Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 251719

Area Forecast Discussion
National Weather Service Cheyenne WY
1119 AM MDT Tue Oct 25 2016

.SHORT TERM...(Today through Thursday)
Issued at 205 AM MDT Tue Oct 25 2016

Radar pix show a steady stream of showers moving up from northwest
Colorado early this morning. Cooling cloud tops on IR
imagery suggest there could be pockets of moderate rain showers
within this band, so bumped up QPF totals a bit through sunrise
over the high country, along with snow totals above 9000kft.
Thinking we could see a couple inches of accumulation in these
higher elevations. Expanded low end PoPs further east across the
Wyoming plains as well since both synoptic models and CAMs show a
few light rain showers overnight here too. Once the shortwave
responsible for this activity moves overhead later this morning,
precip will end for the most part. The exception will be in the
higher mountains where the nose of a weakening jet should aide in
producing orographic rain showers this afternoon.

Dry conditions will return tonight and continue through Thursday
as the Pacific trough deepens and amplifies the downstream upper
ridge over the Rockies. After a slight cool down on Wednesday in
the wake of a weak Pacific front, will see temps warm once again
for Thursday. High pressure building over the west in combination
with leeside troughing induced by energetic southwest flow over
the PacNW will strengthen the sfc pressure gradient across
Wyoming, producing gusty westerly winds. Thus, may see a brief
return of critical fire weather conditions on Thursday afternoon
across the plains within warm and dry downslope flow.

.LONG TERM...(Thursday night through Monday night)
Issued at 305 AM MDT Tue Oct 25 2016

Medium range models in reasonable agreement late this week and
next weekend...but still have timing difficulties with energy
moving eastward from the Pacific associated with the main upper
level low near the west coast. Models continue to show generally
dry conditions across the eastern plains...but vary greatly when
it comes to wind speeds and mountain snow shower activity. The
timing of fronts is also in question with the ECMWF about 12 to 18
hours faster compared to the GFS...Canadian and the ensembles on
Friday. The same thing applied for Sunday as the next piece of
energy ejects northeast...but the GFS is much more aggressive
compared to the other models. This leaves Friday and Sunday`s high
temperatures in question with a wide spread of possible solutions.
Yesterday`s 00Z models were showing a back door cold front moving
across the plains. 00Z models last night show this front
considerably further north. Kept high temperatures in the upper
60`s to upper 70`s...which is consistent with model consensus.

Looking further appears a major pattern shift will be
underway for the last few days of October and into early November.
This typically leads to poor performance in long range models and
overall poor run to run consistency. Ensembles continue to show a
wide range of solutions...which is typical during major pattern
shifts. Overall...believe a more stormy pattern is possible for
the central Pacific coastline which will likely influence the
overall weather in Wyoming with more wind and a better chance for
precipitation for the first week of November. Before that...Will
continue with mild temperatures into Sunday due to southwest flow
aloft...but then expect a slow cool down by early next week. Too
difficult to say when the best chance of precipitation will be due
to timing differences...but it appears some shower activity will
be possible across Wyoming by early next week...with snow in the


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1119 AM MDT Tue Oct 25 2016

Breezy west winds 20 to 30 knots today across southeast Wyoming
with lighter but still increasing winds this afternoon from the
west and northwest across the western Nebraska Panhandle. Minor
upper disturbance tracking slowly east across eastern Wyoming
producing a mid-deck ceiling around 10,000 ft msl for Laramie,
Cheyenne, Scottsbluff, Chadron, Alliance and Sidney with a few
sprinkles possible but most precipitation falling out of that mid-
deck likely not reaching the ground. Upper level winds start to
pick up quite a bit tonight as a 90 knot 250 mb jetmax moves
across southeastern Wyoming. With sufficiently dry mid to low
level airmass about all that we expect from that upper jetmax to
generate are some standing wave clouds at or above 20,000 ft msl
on the west side of the mountains with no impacts to ground,
takeoff or landing operations at our area airports tonight into
tomorrow. VFR category expected over the next 24 hours.


Issued at 205 AM MDT Tue Oct 25 2016

Fire weather concerns will remain low today and Wednesday with
minimum humidity values expected to remain above 25 percent. Dry
and very warm conditions look to return on Thursday along with
breezy westerly winds. This could enhance fire weather concerns
mainly along and east of the Laramie Range on Thursday afternoon.




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