Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 251615
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
915 AM MST SAT APR 25 2015

.SYNOPSIS...
A STRONG COLD FRONT IS FORECAST TO MOVE INTO THE REGION LATE THIS
AFTERNOON AND EVENING. AHEAD OF THE FRONT...GUSTY AFTERNOON
SOUTHWEST WINDS WILL DEVELOP...STRONGEST IN SOUTHEAST CALIFORNIA AND
THE COLORADO RIVER VALLEY. THE CHANCE OF SHOWERS AND THUNDERSTORMS
WILL ALSO INCREASE LATE TODAY AND TONIGHT...BUT MAINLY ACROSS
PORTIONS OF SOUTHWEST AND SOUTH CENTRAL ARIZONA. LINGERING SHOWERS
ARE EXPECTED SUNDAY OVER EASTERN ARIZONA...WITH CLEARING OVER
SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA. DRIER AND MUCH WARMER
WEATHER IS EXPECTED NEXT WEEK.

&&

.DISCUSSION...

...POTENT UPPER TROUGH AND FRONTAL PASSAGE ACROSS THE REGION TODAY
WITH STRONG GUSTY WINDS AND THUNDERSTORM CHANCES...

INCOMING UPPER TROUGH CONTINUES TO QUICKLY APPROACH FROM THE
NORTHWEST WITH THE MAIN SHORTWAVE IN EAST-CENTRAL CALIFORNIA. A
SECOND SHORTWAVE TROUGH...EASILY SEEN ON WATER VAPOR IMAGERY MOVING
INTO SOUTHEAST CALIFORNIA...WAS NOT PICKED UP WELL BY THE MODELS AND
MAY GIVE US A BETTER CHANCE OF SHOWERS ACROSS OUR NORTHERN ZONES BY
MID TO LATE AFTERNOON. THE LATEST HRRR RUN SHOWS A BAND OF SHOWERS
QUICKLY DEVELOPING AROUND 21Z ACROSS EASTERN RIVERSIDE COUNTY
CALIFORNIA AND OVER LA PAZ COUNTY ARIZONA AND THEN QUICKLY SPREADING
EASTWARD THROUGH SOUTH-CENTRAL ARIZONA. MODEL POP GUIDANCE STILL IS
A BIT ON THE LOW SIDE...BUT FEEL OUR A BIT MORE AGGRESSIVE FORECAST
POPS ARE JUSTIFIED BASED ON IMPRESSIVE WATER VAPOR SHORTWAVE TROUGH
SIGNATURE. WINDS HAVE YET TO PICK UP MUCH...BUT ONCE THIS FIRST
TROUGH SLIDES EASTWARD THIS AFTERNOON...GUSTY WINDS WILL DEVELOP
OVER SOUTHEAST CALIFORNIA AND THEN A BIT LATER OVER SOUTH-CENTRAL
ARIZONA. BEST CHANCES FOR RAIN AND POTENTIALLY A FEW THUNDERSTORMS
STILL SEEMS TO BE CENTERED AROUND 06Z TONIGHT OVER SOUTH-CENTRAL
ARIZONA AS THE MAIN SHORTWAVE TROUGH SWINGS THROUGH.

&&

.PREVIOUS DISCUSSION...
TODAY THROUGH SUNDAY...
REGIONAL WEATHER BALLOON SOUNDINGS FRIDAY EVENING CONTINUED TO SHOW
A RELATIVELY MOIST BOUNDARY LAYER ABOUT 6 TO 7000 FEET DEEP
EXTENDING FROM SOUTHERN CA TO SOUTHWEST AND SOUTH CENTRAL AZ. THIS
MOISTURE IS SIGNIFICANT RELATIVE TO THE COOLER TEMPS ALOFT...AND
FRONTAL PASSAGE EXPECTED LATE SATURDAY AFTERNOON AND EVENING.

OTHERWISE...A POWERFUL AND FAST MOVING NEGATIVE TILT DIFLUENT TROF
IS STILL FORECAST TO MOVE INTO CENTRAL AZ LATE SATURDAY AFTERNOON
AND EVENING. CURRENT MODELS...SPECIFICALLY THE GFS...IS NOT ONLY A
LITTLE FASTER WITH THE COLD FRONT...BUT IT DEEPENS THE TROF SLIGHTLY
MORE EASTWARD INTO CENTRAL AZ. A VERY PROGRESSIVE UPSTREAM PACIFIC
FLOW PATTERN IS PERHAPS PUSHING THIS SYSTEM FASTER/EASTWARD THAN
EARLIER MODEL RUNS. THEREFORE PRECIP CHANCES ACROSS THE FORECAST
AREA...INCLUDING PHOENIX WILL LIKELY START A LITTLE EARLIER...
MEANING LATE AFTERNOON. THE HEAVIEST PRECIP WITH A CHANCE OF TSTMS
HOWEVER IS SLATED FOR THIS EVENING...AFTER DARK...IN SOUTH CENTRAL
AZ.

FOR TODAY AND TONIGHT...
INCREASING CLOUDS BUT NO PRECIP IS EXPECTED THE FIRST HALF OF THE
DAY. BACKING PRE-FRONTAL WINDS AND WARM ADVECTION AHEAD OF THE COLD
FRONT WILL MAKE FOR A WINDY AFTERNOON... WITH THE STRONGEST WINDS IN
SOUTHEAST CA/COLORADO RIVER WHERE A WIND ADVISORY IS POSTED FOR
GUSTS BETWEEN 35 AND 45 MPH.

