880 
FXUS65 KCYS 081148
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
445 AM MST Wed Mar 8 2023

.SHORT TERM...(Today through Friday)
Issued at 244 AM MST Wed Mar 8 2023

Today...Conditions still have been unfavorable for our current 
Winter Weather Advisory for freezing drizzle and dense fog from the 
Southern Laramie Range through Laramie County looking at webcams and 
surface observations. However, we will closely monitor the situation 
and if freezing drizzle and dense fog have not materialized by 5 to 
6 AM, we will cancel the advisory early. 

Maximum temperatures still remain below normal with 700 mb 
temperatures near -5 Celsius and low level upslope east to 
southeast winds along with cloud cover. The models are likely 
underdoing areal coverage of snow due to too limited low and mid 
level moisture coverage, thus will continue with 30 to 60 percent 
POPS for much of our forecast area. Light snow will increase in 
coverage, especially along and east of I-25, as the low level 
southeast upslope lift is enhanced by the approach of the next 
shortwave trough aloft from western Colorado.

Tonight/Thursday...A fairly potent and progressive shortwave 
trough aloft moves overhead tonight and early Thursday 
producing decent 300-500 mb and 500-700 mb quasigeostrophic lift of 
the moist low and mid levels, and producing widespread light to 
moderate snow, with the areal coverage greatest north of a Douglas 
to Torrington to Alliance line. The snow looks to quickly end from 
west to east Thursday morning and early afternoon in the wake of the 
shortwave trough aloft and with fairly decent subsidence. Projected 
snowfall totals suggest a borderline situation for Winter Weather 
Advisories for snowfall for Niobrara County, as well as northern 
Sioux and Dawes Counties of the northern Nebraska panhandle, where 
2 to 4 inches of snow may fall. For now, we have opted to keep an 
eye on the future development and let our day shift forecasters take 
another look before issuing a Winter Weather Advisory.

In the wake of the passing cold front, decent surface and low level 
gradients suggest a blustery and cold northwest wind of 25 to 35 mph 
gusting to 50 mph Thursday afternoon along and east of Interstate 
25 and south of a Douglas to Alliance line. Maximum temperatures 
will still remain cold with 700 mb temperatures near -10 Celsius, 
yielding high temperatures mostly in the 30s to lower 40s.

Thursday night/Friday...A decent warming trend is anticipated for 
Friday as 500 mb heights aloft rise some 60 meters on zonal flow, 
with a surface lee trough developing Friday afternoon. With 700 mb 
temperatures reaching near 3 Celsius, maximum temperatures will 
reach the 40s to lower 50s. With the models projecting increasing 
low and mid level moisture, orographic snow showers will spread 
eastward across and near our Snowy and Sierra Madre Ranges. 

We will issue a High Wind Watch for the North Snowy Range Foothills 
including Arlington and Elk Mountain from 6 AM Friday to 6 AM 
Saturday as the models are projecting 50 to 60 knot winds at 
700 mb, along with our local guidance random forecast and 
700 mb Craig to Casper height gradients near 70 meters suggesting 
winds exceeding high wind criteria.

.LONG TERM...(Friday night through Tuesday)
Issued at 244 AM MST Wed Mar 8 2023

Medium to long range models in decent agreement and show quasi- 
zonal flow for most of the weekend. A general warming trend is 
expected with a brief cool down late Saturday through Sunday 
night. In fact, some of the mildest temperatures we've seen in a 
while are possible for Tuesday of next week. 

Models indicate another Pacific upper level trough pushing
onshore Thursday and Friday, but this time ejecting east 
northeast across Idaho and Montana. This solution is reasonable 
given the current pattern with a strong jet stream along the
central Rocky Mountain Region and the northern Great Plains. Any
push of cold arctic air seems to be displaced into the eastern
Pacific and eastern Gulf of Alaska on the eastern edge of the 
strong Omega Block currently south of Alaska. As this upper level
trough ejects northeast, mainly strong gusty winds are expected
across the eastern plains with any precipitation mainly confined
to areas west of the I-25 corridor, especially the mountains.
Sierra Madre Range and Snowy Range may do very well with this next
shot of moderate to heavy snowfall...with 10 to 18 inches
possible. Much lower amounts expected in the valleys with even a
chance at rain/snow mix down to 6500 feet before the cold front
moves across the area. Winds will be the primary concern for most
of the lower elevations with gusts over 55 MPH possible Friday
night through Saturday night. Models in agreement with 700mb 
winds of 50 to 60 knots through the potential event along with 
strong subsidence and favorable near-surface pressure tendencies 
over the Continental Divide (increasing) in contrast to areas 
further east across the central plains (slightly decreasing). So
far, this looks like mostly an event for southeast Wyoming with
western Nebraska missing out on the strongest winds as the peak
winds aloft don't move over that area until late at night and the
best surface pressure gradient remains west and north of western
Nebraska. Increased winds slightly over the previous forecast and
trended wind forecast towards the 90th percentile for the wind
prone areas. Otherwise, there is a small chance at some
thunderstorm activity across western Nebraska Saturday afternoon
before FROPA. Models, including the NAM and GFS, are showing LI
below -2 with a marginally unstable BL. Models show bands of 
convection developing near the jet axis ahead of the cold front. 
Increased prob thunder to around 10 percent, but did not add it 
into the forecast quite yet.

A few cooler days expected Sunday and Monday with highs near or
slightly below normal. However, daytime temperatures in the 30s 
and 40s are much better than what we were experiencing a month
ago. Models then show an upper level ridge axis amplifying
northward on Tuesday with 700mb temperatures climbing to +2c to 
+6c. For mid March, this translates to 50s to even middle 60s for
high temperatures for most areas...with 40s to near 50 for the 
areas with lingering snowpack. So maybe a little taste of spring 
on Tuesday before the next Pacific storm approaches the area for 
the middle of next week.

&&

.AVIATION...(For the 12Z TAFS through early Thursday morning)
Issued at 445 AM MST Wed Mar 8 2023

A strong jet stream will remain over the region today as a Pacific 
storm system approaches from the west later today. Weather 
conditions today will not change much compared to 24 hours ago with 
persistent IFR conditions, especially at night, and occasional light 
snow and fog/freezing drizzle across the eastern plains. 

HAZARDS/WEATHER TRENDS: Most of the region will remain in IFR or 
near IFR (low-end MVFR conditions) this morning including KLAR. KRWL 
will be the only terminal in VFR until widespread snow develops this 
evening. Western Nebraska terminals and KCYS will remain in IFR 
conditions with occasional freezing drizzle and fog at KCYS, and 
possibly extending eastward to KSNY this morning. A 6 hour window of 
improving CIGS and MVFR conditions is still expected from 16z today 
to 02z Thursday due to some surface heating. Otherwise, most 
terminals will drop to IFR conditions once again after 02z this 
evening...with light snow and low VIS possible at KRWL, KCDR, and 
possibly KBFF and KAIA.  

&&

.FIRE WEATHER...
Issued at 244 AM MST Wed Mar 8 2023

No fire weather concerns are expected for the next week due to a 
cold, unsettled weather pattern with accumulating snow. Winds are 
expected to increase across southeastern Wyoming on Thursday and 
remain strong through Sunday. Temperatures warm Friday and Saturday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...

WY...High Wind Watch from Friday morning through late Friday night 
     for WYZ110.

     Winter Weather Advisory until 10 AM MST this morning for 
     WYZ116>119.

NE...None.
&&

$$

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