Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 262221
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
320 PM MST THU FEB 26 2015

.SYNOPSIS...
DRY WEATHER WITH ABOVE NORMAL TEMPERATURES ARE EXPECTED THROUGH THE
END OF THE WEEK. HOWEVER...LOW PRESSURE WILL APPROACH THE AREA THIS
WEEKEND BRINGING GUSTY WINDS AND WIDESPREAD RAINFALL TO THE AREA
ALONG WITH MUCH COOLER TEMPERATURES. COOL AND UNSETTLED WEATHER IS
LIKELY TO CONTINUE INTO EARLY NEXT WEEK.

&&

.DISCUSSION...
EARLY AFTERNOON SATELLITE IMAGERY REVEALING MOSTLY CLEAR SKIES FOR
THE SOUTHERN HALF OF ARIZONA AND MOST OF SOUTHEAST CALIFORNIA. THE
UPPER LEVEL RIDGE OF HIGH PRESSURE IS STILL IN PLACE ACROSS THE
EASTERN PACIFIC...DRIVING A NORTHWEST FLOW OF DRY AIR INTO THE
SOUTHWEST STATES. INCREASING MID AND HIGH CLOUDS OVER THE NEXT 24
HOURS WITH THE PASSAGE OF A SHORTWAVE FEATURE AND BROAD AREA OF
HEIGHT FALLS WILL START FILTERING INTO THE SOUTHWEST. TEMPERATURES
TOMORROW WILL BE SIMILAR TO THAT OF TODAY...SEVERAL DEGREES ABOVE
NORMAL.

THE BIG WEATHER CHANGE WILL START SATURDAY AS THE UPPER LEVEL LOW
DIGS DOWN THE WEST COAST AND THE JET STREAM NOSES INTO SOUTHEAST
CALIFORNIA AND SOUTHWEST ARIZONA. A MODEST AMOUNT OF MOISTURE
INCREASE OVER THE AREA STARTING SATURDAY WILL HELP INITIATE A
PROLONGED PERIOD OF UNSETTLED WEATHER SATURDAY THROUGH MONDAY.
PRECIPITABLE WATER VALUES CLIMB TO OVER HALF AN INCH BY SATURDAY
MORNING...AND CONTINUE TO RISE TO OVER AN INCH ACROSS SOUTHCENTRAL
ARIZONA BY MONDAY. A 115 KT JET NOSES INTO SOUTHWEST ARIZONA WHICH
CREATES A TIGHT TEMPERATURE GRADIENT...500 MB TEMPS SPANNING -15C TO
-26C...AND WILL INCREASE THE WIND SPEEDS MAINLY ACROSS SOUTHEAST
CALIFORNIA FOR SATURDAY. WINDS GUSTING SATURDAY BETWEEN 30 TO 35 KTS
INTERMITTENTLY AS THE FRONT PUSHES THROUGH WILL APPROACH WIND
ADVISORY CRITERIA BUT AT THIS TIME THINK WE`LL HOLD OFF ON ANY
HEADLINES. FROM LATE SATURDAY THROUGH MOST OF MONDAY...THE COLD
FRONT APPEARS TO STALL AND HAVE A VERY SLOW PROGRESSION AS THE LOW
BEGINS TO STRETCH OUT. BY LATE MONDAY...THE TROUGH WILL BEGIN TO
FLATTEN OUT AND LIFT EASTWARD...WITH ANOTHER WAVE OF ENERGY ROTATING
AROUND THE TROUGH TUESDAY.

AS WITH ANY MAJOR PRECIPITATION EVENT...THE TIMING AND EXACT AMOUNTS
ARE OF HIGH QUESTION. OPERATIONAL MODEL GUIDANCE SUGGESTS PRECIP
WILL BEGIN AFTER 12Z SATURDAY ACROSS NORTHERN ARIZONA AND SOUTHERN
CALIFORNIA AND WILL FILL IN ACROSS THE LOWER DESERTS LATE SATURDAY
INTO SUNDAY...AND AGAIN LINGER THROUGH LATER IN THE DAY MONDAY. AS
MODELS CONTINUE TO MAKE ADJUSTMENTS...12Z SUNDAY THROUGH 12Z MONDAY
SEEMS TO HAVE A DECENT HEAVY RAIN TIME PERIOD WITH THE 00Z MONDAY
THROUGH 12Z MONDAY POTENTIALLY HOLDING THE HIGHER RAIN AMOUNTS. POP
GRIDS WERE ADJUSTED ACCORDINGLY...AS WELL AS SOME MINOR CHANGES TO
THE QPF GRIDS. THIS STORM IS PANNING OUT FOR A DECENT CHANCE OF 1 TO
1.25 INCHES AROUND THE PHOENIX AREA AND VALUES UPWARDS OF 1.5 TO 2
INCHES ALONG THE HIGHER TERRAIN NORTH AND EAST OF PHOENIX...OVER A
36 TO 48 HOUR TIME PERIOD.

