Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 311152
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
452 AM MST FRI OCT 31 2014

.UPDATE...UPDATED AVIATION DISCUSSION...

&&

.SYNOPSIS...
ANOTHER DAY OF WELL ABOVE NORMAL TEMPERATURES IS EXPECTED TODAY
UNDER MOSTLY SUNNY SKIES. SIGNIFICANTLY COOLER READINGS ARE THEN
EXPECTED FOR THE WEEKEND... AS A LOW PRESSURE SYSTEM AND COLD FRONT
PUSH THROUGH THE DESERT SOUTHWEST. HIGHS IN THE LOWER DESERTS WILL
DROP INTO THE UPPER 70S OR LOW 80S ON SATURDAY AND FALL TO THE LOWER
70S ON SUNDAY. IN ADDITION TO THE COOLER TEMPERATURES...PERIODS OF
BREEZY CONDITIONS CAN BE EXPECTED THROUGHOUT THE WEEKEND. RAIN
CHANCES WILL BE SLIGHT AND CONFINED MOSTLY TO THE HIGHER TERRAIN
EAST OF PHOENIX. A GRADUAL WARMING TREND WILL BEGIN MONDAY INTO THE
MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...
STRONG UPPER LEVEL RIDGE THAT LED TO RECORD HIGH TEMPERATURES IN
SOME OF THE WARMER DESERT LOCALES YESTERDAY CONTINUED TO SHIFT TO
THE EAST EARLY THIS MORNING...AS A DEEP AND COLD UPPER TROF
APPROACHED THE WEST COAST. A FAIR AMOUNT OF COLD AIR CU WAS VISIBLE
ON IR IMAGERY JUST OFF THE PAC NW/NRN CA COAST...AND WHEN THIS COLD
SYSTEM PASSES THROUGH ARIZONA THIS WEEKEND WE CAN EXPECT HIGH TEMPS
TO FALL 20 DEGREES OR MORE OVER THE LOWER DESERTS. UPPER RIDGE AXIS
HAS ALREADY SHIFTED EAST OF PHOENIX WITH THE AXIS MOVING INTO NEW
MEXICO EARLY THIS MORNING...AND THE INCREASING SWLY FLOW ALOFT WILL
LEAD TO SOME BREEZY CONDITIONS THIS AFTERNOON OVER SERN CA AND THE
WESTERN AZ DESERTS. AT 3 AM VARIABLE AMOUNTS OF HIGH CLOUDS WERE
PUSHING EAST ACROSS THE DESERTS...BUT WE SHOULD SEE SOME CLEARING
THIS MORNING...WITH SKIES BECOMING PARTLY TO MOSTLY SUNNY. LOW LEVEL
WINDS BACKING AHEAD OF THE APPROACHING TROF WILL PULL SOME MOISTURE
INTO FAR EASTERN AZ THIS AFTERNOON...AND 850MB DEWPOINTS WILL
APPROACH 8C ACROSS THE HIGHER TERRAIN EAST OF PHOENIX. AS SUCH WE
HAVE A SLIGHT CHANCE FOR THUNDERSTORMS MAINLY EAST OF GLOBE
DEVELOPING INTO THE AFTERNOON AND EARLY EVENING HOURS. AS FAR AS
TEMPS GO...TODAY SHOULD BE THE LAST 90 DEGREE DAY THAT WE SEE THIS
CALENDAR YEAR. 850MB TEMPS WILL STAY ELEVATED...AND WILL ONLY DROP
OFF BY A DEGREE OR SO OVER THE CENTRAL DESERTS. AS SUCH WE WILL CALL
FOR LOW 90S AGAIN OVER THE WARMER WESTERN AND CENTRAL DESERTS WITH A
HIGH OF 92 FORECAST FOR PHOENIX.

MODEL GUIDANCE...INCLUDING GFS ENSEMBLE MEMBERS...REMAIN CONSISTENT
IN CALLING FOR THE DEEP AND COLD TROF TO PUSH ACROSS ARIZONA THIS
WEEKEND...BRINGING MUCH COOLER TEMPS...A SLIGHT CHANCE FOR SHOWERS
ACROSS SOUTH CENTRAL AZ...AND BREEZY/LOCALLY WINDY WEATHER ON
SATURDAY. THE TROF WILL MOVE THROUGH AS A SERIES OF WAVES...WITH THE
FIRST WAVE QUICKLY RACING NORTHEASTWARD AND ACROSS THE STATE
SATURDAY. THE FIRST COLD FRONT SATURDAY WILL LEAD TO ABOUT 10
DEGREES OF COOLING TO GO ALONG WITH BREEZY OR LOCALLY WINDY
SOUTHWEST WINDS. MOISTURE AND DYNAMICS WILL BE SOMEWHAT LIMITED SO
PRECIP WILL BE CONFINED TO AREAS MAINLY NORTH AND EAST OF
PHOENIX...ACROSS THE HIGHER TERRAIN...AND POPS WILL STAY MOSTLY
BELOW 15 PERCENT. THE SECOND...AND STRONGER...WAVE MOVES ACROSS
THE STATE SUNDAY INTO SUNDAY NIGHT...AND THE GFS ACTUALLY DEVELOPS A
CLOSED UPPER LOW THAT TREKS ACROSS NRN AZ DURING THE DAY. STRONGER
DYNAMICS ARE BEING ADVERTISED...AS THE H3 JET DIVES FURTHER TO THE
SOUTH PUTTING SOUTH CENTRAL AZ UNDER THE FAVORED FRONT LEFT QUAD OF
THE JET. ALSO...AN IMPRESSIVE BULLSEYE OF MID LEVEL Q CONVERGENCE IS
FORECAST TO PUSH ACROSS MUCH OF CENTRAL AND NORTHERN AZ. WITH TEMPS
BEING MUCH COOLER RH VALUES WILL BE HIGHER...AND IT WILL BE EASIER
TO WRING SMALLER AMOUNTS OF QPF OUT OF THE ATMOSPHERE. AS SUCH WE
RAISED POPS INTO THE 15-20 PERCENT BALLPARK OVER SOUTH CENTRAL AZ ON
SUNDAY...INCLUDING THE LOWER DESERT AREAS. HIGH TEMPS ARE EXPECTED
TO DROP ANOTHER 10 DEGREES OR SO WITH HIGHS IN THE GREATER PHOENIX
AREA TO FALL TO NEAR 70 DEGREES. THOSE NUMBERS WOULD REPRESENT HIGHS
MORE THAN 10 DEGREES BELOW SEASONAL NORMALS.

