Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000 FXUS65 KPSR 080305 AFDPSR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PHOENIX AZ 805 PM MST TUE JUL 7 2015 .UPDATE... QUIET EVENING ACROSS MUCH OF ARIZONA. FROM 02Z TO 03Z THERE WERE ABOUT 500 PULSES OF LIGHTNING STATEWIDE...AND THAT TREND WAS QUICKLY SUBSIDING. PER 08.00Z SOUNDINGS...WESTERLY FLOW IS NOW ESTABLISHED ACROSS ALL OF SOUTHERN CALIFORNIA AND ARIZONA FROM THE TROPOSPHERE DOWN TO 700MB. THIS IS ADVECTING DRIER AIR INTO OUR SLICE OF THE WORLD/COUNTY WARNING AREA...PWAT VALUE AT KPSR WAS 1.1 INCHES...K1Y7 AT 0.9 INCHES...AND 1.2 INCHES AT KTUS WHICH IS IN THE RANGE OF AVERAGE FOR JULY. SURFACE DEWIES ARE 40S TO LOWER 50S. THIS ALL POINTS TO NO ACTIVITY FOR THE LOWER DESERTS FOR THE REST OF TONIGHT AND EVEN LIMITED TO NO ACTIVITY FOR THE HIGHER LOCATIONS IN MARICOPA/SRN GILA COUNTIES. THIS IS CONFIRMED WITH THE PAST SEVERAL RUNS OF THE HRRR. THEREFORE HAVE DROPPED POPS TONIGHT. && .SYNOPSIS... THUNDERSTORM CHANCES WILL BE SIGNIFICANTLY LOWER THAN USUAL FOR THE MIDDLE OF THE MONSOON SEASON...AND PRIMARILY RELEGATED TO THE MOUNTAINS OF NORTHERN AND EASTERN ARIZONA THE NEXT SEVERAL DAYS. DESPITE THE LACK OF STORM ACTIVITY...TEMPERATURES WILL REMAIN NEAR TO SLIGHTLY BELOW NORMAL. BEYOND THIS UPCOMING WEEKEND...HIGH PRESSURE WILL REPOSITION AND STRENGTHEN AGAIN LEADING TO WARMER TEMPERATURES AND POSSIBLY AN INCREASE IN MOISTURE. && .DISCUSSION... UNUSUALLY STRONG SWLY FLOW ALOFT CONTINUES ACROSS THE SWRN CONUS AHEAD OF AN ANOMALOUSLY DEEP GYRE OFF THE CNTRL CALIFORNIA COAST. 12Z KTWC AND KPSR SOUNDING DATA STILL SHOWED LINGERING PESKY SFC-H7 MOISTURE (MIXING RATIOS 10-11 G/KG)...WITH SUBSTANTIALLY DRIER AIR ALOFT. HOWEVER...SFC DEWPOINTS THROUGH SWRN ARIZONA HAVE TANKED SIGNIFICANTLY TODAY...WITH WIDESPREAD READINGS IN THE LOWER/MID 40S. THIS DRIER AIRMASS (MIXING RATIOS BELOW 8 G/KG) HAS ADVECTED NORTHEAST BEGINNING TO MIX AND SCOUR HIGHER BOUNDARY LAYER MOISTURE OUT OF CNTRL ARIZONA. AS SUCH...DEEP CONVECTION HAS BEEN PRIMARILY TIED TO TERRAIN FEATURES NORTH AND EAST OF PHOENIX...WITH STRONG STEERING FLOW PUSHING DEBRIS CLOUDS/ANVILS WELL TO THE EAST. GIVEN THE LONG AWAITED INTRODUCTION OF THIS DRIER AIRMASS UNSUPPORTIVE FOR ORGANIZED STORMS...HAVE CUT POPS THROUGH THIS EVENING TOWARDS JUST THE PERIPHERY OF THE FORECAST AREA...WITH MINIMAL CHANCES OF CONVECTION IMPACTING LOWER DESERT LOCATIONS. WEDNESDAY THROUGH FRIDAY... AS THE UPPER LOW CENTER APPROACHES AND MOVES OVER CNTRL/SRN CALIFORNIA...UPPER LEVEL WINDS MAY BACK TO A MORE SOUTHERLY DIRECTION (ESPECIALLY THURSDAY) TEMPORARILY INCREASING MOISTURE OVER SOUTHEAST ARIZONA...WITH A VERY SHARP DROP OFF INTO CENTRAL ARIZONA. A VORT LOBE AND JET SEGMENT WILL SWING THROUGH SOUTHEAST CALIFORNIA AND WESTERN ARIZONA THURSDAY...BRUSHING EASTERN ARIZONA AND THE MIDLEVEL MOISTURE PLUME. ASSOCIATED DYNAMICAL FORCING LOOKS TO BE LESS THAN ROBUST OVER THE AREA WITH THE JET AXIS REMAINING TO THE WEST. HOWEVER...NUDGED UP THE POPS OVER ZONE 24 AS EVEN SUBTLE INFLUENCES CAN MAKE A DIFFERENCE THIS TIME OF YEAR. THE LOW QUICKLY SHIFTS OFF AND WEAKENS LATE IN THE WEEK...BUT WILL BE REPLACED BY RENEWED TROUGHING AND ANOMALOUSLY STRONG SOUTHWEST FLOW. WITH H5 HEIGHTS FALLING INTO A 576-582DM RANGE LATER IN THE WEEK AND 1000-850MB THICKNESSES ONLY TOUCHING 143DM...HIGH TEMPERATURES WILL FALL INTO A