Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000 FXUS65 KPSR 010323 AFDPSR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PHOENIX AZ 820 PM MST SAT FEB 28 2015 ...PROLONGED WET WINTER WEATHER EVENT ACROSS THE DESERT SOUTHWEST SUNDAY THROUGH LATE MONDAY... && .SYNOPSIS... LOW PRESSURE WILL CONTINUE A SLOW APPROACH OF THE FORECAST AREA...BRINGING MOISTURE INTO THE REGION ALONG WITH INCREASING CHANCES OF SHOWERS SUNDAY AND MONDAY. PERIODS OF HEAVY RAIN ARE POSSIBLE AT TIMES ESPECIALLY SUNDAY NIGHT THROUGH MONDAY AFTERNOON. COOLER TEMPERATURES WILL ALSO ACCOMPANY THIS STORM WITH BELOW NORMAL READINGS EXPECTED MONDAY THROUGH LATE WEEK. && .DISCUSSION... THE STORM TRACK HAS SHIFTED SOUTH FROM SOUTHERN CA TO CENTRAL AZ. ONE DISTURBANCE MOVED THROUGH CENTRAL AND NORTHERN AZ SATURDAY WITH A SECOND AND MORE POWERFUL ONE DEVELOPING AND INTENSIFYING OFF THE CENTRAL CA COAST THIS EVENING. THIS DISTURBANCE WILL MOVE THROUGH AZ MONDAY...HOWEVER IN THE INTERIM TONIGHT THROUGH SUNDAY NIGHT...THE COLD FRONT WILL REMAIN NEARLY STATIONARY ACROSS CENTRAL AZ. REGIONAL WEATHER BALLOON SOUNDINGS SAT MORNING AND EVENING SHOWED LOW LEVEL MOISTURE ALONG THE FRONTAL ZONE HAD BEEN SLOWLY INCREASING WITH TIME. AT 5 PM MST A RELATIVELY HIGH LOW LEVEL MOISTURE PLUME EXTENDED FROM NORTHERN BAJA INTO SOUTHERN AZ. AS THE DISTURBANCE OFFSHORE DEVELOPS SOUTHWARD TONIGHT AND SUNDAY...ADDITIONAL MOISTURE WILL SPIN UP INTO THE SYSTEM FOR A SIGNIFICANT RAIN EVENT LATE SUNDAY NIGHT AND MONDAY. AS THE MOISTURE INCREASES ALONG THE FRONTAL ZONE TONIGHT AND SUNDAY...SCT LIGHT SHOWERS ARE EXPECTED...WITH MAYBE SLIGHTLY HEAVIER AMOUNTS FOR A 6 HOUR PERIOD SUNDAY MORNING. UPDATES WERE TO INCREASE PRECIP PROBABILITIES IN SOUTH CENTRAL AZ TONIGHT AND SUNDAY...INCLUDING THE PHOENIX AREA. OTHERWISE AS NOTE ABOVE...A SIGNIFICANT AMOUNT OF MOISTURE IS FORECAST TO SURGE INTO SOUTHWEST AND SOUTH CENTRAL AZ LATE SUNDAY NIGHT AND MONDAY AS THE PACIFIC DISTURBANCE APPROACHES. LOW LEVEL SOUTHWEST WINDS SHOULD BE FAIRLY STRONG MONDAY...IN THE 20 TO 35 KNOT RANGE...ENHANCING THE POTENTIAL FOR UPSLOPE PRECIP IN LA PAZ...NORTHERN MARICOPA...AND SOUTHERN GILA COUNTIES. THE FLOOD WATCH FOR THESE AREAS STARTING SUNDAY AFTERNOON THROUGH MONDAY AFTERNOON LOOKS OK FOR NOW. OTHERWISE...FORECASTS LOOK GOOD SHOWING A PROLONGED CHANCE OF PRECIP TONIGHT THROUGH MONDAY...CULMINATING IN THE HEAVIEST PRECIP LATE SUNDAY NIGHT AND MONDAY ACROSS SOUTHWEST AND SOUTH CENTRAL AZ. PREVIOUS DISCUSSION BELOW STILL APPLIES. .PREVIOUS DISCUSSION...342 PM MST... AFTERNOON IR/WV IMAGERY LOOPS SHOW THE UPPER LOW CONTINUING TO TRAVEL SOUTHWARD THROUGH CA...WITH THE CIRCULATION CENTER NOW SOUTH OF THE SAN FRANCISCO BAY AREA. DOWNSTREAM FROM THE MAIN UPPER LOW...UNSETTLED WESTERLY MID AND UPPER JET FLOW SPANS FROM THE CA COAST AND ACROSS MUCH OF THE SOUTHERN CONUS. SPOTTY LIGHT RAIN SHOWER COVERAGE CONTINUES ACROSS THE NORTHERN FRINGE OF MARICOPA COUNTY THIS AFTERNOON. ADDITIONAL