Area Forecast Discussion
Issued by NWS Cheyenne, WY

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798
FXUS65 KCYS 110526
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1010 PM MST Sun Dec 10 2017

.UPDATE...
Issued at 902 PM MST Sun Dec 10 2017

Evening water vapor imagery showed a well-defined cyclonic circulation
over southeast Alberta Canada associated with a fast-moving clipper
system. Well in advance of the cold front was a band of scattered
high clouds from the eastern Dakotas into southern WY. Skies clear
behind this band, with a swath of mid/high clouds spilling south
across MT. Skies tonight will be mostly clear, with partly cloudy
across the northern CWFA. It will be breezy for the wind corridors
near Arlington and Bordeaux tonight, with lighter winds elsewhere.

UPDATE Issued at 501 PM MST Sun Dec 10 2017

Reds Flag Warning for fire weather zones 312-313 in western Nebraska
Panhandle was allowed to expire at 5 PM this afternoon. Sustained
northwest winds have decreased to 10-15 mph with humidities expected
to slowly recover as temperatures cool after sunset.

&&

.SHORT TERM...(This evening through Monday)
Issued at 232 PM MST Sun Dec 10 2017

Tranquil weather prevails. A 1040-mb surface high remains over the
Intermountain West this afternoon, contributing to sunny skies and
dry conditions across the entire area. This is also resulting in a
fairly tight pressure gradient, so winds have been fairly gusty so
far today w/ critical to near critical fire weather conditions for
the western NE Panhandle. Inherited Red Flag Warnings have been on
the marginal side, with generally sporadic wind gusts in the range
of 25-30 MPH so far today. RHs are below 10 percent, however.

Windy again on Monday w/a strong shortwave & associated cold front
progged to push across the Dakotas into Nebraska from late tonight
through Monday. The GFS shows a swath of H7-H8 flow between 50 and
60 knots along/east of a Lusk-Sidney line at 15z Monday, but flows
decrease markedly in the afternoon. A few gusts to 50-55 MPH could
occur, but do not think mixing will be deep enough to warrant high
wind headlines at this time. Concerning RFW conditions, RHs should
remain above the 15 percent threshold over western NE thanks to an
early arrival of the cold front. No precipitation is expected.

.LONG TERM...(Tuesday night through Saturday)
Issued at 247 AM MST Sun Dec 10 2017

Upstream ridge of high pressure will yield northwest flow through
the period. The result will be an above average week for
temperatures along with mainly dry conditions. After a very mild
day on Tuesday, a series of moisture-starved clipper systems will
dive into the northern high plains and upper midwest on Wednesday
and Thursday. The main story with these clippers will be the
reinforcing shot of cooler (still above normal) temps Wednesday-
Thursday. Highs will fall into the 40s to near 50 both days. Flow
deamplifies a tad on Friday, as weak shortwave transitory ridge
moves through. In addition, low-level gradients should begin to
kick winds up close to high wind criteria across wind prone areas.
Medium range guidance is consistent in driving another front thru
the region Friday night. There may be a period of light precipitation
late Friday night/early Saturday morning, but latest models have
trended drier. Temperatures will again cool slightly behind the
front for Saturday. Long range outlook suggests another high wind
event Sunday afternoon through Monday morning.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday evening)
Issued at 1010 PM MST Sun Dec 10 2017

VFR. An Alberta clipper system and cold front move quickly southeast
across the Dakotas and Nebraska Monday morning bringing broken
clouds AOA 20000 FT AGL. Westerly surface winds 8-15 KT tonight will
shift to northwesterly and increase along and east of the Laramie
Range after 15Z Monday. Gusts of 25-40 KT are likely along and east
of I-25. Winds diminish with clear skies after 00Z.

&&

.FIRE WEATHER...
Issued at 247 AM MST Sun Dec 10 2017

Another critical fire weather day across the Nebraska Panhandle.
Will be a period late morning through mid afternoon where gusty
winds and low humidity combines to create critical fire weather
conditions. A Red Flag Warning is in effect from 10 AM this morning
through 5 PM this afternoon for FWZs 312 and 313. Winds picking
up again Monday as a Clipper system tracks across central South
Dakota and central Nebraska. Fortunately...humidity Monday afternoon
is expected to be a little better than today. Windy conditions again
Wednesday across the Panhandle as yet another Clipper system tracks
across central Nebraska.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

UPDATE...MAJ
SHORT TERM...CLH
LONG TERM...CAH
AVIATION...MAJ
FIRE WEATHER...GCC



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