Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 010327
AFDPSR

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

.SYNOPSIS...
SIGNIFICANTLY COOLER TEMPERATURES WILL ARRIVE THE WEEKEND AS A LOW
PRESSURE SYSTEM AND COLD FRONT PUSH THROUGH THE DESERT SOUTHWEST.
HIGHS WILL DROP INTO THE UPPER 70S AND LOW 80S ON SATURDAY...FALLING
FURTHER TO THE UPPER 60S AND LOWER 70S ON SUNDAY. IN ADDITION TO THE
COOLER TEMPERATURES...OCCASIONALLY BREEZY CONDITIONS CAN BE EXPECTED
THROUGHOUT THE WEEKEND. RAIN CHANCES WILL BE SLIGHT...CONFINED
MOSTLY TO HIGHER TERRAIN NORTH AND EAST OF PHOENIX...AND AMOUNTS
VERY LIGHT. A GRADUAL WARMING TREND WILL BEGIN DURING THE MIDDLE OF
NEXT WEEK.

&&

.DISCUSSION...
A VERY WEAK SHORTWAVE CAN BE SEEN IN EVENING WV IMAGERY ACROSS SRN
ARIZONA EJECTING AHEAD OF THE LARGER FULL LATITUDINAL TROUGH
CRASHING INTO THE WRN CONUS. 00Z KTWC SOUNDING DATA DEPICTED A
SUBTLE BACKING OF WINDS AROUND THE H7 LAYER IN CONJUNCTION WITH
MIDLEVEL COOLING SUPPORTING THE PRESENCE OF THIS SHORTWAVE AND
FOCUSED ASCENT...WHICH HAS LED TO EXTENSIVE ACCAS AND AN ISOLD
TSTM (WHICH HAS SINCE DISSIPATED). RECENT HRRR ITERATIONS AS WELL AS
OTHER ARW AND NMM HIGH RESOLUTION CORES CAPTURED THIS FEATURE AND
ATTENDANT CONVECTION...WHICH MAY CONTINUE TO PERCOLATE THROUGH THE
EVENING...HOWEVER LARGELY REMAIN JUST EAST OF THE FORECAST AREA.

OTHER THAN ACCOUNTING FOR SOME SHORT TERM TRENDS IN THIS EVENINGS
UPDATE...OVERNIGHT LOW TEMPERATURES WERE SELECTIVELY BUMPED UP A FEW
DEGREES (PARTICULARLY THOUGH SERN CALIFORNIA) AS THE COMBINATION OF
INCREASINGLY THICK HIGH CLOUDS AND LACK OF DECOUPLED WINDS DUE TO
THE INCREASED PRESSURE GRADIENT SHOULD HOLD READINGS UP MORE THAN
ANTICIPATED. ALSO...INVESTIGATION OF NUMEROUS HIGH RESOLUTION MODELS
AND EARLY 00Z MODEL OUTPUT STRONGLY SUGGESTS NOTABLE LOW/MID LEVEL
FRONTOGENETICAL FORCING THROUGH PARTS OF CNTRL/WRN ARIZONA SATURDAY
MORNING. WHILE MOST ACTUAL PRECIPITATION REACHING THE GROUND WILL
LIKELY BE TIED WITH OROGRAPHIC ENHANCEMENT NORTH OF THE CWA...A FEW
ISOLD SPRINKLES/SHOWERS LOOK MORE POSSIBLE DURING THE MID MORNING
HOURS. HAVE MODESTLY INCREASED SOME POPS (AS WELL AS CLOUD COVER) IN
THE 12-18Z TIME FRAME THOUGH IMPACTS SHOULD BE MINIMAL TO NIL.

&&

.PREVIOUS DISCUSSION...
/315 PM MST FRI OCT 31 2014/
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.

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...
AVIATION IMPACTS WILL BE TIED TO BOTH THE POSSIBILITY OF LOWER CIGS
AND SHIFTING AND GUSTY WINDS SATURDAY. INCREASING MOISTURE WILL LEAD
TO EVENTUAL DEVELOPMENT OF LOWER CIGS SATURDAY AFTER SUNRISE...WITH
BOTH BUFR SOUNDINGS AND STATISTICAL GUIDANCE SUPPORT CIGS IN THE
4K-6K LEVEL. WHILE CONFIDENCE IS MODERATE REGARDING THE PRESENCE OF
LOWER CLOUDS...THE PERSISTENCE OF CLOUDS AND TIMING OF DEVELOPMENT
AND SUBSEQUENT SCATTERING LATER IN THE DAY CARRY MUCH LOWER
CONFIDENCE. SCATTERED VIRGA WILL BE LIKELY... AND A FEW
SPRINKLES/SHOWERS MAY ALSO BE BRIEFLY POSSIBLE. WHILE SOME HIGHER
WIND GUSTS MAY BE POSSIBLE WITH THE WIND SHIFT TO THE SOUTHWEST LATE
SATURDAY MORNING...SPEEDS SHOULD REMAIN BELOW 25KT.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
GUSTY WINDS AND TIMING OF WIND SHIFTS WILL BE THE PRIMARY AVIATION
IMPACTS THROUGH SATURDAY AFTERNOON. A COLD FRONT WILL PASS THROUGH
TERMINAL SITES SATURDAY MORNING WITH THE POSSIBILITY OF VARIABLY
SHIFTING WINDS AROUND FROPA. DURING THE AFTERNOON HOURS...STRONGER
WEST AND SOUTHWEST WIND GUSTS APPROACHING 30KT MAY BE POSSIBLE
BEFORE DECOUPLING AROUND SUNSET. FORECAST CONFIDENCE IS MODERATE.

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






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