THE COLD FRONT BY 5 PM LOCAL TIME WILL HAVE JUST MOVED ACROSS THE
COLORADO RIVER...THEN INTO PHOENIX AREA BY 8 PM. THE BEST CHANCE OF
SHOWERS AND THUNDERSTORMS BY 5 PM WILL DEVELOP JUST NORTHWEST AND
NORTH OF BLYTHE CA ALONG THE COLORADO RIVER...AND OVER PORTIONS OF
LA PAZ COUNTY. SHOWERS AND TSTMS DEVELOP ALONG THE COLD FRONT IN
PHOENIX BY 8 PM. IF THUNDERSTORMS DEVELOP...THEIR FAST MOVEMENT
COMBINED WITH PRECIP FALLING THROUGH 20-30 KNOT 850-700 MB
SOUTHWESTERLY WINDS COULD CAUSE SUDDEN GUSTS TO PERHAPS 45 MPH.

SINCE THIS IS A FAST MOVING SYSTEM...MOST SHOWERS BY 5 AM SUN WILL
BE CONFINED TO AREAS GENERALLY FROM PHOENIX EASTWARD. SAME FOR THE
SUNDAY AFTERNOON/EARLY EVENING PERIOD.

SUNDAY NIGHT...RAPID CLEARING IS EXPECTED.

MONDAY THROUGH FRIDAY...
DRY NORTHERLY FLOW WILL DEVELOP MONDAY AND TUESDAY FOLLOWED BY A
BUILDING RIDGE OVER THE REGION WEDNESDAY AND THURSDAY. MUCH WARMER
TEMPERATURES ARE FORECAST WEDNESDAY WITH NEAR 100 DEGREE HEAT ON THE
WARMEST DESERTS.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
APPROACHING UL TROUGH AND COLD FRONT WILL INCREASE WINDS BEGINNING
LATE AM GNLY POST 17Z...BECOMING GUSTY UP TO 25KT OR SO DURING THE
AFTERNOON...EVEN STRONGER TO 30KT SATURDAY EVENING. EXPECT THE
STRONGEST WINDS IN A BURST RIGHT ALONG PASSING COLD FRONT. SOME
TIMING DIFFERENCES REMAIN BETWEEN MODEL FCSTS...BUT LIKELY WINDOW OF
FROPA AND STRONGEST WEST WINDS AROUND 26/02-04Z WINDOW.

PRECIPITATION CHANCES ALSO INCREASE AFTER 21Z...WITH SCATTERED
SHOWER/THUNDERSTORM COVERAGE BEGINNING OVER THE WESTERN DESERTS. VCSH
WILL BEGIN TO FILL IN AROUND PHX METRO PERIPHERY AFTER 26/00Z...WITH
SHOWERS STARTING EARLIER FOR KSDL AND KIWA BEFORE KPHX. CHANCE OF
THUNDER POSSIBLE AS WELL WITH THIS STRONG SYSTEM...SO INCLUDED
OVERNIGHT MENTION OF -TSRA POST-MIDNIGHT LOCAL 26/07Z. CIGS
STARTING OFF IN THE AFTERNOON 7-9KFT BEFORE DROPPING INTO THE 3-5KFT
RANGE WITH ONSET OF STEADY PRECIP LATE IN THE EVENING.


SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
APPROACHING UL TROUGH WILL PERSIST STRONG WINDS STEADILY INCREASING
AFTER 25/16Z...PEAK GUSTS UP TO 40KT WILL BE COMMON ACROSS THE AREA
BY LATE AFTERNOON CONTINUING INTO THE EVENING HOURS. PERIODS OF
BLOWING DUST REDUCING VISIBILITY DOWN TO 2SM WILL BE COMMON WITH THE
STRONGER WINDS...ESPECIALLY ACROSS IMPERIAL COUNTY AND NEAR YUMA.
12Z TAFS TAKE AIRFIELD VSBYS DOWN TO 5SM BUT CANNOT RULE OUT LOCALLY
LOWER VALUES FOR SHORTER PERIODS. SLANT VSBYS LIKELY IMPACTED DUE TO
LOFTED DUST. THE STRONGEST WINDS TO ABATE LATER INTO THE EVENING BUT
REMAIN ELEVATED IN THE 10-15KT RANGE WITH GUSTS STILL TOWARDS 20KTS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
IN THE WAKE OF THE DEPARTING TROUGH...NEXT WEEK WILL SEE THE ARRIVAL
OF A STRONG UPPER RIDGE OVER THE SOUTHWESTERN CONUS FROM MONDAY
THROUGH MOST OF THE WEEK. TEMPERATURES WILL WARM SUBSTANTIALLY AND
APPROACH THE TRIPLE DIGIT MARK FOR THE LATTER PART OF THE WEEK.
AFTERNOON HUMIDITIES WILL DROP INTO THE LOWER TEENS AND UPPER SINGLE
DIGITS WITH FAIR OVERNIGHT RECOVERIES EXPECTED. WINDS WILL BE GNLY
LIGHT AND SHOULD FOLLOW TYPICAL DIURNAL PATTERNS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.

CA...WIND ADVISORY FROM 1 PM TO 9 PM PDT TODAY FOR CAZ030>033.

&&

$$

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

DISCUSSION...KUHLMAN
PREVIOUS DISCUSSION...VASQUEZ
AVIATION...NOLTE
FIRE WEATHER...NOLTE/LEINS


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