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AREA FORECAST DISCUSSION

 
 FXUS65 KTWC 200910
 AFDTWC
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE TUCSON AZ
 210 AM MST SUN JUL 20 2008
 
 .SYNOPSIS...HIGH PRESSURE ALOFT WILL RESIDE NEAR THE FOUR CORNERS 
 REGION TODAY...WHILE A LARGE UPPER LEVEL DISTURBANCE MOVES SLOWLY 
 WEST THROUGH TEXAS. THESE TWO FEATURES...COMBINED WITH PLENTIFUL 
 MONSOON MOISTURE ACROSS SOUTHERN ARIZONA...WILL LEAD TO A 
 SIGNIFICANT UPSWING IN SHOWERS AND THUNDERSTORMS TODAY. SOME OF 
 THESE STORMS MAY BE STRONG AND PRODUCE HEAVY RAIN. HIGH PRESSURE 
 WILL REMAIN OVER THE CENTRAL ROCKIES THROUGH THE MIDDLE OF NEXT 
 WEEK...WHICH WILL KEEP SOUTHEAST ARIZONA IN AN ACTIVE MONSOON FLOW 
 REGIME.
 
 &&
 
 .DISCUSSION...YESTERDAY EVENING A LARGE MCS DEVELOPED OVER SOUTHEAST 
 ARIZONA...SPECIFICALLY OVER COCHISE COUNTY AND PUSHED INTO PIMA 
 COUNTY. IR SATELLITE IMAGERY IS NOW SHOWING THE SYSTEM WEAKENING 
 WITH CLOUD TOPS WARMING DOWN TO AROUND MINUS 60 DEGS C FOR THE BULK 
 OF THE STORM. EARLIER SATURDAY EVENING THE STORM EXHIBITED TOPS OF 
 MINUS 78 DEGS C AND OVER A MUCH LARGER AREA. AT THE PRESENT TIME 
 SATELLITE AND RADAR INDICATE THAT THE WORST OF THE SYSTEM IS NOW 
 PUSHING WEST OF MY CWA (WEST OF AJO)...AND DEVELOPING OVER THE 
 PHOENIX METRO AREA. MANY REPORTS OF HEAVY RAIN WERE RECEIVED 
 YESTERDAY EVENING WITH AMOUNTS TYPICALLY WELL OVER AN INCH...AND 
 SOME 2 TO 4 INCH AMOUNTS NOT UNCOMMON. REPORTS OF SWIFT WATER 
 RESCUES FOR AREAS IN NE PIMA COUNTY WERE RECEIVED YESTERDAY 
 EVENING.  
 
 AN URBAN AND SMALL STREAM FLOOD ADVISORY CONTINUES IN EFFECT UNTIL 3 
 AM MST FOR COCHISE COUNTY...AND 4 AM MST FOR MUCH OF PIMA COUNTY. 
 RADAR STILL SHOWING LIGHT TO OCCASIONALLY MODERATE RAIN OVER PIMA 
 COUNTY...BUT THE ACTIVITY IS RAPIDLY DECREASING IN BOTH AREAL 
 COVERAGE AND INTENSITY.    
 
 WITH SO MUCH ACTIVITY ACROSS MY FORECAST AREA THE BOUNDARY LAYER HAS 
 OBVIOUSLY COOLED CONSIDERABLY. LOOKING AT SURFACE OBS SHOWS THAT 
 TEMPS NOW RANGE FROM THE LOWER 60S TO THE LOWER 70S. THESE VALUES 
 RANGE FROM 2 TO 8 DEGS COOLER THAN THIS TIME YESTERDAY. WE SHOULD 
 ALSO SEE A MASSIVE CLOUD DECK OVERHEAD TO START THE DAY AS THE 
 COMPLEX DECAYS. WITH THESE TWO FACTORS IN PLAY (COOLED BOUNDARY 
 LAYER...AND A THICK CLOUD DECK)...IT SHOULD SERVE TO INHIBIT 
 CONVECTION TODAY. AVERAGE MOS POP GUIDANCE FROM THE 00Z MODEL RUNS 
 INDICATES 71 PERCENT CHANCE OF RAIN FOR TUCSON TODAY. OF COURSE THE 
 MODELS DIDN`T SEE WHAT TRANSPIRED AFTER THE DATA INGEST...SO WILL BE 
 CURIOUS TO SEE WHAT 06Z MODEL RUN HAS TO SAY. GIVEN THE ABOVE 
 SCENARIO I KEPT THE 50 PERCENT POP GOING WHICH UNDERCUTS MOS...BUT 
 PERHAPS NOT ENOUGH. I JUST FIND IT DIFFICULT TO THINK WE WILL SEE 
 ANOTHER DAY TODAY...LIKE YESTERDAY. COULD STILL BE SOME SCATTERED 
 SHOWERS AND THUNDERSTORMS DEVELOP...BUT LIKELY NOT DEVELOPING UNTIL 
 VERY LATE IN THE AFTERNOON OR EARLY EVENING.  
 
