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AREA FORECAST DISCUSSION

 
 FXUS65 KTWC 032200
 AFDTWC
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE TUCSON AZ
 300 PM MST FRI JUL 3 2009
 
 .SYNOPSIS...THE COMBINATION OF SOLAR HEATING...A MOIST AIRMASS IN 
 PLACE ACROSS ALL OF SOUTHEAST ARIZONA...WEAK STORM MOTIONS AND A 
 LIFTING MECHANISM IN THE MIDDLE LEVELS OF THE ATMOSPHERE PUSHING 
 INTO THE AREA FROM THE SOUTH WILL RESULT IN NUMEROUS SHOWERS AND 
 THUNDERSTORMS WITH AN ENHANCED THREAT OF PRODUCING HEAVY RAINFALL 
 THIS AFTERNOON AND TONIGHT. 
 
 OTHERWISE...ABUNDANT MOISTURE WILL BRING SCATTERED AFTERNOON AND 
 EVENING THUNDERSTORMS THIS HOLIDAY WEEKEND. AS A TROUGH PROGRESSES 
 INTO THE WEST COAST...DRIER AIR WILL MOVE INTO ARIZONA NEXT WEEK FOR A 
 DECREASE IN MOISTURE AND THUNDERSTORM ACTIVITY. 
 
 &&
 
 .DISCUSSION...KEMX RADAR INDICATED MAINLY ISOLATED THUNDERSTORMS 
 OVER THE HIGHER TERRAIN OF SOUTHEAST ARIZONA EARLY THIS AFTERNOON... 
 WITH SCATTERED THUNDERSTORMS ACROSS SOUTH-CENTRAL ARIZONA. A LOOP OF 
 THE RADAR IMAGERY INDICATES THE WEAK MCV/MID-LEVEL FEATURE THAT WAS 
 OVER COCHISE COUNTY THIS MORNING IS NOW TRACKING WEST ACROSS SANTA 
 CRUZ COUNTY. I WOULD EXPECT THIS FEATURE WILL ENHANCE THUNDERSTORM 
 DEVELOPMENT AS IT TRACKS FURTHER WEST INTO THE LATE AFTERNOON HOURS. 
  
 THE 12Z KTWC UPPER AIR SOUNDING SHOWED A VERY MOIST AIRMASS RESIDING 
 ACROSS THE AREA...WITH A PRECIPITABLE WATER VALUE OF 1.56 INCHES. 
 THIS MOISTURE IS ALSO EVIDENT AT THE SURFACE...WITH SURFACE 
 DEWPOINTS IN THE UPPER 50S TO LOWER 60S. WEAK FLOW IS ALSO EVIDENT 
 ON THE UPPER AIR SOUNDING FROM THE SURFACE TO 500 MB. THIS WOULD 
 SUGGEST A WEAK MOTION TO STORMS TODAY ACROSS THE FORECAST AREA. THIS 
 FACT COMBINED WITH A VERY MOIST AIRMASS WOULD SUGGEST THAT THE MAIN 
 THREAT TODAY WILL BE VERY HEAVY RAIN...WITH A LOWER RISK FOR STRONG 
 THUNDERSTORM OUTFLOWS.
 
 THE 500 MB HIGH CENTER IS OVER THE SOUTHERN PLAINS TODAY. WE SHOULD 
 CONTINUE TO SEE A MID-LEVEL DEFORMATION ZONE ROTATING NORTHWARD INTO 
 THE FAR SE CORNER OF THE STATE INTO THE EARLY EVENING. THIS FEATURE 
 WILL SERVE AS AS AN MECHANISM FOR THUNDERSTORM CONVECTION ACROSS THE 
 FORECAST AREA. GIVEN THE WEAK STORM MOTION...THE VERY MOIST 
 AIRMASS AND THIS FOCUSING MECHANISM ROTATING NORTHWARD ACROSS OUT 
 NECK OF THE WOODS...I CONSIDERED THE POSSIBILITY OF ISSUING A FLASH 
 FLOOD WATCH FOR PORTIONS OF MY FORECAST AREA. HOWEVER...I BELIEVE 
 THAT THE WEAK FEATURES MOVING ACROSS THE FORECAST AREA ARE NOT 
 SUFFICIENT ENOUGH TO ALLOW STORMS TO ORGANIZE INTO AND SIGNIFICANT 
 THUNDERSTORM CLUSTERS. GIVEN THIS...I DO NOT BELIEVE THAT THE HEAVY 
 RAIN WILL BE WIDESPREAD ENOUGH TO WARRANT THE WATCH.
 
