrence is high that this
system will develop, the track of the system is still very
uncertain. With our forecast area right on the transition line, any
slight wobbles north or south with the system could have significant
impacts on the overall forecast. For now, will stick with the
freezing rain forecast for much of Sunday night. Current model
soundings are indicating a fairly decent low level warm layer across
the region which has allowed for a fairly high confidence in
freezing rain potential. As the system moves northward early Monday
morning, colder air will being to move into the system allowing a
transition to all snow and ice pellets before switching over to all
snow on Monday morning. Timing for transition to snow is looking to
occur around 2am south of a line from Ogallala to O`Neill. Across
the north, freezing rain is possible for another couple hours before
also changing to all snow around 6am. Total ice accumulations before
changing to snow are expected to be under 0.10 inches.

As the system continues to move into the central Plains on Monday,
snow will continue much of the day. While amounts are expected to be
low, snow falling on surfaces that are ice covered from Sunday night
could cause an additional travel hazard as ice covered surfaces will
be difficult to see. A big uncertainty in the snow aspect of the
storm is where the deformation band will set up. Models are
consistent in highlighting an area of higher snowfall rates, but the
location of this band is inconsistent. Have put the band over a line
from Imperial to O`Neill. Along this line snow totals could be in
the 2 to 5 inch range. Again, any slight movement in the overall
track of this system could shift this heavier band over a different
location. We have an update to headlines with this afternoon
package. Our Winter Storm Watch has been upgraded to a Winter Storm
Warning for all the counties that were previously under the watch.
Timing has changed just a little for the warning. Have divided the
start times into two fragments to account for the northward movement
of the overall system. The southern half (south of highway 92) will
start Sunday at noon to account for the high freezing rain chances
Sunday afternoon and the earlier arrival of the system. The rest of
the counties from the original watch area will have the warning
start at 6pm. Have opted against issuing any headlines north of the
warning (Winter Weather Advisory) at this time. This may be
something that will have to added in a future forecast package as
the system pushes into the area.

By Monday night, the system will be starting to pull off to the
northeast. Therefore, precipitation will come to an end by 6pm
Monday. High pressure and strong upper level ridging move into the
central US allowing for dry conditions through much of the week. The
major story for next week will be the increase in temperatures mid-
week. By Wednesday and Thursday, high temperatures could reach into
the low to mid 50s. The next weather system arrives Friday, however,
much uncertainty remains regarding the system an nothing more than
a mention is necessary at this time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1122 AM CST Sat Jan 14 2017

VFR conditions are light winds are expected to prevail across
much of western and north central Nebraska through the next 24
hours. Only forecast concern will be the threat for light freezing
rain in southwest Nebraska Sunday morning. At this point,
confidence is not high enough to include any mention of -FZRA in
the KLBF TAF as the better chances look to hold off until after
18z.


&&

.LBF WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from noon CST /11 AM MST/ Sunday to 6 PM
CST /5 PM MST/ Monday for NEZ036>038-057>059-069>071.

Winter Storm Warning from 6 PM Sunday to 6 PM CST Monday for
NEZ007>010-025>029.

&&

$$

SHORT TERM...Martin
LONG TERM...Kulik
AVIATION...Martin


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