BELOW NORMAL CATEGORY (BARELY ECLIPSING THE 100F THRESHOLD AT LOWER ELEVATIONS). CONCURRENTLY...WITH DEWPOINT/WETBULB TEMPERATURES SUBSTANTIALLY LOWER THAN IS TYPICAL FOR THE MIDDLE OF THE MONSOON SEASON...OVERNIGHT LOWS WILL ALSO FALL BELOW NORMAL LEADING TO VERY COMFORTABLE WEATHER FOR MID JULY. IN FACT...THE ENTIRE PATTERN AND ATMOSPHERIC THERMAL PROFILES ARE MORE REMINISCENT OF MID MAY VERSUS JULY. SATURDAY THROUGH MONDAY... MODELS CONTINUE TO DEPICT A WESTWARD EXPANSION OF THE HIGH CENTERED TO OUR EAST WITH MOISTURE IMPROVING OVER THE LOWER DESERTS...AS SWLY FLOW LIFTS NORTH. THE GFS CONTINUES TO BE MORE GENEROUS WITH THE MOIST ADVECTION THAN THE ECMWF....LIKELY DUE IN PART TO MORE OF A SOUTHERLY FLOW COMPONENT AND DEEPER COASTAL TROUGHING DEPICTED BY THE GFS. ACCORDINGLY...IT ALSO SHOWS STRONGER WINDS ALOFT OVER OUR FORECAST AREA. THE OPERATIONAL GFS SHIFTS THE TROUGH NORTHEASTWARD SUNDAY WITH A JET STREAK MOVING INTO THE GREAT BASIN...PLACING THE ENTRANCE REGION BRIEFLY OVER OUR FORECAST AREA. TAKING A CONSERVATIVE APPROACH DUE TO INHERENT UNCERTAINTIES...ONLY SLIGHT CHANCE POPS OVER THE SOUTH-CENTRAL DESERTS ARE ADVERTISED SUNDAY (WHICH IS AN WESTWARD EXPANSION COMPARED TO PREVIOUS FORECASTS). THERE IS AN EVEN GREATER DIFFERENCE BETWEEN GFS AND ECMWF MOISTURE PROFILES ON MONDAY...AS THE ECMWF HOLDS ONTO THE WEST COAST TROUGHING NUDGING IT FURTHER EAST AND YIELDING ADDITIONAL DRYING. THE GFS MEANWHILE EXPANDS THE HIGH FURTHER WEST FOR A BIT OF ADDITIONAL WARMING ALOFT. BOTH OF THOSE SCENARIOS...ESPECIALLY ECMWF...COULD HAVE A NEGATIVE IMPACT ON STORM POTENTIAL AND SO PULLED BACK POPS FROM THE LOWER ELEVATIONS OF SOUTH-CENTRAL ARIZONA MONDAY. && .AVIATION... SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL... EXPECTING A QUIET NICE ACROSS CENTRAL ARIZONA WITH WESTERLY FLOW SWITCHING TO E/SE AROUND 07-10Z. WINDS WILL HAVE MORE OF A SOUTHERLY TRAJECTORY TOMORROW /WEDNESDAY/ AFTERNOON AND WILL BE GUSTY AT TIMES. NO THUNDERSTORM ACTIVITY EXPECTED IN THE PHOENIX AREA. SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH... NO AVIATION IMPACTS UNDER MOSTLY CLEAR SKIES THROUGH WEDNESDAY AFTERNOON. SFC WINDS COULD OCCASIONALLY INCLUDE HIGHER GUSTS LATE AFTERNOON/EARLY EVENING...THOUGH WILL RETAIN LOWER SPEEDS BY SUNRISE. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... FRIDAY THROUGH TUESDAY... THE FLOW PATTERN WILL TRANSITION FROM SOUTHWESTERLY AND UNFAVORABLE FOR EXTENSIVE MOISTURE AND STORMS DURING THE FIRST PART OF THE WEEKEND...TO MORE TRADITIONAL MONSOON SEASON SOUTHERLY EARLY NEXT WEEK. THUNDERSTORM CHANCES WILL MOSTLY BE LIMITED TO HIGHER TERRAIN LOCATIONS NORTH AND EAST OF PHOENIX...THOUGH COULD BEGIN MOVING WESTWARD NEXT WEEK. AFTERNOON HUMIDITY LEVELS IN A 10-20 PERCENT RANGE DURING THE WEEKEND WILL INCREASE TO A 15-25 PERCENT RANGE NEXT WEEK. OVERNIGHT RECOVERY WILL BE GOOD. DIURNALLY DRIVEN WINDS SPEEDS AND DIRECTIONS WILL PREDOMINATE MUCH OF THIS TIME...THOUGH STRONGER THAN USUAL AFTERNOON UPSLOPE GUSTINESS WILL STILL BE EVIDENT ACROSS MUCH OF THE DISTRICT. && .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT ANY SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...NONE. CA...NONE. && $$ VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX DISCUSSION...INIGUEZ/MO/AJ AVIATION...INIGUEZ/MO FIRE WEATHER...MO

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