Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 160332
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
830 PM MST TUE APR 15 2014

.SYNOPSIS...
DRY WESTERLY FLOW ALOFT WILL PERSIST THROUGH MUCH OF THE WORK WEEK
WITH HIGH TEMPERATURES WARMING INTO THE 90S OVER THE WARMER DESERTS.
A WEAK UPPER LEVEL LOW APPROACHING FROM THE EAST PACIFIC WILL SPREAD
INCREASING MOISTURE AND CLOUDS INTO THE AREA FRIDAY INTO THE
EARLY WEEKEND...LEADING TO A SLIGHT CHANCE OF SHOWERS ACROSS SOUTH
CENTRAL ARIZONA AND THE POSSIBILITY FOR SLIGHTLY COOLER DAYTIME
TEMPERATURES. THE COOL DOWN WILL BE SHORT LIVED...AS HIGH PRESSURE
QUICKLY RETURNS FOR EARLY NEXT WEEK.

&&

.DISCUSSION...
EVENING WV IMAGERY DEPICTS THE FORECAST AREA TRAPPED IN WEAK NWLY
FLOW BETWEEN THE MAIN MID LATITUDE JET AND PROGRESSIVE SHORTWAVES
ACROSS THE NRN ROCKIES...AND ANTI-CYCLONIC SUBTROPICAL FLOW OVER THE
SERN PACIFIC BASIN. TRAJECTORY ANALYSIS SUGGESTS MOSTLY CLEAR SKIES
WILL PREVAIL THROUGH THE OVERNIGHT HOURS FLANKED BY MORE EXTENSIVE
CIRRUS BORDERING THE CWA TO BOTH THE NORTH AND SOUTH. WITH NO
IMPACTS ANTICIPATED THROUGH AT LEAST THE NEXT 24 HOURS...AND
PREVIOUS FORECAST TRENDS HOLDING NICELY...LITTLE TO NO CHANGES WERE
NECESSARY IN THIS EVENINGS UPDATE.

&&

.PREVIOUS DISCUSSION...
/220 PM MST TUE APR 15 2014/
DRY NORTHWESTERLY FLOW WILL REDEVELOP WEDNESDAY AS A RIDGE BUILDS
ALONG THE WEST COAST AND A TROUGH MOVES INTO THE FOUR CORNERS. A
DISCERNIBLE WEAKENING TREND IS NOTED IN BOTH THE GFS/NAM WITH REGARD
TO THE AMPLITUDE OF THIS TROUGH. CONSEQUENTLY...HIGH TEMPERATURES
HAVE BEEN NUDGED UPWARDS WEDNESDAY INTO THE LOWER 90S ACROSS THE
LOWER DESERTS UNDER MOSTLY SUNNY SKIES. ALTHOUGH SOME AFTERNOON
BREEZINESS IS ALSO ANTICIPATED ACROSS SOUTH-CENTRAL AZ...THE
MAGNITUDE OF THE WIND HAS ALSO TRENDED DOWNWARD OVER THE PAST DAY OR
SO.

BY LATE THURSDAY...LONGWAVE TROUGHING OVER THE WEST WILL SYNC UP
WITH AN AREA OF LOW PRESSURE...CURRENTLY CIRCULATING IN THE EASTERN
PACIFIC...INTRODUCING SOUTH/SOUTHWESTERLY FLOW ALOFT INTO THE
SOUTHWEST STATES. THIS LOW AND LIMITED AMOUNT PACIFIC MOISTURE WILL
MOVE THROUGH THE AREA FRIDAY INTO SATURDAY. MODEL SOUNDINGS PLOT THE
MAJORITY OF THE MOISTURE AT AND ABOVE THE 600MB LEVEL WITH VERY DRY
SUB-CLOUD LAYERS AND INVERTED V TRACES BELOW...PARTICULARLY OVER
SOUTH-CENTRAL ARIZONA. STILL DO NOT BELIEVE THIS SYSTEM TO BE MOIST
ENOUGH TO WARRANT ANYTHING MORE THAN LOW-END SLIGHT CHANCE POPS FOR
OVERNIGHT FRIDAY AND EARLY SATURDAY ACROSS CENTRAL ARIZONA WITH ONLY
SLIGHTLY HIGHER AMOUNTS OVER THE MORE FAVORABLY ORIENTED HIGHER
TERRAIN. SIGNIFICANT RAINFALL IS NOT EXPECTED...BUT LIGHT SPRINKLES
AND VIRGA ARE MORE LIKELY FROM MARICOPA COUNTY EASTWARD. AS WE`VE
ALREADY SEEN BEFORE THIS SPRING...HIGH BASED SHOWERS AND DRY
SUB-CLOUD LAYERS COULD ENHANCE WIND GUSTS IN THE AFTERNOON HOURS.
WITH THE LOWER HEIGHTS...STILL IN THE 568-570DM RANGE AT 500MB AND
850MB TEMPS FALLING IN THE 16C TO 17C RANGE...TEMPERATURES SHOULD
SEE A SLIGHT COOL DOWN AND DROP BACK TOWARDS MORE SEASONABLE
READINGS IN THE MID TO UPPER 80S FRIDAY AND SATURDAY.

