429  
FXUS65 KGJT 172340  
AFDGJT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND JUNCTION CO  
540 PM MDT SUN OCT 17 2021  
   
SHORT TERM
 
(TONIGHT THROUGH MONDAY NIGHT)  
ISSUED AT 246 PM MDT SUN OCT 17 2021  
 
THE RIDGE ARCED ALONG THE ROCKIES ON THIS MORNING'S 12Z H500 HAND  
ANALYSIS MAP IS ALREADY BEING PUSHED EASTWARD BY THE ARRIVAL OF A  
LARGE TROUGH TO THE PACIFIC COAST. MODELS REMAIN CONSISTENT  
DROPPING A CLOSED LOW OUT OF THIS TROUGH INTO THE WESTERN GREAT  
BASIN BY THIS TIME TOMORROW. THE CIRA ALL LEVEL PWAT PRODUCT IS  
SHOWING TWO MAIN MOISTURE SOURCES WE WILL BE DEALING WITH OVER THE  
NEXT FEW DAYS. FIRST IS MOISTURE BEING PULLED NORTHWARD INTO THE  
DESERT SW BY THE LOWERING HEIGHTS TO THE WEST. 305-310K THETA  
SURFACES SHOW THIS MOISTURE ADVECTING NORTHWARD INTO OUR CWA  
OVERNIGHT MAINLY IN THE FORM OF HIGH CLOUDINESS. MODELS CONTINUE  
TO INDICATE THE FERTILE CRESCENT OF THE SAN JUANS SNAGGING SOME OF  
THIS MOISTURE AND PRODUCING SOME LIGHT PRECIPITATION. THIS  
SCENARIO IS NOT OUT OF THE QUESTION BUT REALLY THE SOUNDINGS ARE  
NOT FAVORABLE FOR EFFICIENT DENDRITIC GROWTH AND LOW LAYERS  
REMAIN DRY. THEREFOR KEPT PRECIPITATION OUT OF THE VALLEYS AND  
KEPT ANY SNOW ACCUMS OVER THE HIGHEST TERRAIN FROM THE NM BORDER  
ARCING BACK EAST TOWARD HIGHWAY 550. TOMORROW WILL BE BREEZIER AS  
THE SOUTHERLY GRADIENT TIGHTENS AHEAD OF THE SYSTEM MARCHING OUT  
OF NV INTO UT. THE SECOND SOURCE OF MOISTURE IS THE WEAK AR3 THAT  
IS IMPACTING THE PACNW COASTLINE ATTM. SOME OF THIS MOISTURE WILL  
BE ENTRAINED INTO THE COMPACT CYCLONE OVER THE GREAT BASIN AND  
USED FOR PRECIPITATION WITH MODERATELY STRONG DYNAMICS OVER THE  
CENTRAL ROCKIES MONDAY NIGHT THROUGH EARLY WEDNESDAY. MUCH OF THE  
DAY WILL BE DRY TOMORROW WITH MIXING HELPING TO PUSH TEMPERATURES  
ABOVE NORMAL AHEAD OF THE APPROACHING COLD FRONT. A RAIN/SNOW MIX  
WILL MOVE INTO THE NORTHEAST UTAH BY LATE AFTERNOON WITH THE COLD  
FRONT SWINGING THROUGH THE CWA OVERNIGHT. FORCING ALOFT AND ALONG  
THE COLD FRONT WILL BE MAXIMIZED FROM THE HIGH PLATEAUS TO THE  
WYOMING BORDER THROUGH SUNRISE ON TUESDAY AND WHEN THE BULK OF THE  
LOWER ELEVATION PRECIPITATION CAN BE EXPECTED. THIS SHOULD MAINLY  
BE IN THE FORM OF RAIN THROUGH THE LATE EVENING IN THE LOWER  
ELEVATIONS BEFORE MIXING AND CHANGING TO SNOW DURING THE EARLY  
MORNING HOURS...LIMITING ACCUMULATIONS BELOW MOUNTAIN BASES. THE  
BEST ACCUMULATIONS CONTINUE TO FAVOR THE CENTRAL AND NORTHERN  
MOUNTAINS ABOVE THE 9KFT MARK WITH 3-5 POSSIBLE OVER SOME RANGES  
BY SUNRISE TUESDAY. MORE SNOW COMES TO THE NORTHERN MOUNTAINS ON  
THE BACK SIDE OF THE SYSTEM FOR TUESDAY.  
   
