Area Forecast Discussion
Issued by NWS Phoenix, AZ

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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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