Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 170518 AAB
AFDLBF

Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
1118 PM CST Sat Dec 16 2017

.SYNOPSIS...
Issued at 320 PM CST Sat Dec 16 2017

A fairly low amplitude pattern was present across the
eastern two thirds of the CONUS this morning. Broad west to east
flow extended from the Rockies east to the Atlantic coast. A trough
of low pressure, in association with a closed low over Labrador
Canada, was present from southern Quebec into New England. Another
trough of low pressure extended from the Idaho panhandle, south
southeast into central California. East of this trough, a nice
shortwave was present over Saskatchewan while a closed low was
present over northern Mexico. At the surface, Low pressure was
located over sern Colorado with a cold front extending east
northeast into far sern Nebraska and far nwrn Missouri. Abundant mid
and high level moisture continues to stream into the Rockies and
northern plains today from the eastern Pacific. Further south, gulf
moisture is streaming north from the western Gulf of Mexico into
Texas. The leading edge of this has pushed into Oklahoma this
afternoon. Under a veil of high cloudiness this afternoon, 3 PM CST
temperatures ranged from 38 at Ainsworth to 50 at Imperial.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 320 PM CST Sat Dec 16 2017

Weak upslope with an approaching wave will
provide a focus for rain and snow development late this afternoon
across northwestern portions of the forecast area.  Recent radar
trends show increasing mid level reflectivity across Sheridan county
with SFC TDs starting to increase.  We expect the coverage to expand
across our northwest and the eastern panhandle this evening with an
additional increase in coverage across the Sandhills overnight as a
wave from the southern plains rotates northeast toward the Missouri
Valley.  Light snow is expected across northwest Nebraska as PVA
increases, but moisture is somewhat sparse, so only a few tenths
accumulations is expected.  For the Sandhills, proximity soundings
reveal deep saturation below the DGZ, but dry aloft. The saturation
and slight PVA is sufficient for fzdz or fog this evening and
overnight, some of which may expand as far east as north central
Nebraska.  The NAM model today indicates this potential but a lesser
eastward threat from the GFS. So, will expand the fzdzfg eastward
some to include the Sandhills, but monitor trends overnight for an
further eastward expansion.  Accumulations are shown to be a few
hundreths or less in most places, but still, impacts to travel are
expected, especially across western portions of the forecast area.
Short-fused weather headlines are possible if a few hundreths or
more of ice begins to accumulate.

The lower troposphere is shown to remain saturated well into Sunday
afternoon for most locations.  Will keep a fog mention going where
winds are less than 7kts until at least 17z.  The drizzle may linger
as well, but temperatures should warm sufficiently for a changeover
to liquid.

Seasonal lows are expected overnight with temperatures cooling
slightly on Sunday as weak cold air advection and some clouds
continue.  Highs are expected to climb above freezing however with
readings tomorrow in the 30s to lower 40s.

.LONG TERM...(Sunday night through Saturday)
Issued at 320 PM CST Sat Dec 16 2017

Mid Range...Sunday night through Tuesday: A fairly benign weather
pattern will close out the weekend, continuing into the first
portion of next week. On Sunday night, a weak upper level trough of
low pressure will force a surface trough of low pressure through the
forecast area overnight Sunday night. This will lead to westerly
surface winds and warmer air pushing into the forecast area for
Monday. Highs Monday will reach the 50s, and westerly winds around
10 MPH will limit any fire weather concerns for Monday afternoon.  A
cold front will push into northern Nebraska Monday night resulting
in slightly cooler readings in the upper 40s to around 50 Tuesday.

Long Range...Tuesday night through Saturday: Benign conditions will
carry over into Wednesday. Warm air will push into the Central
Plains, downstream of a deepening trough of low pressure across the
intermountain west. Highs Wednesday will reach well into the 50s
once again. Elevated fire weather concerns may arise on Wednesday
afternoon, however, low confidence exists in the wind forecast
Wednesday afternoon. If a lead surface trough can push east of the
panhandle Weds afternoon, winds will be light, limiting fire weather
concerns.

Much colder air will push into the forecast area Wednesday night as
a strong arctic cold front passes through the forecast area. By 12z
Thursday, H85 temps range from -7c in the far southeast, to -15c
along the SD/Nebr border. Mid level frontogenesis will increase
behind the surface front, leading to a good chance for accumulating
snows Wednesday night into Thursday. Pops in the 60-70 percent range
were inherited with this morning`s forecast and will continue on
this track based on decent agreement with the GFS, ECMWF and
Canadian model solutions this morning, indicating a nice band of
snow extending from the panhandle and swrn Nebraska into the
northeastern forecast area. The main difference between the models
attm is the amount of qpf they develop. The ECMWF is on the heavy
side attm, with the Canadian the lightest and the GFS in the middle.
Looking at the GEFS plumes, the operational GFS and GEFS mean is on
the order of 0.10 to 0.20 inches of qpf with this system across the
forecast area. That being said, will keep snow accumulations on the
order of 2 to 3 inches with this system. Gusty northerly winds
behind the front will be an issue also Thursday and will continue to
hit this in the HWO. The cold temperatures will carry over into
Friday and Saturday with H85 temps continuing in the -7c to -15c
range. A reinforcing shot of arctic air will drop south into the
forecast area on Saturday with an increased threat for light snow in
the west. Highs will be in the 20s with lows in the single digits to
lower teens.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1118 PM CST Sat Dec 16 2017

The Rapid Refresh models, the RAP and HRRR, suggest the better
chances for LIFR in very low cigs and -S/FZDL/FG will be across
Swrn Neb...south or along and south of I-80 where CIGS are lowest
at this time. Flight conditions are expected to improve from
15-17z Sunday onward with VFR generally expected Sunday evening.


&&

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

$$

SYNOPSIS...Buttler
SHORT TERM...Jacobs
LONG TERM...Buttler
AVIATION...CDC



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