BY MONDAY MORNING THE TROF AXIS WILL HAVE SHIFTED SOUTHEAST OF THE
GREATER PHOENIX AREA...PUTTING MOST OF THE CWA UNDER A SUBSIDENT
NORTHWEST FLOW ALOFT. MOISTURE WILL CONTINUE TO THIN...WITH SKIES TO
BECOME MOSTLY SUNNY BY EARLY AFTERNOON OVER ALL BUT THE HIGH TERRAIN
OF SRN GILA COUNTY. LITTLE CHANGE IN HIGH TEMPS IS EXPECTED...AS
COOLER AIR CONTINUES TO FILTER OVER THE LOWER DESERTS. THE FORECAST
HIGH FOR PHOENIX MONDAY WILL BE JUST 72 DEGREES.

DRY NORTH TO NORTHEAST FLOW ALOFT CONTINUES ACROSS THE AREA IN THE
WAKE OF THE DEPARTED UPPER TROF ON TUESDAY...FOR GENERALLY SUNNY
SKIES. HIGH TEMPS WILL RISE A FEW DEGREES AS HEIGHTS/THICKNESSES
START TO CLIMB...BUT OVERALL TEMPS WILL STAY BELOW SEASONAL NORMALS
WITH PHOENIX SITTING IN THE MID TO UPPER 70S.

QUITE A BIT OF MODEL UNCERTAINLY DEVELOPING FOR THE LATTER PORTION
OF THE EXTENDED PERIOD. GFS KEEPS HIGH PRESSURE ALOFT IN PLACE
ACROSS THE DESERT SOUTHWEST...AND DEVELOPS A CLOSED LOW WELL OFF TO
THE SOUTHEAST...OVER PORTIONS OF TEXAS AND NRN MEXICO. ON THE OTHER
HAND...THE ECMWF DEVELOPS THAT SAME UPPER LOW MUCH FURTHER TO THE
WEST...AND ACTUALLY MOVES THE LOW CENTER INTO SERN AZ BY WED
AFTERNOON. THE LOW STARTS TO ADVECT QUITE A BIT OF MOISTURE INTO
SERN AZ...SOME OF THAT MOISTURE TROPICAL IN NATURE. VERY LOW
CONFIDENCE IN THE ECMWF SOLUTION AS MODEL RUN TO RUN CONSISTENCY HAS
BEEN VERY LOW. FOR NOW...WILL KEEP A DRY FORECAST IN PLACE ACROSS AZ
FOR WEDNESDAY AND THURSDAY...BUT WILL KEEP SOME SINGLE DIGIT POPS IN
PLACE FROM PHOENIX EASTWARD...AND ADD IN SOME CLOUD COVER AS
WELL...IN A NOD TO THE MODEL UNCERTAINTY.

&&

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

PERIODIC MID AND HIGH CLOUDS TO AFFECT THE REGION THROUGH THE PERIOD
AS LOW PRESSURE APPROACHES. WINDS ACROSS THE PHOENIX AREA ARE
EXPECTED TO REMAIN OUT OF THE EAST FOR THE MAJORITY OF THE PERIOD
WITH THE POSSIBILITY OF GOING VARIABLE OR SWITCHING OUT OF THE WEST
FOR AN HOUR OR TWO LATE THIS AFTERNOON. WINDS ACROSS SOUTHEAST
CALIFORNIA WILL BECOME BREEZY LATE THIS AFTERNOON AND EVENING WITH
GUSTY WESTERLY WINDS AT KIPL LIKELY PERSISTING THROUGH THE OVERNIGHT
HOURS TONIGHT.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...
SLIGHTLY COOLER THAN NORMAL TEMPERATURES WILL FILTER INTO THE
DISTRICT THE FIRST PART OF NEXT WEEK...BEFORE MODERATING THE LATTER
HALF OF THE WEEK. OCCASIONALLY GUSTY AFTERNOON NORTHWEST AND WEST
WINDS WILL BE COMMON SUNDAY AND MONDAY...WITH GUSTS TO AROUND 25 MPH
POSSIBLE ALONG RIDGE TOPS AND THROUGH FAVORED RIVER VALLEY
LOCATIONS. MINIMUM RELATIVE HUMIDITY VALUES WILL INITIALLY HOVER IN
A 20-40 PERCENT RANGE SUNDAY BUT WILL FALL INTO THE TEENS THE
REMAINDER OF THE WEEK AS DRIER AIR GRADUALLY OVERSPREADS THE AREA.
OTHERWISE...OVERNIGHT RECOVERY WILL BE GOOD WITH ONLY MINIMAL
CHANCES OF WETTING RAINS OVER HIGHER TERRAIN EARLY NEXT WEEK.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...CB
AVIATION...KUHLMAN
FIRE WEATHER...MO






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