355  
FXUS65 KFGZ 151617  
AFDFGZ  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE FLAGSTAFF AZ  
917 AM MST MON JUL 15 2019  
   
SYNOPSIS
 
DRIER WEST TO SOUTHWEST FLOW WILL PUSH MONSOON  
MOISTURE AND STORM COVERAGE EASTWARD TODAY THROUGH WEDNESDAY.  
GUSTY AFTERNOON WINDS WILL ACCOMPANY THIS PUSH ESPECIALLY TUESDAY  
AND WEDNESDAY. HIGH PRESSURE WILL THEN BEGIN TO BOUNCE BACK  
TOWARD THE FOUR CORNERS WITH A GRADUAL RETURN OF MOISTURE.  
DAYTIME TEMPERATURES AT LOWER ELEVATIONS WILL BE VERY HOT OVER THE  
NEXT FEW DAYS.  
 

 
   
DISCUSSION
 
THE MAIN STORIES OVER THE NEXT COUPLE DAYS WILL BE  
DECREASING THUNDERSTORM CHANCES, HOT TEMPERATURES, AND GUSTY  
AFTERNOON WINDS. WEST TO SOUTHWEST FLOW IS ADVECTING A DRIER  
AIRMASS INTO THE REGION WHICH WILL ACT TO DECREASE THUNDERSTORM  
CHANCES ACROSS NORTHERN ARIZONA. EXPECT GENERALLY ISOLATED  
COVERAGE TODAY, WITH THE HIGHEST CHANCES REMAINING OVER THE WHITE  
MOUNTAINS. THUNDERSTORM CHANCES WILL BE LIMITED TO NAVAJO AND  
APACHE COUNTIES ON TUESDAY AND WEDNESDAY. THE PRIMARY HAZARDS WITH  
THESE STORMS WILL REMAIN GUSTY OUTFLOW WINDS AND LIGHTNING.  
LOCALIZED HEAVY RAINFALL IS ALSO POSSIBLE.  
 
VERY HOT TEMPERATURES WILL OCCUR THROUGH MID WEEK OVER THE LOWER  
ELEVATIONS. AN EXCESSIVE HEAT WARNING REMAINS IN EFFECT THROUGH  
8PM TUESDAY FOR PORTIONS OF THE LOW DESERT IN CENTRAL ARIZONA  
(INCLUDING SOUTHERN YAVAPAI COUNTY) AS WELL AS LOWER ELEVATIONS IN  
THE GRAND CANYON INCLUDING PHANTOM RANCH. TEMPERATURES OF THIS  
NATURE WILL SUBSTANTIALLY INCREASE THE THREAT OF HEAT ILLNESS. BE  
SURE TO STAY HYDRATED AND OUT OF THE SUN AS MUCH AS POSSIBLE.  
 
THE TROUGH WHICH IS DRIVING THE WEST TO SOUTHWEST FLOW WILL ALSO  
GENERATE GUSTY WINDS OF 25-35 MPH ACROSS THE REGION TUESDAY AND  
WEDNESDAY. NEAR CRITICAL FIRE WEATHER CONDITIONS ARE POSSIBLE IN  
WESTERN COCONINO/YAVAPAI COUNTIES ON TUESDAY AFTERNOON. AFTERNOON  
WIND SPEEDS ARE EXPECTED TO WEAKEN THURSDAY THROUGH THE REMAINDER  
OF THE WEEK.  
 
THE CURRENT FORECAST HANDLES THIS WELL AND NO UPDATES ARE NEEDED  
THIS MORNING.  
 

 
   
PREV DISCUSSION /324 AM MST/
 
HIGH PRESSURE WAS IN THE PROCESS  
OF SHIFTING SOUTHEASTWARD IN RESPONSE TO A WEST TO EAST MOVING  
TROUGH ENTERING THE WESTERN STATES.  
 