MONDAY WILL BE A TRANSITION DAY AS THE COLD CORE OF THE SYSTEM MAKES
SOME PROGRESS EASTWARD. 500 MB TEMPS DIP INTO -23C FIRST OVER
PORTIONS OF JOSHUA TREE NATIONAL PARK AND INTO CENTRAL ARIZONA BY
00Z TUESDAY. THE TIMING OF PRECIPITATION RIGHT NOW LOOKS TO BE
SLIGHTLY OFF WHEN THE COLD CORE PUNCHES THROUGH SOUTHEAST
CALIFORNIA...SO THE RAIN-SNOW MIX SHOULD NOT ACCUMULATE IN JOSHUA
TREE. HOWEVER...WHEN THE COLD CORE MOVES INTO CENTRAL ARIZONA LATE
MONDAY INTO TUESDAY A CONVECTIVE PRECIP THREAT WILL REMAIN INTO THE
HIGHER TERRAIN AREAS NORTH AND EAST OF PHOENIX. RAIN TO SNOW
ACCUMULATION BETWEEN 00Z TUESDAY AND 00Z WEDNESDAY WILL LIKELY BE
RESTRICTED TO ELEVATIONS OF SOUTHERN GILA COUNTRY ABOVE 5500 FT. ALL
THIS SAID...AT THIS TIME...NOT TOO CONCERNED WITH MAJOR FLOODING OR
ANY HEADLINE PRODUCTS AT THIS TIME.


CONDITIONS REMAIN UNSETTLED INTO TUESDAY AS WELL AS A SECONDARY
TROUGH DIVES THROUGH THE GREAT BASIN INTO ARIZONA. THE IMPACTS OF
THIS TROUGH ARE MUCH LESS CLEAR AS THERE IS A TREMENDOUS AMOUNT OF
SPREAD IN THE ENSEMBLES WITH RESPECT TO THE MAGNITUDE OF THIS TROUGH
AND ITS EXPECTED TRAJECTORY THROUGH THE GREAT BASIN. GFS-BASED
GUIDANCE INDICATES A MORE SOUTHWARD TRAJECTORY ALONG WITH SCATTERED
SHOWERS ACROSS THE AREA WHEREAS THE ECMWF AND ITS MEMBERS KEEP ALL
PRECIP WELL NORTH OF THE FORECAST AREA. GOING TO MAINTAIN POPS FOR
SOME PORTIONS OF THE AREA ON TUESDAY PER THE GFS. WITH ANOMALOUSLY
COLD TEMPERATURES ALOFT IT SHOULD BE EASY FOR SCATTERED SHOWERS TO
DEVELOP WITH A MINIMAL AMOUNT OF FORCING BUT THE FINER DETAILS WILL
NEED TO BE SORTED OUT DOWN THE ROAD. FINALLY BY MID WEEK ANY/ALL
FORCING ASSOCIATED WITH THIS UPPER LOW SHIFTS TO THE EAST AND DRY
NORTHWESTERLY FLOW TAKES HOLD.

FOR AS WARM AS FEBRUARY HAS BEEN...TEMPERATURES THIS WEEKEND INTO
THE FIRST FEW DAYS OF MARCH WILL MORE THAN MAKE UP FOR IT.
CLOUDS/SHOWERS ON SUNDAY AND MONDAY COULD CONCEIVABLY KEEP HIGH
TEMPS IN THE UPPER 50S ACROSS THE DESERTS ALTHOUGH SOME MODERATION
IS EXPECTED BY THE MIDDLE OF THE WEEK. POST-FRONTAL DRY ADVECTION
TUESDAY/WEDNESDAY WILL RESULT IN SOME CHILLY MORNINGS BY MID WEEK
WITH LOWS IN THE MID 30S TO LOWER 40S ACROSS THE DESERTS. DEPENDING
ON HOW QUICKLY SKIES CLEAR AND WINDS DIE DOWN...MAY NEED TO ADDRESS
THE POTENTIAL FOR FREEZE HEADLINES IN SOME PORTIONS OF THE FORECAST
AREA /ESPECIALLY IF THE COOLER AND DRIER ECMWF VERIFIES/.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...
SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...

NORTHWESTERLY FLOW ALOFT WILL BRING PERIODIC HIGH CLOUDS THROUGH THE
PERIOD WITH NO AVIATION IMPACTS. WINDS WILL REMAIN LESS THAN 10
KNOTS AND FOLLOW TYPICAL DIURNAL DIRECTIONAL PATTERNS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
CONDITIONS WILL TURN MUCH COOLER...WETTER AND UNSETTLED STARTING
SATURDAY AS A STRONG LOW PRESSURE SYSTEM NEARS THE REGION. BREEZY TO
WINDY WESTERLY WINDS CAN BE EXPECTED ACROSS SOUTHEAST CALIFORNIA AND
SOUTHWEST ARIZONA FOR SATURDAY AFTERNOON. RAIN WILL BECOME LIKELY
SATURDAY NIGHT ACROSS SOUTH-CENTRAL ARIZONA AND PERSIST THROUGH
SUNDAY. HIGH TEMPERATURES ACROSS THE DESERTS WILL FALL INTO THE
UPPER 50S TO LOW 60S STARTING SUNDAY...LASTING INTO THE MIDDLE OF
THE WEEK. HUMIDITY LEVELS WILL BE ELEVATED THROUGHOUT THE ENTIRE
PERIOD. A SECOND LOW PRESSURE SYSTEM MAY BRING CONTINUED
PRECIPITATION CHANCES FOR TUESDAY AND WEDNESDAY.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX

DISCUSSION...DEWEY/LEINS
AVIATION...KUHLMAN
FIRE WEATHER...KUHLMAN







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