Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 172340 CCA
AFDLBF

Area Forecast Discussion...CORRECTED
National Weather Service North Platte NE
540 PM CST Sun Dec 17 2017

.SYNOPSIS...
Issued at 340 PM CST Sun Dec 17 2017

H5 analysis this morning had a low amplitude pattern
along the US/Canadian border into southern Canada. Further south, a
closed low was present over swrn Arizona and was part of a trough of
low pressure which extended from Wyoming into Baja California.
Upstream of this feature, high pressure was located over the eastern
Pacific with a ridge extending northeast into Washington state.
Downstream of the trough, a shortwave was present over eastern
Kansas. This feature spread light rain to southeastern Nebraska and
the mid Missouri valley earlier this morning. At the surface: A
trough of low pressure extended from eastern Montana into eastern
Wyoming while a cold front extended from western Oklahoma into
northwestern Missouri and southern Iowa. North of this feature:
Northeasterly winds earlier this morning have gradually shifted
around to the west. This has allowed cloud cover to dissipate this
afternoon across the eastern panhandle and portions of north central
Nebraska. Under partly to mostly cloudy skies, 3 PM CST temperatures
ranged from 38 at Broken Bow to 43 at Ogallala.

&&

.SHORT TERM...(This evening through Monday)
Issued at 340 PM CST Sun Dec 17 2017

There will be a period of northwest flow and
subsidence tonight and tomorrow behind the departing wave.  Warm air
advection with the lower tropospheric wind backing from southerly to
westerly will promote warming temperatures on Monday.  So after lows
in the teens and 20s, highs will rebound into mid to upper 50s for
most locations.  The atmosphere is dry, so the above normal
temperatures will allow for minimum relative humidity in the 20s
across the entire forecast area, but with wind speeds only peaking
in the teens Monday afternoon, fire concerns are somewhat low. Skies
under the subsidence and warming downsloping low level flow will
keep clouds largely at bay.

.LONG TERM...(Monday night through Sunday)
Issued at 340 PM CST Sun Dec 17 2017

Monday night through Wednesday: An upper level trough
will traverse south central Canada Monday night forcing a weak cold
front into the forecast area. This will be a dry frontal passage as
the low level moisture profile is fairly dry per NAM12 and GFS cross
sections. With respect to the degree of cold air accompanying the
front, it will only be a glancing blow as the core of this airmass
passes off to the east. Highs Tuesday will range from the upper 40s
in the north to the lower 50s in the south. By Tuesday night, a
closed low and trough will deepen across the Pacific Northwest with a
downstream ridge developing across the high plains from Western
Nebraska to eastern Montana. H85 temps will surge to 8 to 10C
Wednesday afternoon with highs touching the 60 degree mark in swrn
Nebraska. Fire weather concerns will be minimal Weds afternoon with
minimum RH running around 25 percent and winds under 10 MPH.

Wednesday night through Sunday: An arctic cold front
will be forced into northwestern Nebraska late Wednesday night. This
feature is expected to pass through the forecast area by midday
Thursday. Mid level frontogenesis will increase behind the front
Thursday afternoon into Thursday night with light snow expected to
develop from the Panhandle into north central Nebraska. ATTM,
confidence in the development of light snow is fairly high given the
good model agreement between the GFS and ECMWF solutions this
morning. Utilizing a compromise of the GFS and EC solution, the
strongest mid level frontogenesis is from the panhandle into the
northeastern forecast area. Looking at the GEFS plumes,
precipitation amounts in the operational GFS ar running roughly 0.1
to 0.2 inches, which would equate to 1 to 3 inches of snow utilizing
a snow to water ratio of around 12 or 13 to one. That being said,
the highest pops will continue from the panhandle into the northeast
with lower pops in swrn Nebraska. Snow will come to an end Friday
morning with dry and cold conditions forecast Friday. A secondary,
stronger surge of arctic air will push into the forecast area Friday
night with snow chances increasing once again through Sunday. ATTM,
the best chances for snow will lie across the west and swrn forecast
area INVOF the mid level frontal boundary. This front will remain
anchored from nern Colorado into eastern Nebraska Friday night into
Sunday. That being said, we should see a chance for light snow next
weekend. Other than cold temperatures with highs in the teens,
impacts to travel should be minimal as this second snow episode will
be a long duration, light snow event.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 540 PM CST Sun Dec 17 2017

VFR is generally expected tonight and Monday.

Weak high pressure will build through wrn and ncntl Neb. The area
of MVFR across ncntl Neb is expected to exit that region to the
east around 03z. Conditions would seem to favor fog development
Monday morning but none of the models indicate it. So the forecast
is for VFR.

&&

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

$$

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



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