AREA OF LIGHT RAIN SHOWERS HAVE BEGUN TO PERCOLATE WELL EAST OF THE PHOENIX METRO...ALONG THE US60 CORRIDOR. IN ADDITION...STRONG SURFACE WINDS CONTINUE ACROSS MUCH OF THE REGION...ESPECIALLY THE SOUTHEAST CA FORECAST ZONES...WITH MANY SITES REPORTING GUSTS INTO THE 30 KT/MID 30 MPH RANGE. STRONG WINDS WILL EVENTUALLY TAPER BACK IN SPEEDS LATER INTO THE EVENING WHILE STILL REMAINING SLIGHTLY ELEVATED OVER AREA RIDGETOPS. SPOTTY SHOWER COVERAGE WILL ALSO CONTINUE...ESPECIALLY FOR THE FOOTHILL/HIGH TERRAIN LOCALES NORTH/EAST OF PHOENIX WITH ADDITIONAL ACCUMULATIONS ON THE ORDER OF A COUPLE HUNDREDTHS TO POSSIBLE 0.10" OR SO. POP FORECASTS FOR THE REST OF THE AFTERNOON KEEP ISOLATED SHOWER MENTION OVER PORTIONS OF THE SOUTH-CENTRAL AZ DESERTS...WITH INCREASING PERCENTAGES AND COVERAGE BECOMING SCATTERED THE FURTHER NORTH/NORTHEAST OF PHOENIX YOU GO. IN GENERAL...VERY LITTLE HAS CHANGED WITH THE OVERALL NARRATIVE OF SENSIBLE WEATHER IMPACTS ASSOCIATED WITH THIS SYSTEM FOR SUNDAY AND THE EARLY WORK WEEK. HOWEVER...FORECAST SOLNS HAVE ONCE AGAIN SHIFTED THE SIGNIFICANT IMPACT WINDOWS OUT BY ANOTHER 6-HRS OR SO. THE TRANSLATES TO THE WINDOWS WITH MODERATE TO HEAVY RAINFALL CONCERNS OVER SOUTHEAST CA LATER INTO THE DAY SUNDAY...MORE LIKELY AFTER 18Z. IN ADDITION...THE WINDOW FOR MODERATE TO HEAVY RAINFALL OVER THE SOUTH-CENTRAL AZ DESERTS/FOOTHILLS HAS SHIFTED PRIMARILY TO MONDAY. ONLY SLIGHT ADJUSTMENTS WERE WORKED INTO THE QPF GRIDS...WITH UPWARD NUDGES OF STORM TOTAL VALUES PUSHING 2 INCHES POSSIBLY OVER THE FAR NORTHEAST MARICOPA COUNTY CORNER AND 1.5 INCH VALUES FOR WICKENBURG AND NORTHWEST MARICOPA COUNTY. AROUND 1 INCH STORM TOTAL HOLDS ACROSS THE PHOENIX METRO WITH 0.60 TO 0.90 OR SO READINGS POSSIBLE OUT ALONG THE LOWER CO RIVER VALLEY AND SOUTHEAST CA. THE UPPER LOW WILL CONTINUE TO DIG DOWN TO THE SOCAL COAST THROUGH THE EVENING...STALLING OUT WEST OF SAN DIEGO/LA FOR MUCH OF THE DAY SUNDAY. MEANWHILE...DECENT BAND OF ELEVATED SUBTROPIC MOISTURE WILL BE DRAWN NORTHWARD TOWARDS THE UPPER LOW AND OVER THE BAJA PENINSULA. SOME DISCREPANCY LINGERS BETWEEN FORECAST VALUES THIS AFTERNOON AND OBSERVED TPW PWAT SAT READINGS WITH THE MODELS OVER-DOING PWAT FCSTS BY ABOUT A TENTH OF AN INCH ATTM. HOWEVER...QPF FORECAST VALUES REMAIN IN FAIRLY GOOD AGREEMENT ON TIMING AND AMOUNTS BETWEEN ALL THE MODELS. MAIN FRONTAL FEATURE OFF THE PARENT LOW AND ASSOCIATED PRECIPITATION BAND WILL SLOWLY WORK THROUGH SOCAL SUNDAY...AND INTO SOUTHEAST CA BY THE AFTERNOON. THE UPPER LOW WILL BEGIN TO TRANSITION EASTWARD OVERNIGHT SUNDAY INTO MONDAY...AS A SECONDARY KICKER SYSTEM QUICKLY DROPS OUT OF THE PAC NW. MAIN PRECIP FRONTAL BAND...WITH MODERATE TO AT TIMES HEAVY RAINFALL...WILL TRANSITION FROM PORTIONS OF THE CO RIVER VALLEY AND WESTERN AZ LATER SUNDAY INTO SOUTH-CENTRAL AZ BY MONDAY MORNING. RAIN WILL TRANSITION FROM WEST TO EAST DURING THE MONDAY...WITH EVEN THE THREAT FOR SOME EMBEDDED THUNDERSTORM DEVELOP LATER