427  
FXUS65 KCYS 231134  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
534 AM MDT MON SEP 23 2019  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 338 AM MDT MON SEP 23 2019  
 
MAIN HIGHLIGHT TODAY WILL THE NEAR-CRITICAL TO BRIEFLY CRITICAL  
FIRE WEATHER HAZARD AND THE ABOVE NORMAL TEMPERATURES OF 5-9F  
DEGREES.  
 
SHORTWAVE H5 RIDGING IS OCCURRING FROM SOUTH-CENTRAL CANADA  
SOUTHWARD ALONG THE ROCKIES AND FRONT RANGE THIS MORNING PER WATER  
VAPOR AND RAP ANALYSIS. A NOTABLE SHORTWAVE TROUGH IS POSITIONED  
ACROSS OR TO NV FARTHER WEST BUT WILL BE SHIFTING SOUTHEAST TO CA  
AND AZ WITH MINIMAL IMPACTS TO WY/NE. THE SHORTWAVE RIDGING AND  
RESULTANT SUBSIDENCE WILL AID DRY WEST WINDS AND ABOVE NORMAL  
TEMPERATURES TODAY WITH LOTS OF SUN. AFTERNOON RELATIVE HUMIDITY  
WILL FALL INTO THE 10-15 PERCENT RANGE ACROSS MUCH OF SOUTHEAST WY  
AND WITH WIND GUSTS REACHING NEAR 25 MPH AT TIMES, NEAR-CRITICAL  
TO BRIEFLY CRITICAL FIRE WEATHER CONDITIONS WILL OCCUR. SEE FIRE  
WEATHER DISCUSSION BELOW FOR MORE DETAILS. OUTSIDE OF THE ELEVATED  
FIRE WEATHER HAZARD, IT WILL BE A WARM AND PLEASANT DAY ACROSS  
THE REGION WITH ABOVE NORMAL TEMPERATURES. A QUICK MOVING  
SHORTWAVE TROUGH WILL PASS OVER WY LATE TONIGHT INTO TUESDAY WITH  
NO SENSIBLE WEATHER IMPACTS GIVEN THE DRY AIR IN PLACE OTHER THEN  
A FEW MORE MID- AND HIGH-LEVEL CLOUDS.  
   
LONG TERM
 
(TUESDAY THROUGH SUNDAY)  
ISSUED AT 338 AM MDT MON SEP 23 2019  
 
CONTINUED WARM TUESDAY WITH A QUICK COOL OFF WEDNESDAY FOLLOWED BY  
A WARMUP THURSDAY AND THEN A MUCH MORE ACTIVE PATTERN FOR THE LATE  
WEEK AND WEEKEND INTO NEXT WEEK. PRECIPITATION CHANCES WILL BE LOW  
UNTIL LATE THURSDAY INTO FRIDAY AND STAY ELEVATED THROUGH THE  
UPCOMING WEEKEND AND EARLY NEXT WEEK. SOME WINTRY PRECIPITATION  
COULD BE POSSIBLE LATE WEEKEND INTO EARLY NEXT WEEK FOR PORTIONS  
OF THE HIGH TERRAIN IN SE WY.  
 
A QUICK MOVING FRONT WILL BRUSH FAR NE WY AND THE NORTH NEBRASKA  
PANHANDLE TUESDAY FOR A SLIGHT COOL OFF BUT MOST OF THE REGION  
WILL SEE SIMILAR TEMPERATURES TOMORROW AS THEY DID TODAY WITH  
READINGS PERHAPS 1-3F DEGREES COOLER. A BROAD, LOW-AMPLITUDE  
LONGWAVE TROUGH WILL TAKE SHAPE OVER THE NORTHERN CONUS LATE  
TUESDAY INTO WEDNESDAY AND WILL AID IN ANOTHER COLD FRONT PASSING  
THROUGH WEDNESDAY THAT WILL DROP TEMPERATURES 10F DEGREES OR SO  
TO MORE NORMAL VALUES FOR THIS TIME OF YEAR. HOWEVER, WAA WILL  
LIKELY OCCUR THURSDAY WITH ABOVE NORMAL READINGS AGAIN. ALL THE  
WHILE, PRECIPITATION CHANCES WILL REMAIN LOW DUE TO THE LACK OF  
A DEEPER VERTICAL LIFT MECHANISM.  
 
THE VERTICAL LIFT DYNAMICS WILL CHANGE BY LATE THURSDAY, LATE  
WEEK, AND WEEKEND AS A STRONGER FRONT AND GREATER DIVERGENCE  
ALOFT IS ADVERTISED PER GFS/ECMWF. PRECIPITATION SHOULD PRIMARILY  
BE RAIN THROUGH THIS PERIOD UNTIL LATE WEEKEND WHEN A GREATER  
AMPLIFIED STRONGER WESTERN CONUS TROUGH DEVELOPS OVER THE PACIFIC  
NW AND SHIFTS TOWARDS THE INTER-MOUNTAIN WEST. WILL NEED TO KEEP  
CLOSE WATCH ON SURFACE BOUNDARY TIMING VS. DEEPER LIFT TIMING FOR  
HIGH PLAINS RAIN/STORMS AND HIGH TERRAIN SNOW SHOWERS A WEEK FROM  
NOW. IT IS TOO FAR OUT TO SPECULATE ON IMPACTS OR SNOW AMOUNTS BUT  
MULTI-MODEL GUIDANCE DOES SUGGEST WINTRY PRECIPITATION BEING  
POSSIBLE IN THE MOUNTAINS.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)  
ISSUED AT 531 AM MDT MON SEP 23 2019  
 
VFR CONDITIONS ACROSS ALL TERMINALS UNDER FEW TO SCT HIGH  
AFTERNOON CEILINGS. WIND GUSTS FROM THE WEST TO 25 KTS ALONG AND  
WEST OF THE LARAMIE RANGE BEGINNING AS EARLY AS 23/17Z,  
DIMINISHING BY 24/02Z. OTHERWISE, WEST WINDS AROUND 10 KTS OR  
LESS, BECOMING SOUTHERLY ACROSS THE PANHANDLE TERMINALS BY 23/23Z.  
WINDS TURN WESTERLY ONCE AGAIN AROUND 24/06Z AHEAD OF A DRY NORTH  
TO SOUTH MOVING FRONT.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 338 AM MDT MON SEP 23 2019  
 
NEAR-CRITICAL TO BRIEFLY CRITICAL FIRE WEATHER CONDITIONS ANTICIPATED  
THIS AFTERNOON TO EARLY EVENING AND AGAIN TUESDAY. RELATIVE HUMIDITY  
VALUES WILL FALL TO 10 TO 15 PERCENT WITH WIND GUSTS 18 TO 23 MPH AND  
OCCASIONAL GUSTS TO 25 MPH POSSIBLE ACROSS THE HIGH TERRAIN AND HIGH  
PLAINS OF WYOMING TODAY. MOST LIKELY ZONES OF GREATEST CHANCE FOR A RED  
FLAG WARNING WOULD BE ZONES 302-303. SPATIAL COVERAGE OF MARGINAL WINDS  
WILL PRECLUDE THE ISSUANCE OF A RED FLAG WARNING AT THIS TIME BUT THIS  
WILL BE MONITORED CLOSELY THROUGH THE DAY. TUESDAY WILL HAVE HIGHER  
WINDS BUT SLIGHTLY HIGHER HUMIDITY. WEDNESDAY WILL BE COOLER WITH  
GREATER MOISTURE.  
 

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

 
 

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