999  
FXUS65 KCYS 181148  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
548 AM MDT SAT AUG 18 2018  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 427 AM MDT SAT AUG 18 2018  
 
MAIN FOCUS NEXT 24-36 HOURS WILL BE ON THE SCATTERED TO NUMEROUS  
SHOWERS AND THUNDERSTORMS EXPECTED THROUGH THIS PERIOD WITH A  
WINDOW OF STRONG TO MARGINALLY SEVERE STORMS FROM 12PM TO 10PM  
TODAY. THE STRONG TO SEVERE STORM RISK AREA WILL BE ACROSS FAR  
EAST WYOMING AND MORESO INTO THE NEBRASKA PANHANDLE THIS  
AFTERNOON AND EARLY EVENING. PENNY TO QUARTER-SIZED HAIL, 40-60  
MPH WINDS, AND LOCALIZED HEAVY RAINFALL LEADING TO ISOLATED FLASH  
FLOODING CONCERNS COULD BE POSSIBLE, ESPECIALLY FOR THE NE  
PANHANDLE.  
 
A POTENT SHORTWAVE TROUGH IS CURRENTLY PIVOTING ACROSS ID INTO  
WESTERN WY WITH NOTED UPPER-LEVEL DIVERGENCE PER WATER VAPOR  
IMAGERY CHANNELS. THE DIVERGENCE ALOFT PLUS WEAK ISENTROPIC  
UPGLIDE IN WEAKLY UNSTABLE MID-LEVELS IS GENERATING SHOWER AND  
EMBEDDED THUNDERSTORM ACTIVITY ACROSS NORTH COLORADO AND INTO  
SOUTH-CENTRAL WY THIS MORNING. THE SHOWERS AND EMBEDDED  
THUNDERSTORMS ARE EXPECTED TO SPREAD NORTH AND EAST THROUGH THE  
DAY ACROSS MOST OF THE REGION. THE SPEED OF THE SHORTWAVE IMPULSE  
THIS MORNING MIGHT INHIBIT THE POTENTIAL FOR MORE WIDESPREAD  
THUNDERSTORMS THIS AFTERNOON IN WY AS A FRONT MOVES IN FROM WEST  
TO EAST. THE PROGRESSION OF THIS FRONT WILL BE KEY AS TO WHERE THE  
BEST LOW-LEVEL FORCING WILL BE FOR STRONGER THUNDERSTORM  
POTENTIAL THIS AFTERNOON. GROWING SURFACE INSTABILITY WILL OCCUR  
ALONG AND AHEAD OF THE FRONT THIS AFTERNOON WHERE DEEPER MOISTURE  
WILL RESIDE ACROSS THE HIGH PLAINS, AND MORESO INTO THE  
PANHANDLE/CENTRAL NE AND NORTHEAST COLORADO. NEAR UNIDIRECTIONAL  
FLOW DEEP-LAYER SHEAR WILL INCREASE TO NEAR 35 KNOTS ACROSS  
EASTERN ZONES OF WY AND THE NE PANHANDLE AND FAVOR A MORE LINEAR  
CONVECTIVE EVOLUTION. WITH PWATS NEAR 1.2-1.3", A FEW AREAS OF  
HEAVY RAIN COULD OCCUR FOR THE NE PANHANDLE. THE STRONG STORM AND  
HEAVY RAINFALL RISK WILL DIMINISH THROUGH THE LATE EVENING HOURS  
AS THE AXIS OF SHOWERS/STORMS SHIFTS INTO CENTRAL NE.  
   
LONG TERM
 
(SUNDAY THROUGH FRIDAY)  
ISSUED AT 427 AM MDT SAT AUG 18 2018  
 
NO MAJOR HIGHLIGHTS IN THE LONG TERM OUTSIDE OF BELOW NORMAL  
TEMPERATURES EXPECTED MONDAY MORNING WITH A FEW FREEZING  
TEMPERATURES POSSIBLE IN THE HIGHER TERRAIN LOCATIONS. A WARMING  
TREND IS EXPECTED FOR MID- TO LATE-WEEK.  
 
