Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 290314

Area Forecast Discussion
National Weather Service Cheyenne WY
914 PM MDT Fri Apr 28 2017

Issued at 905 PM MDT Fri Apr 28 2017

Freezing fog, patchy freezing drizzle and light snow will be the
main theme overnight across areas mainly along the I-25 corridor.
Latest water vapor loop was showing some the bulk of snow falling
across Colorado in closer proximity to the vort lobe. Weak
isentropic lift and upslope flow is expected to persist overnight,
but any additional snowfall amounts will generally be an inch or

UPDATE Issued at 549 PM MDT Fri Apr 28 2017

We sent out a quick update to include some freezing drizzle, fog
and light snow in areas along I-80 between the Summit and Sidney
Nebraska. Latest satellite loop was showing low clouds over this
area with very minimal high cloud cover. As a result, we are
seeing mostly supercooled water droplets with minimal dendritic
ice crystal growth. This trend may continue during the next couple
of hours before we see more lift at higher levels which will
cause things to saturate more at higher levels this evening, and
cause the precip. to change back over to snow.


.SHORT TERM...(This evening through Sunday)
Issued at 319 PM MDT Fri Apr 28 2017

Snow continuing over much of the area this afternoon but a very
narrow dry wedge of air at mid atmospheric levels has held over
far southern parts of the CWA and kept pcpn away in areas such as
Cheyenne to Laramie. Snow has had difficulty sticking as well
due to marginal temperatures and high Sun angle with most roadways
just wet.

The upper low responsible for the pcpn is deepening over eastern
Utah and is expected to drop south then southeast into central New
Mexico through Saturday morning then move east into the southern
plains Saturday night then slowly northeast on Sunday. This track
will pull pcpn southward overnight with pcpn expected to come to
an end across the CWA by Saturday afternoon. A few inches of
snowfall still expected mainly over the southern mtns tonight with
lighter snows elsewhere thus have made some modifications to
highlights through this evening in view of this.

Dry weather expected over the CWA late Saturday through Sunday as
a narrow upper ridge moves over the area on the back side of the
plains upper low.

.LONG TERM...(Sunday night through Friday)
Issued at 319 PM MDT Fri Apr 28 2017

The 12Z medium range models and their ensembles are in reasonable
agreement with the large scale pattern. Upper closed low and the
associated trough over the eastern Great Plains/MS Valley early in
the period lifts northeast across the Great Lakes, OH valley and
Northeast by Wednesday. A progressive northwest flow aloft will
dominate the Rockies and plains through mid-week, with a couple of
Alberta clipper low pressure systems producing scattered rain/snow
showers and gusty northwesterly winds through mid-week. Snowfall
over the higher elevations will be light to moderate with
potentially several inches during this time period. Below normal
temperatures are forecast for Monday through Wednesday with highs in
the 40s and 50s lower elevations and 30s mountains. A high amplitude
upper ridge along the Pacific coast will shift east across the
Intermountain West and Rockies late next week, bringing drier
conditions and warmer than normal temperatures.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 549 PM MDT Fri Apr 28 2017

IFR/MVFR ceilings and light precipitation will linger through the
evening at the CYS, LAR, SNY and BFF Taf sites. Could have a mix
of fzdz and sn at CYS, and SNY through 02z or so, due to lack of
deeper moisture. However, we should see deeper saturation after
02z which would favor a switch over to more snow. This will be in
response to the upper level low developing over southwest
Colorado. This will also favor good upslope flow, but the deepest
moisture and bulk of the precipitation should stay south of the
Wyoming/Colorado border tonight. The lower ceilings should move
out of CDR and AIA during the next couple of hours, with the rest
of the taf sites possibly hanging on to the IFR/MVFR ceilings
through much of the night. CYS may clear out the latest due to
more favorable upslope flow.


Issued at 319 PM MDT Fri Apr 28 2017

No fire weather concerns seen into at least early next week with
fuel and weather conditions remaining mostly non-critical.


WY...Winter Storm Warning until midnight MDT tonight for WYZ104-114.

     Winter Weather Advisory until midnight MDT tonight for WYZ103-



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