FOR TODAY THROUGH WEDNESDAY...THE WESTERN STATES TROUGH WILL  
INTRODUCE A DRIER AIR MASS TO NORTHERN ARIZONA ALONG WITH A  
VERTICAL WIND PROFILE UNFAVORABLE FOR MONSOON STORM DEVELOPMENT.  
LINGERING MOISTURE WILL ALLOW FOR JUST ONE MORE DAY OF LIMITED  
ACTIVITY BEFORE THUNDERSTORMS AND SHOWERS ARE CONFINED TO THE  
WHITE MOUNTAINS AREA EAST-CENTRAL ARIZONA. IN ADDITION, ALONG THE  
WITH THE DRIER AIR MASS, DAYTIME TEMPERATURES WILL BE ON THE  
INCREASE. IN GENERAL IT WILL BE HOT WITH ELEVATIONS BELOW 3500  
FEET CLIMBING TO TEMPERATURES RANGING FROM 107-112 DEGREES. AS A  
RESULT AN EXCESSIVE HEAT WARNING IS IN EFFECT FOR POTIONS OF THE  
LOW DESERT IN CENTRAL ARIZONA (INCLUDING SOUTHERN YAVAPAI COUNTY)  
AS WELL AS LOWER ELEVATIONS IN THE GRAND CANYON INCLUDING PHANTOM  
RANCH.  
 
FROM THURSDAY ONWARD...HIGH PRESSURE BOUNCES BACK NORTHWARD AS THE  
WESTERN STATES TROUGH MAKES IT'S WAY TO THE NORTHEAST. THE RESULT  
WILL BE A GRADUAL RETURN OF MONSOON MOISTURE TO PORTIONS OF  
NORTHERN ARIZONA. THERE ARE A COUPLE FACTORS THAT COULD SPEED UP  
OR SLOW DOWN THE LATE WEEK UPWARD TREND IN MOISTURE. ONE, A  
SECONDARY TROUGH COULD PUT THE NORTHWARD MOVEMENT OF MOISTURE IN  
A HOLDING PATTERN. TWO, IF A THUNDERSTORM COMPLEX DEVELOPS OVER  
NORTHWEST MEXICO OR SOUTHEAST ARIZONA A MOIST OUTFLOW BOUNDARY  
COULD PUSH MOISTURE ACROSS THE AREA (REGARDLESS OF ANY SECONDARY  
TROUGH). HOW IT WILL BALANCE OUT IS SIMPLY A GUESS AT THIS POINT  
SO WE OPTED FOR A SLOW INCREASE IN MOISTURE AND STORM ACTIVITY  
THROUGH THE PERIOD. CHECK BACK FOR UPDATES.  
 

 
   
AVIATION...FOR THE 18Z PACKAGE
 
EXPECT VFR CONDITIONS OVER  
NORTHERN ARIZONA THROUGH THE TAF PERIOD. SURFACE WINDS SOUTHWEST AT  
5-10 KTS WITH STRONGER BREEZES AT 10 GUSTING 20 KTS OVER THE HIGHER  
TERRAIN. WINDS WILL BECOME LIGHT AND VARIABLE AROUND SUNSET.  
ISOLATED TO SCATTERED -TSRA WILL DEVELOP ALONG THE HIGHER TERRAIN OF  
NORTHERN ARIZONA BETWEEN 19Z MON AND 03Z TUES. LOCAL MVFR CONDITIONS  
AND GUSTY AND ERRATIC OUTFLOW WINDS WILL BE POSSIBLE NEAR  
THUNDERSTORMS. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.  
 

 
   
FIRE WEATHER
 
EXPECT ISOLATED TO SCATTERED HIGH-BASED  
THUNDERSTORMS PRODUCING GUSTY AND ERRATIC OUTFLOW WINDS TODAY,  
MAINLY ALONG THE HIGH TERRAIN. TUESDAY WILL HAVE NEAR CRITICAL  
FIRE WEATHER CONDITIONS IN ZONES 104 AND 106-108. THUNDERSTORMS  
WILL BE LIMITED TO THE HIGHER TERRAIN IN NAVAJO AND APACHE  
COUNTIES.  
 
WEDNESDAY THROUGH FRIDAY...WEDNESDAY WILL HAVE BREEZY WEST TO  
SOUTHWEST WINDS AGAIN WITH AN INCREASE IN SURFACE RH. THUNDERSTORMS  
WILL CONTINUE EACH DAY, MOSTLY IN THE WHITE MOUNTAINS, AND WITH A  
SLIGHT CHANCE ALONG THE MOGOLLON RIM AND CHUSKA MOUNTAINS.  
 

 
   
FGZ WATCHES/WARNINGS/ADVISORIES
 
EXCESSIVE HEAT WARNING UNTIL 8  
PM MST TUESDAY FOR AZZ006-037.  
 

 
 

 
 
PUBLIC...TPS/MCCOLLUM  
AVIATION...DB  
FIRE WEATHER...DB  
 
FOR NORTHERN ARIZONA WEATHER INFORMATION VISIT  
WEATHER.GOV/FLAGSTAFF  
 
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