THE PARENT SHORTWAVE TROUGH WILL LINGER OVER EASTERN WYOMING  
THROUGH SUNDAY MORNING AND SHOWERS WITH EMBEDDED LIGHTNING WILL  
PERSIST ACROSS PORTIONS OF THE REGION. OVERALL RAINFALL RATES  
WILL REMAIN LOW AS TO NOT CAUSE FLASH FLOODING DURING THIS TIME  
FRAME BUT MUCH COOLER TEMPERATURES WILL ARRIVE BEHIND THE FRONT AS  
THE CLOSED H5 LOW SHIFTS TO THE EAST. TEMPERATURES SUNDAY WILL  
ONLY BE IN THE 60S TO LOW 70S. MONDAY MORNING WILL BE THE COOLEST  
MORNING SINCE APRIL AS SOME HIGH MOUNTAIN LOCATIONS WILL LIKELY  
DROP BELOW FREEZING.  
 
AFTER A PLEASANT MONDAY WITH TEMPERATURES SLOWLY REBOUNDING WITH  
AMPLE SUN, SLIGHT RAIN CHANCES WILL RETURN ON TUESDAY INTO EARLY  
WEDNESDAY WITH THE PASSAGE OF ANOTHER WEAK SHORTWAVE TROUGH.  
 
LONGWAVE RIDGING LOOKS TO TAKE FORM OVER THE INTERMOUNTAIN WEST  
MID-WEEK AND A GRADUAL WARM-UP IS EXPECTED WITH DRIER CONDITIONS.  
PERHAPS THE NEXT BEST CHANCE OF RAIN WILL THEN BE LATE IN THE  
WEEK WITH A POSSIBLE BRISK MOVING TROUGH AXIS ACROSS MONTANA AND  
NORTHERN WY BUT WITH THE REGION STAYING ON THE WARM SOUTHWEST FLOW  
SIDE OF THE MID-LEVEL PATTERN.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)  
ISSUED AT 548 AM MDT SAT AUG 18 2018  
 
SHOWERS AND SCATTERED THUNDERSTORMS WILL MOVE WEST TO EAST ACROSS  
THE REGION TODAY AS A SHORTWAVE PASSES THROUGH. FIRST BATCH OF  
MOSTLY SHOWERS WILL PASS THROUGH RAWLINS 12Z-16Z, WITH HRRR  
SHOWING SHOWERS WITH SCATTERED THUNDERSTORMS IN THE AFTERNOON AND  
EVENINGS. CIGS AND VSBY WE KEPT MVFR AND HIGHER.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 447 AM MDT SAT AUG 18 2018  
 
LIMITED FIRE WEATHER CONCERNS FOR THE WEEKEND AS COOLER TEMPERATURES  
AND HIGHER HUMIDITY VALUES OCCUR OVER MOST OF THE REGION. SCATTERED  
TO NUMEROUS SHOWERS AND A FEW THUNDERSTORMS ARE EXPECTED THIS  
AFTERNOON WITH CHANCES OF WETTING RAIN RANGING FROM 30 TO UPWARDS  
OF 70 PERCENT FOR SOUTHEAST WYOMING AND INTO NEBRASKA OVER THE NEXT  
24-36 HOURS.  
 
RAIN SHOWERS WILL DECREASE THROUGH THE DAY SUNDAY FROM WEST TO EAST  
BUT WINDS WILL INCREASE SUBSTANTIALLY ACROSS THE HIGHER TERRAIN  
SUNDAY MORNING WITH GUSTS UPWARDS OF 30 MPH.  
 
LOWER RELATIVE HUMIDITY VALUES WILL BE IN PLACE BY MONDAY AND  
WINDS REMAIN NEAR 20 TO 25 MPH FOR THE HIGHER TERRAIN. THESE  
CONDITIONS COULD EQUATE TO ELEVATED FIRE WEATHER CONDITIONS  
MONDAY AFTERNOON.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...NONE.  
NE...NONE.  

 
 

 
 
SHORT TERM...JSA  
LONG TERM...JSA  
AVIATION...JG  
FIRE WEATHER...JSA  
 
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