LONG TERM
 
(TUESDAY THROUGH SUNDAY)  
ISSUED AT 246 PM MDT SUN OCT 17 2021  
 
WRAPAROUND MOISTURE SURROUNDING THE DEPARTING CLOSED LOW WILL  
ALLOW SNOW SHOWERS TO LINGER OVER THE NORTHERN MOUNTAINS LONGER  
THAN PREVIOUSLY THOUGHT, WITH ACTIVITY PERSISTING THROUGH TUESDAY  
EVENING. TEMPERATURES ARE STILL ANTICIPATED TO RUN WELL BELOW  
NORMAL AS THE COLDER AIRMASS SETTLES OVERHEAD WITH HIGHS TRENDING  
GENERALLY 6 TO 12 DEGREES ABOVE NORMAL FOR MUCH OF THE AREA.  
EXCEPTIONS WILL BE IN THE SOUTHERN VALLEYS WITH HIGHS CLOSER TO 4  
TO 8 DEGREES BELOW NORMAL AND THE HIGHER ELEVATIONS OF NORTHWEST  
COLORADO WHERE TUESDAY'S HIGHS LOOK TO END UP RUNNING CLOSE TO 20  
DEGREES BELOW NORMAL IN SPOTS! THE BELOW SEASONAL TREND WILL  
CONTINUE THROUGH THE OVERNIGHT PERIOD BUT, INTERESTINGLY ENOUGH,  
IT STILL DOES NOT LOOK LIKE WE'LL SEE A SEASON-ENDING FREEZE IN  
THE REMAINING LOWER VALLEYS IN WEST-CENTRAL COLORADO AND EASTERN  
UTAH IN THE WAKE OF THIS LOW.  
 
HIGH PRESSURE IS STILL ON TRACK TO SLIDE OVER THE REGION ON  
WEDNESDAY BEFORE REMAINING IN PLACE THROUGH THE END OF THE WORK  
WEEK. DURING THIS TIME, THE NEXT PACIFIC LOW WILL ELONGATE AND  
BREW OFF THE COAST OF THE NORTHWESTERN STATES. THIS WILL BE THE  
START OF A PROLONGED ATMOSPHERIC RIVER (AR) EVENT AS A SERIES OF  
SHORTWAVE TROUGHS WILL BE EJECTED OUT AHEAD OF THE MAIN SYSTEM  
EVERY FEW DAYS. UNFORTUNATELY, BOTH WEDNESDAY AND FRIDAY'S  
FEATURES WILL TRACK WELL TO OUR NORTH ACROSS THE INTERMOUNTAIN  
WEST, ALLOWING THE DRY AND NEAR SEASONABLE WEATHER TO CONTINUE.  
THE WEEKEND WILL SEE THE PARENT TROUGH BEGIN TO MOVE INLAND,  
ALLOWING THE LOWER HEIGHTS AND INCREASED MOISTURE TO ENCROACH UPON  
OUR FORECAST AREA AS UPPER LEVEL FLOW BEGINS TO SHIFT TO THE  
SOUTHWEST. SOME INFLUENCE FROM THE JET ALOFT ALSO LOOKS TO COME  
INTO PLAY LATE IN THE WEEKEND, AIDING IN THE POTENTIAL DEVELOPMENT  
OF SHOWERS OVER THE WESTERN COUNTIES. THIS IS MOST EVIDENT IN THE  
LATEST GFS SOLUTION WHICH BRINGS YET ANOTHER EJECTED SHORTWAVE  
DIRECTLY OVER OUR CWA ON SUNDAY, BUT THE OTHER MODELS AREN'T QUITE  
SOLD ON THAT YET. GIVEN THE PROLONGED POTENTIAL OF THE AR AND ITS  
INFLUENCE ON THE WESTERN CONUS, IT'S FAR TOO EARLY TO HONE IN ON  
SPECIFICS FOR IMPACTS ON THE WESTERN SLOPE.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)  
ISSUED AT 535 PM MDT SUN OCT 17 2021  
 
GRADUAL INCREASE IN HIGH CLOUD COVER WILL CONTINUE ACROSS EASTERN  
UTAH AND WESTERN COLORADO TONIGHT AND MONDAY WITH MID-LEVEL CLOUD  
DECKS ARRIVING BY MONDAY AFTERNOON. WINDS INCREASE OVERNIGHT AND  
BECOME GUSTY THROUGHOUT THE DAY ON MONDAY WITH SOUTHWEST  
COMPONENT FAVORED. VALLEY WIND GUSTS MAY EXCEED 30 KTS AT TIMES,  
WITH STRONG SPEEDS OVER THE MOUNTAINS.  
 

 
   
GJT WATCHES/WARNINGS/ADVISORIES
 
 
CO...NONE.  
UT...NONE.  
 

 
 

 
 
SHORT TERM...15  
LONG TERM...MMS  
AVIATION...JDC  
 
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