 ALL MODELS SHOW A DECREASE IN POPS FOR MONDAY...AND ESPECIALLY 
 TUESDAY. NAM IS SHOWING PWAT`S DROPPING TO JUST ABOVE THE 1 INCH 
 MARK BY THEN. MOS POP FOR MONDAY AVERAGES AROUND 20 PERCENT FOR 
 TUCSON AND SINGLE DIGIT TO BELOW 20 FOR TUESDAY. DIDN`T GO THAT LOW 
 JUST YET...BUT DID TRIM POPS A BIT. MY FORECAST STILL HAS SCATTERED 
 STORM COVERAGE FOR MOST PLACES FOR BOTH MONDAY AND TUESDAY...WITH 
 THE EXCEPTION OF THE FAR WESTERN DESERTS WITH ONLY ISOLATED COVERAGE 
 ANTICIPATED.
 
 MODELS ARE STILL SHOWING THE UPPER LOW OVER TEXAS SLOWLY TRYING TO 
 WORK ITS WAY WEST...BUT STRUGGLES TO DO SO. DIDN`T TOUCH THE 
 EXTENDED FORECAST AT ALL. STILL KEPT LOW END OF CHANCE FOR MOST 
 AREAS. WILL HAVE TIME TO FINE TUNE THE EXTENDED FORECAST WITH 
 SUBSEQUENT SHIFTS. 
 
 HIGH TEMPS WILL BE A CHALLENGE TODAY. I WENT WITH A HIGH FOR TUCSON 
 OF 90 DEGS...BUT IF CLOUD DECK REMAINS IN PLACE LONG ENOUGH...WE MAY 
 STRUGGLE TO GET OUT OF THE 80S. AFTER TODAY SHOULD SEE A GRADUAL 
 WARMUP INTO THE MID TO UPPER 90S FOR THE REMAINDER OF THE FORECAST 
 PERIOD...WHICH IS SLIGHTLY BELOW TO NEAR NORMAL. 
 
 &&
 
 .AVIATION...EXPECT SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS 
 TO CONTINUE TO PUSH WEST THROUGH THE REMAINDER OF THE EARLY MORNING 
 HOURS. CEILINGS SHOULD REMAIN RELATIVELY LOW THROUGH SUNRISE OR SO 
 WITH CIGS BETWEEN 1500 FT TO AROUND 4000 FT. HOWEVER...AS THE DAY 
 PROGRESSES CIGS SHOULD CLIMB TO AROUND 8-10K FEET OR SO. WHEN 
 THUNDERSTORMS DEVELOP LATE THIS AFTERNOON SHOULD ONCE AGAIN SEE 
 CIGS/VSBYS DROP EASILY TO WITHIN MVFR CONDITIONS WHEN CLOSE TO A 
 THUNDERSTORM...AND POSSIBLY TO IFR CONDITIONS. AVIATION DISCUSSION 
 NOT UPDATED FOR TAF AMENDMENTS.
 
 .TWC WATCHES/WARNINGS/ADVISORIES...NONE.
 
 

 
 MOLLERE
 
 WEATHER.GOV/TUCSON
 
 
 
 
 
 
 
 
 
 

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