Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 280537 AAA
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1040 PM MST THU NOV 27 2014

.UPDATED AVIATION DISCUSSION...

.SYNOPSIS...
A WARM AND DRY STRETCH OF WEATHER WILL AFFECT THE REGION THROUGH THE
UPCOMING WEEKEND UNDER HIGH PRESSURE ALOFT. HIGH TEMPERATURES WILL
BE THE WARMEST TODAY AND THEN SLOWLY COOL THROUGH EARLY NEXT WEEK
WHILE STILL REMAINING WELL ABOVE SEASONAL NORMALS. A LOW PRESSURE
SYSTEM IS EXPECTED TO AFFECT THE WESTERN STATES NEXT WEEK BRINGING A
SLIGHT CHANCE OF LIGHT SHOWERS TUESDAY INTO WEDNESDAY AND COOLER
TEMPERATURES.

&&

.DISCUSSION...

THE COMBINATION OF A VERY WARM AIRMASS (850MB TEMPERATURES NEAR
20C)...DEEP EASTERLY DOWNSLOPE FLOW...AND WALL-TO-WALL SUNSHINE
ALLOWED TEMPERATURES TO SPIKE TO RECORD LEVELS ACROSS SOUTH-CENTRAL
ARIZONA TODAY. THE HIGH TEMPERATURES AT SKY HARBOR OF 87 BROKE THE
OLD RECORD OF 86...WHICH WAS SET IN 1950. THE COMBINATION OF THESE
VERY WARM TEMPERATURES AND SLIGHTLY HIGHER DEWPOINTS ARE EXPECTED TO
LEAD TO A WARMER NIGHT TONIGHT THAN WHAT WE SAW LAST NIGHT...WITH
MANY OF THE MORE URBAN LOCATIONS REMAINING IN THE 50S
TONIGHT...SEVERAL DEGREES WARMER THAN THE 40S THAT WERE OBSERVED IN
THESE LOCATIONS LAST NIGHT. THE LATEST MODEL RUNS CONTINUE TO
INDICATE A SLOW COOLING TREND OVER THE NEXT FEW DAYS AS A STRONG
UPPER TROF APPROACHING THE CA COAST BEGINS TO FLATTEN THE STRONG
RIDGING THAT IS NOW OVER THE SW US. FOR THE VERY SHORT TERM...OTHER
THAN SOME MINOR ADJUSTMENTS TO THE HOURLY TEMPERATURE AND DEWPOINT
TRENDS...CURRENT INHERITED GRIDDED AND ZONE FORECASTS LOOK OK...AND
NO UPDATES ARE PLANNED.

&&

.PREVIOUS DISCUSSION...
REST OF TODAY THROUGH SUNDAY...
THE REST OF THE WARMTH IN THE LOWER LEVELS CERTAINLY REACHED THE
SURFACE THIS AFTERNOON LIKELY AIDED BY THE PRESSURE GRADIENT ACROSS
MUCH OF ARIZONA. TEMPERATURES IN THE PHOENIX AREA HAVE ALREADY
CLIMBED WELL INTO THE 80S WITH SKY HARBOR TYING A RECORD FOR THE
DATE AT 86 DEGREES. FRIDAY WILL ONLY BE A LITTLE BIT COOLER AS THE
RIDGE STARTS TO WEAKEN AND WE HAVE SOME HIGH CLOUDS. THIS VERY
GRADUAL TREND CONTINUES THROUGH THE WEEKEND. ANTICIPATE MORE HIGH
CLOUDS ON SUNDAY AS A WEAKENED SHORT WAVE MOVES THROUGH THE
SOUTHWESTERLY FLOW ALOFT. MEANWHILE...A NEW LOW PRESSURE SYSTEM
TAKES SHAPE OFF THE WEST COAST BECOMING CENTERED WEST OF NORTHERN
CALIFORNIA BY SUNDAY AFTERNOON. ALSO BY THIS TIME...MOISTURE FROM
TROPICAL LATITUDES MOVES NORTHEASTWARD TOWARD THE BAJA PENINSULA.

