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Area Forecast Discussion (AFD)

Issued by Cheyenne, WY (CYS)

FXUS65 KCYS 181200

Area Forecast Discussion
National Weather Service Cheyenne WY
555 AM MDT Sun Aug 18 2019

.SHORT TERM...(Today and Monday) 
Issued at 253 AM MDT Sun Aug 18 2019

...Main weather threat for the short term are continued fire 
weather concerns today and Monday...

Frontal passage occurred earlier this evening bringing a shot of
moist and cooler air into southeastern Wyoming and western 
Nebraska. Observations this morning show fog, low ceilings, and 
northerly low level flow over much of the region. Further west, a 
much drier air mass remains in place. The cooler airmass will be 
short lived as dry westerly winds will push the front back east 
later this afternoon and evening. Fog and ceilings will lift 
quickly this morning with the drier air starting the push east by
14z. Temperatures will warm quickly into the upper 80s and low 
90s. Gradients aloft are slightly weaker than yesterday with 
height rises expected as a shortwave ridge builds in. Despite the 
weakening, 35 kts of H5 flow should be more than sufficient to 
promote deep mixing and surface momentum transfer. Winds will 
increase with daytime heating to between 15 and 25 mph. Gusts of 
35 mph will be likely through 7 pm this evening. This will bring
favorable fire weather conditions to much of the area. Sea latest
Red Flag Warnings for more info. 

Tonight, lows will be a few degrees warmer than the past several 
days as the ridge becomes full established aloft. Mostly clear to 
partly cloudy skies are expected. Winds will gradually back to 
south by southwest as mixing subsides. Mostly dry weather is 
expected with little chance for rain. 

Monday will be similar to Today, with warm temperatures and dry
west winds through much of the afternoon. Shortwave ridging aloft
will continue with 700 mb temperatures increasing to about 20c. Fire
Weather will again be a concern through this timeframe, as will 
very warm temperatures. Daytime highs are expected to peak in the 
mid 90s to 100 for much of the eastern plains. An isolated thunder
storm is possible for far western Nebraska late Monday but 
confidence is low. 

Monday evening, a shortwave trough embedded in the flow aloft 
will start to flatten the shortwave ridge. Low level flow will 
gradually veer to west north westerly and eventually northerly as 
surface pressure falls increase. A cold front is expected to pass 
through sometime late Monday night and Tuesday morning. Model 
timing on the front has been inconsistent, showing periodic slow 
downs uncharacteristic of past events. Expect the front late 
Monday night and early Tuesday, with a transition to cooler 
temperatures and the arrival of a much more humid airmass. 

.LONG TERM...(Tuesday through Saturday) 
Issued at 253 AM MDT Sun Aug 18 2019

Tuesday will be markedly different from the pasts several days 
with a much cooler and more humid airmass in place. Scattered 
showers and thunderstorms are expected as the shortwave trough and
front move through. A few strong to severe storms will also be 
possible, owing to the enhanced lift and shear from the shortwave
trough. Hail and damaging winds will be the main threats. 

Showers and thunderstorms will continue Wednesday and Thursday as
upper level flow weakens allowing deeper moisture to push west. A
more significant upper level trough is expected to move on shore 
Thursday and Friday bringing even greater chances of 
precipitation to the area. CPC outlooks over the next week show a
period of near to slightly above average temps with above average
precipitation expected. This matches well with the model 
consensus through day 8. Beyond, models lose consensus but show a
general trend of increasing zonal flow aloft. This would favor 
average to slightly above average chances for precipitation 
through next weekend. 


.AVIATION...(For the 12Z TAFS through Sunday night)
Issued at 555 AM MDT Sun Aug 18 2019

Widespread MVFR CIGS between 1k and 2k feet AGL will continue early 
this morning, with IFR CIGS around 500 feet at KCYS. Fog seems to 
have dissipated this morning, so removed fog from the TAF. These 
lower CIGS will lift by 15z, with dry conditions expected through 
this evening. It will be windy across the southeast Wyoming 
terminals today, with gusts up to 35 knots mainly at KLAR and KRWL.


Issued at 253 AM MDT Sun Aug 18 2019

Critical fire weather conditions will continue across 
southeastern Wyoming as a ridge of high pressure builds aloft. 
Continued westerly winds will bring dry air to the surface along 
with strong gusts. This will continue to cure fuels and provide 
Red Flag conditions today and through Monday. A cold front will 
move south and west on Tuesday bringing cooler air and more humid 


WY...Red Flag Warning from noon today to 8 PM MDT this evening for 

     Red Flag Warning from noon to 8 PM MDT Monday for WYZ303-304.

     Fire Weather Watch from Monday afternoon through Monday evening 
     for WYZ310.