MONDAY WITH THE MOVEMENT OF THE UPPER LOW COLD CORE ACROSS AZ. THINK THE THREAT FOR THUNDER SHOULD WRAP FAIRLY EARLY MONDAY EVENING...BUT DID EXPAND SLIGHT CHANCE THUNDER MENTION FOR A FEW EXTRA HOURS GIVEN THE LATEST ROUND OF TIMING ADJUSTMENTS. THE SECONDARY KICKER SYSTEM QUICKLY SKIRTS DOWN THE WEST COAST AND DROPS OVER BAJA FOR TUESDAY...NOW PRESENTING A POTENTIALLY DRIER TUESDAY OVER THE SOUTHWEST DESERTS. GIVEN THE SHORT-TERM STRUGGLES IN THE MODEL SOLNS...LEFT THE FORECAST POPS FOR TUESDAY AND WEDNESDAY MAINLY UNTOUCHED. THEY RESULT IN SLIGHT SHOWER CHANCES LINGER OVER MUCH OF THE SOUTH-CENTRAL AZ DESERTS/HIGHER TERRAIN TUESDAY AND DRIER CONDITIONS BEGINNING WEDNESDAY. UNSETTLED AND DRIER NORTHWEST FLOW FILTERS INTO THE AREA FOR THE REMAINDER OF THE WORK WEEK...WITH ANOTHER SHORTWAVE/CUTOFF FEATURE SKIRTING THE AREA LATE THURSDAY/FRIDAY. THIS MAY HELP TO KEEP TEMPERATURES ON THE COOL SIDE...BUT LOOKS TO KEEP OUR AREA DRY AND FREE FROM ANY ADDITIONAL PRECIP ACTIVITY. TEMPERATURES WILL REACH THEIR LOWEST VALUES ON MONDAY AND WILL SLOWLY REBOUND BACK INTO THE MID 70S/LOWER 80S BY LATE NEXT WEEK. && .AVIATION... SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL... A SLOW APPROACHING COLD FRONT WILL CONTINUE DRAW LOW LEVEL MOISTURE INTO THE AREA FROM NORTHERN BAJA THROUGH SUNDAY AFTERNOON. ISOLATED SHOWERS IN THE PHOENIX VALLEY ARE EXPECTED...WITH A BRIEF HEAVIER PERIOD AROUND SUNRISE SUNDAY. THEREFORE SCT CLDS BASED NEAR 4 THSD AGL WITH BKN-OVC CLDS BETWEEN 5-6 THSD AGL WILL CONTINUE THROUGH AT LEAST 20Z SUN. LIGHT SOUTH WIND IS EXPECTED THROUGH 14Z...INCREASING TO 10 TO 15 KNOTS FROM 14Z-20Z SUN. SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH... THROUGH 16Z SUN...SCT CLDS NEAR 6 THSD AGL..BKN CLDS 10-12 THSD AGL. WEST TO SOUTHWEST WIND 5 TO 10 KNOTS. FROM 16Z SUN TO 20Z SUN... CLDS LOWERING TO BKN 6 THSD AGL WITH SCT RAIN SHOWERS. LIGHT SOUTH WIND 5 TO 10 KNOTS. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... MONDAY THROUGH FRIDAY... COOL AND WET CONDITIONS WILL BE PRESENT ON MONDAY AND LIKELY INTO TUESDAY WITH THE BEST CHANCES FOR WIDESPREAD RAINS ON MONDAY. THERE WILL BE A CHANCE OF A FEW THUNDERSTORMS ON MONDAY. HUMIDITIES WILL BE WELL ABOVE TYPICAL VALUES THROUGH TUESDAY BEFORE MINIMUM VALUES FALL BACK INTO THE TEENS STARTING THURSDAY AFTERNOON. PERIODS OF BREEZY SOUTHWESTERLY WINDS CAN BE EXPECTED ON MONDAY AND AGAIN ON WEDNESDAY. HIGH TEMPERATURES ACROSS THE DESERTS WILL ONLY REACH INTO THE 60S THROUGH WEDNESDAY. HIGH PRESSURE BRINGING WARMER AND DRIER WEATHER SHOULD MOVE IN STARTING LATER WEDNESDAY AND SHOULD PERSIST THROUGH THE END OF THE WEEK. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...FLOOD WATCH FROM SUNDAY AFTERNOON THROUGH MONDAY AFTERNOON AZZ021>024. CA...NONE. && $$ VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX DISCUSSION...VASQUEZ/NOLTE AVIATION...VASQUEZ FIRE WEATHER...KUHLMAN

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