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Area Forecast Discussion (AFD)

Issued by Cheyenne, WY (CYS)

FXUS65 KCYS 192127

Area Forecast Discussion
National Weather Service Cheyenne WY
327 PM MDT Thu Sep 19 2019

.SHORT TERM...(This evening through Friday)
Issued at 319 PM MDT Thu Sep 19 2019

Water Vapor imagery showed a large west coast storm system moving
across the great basin and intermountain west. Visible imagery 
showed scattered cumulus towers developing along the laramie range
and areas of higher terrain across the western portions of 
southeastern Wyoming. Surface obs showed a plume of low level 
moisture sitting across the panhandle and far eastern Wyoming 
with a cold front associated with the upper level impulse slowly 
moving through far western Wyoming. These observations and short 
term guidance suggest that isolated to widely scattered showers 
and thunderstorms will develop across southeastern Wyoming over 
the next few hours. HRRR forecasts continue to show a small 
cluster of mainly elevated storms in proximity to the laramie 
range with another more robust cluster across the southern 
nebraska panhandle into northern Colorado. Some high rise guidance
keeps shower activity around with the cold front as it moves 
through later this evening and overnight. 

Temperatures should see a strong response to the front with highs
on Friday 10 to 15 degrees cooler than today. More widespread 
shower and thunderstorm activity is expected Friday afternoon and
evening as the main upper level storm system moves overhead. 
There will also be potential for severe weather mainly across the 
Nebraska panhandle Friday afternoon and overnight with better 
lift from the upper level system. Regional model soundings show 
moderate instability with unseasonably high moisture across the 
panhandle. Deep layer shear is supportive of organized convection
including supercells. The primary threats with any sustained 
storms would be hail and strong winds. Models do show eventual 
upscale growth across the panhandle overnight Friday. 

Friday night into Saturday morning, the focus shifts to much 
cooler temperatures and the possibility of the first freeze of the
year. Model guidance has continued to show the possibility for 
freeze and borderline hard freeze conditions in some of the 
western valleys of Carbon county. Overnight lows of 30 appear 
common and given recent over estimation trends, lows in the high 
20s for a few hours seem possible for well sheltered locations 
Saturday morning. A Freeze Watch has been put in place for the far
western valleys from Friday night through Saturday morning. 

.LONG TERM...(Saturday night through Thursday) 
Issued at 204 PM MDT Thu Sep 19 2019

Medium and long range guidance has continued to show an active
upper level storm track developing this weekend and continuing 
through next week. A second pacific trough behind this weekends 
system is progged to dive across the CONUS with differing 
solutions on the GFS and the EURO. The GFS shunts a shortwave 
trough the central and southern CONUS early next week while the
EURO cutoff the same system over the 4 corners. While radically 
different, both models keep the northern stream of the mid level 
jet across Wyoming with the potential for some episodes of high 
winds and an occasional shower. The majority of the forecast 
appears to be dry but will likely remain active with weather 
hazards mainly strong winds as more pacific troughs develop later
next week and into the upcoming weekend. Temperatures will likely
remain above average through the period before another stronger 
cold front develops and moves through late next weekend. 


.AVIATION...(For the 18Z TAFS through Friday morning)
Issued at 1125 AM MDT Thu Sep 19 2019

VFR conditions expected today and tonight across the area. There is 
a 10 to 20 percent chance for showers and a few thunderstorms late 
this afternoon and through this evening, but will keep VCTS or VCSH 
out of the TAFs due to limited coverage.  Gusty west to southwest 
winds are expected this afternoon for mainly KRWL and KLAR with 
gusts up to 35 knots possible.  Further east, a strong low level jet 
will develop ahead of a Pacific storm system which will impact the 
region on Friday. Gusty south winds are forecast for KCDR, KAIA, and 
possibly KSNY after sunset with gusts as high as 35 knots possible 
at times mainly between 03z to 10z Friday. 


Issued at 319 PM MDT Thu Sep 19 2019

Gusty winds and low humidity have developed across far western 
portions of zone 304. A cold front will move through later today 
and early Friday bringing cooler conditions and better humidity 
recoveries. This should limit the fire weather threat to the next 
few hours before rain chances and colder temperatures arrive this 


WY...Freeze Watch from late Friday night through Saturday morning for 

     Red Flag Warning until 8 PM MDT this evening for WYZ304.