496 
FXUS65 KCYS 232121
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
321 PM MDT Fri Oct 23 2020

.SHORT TERM...(This evening through Sunday)
Issued at 320 PM MDT Fri Oct 23 2020

Main concerns will be with a period of stronger winds expected in
a couple of the wind prone areas tonight through Saturday, then a
potent winter system affecting the CWA late saturday through early
Monday.

Winds have not come up much yet out west in the Arlington area as
the gradient has not sharpened much. Still expect the wind to 
rise this evening as 7H flow increases to over 50Kts later this 
evening and continues though much of the day Saturday. Have 
delayed the High Wind warming for the Arlington area until mid 
evening and upgraded the watch for the summit area for late 
tonight through Saturday as the stronger winds translate into that
area.

Attention will then turn to a potent upper trough that will drop
into the northern Rockys during the day Saturday. As it does so
the arctic boundary which will retreat a bit over the northeast
part of the CWA early Saturday will surge back south Saturday 
afternoon and early evening returning much colder air. Favorable 
overrunning setup and some jet dynamics will create an expanding 
area of snow which will progress southward across the CWA late 
Saturday afternoon and evening. The trough will progress rather 
slowly southward through Sunday while sharpening with the band of 
snow likewise progressing slowly southward. Snow will continue 
through Sunday then taper off Sunday night as better dynamics 
shift south. Snowfall amounts tricky as not a lot of moisture to 
work with and no real frontogenetical forcing seen so snowfall 
rates look limited and not ideal conditions for good dendritic 
growth. Still looks like a general 4 to 6 inches outside of the 
mountains with around a foot possible over the higher mtns. Have 
opted to go with winter weather advys for most of the plains with 
a Winter Storm Watch for the Snowys, Sierra Madre and the South 
Laramie ranges where heavier snow looks a little more likely. 
Impacts should be aided by the event looking to be somewhat long 
term and not a lot of wind with main impacts to travel. 

.LONG TERM...(Sunday night through Friday)
Issued at 320 PM MDT Fri Oct 23 2020

Monday...Snow looks to be decreasing in areal coverage from north to 
south and ending in the afternoon as the trough aloft moves away 
from the region. With 700 mb temperatures near -9 Celsius, and fresh 
snowpack, maximum temperatures will be quite cold.

Tuesday-Friday...Northwest flow aloft prevails with periods of gusty 
winds, along with a warming trend as the airmass moderates. Looks 
like a dry period with limited low and mid level moisture.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1139 AM MDT Fri Oct 23 2020

Wyoming TAFS...VFR at Rawlins and Laramie. Wind gusts to 23 knots
at Rawlins until 04Z, then to 35 knots. Wind gusts to 30 knots at
Laramie after 06Z.

MVFR at Cheyenne until 19Z, then VFR. Wind gusts to 20 knots until
00Z. 

Nebraska TAFS...MVFR at Chadron, Alliance and Sidney until 19Z,
then VFR. VFR at Scottsbluff. Wind gusts to 27 knots from 04Z to
15Z.

&&

.FIRE WEATHER...
Issued at 320 PM MDT Fri Oct 23 2020

Expect no real fire weather concerns over the weekend into next
week with a strong cold front passing across during the day
Saturday bringing very cold conditions into early next week.
Accumulating snow is also expected to be widespread Saturday 
night through Sunday. 

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory from 3 PM Saturday to 6 PM MDT Sunday 
     for WYZ101>103-105>108.

     Winter Weather Advisory from midnight Saturday night to 6 AM MDT 
     Monday for WYZ110-115-118-119.

     Winter Storm Watch from Saturday evening through Sunday evening 
     for WYZ112-114.

     High Wind Warning from 9 PM this evening to 6 PM MDT Saturday 
     for WYZ110.

     High Wind Warning from 6 AM to 6 PM MDT Saturday for WYZ116.

     Winter Storm Watch from late Saturday night through late Sunday 
     night for WYZ116-117.

NE...Winter Weather Advisory from 3 PM Saturday to 6 PM MDT Sunday 
     for NEZ002-003-019-095-096.

     Winter Weather Advisory from midnight Saturday night to 6 AM MDT 
     Monday for NEZ020-021-054-055.

&&

$$

SHORT TERM...RE
LONG TERM...RUBIN
AVIATION...RUBIN
FIRE WEATHER...RE