797  
FXUS65 KGJT 201749  
AFDGJT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND JUNCTION CO  
1149 AM MDT FRI JUL 20 2018  
   
SHORT TERM
 
(TODAY THROUGH SATURDAY)  
ISSUED AT 253 AM MDT FRI JUL 20 2018  
 
THE FICKLE NATURE OF THIS YEAR'S MANIFESTATION OF THE NORTH  
AMERICAN MONSOON SEASON WILL CONTINUE INTO THIS WEEKEND. AS THE  
MONSOON HAS AFFECTED THE AREA FOR THE LAST TWO WEEKS OR SO, THE  
OPTIMAL FLOW OF MOISTURE HAS MOSTLY ELUDED THE FORECAST AREA.  
ANOTHER EXAMPLE WILL OCCUR INTO THIS WEEKEND. ON FRIDAY AND  
SATURDAY ANOTHER SURGE, MORE LIKE A SPURT, IN THE MONSOON FLOW  
WILL AFFECT THE AREA, WITH THE MAIN FOCUS BEING OVER SOUTHWEST CO  
AND SOUTHEAST UT FRIDAY. HIGH PRESSURE BECOMES CENTERED OVER TX  
WHICH WILL HELP STEER THE MONSOONAL PLUME OVER THE AREA BUT THE  
MOISTURE AND PRECIPITATION PATTERN DON'T APPEAR ALL THAT ORGANIZED.  
A WEAK SHORTWAVE TROUGH WILL RIDE AROUND THE WEST AND NORTHWEST  
PERIPHERY OF THE HIGH FRIDAY BUT DOESN'T SEEM TO PROVIDE MUCH OF A  
FOCUS FOR CONVECTION IN ANY OF THE SHORTER RANGE MODELS. ON  
SATURDAY THE PLUME SEEMS TO RIDE FURTHER NORTH OVER EASTERN UT  
BEFORE TURNING EAST OF CENTRAL AND NORTHWEST CO. THIS PLACES THE  
MAIN PLUME AXIS NORTH OF THE SAN JUAN MOUNTAINS AND SOUTHWEST  
COLORADO. THE MODELS SUGGESTION SHOWERS AND THUNDERSTORMS  
DEVELOPING INITIALLY OVER THE MOUNTAINS, INCLUDING THE SAN JUANS  
THEN THE FOCUS OF THE BEST ACTIVITY SHIFTS NORTH LATE SATURDAY  
AFTERNOON AND INTO THE EVENING.  
   
LONG TERM
 
(SATURDAY NIGHT THROUGH THURSDAY)  
ISSUED AT 253 AM MDT FRI JUL 20 2018  
 
RIDGE OF HIGH PRESSURE WILL REMAIN TO THE EAST OF THE AREA WITH A  
SLIGHTLY MORE DIRECT SOUTHERLY TAP OF MONSOONAL MOISTURE THROUGH  
MONDAY. EMBEDDED SHORTWAVE DISTURBANCES WILL ROTATE AROUND THE  
PERIPHERY OF THE HIGH PRESSURE SATURDAY NIGHT THROUGH MONDAY,  
ALLOWING FOR BETTER COVERAGE OF SHOWERS AND THUNDERSTORMS  
IMPACTING MOUNTAINS DURING THE AFTERNOON AND SPREADING INTO  
VALLEYS LATE AFTERNOON AND EVENING. PRECIPITABLE WATER (PW) VALUES  
WILL REMAIN ABOVE AN INCH FOR MOST AREAS, WHICH MEANS BETTER  
CHANCES FOR HEAVY RAIN TO OCCUR WITH THE STORMS. WHEN EMBEDDED  
SHORTWAVES MOVE THROUGH THE FLOW AND INTERACT WITH THE MOISTURE IN  
PLACE, THIS TYPICALLY MEANS THAT THE POTENTIAL FOR NOCTURNAL  
STORMS INCREASES. DAYTIME TEMPERATURES WILL STILL BE WARM, BUT  
SLIGHTLY COOLER WITH THE INCREASED CLOUD COVER AND SHOWER/STORM  
ACTIVITY, WITH NIGHTTIME LOWS REMAINING FAIRLY WARM.  
 
TUESDAY THROUGH THURSDAY APPEARS TO BE A WILD CARD OF SORTS IN  
TERMS OF HOW MUCH MOISTURE IS GOING TO HANG AROUND. DURING THIS  
PERIOD, THE HIGH PRESSURE WILL BE SHIFTING BACK WESTWARD, BRINGING  
MORE OF A WESTERLY TO NORTHWESTERLY FLOW ACROSS OUR AREA. THIS  
PATTERN WILL SLOWLY ADVECT DRIER AIR IN FROM THE NORTHWEST AS PW  
VALUES LOWER EACH DAY. HOWEVER, IT APPEARS THAT ENOUGH MOISTURE  
HANGS AROUND WITH PW VALUES ABOVE 0.75 INCHES FOR STORMS TO FORM  
EACH AFTERNOON, STARTING FIRST OVER THE HIGHER TERRAIN AND THEN  
DRIFTING INTO SOME VALLEYS BY LATE AFTERNOON/EARLY EVENING.  
EXPECTING STORMS TO FAVOR THE AFTERNOON AND EVENING PERIODS WITH  
TEMPERATURES ALSO REBOUNDING TOWARDS VERY WARM TO HOT BY MID TO  
LATE WEEK. MODELS ARE INDICATING SOME SHORTWAVES ROTATING AROUND  
THE PERIPHERY OF THE HIGH AND DOWN THROUGH THE NORTHERN ROCKIES  
AND FRONT RANGE BUT TIMING THESE WAVES IS A BIT PROBLEMATIC.  
REGARDLESS OF THE TIMING, ENOUGH MOISTURE HANGS AROUND WITH  
OCCASIONAL DISTURBANCES TO HELP KEEP THE POTENTIAL FOR STORMS IN  
THE FORECAST EACH DAY THROUGH THE WEEK, WITH LESS COVERAGE THAN IS  
EXPECTED THIS WEEKEND THROUGH MONDAY.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)  
ISSUED AT 1140 AM MDT FRI JUL 20 2018  
 
CLOUDS WILL BE INCREASING ACROSS SOUTHWESTERN COLORADO AND  
SOUTHEASTERN UTAH THIS AFTERNOON AS MOISTURE STREAMS INTO THE  
REGION AROUND A HIGH PRESSURE TO THE SOUTHEAST. THERE WILL BE  
SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE SOUTHERN COLORADO  
MOUNTAINS THIS AFTERNOON, ALTHOUGH VFR CONDITIONS SHOULD PREVAIL  
AT ALL SITES. THE THREAT OF SHOWERS AND THUNDERSTORMS WILL SPREAD  
ACROSS MORE OF WESTERN COLORADO TOMORROW AFTERNOON.  
 

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

 
 

 
 
SHORT TERM...CC  
LONG TERM...MDA  
AVIATION...MMS/JPF  
 
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