Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 220250 AAA

Area Forecast Discussion...UPDATED
National Weather Service Cheyenne WY
850 PM MDT WED SEP 21 2016

Issued at 843 PM MDT Wed Sep 21 2016

Radars showed scattered light showers developing along and north
of stalled surface boundary near the Front Range this evening. This
activity will persist until midnight. The majority of the short
range model guidance and sounding data indicates low stratus and
fog development east of the Laramie Range overnight. The fog may
be more persistent and cover more areal extent across east central
Wyoming into the northern 2/3 of the Nebraska panhandle, with more
patchy coverage to the south of a Wheatland-Scottsbluff-Bridgeport
line. Updated weather, sky and pop grids to account for these radar
and model trends.


.SHORT TERM...(This evening through Friday night)
Issued at 211 PM MDT Wed Sep 21 2016

Ample mid and high level moisture continuing to move across the
CWA ahead of a digging upper system along the Pacific NW coast.
This system will be the main weather feature affecting the CWA
through Friday as it initially drops into Nevada Thursday then
lifts northeast into Montana late Friday. Main difficulty will be
timing and location of precipitation as this system approaches
then passes by. Models have come into agreement in lifting this
system pretty much intact to the northern high plains Friday night
as opposed to their splitting solutions depicted earlier.

Of more immediate concern will be for some low clouds and fog
across mainly the Panhandle later tonight into Thursday morning
as surface upslope winds increase a bit in response to a
developing low over eastern Colorado. Clouds should lift during
the morning into the afternoon Thursday but would not be surprised
to see them hang on through the day especially towards Chadron and
Alliance. Otherwise mainly dry weather expected across the plains
tonight into Friday with the best forcing looking to remain out
west closer to the upper low. Showers that form there will move
generally northward as the upper flow becomes more southerly as
the low digs into Nevada. Better chances for showers reach the
plains later Friday and Friday night as the upper low turns
northeast and the better forcing shifts east over the high plains.
Still fairly warm across most of the CWA Thursday though went a
bit below guidance across the northeast Panhandle where clouds
should hang on the longest. Some cooler air should filter into
southeast Wyoming Friday but may not get into the Panhandle until
later that day.

.LONG TERM...(Saturday through Wednesday)
Issued at 211 PM MDT Wed Sep 21 2016

The models are in pretty good agreement in shifting the upper trof
to the northern plains by Sunday evening. Until that occurs, we
are looking at unsettled conditions with a chance of afternoon/evening
showers and isolated thunderstorms mainly on Saturday along with
cool conditions. Beyond Sunday, the ensembles are showing this
upper level trof closing off and taking its sweet time on its
journey through the northern plains and upper midwest. Meanwhile,
the deterministic models are even showing the system retrograding
back to the west during the early part of the week. The GFS even
shows us getting some precip on the back side of this system on
Wednesday. We are not that confident this will occur based on the
current ensembles. As a result, we are keeping our forecast area
dry through the middle of the week. With the dry air mass and
gusty northwest winds on the back side of this system we could see
critical fire weather conditions early next week. High temperatures
will also struggle to get out of the 60s with lows between 35 and 40.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 521 PM MDT Wed Sep 21 2016

Widely sct -SHRA will move northeast across southeast WY early this
evening, with no impacts to CYS or LAR. Otherwise, expect VFR cigs
with mid cloud bases between 6000 and 12000 ft AGL through late
tonight. Models still consistent with lowering cigs and vis after
08Z east of the Laramie Range with moist east-northeast flow. IFR
cigs with MVFR vis will prevail thru at least 15Z, with slow
improvement to VFR by midday Thu.


Issued at 211 PM MDT Wed Sep 21 2016

Fire weather concerns expected to remain low for at least the next
few days with conditions trending towards being cooler and more
moist. There will be some rather gusty winds over parts of Carbon
county Thursday afternoon but humidities expected to remain well
above critical levels.


.CYS Watches/Warnings/Advisories...


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