Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 162147

Area Forecast Discussion
National Weather Service Cheyenne WY
247 PM MST Tue Jan 16 2018

.SHORT TERM...(This evening through Thursday night)
Issued at 246 PM MST Tue Jan 16 2018

Tonight...Weak and flattening ridge aloft moves overhead providing
mostly clear skies. Not as cold as last night with moderating
airmass. Compromised between the NAM and GFS MOS minimums for low

Wednesday...Quite weak shortwave trough aloft moves overhead with
only some cloudiness. Warmer day with 700 mb temperatures near -1
Celsius yielding maximum temperatures in the 40s at lower

Wednesday night...The airmass continues to moderate, especially with
low level westerly downslope winds. Thus, low temperatures not quite
as cool as tonight.

Thursday...Flow aloft turns westerly, inducing an even more
significant surface lee trough, which will produce an even warmer
day with 700 mb temperatures near 4 Celsius, yielding maximum
temperatures in the upper 40s to near 60 degrees at lower
elevations. The Craig to Casper 850 mb height gradient exceeds 50
meters, thus will see a corresponding increase in winds, especially
in favored locations near Arlington. Boundary layer winds increase
to 40 to 50 knots, though not confident enough at this time to issue
a High Wind Watch.

Thursday night...Even warmer than Wednesday night as the airmass
moderates further and downslope west winds aid in the mild
temperature trend.

.LONG TERM...(Friday through Tuesday)
Issued at 246 PM MST Tue Jan 16 2018

One more mild and mainly dry day across the CWA Friday under
southwesterly flow aloft ahead of the next upper trough that will
move onshore over the west coast. This system will be the concern
for this area over the weekend as it digs over the southwest CONUS
and closes off an upper low through Saturday night before moving
it over Kansas Sunday. Lee cyclogenesis should be induced over
Colorado early Saturday while colder air filters across the CWA.
This looks to spread snow to much of the CWA during the day
Saturday, continuing Saturday night. Models then diverge Sunday
with the GFS moving the system out quicker thus bringing an
earlier end to the snow, about 12 hours earlier than the EC. Will
favor the slower EC as these systems to tend to slow down when
closing off thus a significant snow event seems to be shaping up.
Not as much snow if the more southerly track depicted by the GFS
pans out. Obviously will have to watch over the next few days.
Otherwise a return to cool temperatures over the weekend,
persisting into early next week with weaker impulses bringing some
snow showers mainly to the mtns.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday morning)
Issued at 1010 AM MST Tue Jan 16 2018

VFR at all terminals through the period with winds less than 10 kts
for the most part.


Issued at 246 PM MST Tue Jan 16 2018

No concerns based on humidity and wind trends.




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