418  
FXUS65 KCYS 181200  
AFDCYS  
 
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.  
 

 
   
FIRE WEATHER
 
 
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  
CONDITIONS.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...RED FLAG WARNING FROM NOON TODAY TO 8 PM MDT THIS EVENING FOR  
WYZ303-304-310.  
 
RED FLAG WARNING FROM NOON TO 8 PM MDT MONDAY FOR WYZ303-304.  
 
FIRE WEATHER WATCH FROM MONDAY AFTERNOON THROUGH MONDAY EVENING  
FOR WYZ310.  
 
NE...NONE.  

 
 

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