Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 312215
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
315 PM MST FRI OCT 31 2014

.SYNOPSIS...
SIGNIFICANTLY COOLER READINGS ARE 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...
FORECAST AREA IS SITUATED BETWEEN AN UPPER LEVEL RIDGE TO THE EAST
AND A TROUGH OFF THE WEST COAST. VEERING PROFILE IS ALSO EVIDENT
WITH EAST WINDS IN THE LOWER LEVELS AND A STRONGER SOUTHERLY FLOW AT
700 MB. DOWNSLOPE COMPONENT TO THE FLOW HAS PERSISTED THIS
AFTERNOON...RESULTING IN WELL ABOVE AVERAGE TEMPERATURES DUE TO WARM
ADVECTION AND THE EFFECTS OF COMPRESSION. CURRENT HIGH TEMPERATURE
OF 95 DEGREES IN PHOENIX IS ONLY ONE DEGREE SHY OF THE DAILY RECORD
LAST SET IN 1988.

HRRR CONTINUES TO SUGGEST THAT ISOLATED CONVECTION WILL DEVELOP THIS
AFTERNOON...THOUGH CONSENSUS AMONG THE HI-RES AND GLOBAL GUIDANCE IS
THAT THIS WILL BE WELL TO OUR SOUTH AND EAST...WHERE INSTABILITY AND
DEEP LAYER SHEAR WILL BE MAXIMIZED. ACROSS THE LOWER
DESERTS...MAINLY CLEAR SKIES WILL PERSIST FOLLOWED BY INCREASING
HIGH CLOUDS THIS EVENING.

&&

.PREVIOUS DISCUSSION...
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...
THROUGH 03Z SAT...SCT CIRRUS CLDS. SOUTH TO SOUTHEAST WIND 10 TO 20
KNOTS. 03Z SAT TO 17Z SAT...SCT CIRRUS CLDS. LIGHT SOUTHEAST WIND
UNDER 7 KNOTS. FROM 17Z SAT TO 23Z SAT...DRY COLD FRONT APPROACHING.
SCT TO BKN CLDS NEAR 8 THSD AGL. INCREASING AFTERNOON SOUTHWEST WIND
15 TO 23 KNOTS.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
THROUGH 08Z...SCT CIRRUS. SOUTH TO SOUTHWEST WIND 10 TO 20 KNOTS.
FROM 08Z SAT TO 17Z SAT...SCT CIRRUS CLDS. SOUTH TO SOUTHWEST WIND
NEAR 10 KNOTS. FROM 17Z SAT TO 23Z SAT...DRY COLD FRONT APPROACHING.
SCT CLDS BASED NEAR 8 THSD AGL. INCREASING SOUTHWEST WIND 15 TO 25
KNOTS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
A COOLER AIRMASS WILL SETTLE OVER THE REGION MONDAY THROUGH
WEDNESDAY. AFTERNOON TEMPERATURES WILL BE SLIGHTLY BELOW NORMAL...
BUT WARMING IN THE WEEK. BREEZY NORTH TO NORTHEAST WINDS ARE
EXPECTED BOTH DAY AND NIGHT MONDAY THROUGH WEDNESDAY...GENERALLY IN
THE 10 TO 15 MPH RANGE WITH GUSTS TO 20 MPH POSSIBLE. LIGHTER WIND
WILL DEVELOP LATE IN THE WEEK. MINIMUM RELATIVE HUMIDITIES WILL
GENERALLY RANGE FROM 15 TO 20 PERCENT. OVERNIGHT RECOVERY WILL BE
POOR MONDAY THROUGH WEDNESDAY WITH THE BREEZES.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...HIRSCH
PREVIOUS DISCUSSION...CB
AVIATION...VASQUEZ
FIRE WEATHER...VASQUEZ





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