MONDAY THROUGH THURSDAY...
DIFFERENCES IN THE MEDIUM RANGE MODELS BECOME MORE EVIDENT BY MONDAY
WITH THE GFS POSITIONING THE UPPER LOW CLOSER TO THE COAST THAN THE
ECMWF AND GEM. THE LATTER ALSO DEPICT A MORE CUTOFF SITUATION WITH
THE LOW. THE GFS ALSO HAS A MORE SUBSTANTIAL SUBTROPICAL JET AND
MOISTURE PLUME THAN THE THE ECMWF AND GEM. HOWEVER...THE LOW WEAKENS
AS IT MOVES INLAND. WHILE THE GFS HAS TRENDED DOWN SUBSTANTIALLY IN
ITS QPF THE PAST COUPLE DAYS...IT SEEMS TO HAVE SETTLED ON A WINDOW
OF TUESDAY AFTERNOON INTO WEDNESDAY FOR PRECIP OVER OUR AREA. THE
EXPERIMENTAL GFS-13KM ALSO SUPPORTS THIS. THE GEFS PROBABILITIES ARE
ALSO WELL INTO THE DOUBLE DIGITS. CONTRAST THAT WITH THE ECWMF AND
GEM WHICH KEEP AT LEAST SOME MEASURE OF RIDGING OVER US AS THE
SYSTEM DISSIPATES MOVING INTO THE PACIFIC NORTHWEST. THE ECENS MEAN
SUPPORTS THE IDEA OF WEAKENING AND SOME SORT OF RIDGING THOUGH A BIT
LESS THAN THE OPERATIONAL RUN. WITH THE PERSISTENCE OF THE GFS/GEFS
IN HOLDING ON TO POPS...LEFT THE EXTENDED AS IS. IF WE WIND UP
GETTING PRECIP NEXT WEEK IT IS NOT LOOKING LIKE IT WILL BE MUCH.
OTHERWISE THERE SHOULD AT LEAST BE SOME THICK CLOUD COVER AROUND
TUE/WED TO NUDGE HIGH TEMPS DOWNWARD. EXTENDED TEMPS MAY NEED SOME
UPWARD ADJUSTMENT IF LESS TROUGHING PANS OUT.


&&

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

STRONG RIDGING ALOFT...AND HIGH PRESSURE AT THE SURFACE WILL KEEP
SKIES MAINLY CLEAR AND WINDS QUITE LIGHT...WITH THE USUAL DIURNAL
TRENDS AT ALL OF THE TERMINALS THROUGH THE TAF PERIOD. ALTHOUGH
THERE IS STILL A CHANCE THAT SLANT VISIBILITIES OVER THE PHX AREA
COULD BE AFFECTED BY SMOKE FROM THE MULCH FIRE NEAR LUKE AFB...WINDS
SHOULD REMAIN LIGHT ENOUGH TO KEEP DENSE SMOKE FROM AFFECTING ANY OF
THE PHOENIX TAF SITES.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
HIGH PRESSURE WILL REMAIN IN CONTROL THROUGH MONDAY...RESULTING IN A
CONTINUED PERIOD OF MOSTLY CLEAR SKIES AND DRY CONDITIONS. SINGLE
DIGIT HUMIDITIES WITH FAIR OVERNIGHT RECOVERIES WILL BE COMMON
THROUGH THE WEEKEND. STILL MONITORING THE POTENTIAL FOR A LARGE
UPPER LEVEL STORM SYSTEM TO MOVE THROUGH THE AREA BY THE MIDDLE OF
NEXT WEEK. SOME MODEL DIFFERENCES HAVE BECOME MORE AND MORE EVIDENT
OVER THE PAST FEW RUNS...THUS CONFIDENCE IN EXACTLY HOW THE FORECAST
WILL EVOLVE NEXT WEEK IS LOW. STILL HANGING ONTO THE IDEA OF
INCREASING RAIN CHANCES AND ELEVATED HUMIDITIES BY
TUESDAY/WEDNESDAY.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...PERCHA/AJ
AVIATION...PERCHA
FIRE WEATHER...LEINS





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