Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 211137
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
537 AM MDT Sat Oct 21 2017

.SHORT TERM...(Today through Sunday)
Issued at 300 AM MDT Sat Oct 21 2017

Currently, very windy conditions continue along the I-25 corridor
as a stout cold front has tracked across the region. Winds have
briefly gusted as high as 60 mph at Whitaker and Bordeaux over
night but have not been consistently gusting that high and thus
have continued with the SPS highlighting strong wind gusts early
this morning. Most short range guidance indicates that these winds
will relax a bit after sunrise as the front pushes further east.
A few showers also continue along the 700mb frontogenesis axis
this morning over the Panhandle and these showers will quickly
exit to the east after 12z.

Any break in the winds will be short-lived today however as a
strong 150kt upper jet impinges on the NW US and extends into the
Northern Rockies tonight. Classic high wind scenario will unfold
with SE Wyoming on the anticyclonic and subsident side of the jet.
Lee troughing develops rapidly after 03z tonight and low level
gradients tighten dramatically. CAG-CPR gradient peak near 78
meters by Sunday morning. 700-750 mb flow increases to around
60kt by the same time frame. Went ahead an upgraded the high wind
watches to warnings as this seems pretty clear cut for the wind
prone areas such as Arlington, Bordeaux, and the South Laramie
Range. Winds will likely gust between 60 and 70 mph by Sunday
morning. The question is how far east will the high winds extend?
GFS soundings for Cheyenne between 12 and 18Z Sunday are pretty
impressive with 50+ kt flow just off the surface. Local wind model
is not producing very high probability for high wind criteria in
Cheyenne currently, likely due to lack of flow above 700 mb and
weaker lapse rates. Too many question marks now to issue any
headlines but later shifts will need to monitor as any increase in
lapse rates or mixing potential will likely bring high wind
potential into Cheyenne Sunday morning.

It will be mostly sunny with much cooler temperatures today with
highs ranging from the low 40s west to around 60 over the
Panhandle. Went slightly above MOS guidance for tonight where the
winds are strongest as downslope warming and mixing should keep
over night lows a bit higher.

.LONG TERM...(Sunday night through Friday)
Issued at 300 AM MDT Sat Oct 21 2017

Elevated winds Sunday night before a backdoor cold front moves
into the area from the northeast. 700mb temperatures drop to -7C
across the northern Panhandle, but cold temperature short lived as
westerly winds return Monday afternoon.

Warming temperatures and windy conditions Tuesday and Wednesday as
700mb temperatures climb back to +10C. GFS 700mb winds close to
50kts, so wind prone areas probably seeing warning level winds.

Stronger system set to move into the area Thursday with fairly
widespread rain and snow mix, turning to snow once the colder
temperatures arrive Thursday night.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 536 AM MDT Sat Oct 21 2017

Mainly VFR through next 24 hours with increasing winds. Skies to
scatter out behind a cold front that pushed through the area
overnight.

&&

.FIRE WEATHER...
Issued at 224 AM MDT Sat Oct 21 2017

Min RH values will drop to between 15 and 20 percent east of the
Laramie Range this afternoon. Some elevated conditions are
possible as it will also be breezy to windy but overall, cooler
temperatures will prevent critical fire conditions from
developing. Dewpoints creep up a bit for Sunday into Monday so in
spite of the dry conditions, the fire weather threat after today
will be low.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from 7 PM this evening to 6 PM MDT Sunday for
     WYZ106-110-116-117.

NE...None.
&&

$$

SHORT TERM...DEL
LONG TERM...GCC
AVIATION...GCC
FIRE WEATHER...DEL


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