BEYOND SATURDAY...CONFIDENCE IN THE MODEL FORECASTS BEGINS TO WANE.
500MB HEIGHTS RAPIDLY RISE INTO THE 580DM RANGE...BRINGING THE 90S
BACK FOR HIGH TEMPERATURES SUNDAY. HOWEVER...BEYOND THAT
POINT...MODEL SOLUTIONS BEGIN TO GREATLY DIVERGE BETWEEN STRONG
RIDGING DIRECTLY OVERHEAD (ECMWF) VERSUS RIDGING ANCHORED TO OUR EAST
(GFS). THIS LEADS TO A WIDE RANGE FOR POTENTIAL HIGH TEMPERATURES
EARLY NEXT WEEK...WITH THE ECMWF INTRODUCING WIDESPREAD TRIPLE-DIGIT
READINGS WHILE THE COOLER GFS LEAVES US IN THE 90S. FOR NOW WENT WITH
A PERSISTENCE HIGH TEMPERATURE FORECAST...LOW TO MID 90S FOR EARLY
NEXT WEEK WITH DRY CONDITIONS AND MOSTLY CLEAR SKIES.

&&

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

NO AVIATION IMPACTS THROUGH WEDNESDAY AFTERNOON WITH MOSTLY CLEAR
SKIES THROUGH THE PERIOD. THE PRESSURE GRADIENT WILL STAY VERY WEAK
THROUGH WEDNESDAY MORNING YIELDING FREQUENT LIGHT AND VARIABLE WIND
HEADINGS. ONLY A SLIGHT INCREASE IN THE GRADIENT WEDNESDAY AFTERNOON
WILL ALLOW WEST WINDS TO INCREASE ABOVE 10KT AT SOME AERODROMES.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
FRIDAY THROUGH TUESDAY...
A WEAK WEATHER DISTURBANCE WILL BRING A MODEST INCREASE IN
MOISTURE...CLOUDINESS...AND AFTERNOON BREEZINESS TO THE DISTRICT
FRIDAY AND SATURDAY...WITH A SLIGHT CHANCE FOR SHOWERS AND
THUNDERSTORMS WITH THIS IMPULSE...PARTICULARLY ACROSS THE HIGHER
TERRAIN NORTH AND EAST OF PHOENIX. EVEN WITH SOMEWHAT MORE MOIST
CONDITIONS...AFTERNOON HUMIDITY LEVELS WILL STILL FALL INTO THE
TEENS...AND ANY THUNDERSTORM GENERATED GUSTY WINDS MAY POSE AN
ENHANCED FIRE WEATHER RISK GIVEN THE ANTECEDENT DRY FUEL CONDITIONS.
HIGH PRESSURE BUILDING OVER THE DESERT SOUTHWEST FROM THE WEST WILL
THEN BRING DRY CONDITIONS BACK OVER THE REGION...ALONG WITH WARMER
TEMPERATURES FOR SUNDAY AND MONDAY. THE FORECAST FOR NEXT TUESDAY IS
MUCH MORE UNCERTAIN...WITH SOME COMPUTER MODELS KEEPING HIGH
PRESSURE IN PLACE...WITH DRY CONDITIONS AND ABOVE NORMAL
TEMPERATURES CONTINUING...WHILE OTHERS ARE BRINGING A VIGOROUS LOW
PRESSURE CENTER INLAND OVER THE REGION...WHICH WOULD BRING MUCH
COOLER TEMPERATURES...GUSTY WINDS...AND A CHANCE FOR SHOWERS TO THE
DISTRICT.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...MO
PREVIOUS DISCUSSION...HIRSCH/NOLTE
AVIATION...MO
FIRE WEATHER...PERCHA






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