 THE 12Z NAM AND GFS MODELS TRY TO PICK UP A MID-LEVEL DISTURBANCE 
 CURRENTLY FIRING STORMS OVER EAST-CENTRAL SONORA MEXICO AND SHIFTS 
 IT INTO SOUTH CENTRAL AZ LATE THIS EVENING INTO THE OVERNIGHT 
 PERIOD. THIS FEATURE...IF IT INDEED MAKES ITS WAY UP INTO OUR NECK 
 OF THE WOODS COULD HELP ORGANIZE CONVECTION ACROSS THE WESTERN HALF 
 OF THE CWA AFTER MIDNIGHT AND HELP PRODUCE HEAVY RAINFALL. IN ANY 
 EVENT...I HAVE REFLECTED THIS THINKING IN THE 06Z-12Z DIGITAL 
 GRIDS.  
 
 OTHERWISE...THE UPPER TROUGH PUSHING INTO THE PACIFIC NORTHWEST 
 SQUASHES THE RIDGE...EVEN RESULTING IN A WEST/NORTHWEST FLOW INTO 
 SOUTHEAST ARIZONA LATE THIS WEEKEND INTO EARLY NEXT WEEK. ALTHOUGH 
 THIS WONT ENTIRELY REMOVE OUR MOISTURE...IT WILL REDUCE IT ENOUGH TO 
 LIMIT THE OVERALL COVERAGE OF STORMS ACROSS OUR FORECAST AREA. 
  
 &&
 
 .AVIATION...THE COMBINATION OF SOLAR HEATING...A MOIST AIRMASS IN 
 PLACE ACROSS ALL OF SOUTHEAST ARIZONA...WEAK STORM MOTIONS AND A 
 LIFTING MECHANISM IN THE MIDDLE LEVELS OF THE ATMOSPHERE PUSHING 
 INTO THE AREA FROM THE SOUTH WILL RESULT IN NUMEROUS SHOWERS AND 
 THUNDERSTORMS WITH AN ENHANCED THREAT OF PRODUCING HEAVY RAINFALL 
 THIS AFTERNOON INTO TONIGHT. THESE STORMS WILL LOWER VISIBILITIES TO 
 1-3 NM IN HEAVY RAIN...WITH LOWER THAN NORMAL CLOUD CEILINGS. 
 ALTHOUGH THE RISK FOR STRONG AND GUSTY THUNDERSTORM WINDS TO 45 MPH 
 STILL EXISTS...THE OVERALL THREAT OF STRONG WINDS IS MINIMAL. 
 AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.
 
 &&
 
 .FIRE WEATHER...A MOIST ATMOSPHERE ACROSS SOUTHEAST ARIZONA WILL 
 RESULT IN SCATTERED THUNDERSTORMS THROUGH THE WEEKEND. A TROUGH 
 MOVING TOWARDS THE WEST COAST WILL SHIFT A DRIER WESTERLY FLOW INTO 
 ARIZONA NEXT WEEK...ALTHOUGH ENOUGH MOISTURE SHOULD REMAIN IN PLACE 
 TO MINIMIZE ANY FIRE WEATHER RISKS AND CONCERNS.
 
 &&
 
 .TWC WATCHES/WARNINGS/ADVISORIES...NONE.
 
 

 
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