Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 230916

Area Forecast Discussion
National Weather Service Cheyenne WY
316 AM MDT Sat Sep 23 2017

.SHORT TERM...(Today through Monday)
Issued at 315 AM MDT Sat Sep 23 2017

Overnight GOES-R water vapor loop showed a closed upper low over
north-central NV within a deep amplitude trough occupying the
Intermountain West. A surface cold front extended from northeast
through southwest NE, central CO to a low near the UT/CO border.
Large scale QG lift on left-front exit of 130-kt upper jet aided
in development of scattered elevated convection from eastern CO
through central NE, and the eastern Dakotas. Further west, shower
coverage was more isolated and lighter in intensity. Moistening
boundary layer in upslope regime will result in patchy early
morning fog between Cheyenne and Laramie.

Short term forecast challenges will focus on temperatures and
precipitation amounts, including high elevation snowfall.

Good consensus with the 00Z short range models/ensembles progging
the NV upper low to move slowly east into UT through Sunday
morning, then weaken as it tracks north into western WY through
Monday morning. The associated upper trough axis will extend from
eastern MT to the Four Corners by Monday evening.

After a lull in the precipitation early this morning, shower
coverage and intensity will increase by late morning and continue
through Sunday. Snow levels will remain above 10000 feet through
tonight, with only a few inches over the highest mountain peaks.
700mb temperatures fall to -2C Sunday, with snow levels lowering
to 8000 feet by Sunday night. Could see several inches of snow
above this elevation, so later shifts may need to contemplate a
winter weather advisory for the Snowy Range where orographics will
be more favorable. Lower elevations, including the valleys and
plains can expect beneficial rainfall, with the heaviest QPF
across the NE Panhandle. High temperatures today will range from
the 40s to mid 50s. Slightly cooler temperatures are forecast
Sunday with highs mostly in the 40s, or at least 20 degrees below
seasonal normals. Shower coverage will become more scattered
Sunday night and isolated Monday. Temperatures Monday will not be
as cool with highs in the 40s and 50s.

.LONG TERM...(Monday night through Friday)
Issued at 235 AM MDT Sat Sep 23 2017

Some lingering showers possible mainly over far se Wy into the
southern NE Panhandle Monday evening as the main upper trof axis
moves by. After that it looks like a mild and dry week under
northwesterly flow aloft. A minor push of cooler air expected Weds
night as a shortwave swings across the northern plains but no
significant cooling expected.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 235 AM MDT Sat Sep 23 2017

Fairly widespread IFR cigs should exist east of the mtns for most
of the period due to moist upslope flow. Mainly VFR conditions
expected for KRWL and KLAR though some patchy MVFR cigs possible
this morning. Rain and showers increasing this morning over and
east of the mtns and continuing through tonight as a low pressure
system moves over Utah.


Issued at 215 AM MDT Sat Sep 23 2017

A slow moving Pacific storm system will bring much cooler temperatures
and wetting rainfall today through Monday. Elevations above 9000 feet
can expect accumulating snow. Warmer temperatures and drier conditions
will return Tuesday and last through the end of the week.




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