Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 192150 AAA
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
250 PM MST FRI SEP 19 2014

.UPDATE...UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS.

&&

.SYNOPSIS...
LINGERING MOISTURE ACROSS THE REGION AND LOW PRESSURE APPROACHING
FROM THE WEST WILL KEEP AT LEAST SLIGHT CHANCES FOR SHOWERS AND
THUNDERSTORMS IN THE FORECAST TODAY THROUGH SATURDAY. DRIER AIR WILL
GRADUALLY FILTER INTO THE REGION SUNDAY AND MONDAY FOR A DECLINE IN
STORM CHANCES. WITH LITTLE CHANGE THROUGH WEDNESDAY...STORM CHANCES
REMAIN VERY SLIGHT AND LIMITED TO THE HIGHER MOUNTAINS OF
SOUTH-CENTRAL ARIZONA. TEMPERATURES WILL GRADUALLY WARM AS WELL. AN
APPROACHING PACIFIC WEATHER SYSTEM LATE NEXT WEEK WILL LEAD TO AN
INCREASE IN STORM CHANCES OVER THE HIGHER TERRAIN OF SOUTH-CENTRAL
ARIZONA.

&&

.DISCUSSION...
LOW PRESSURE SPINNING OFF CALIFORNIA COAST WILL HAVE LITTLE FORWARD
PROPAGATION AND WILL SLOWLY MIGRATE NORTHEASTWARD ACROSS THE GREAT
BASIN THROUGHOUT THE COMING WEEKEND. WITH HIGH PRESSURE SITUATED
ACROSS NORTHERN MEXICO AND SOUTHERN NEW MEXICO...A SOUTHERLY FLOW
WILL CONTINUE TO STREAM IN SOME MOISTURE FROM THE TROPICS KEEPING
OUR MIXING RATIOS AND DEWPOINTS ELEVATED. CHANCES FOR PRECIPITATION
SHOULD BE LIMITED TO HIGHER ELEVATION TERRAIN THROUGH MONDAY WHERE
THE INSTABILITY AND AXIS OF GREATEST DYNAMICS WILL RESIDE. NOT AN
IMPRESSIVE AMOUNT OF INSTABILITY IS FORECAST ACROSS THE LOWER AND
CENTRAL DESERTS THIS WEEKEND BUT CAN NOT RULE OUT A STRAY ISOLATED
SHOWER. FAIRLY MOIST COLUMN OF AIR IN PLACE...PW VALUES REMAINING
AROUND THE 1.5 INCH MARK...ALONG WITH SOME ASCENT FROM THE BOUNDARY
LAYER THROUGH MID-LAYERS /600-700MB OR 10-15K FT/.

MONDAY...AS THE UPPER LEVEL TROUGH PUSHES NORTHEAST THROUGH THE
GREAT BASIN...HIGH PRESSURE WILL DEVELOP BACK ACROSS THE SOUTHWEST
DESERTS ALLOWING THE TEMPERATURE TO NUDGE UP A DEGREE OR TWO EACH
DAY. THE PREVIOUS SHIFT DID WELL WITH TEMPERATURES SO VERY MINOR
CHANGES WERE MADE...KEEPING TEMPERATURES A HANDFUL OF DEGREES ABOVE
OR BELOW SEASONAL NORMAL /99F FOR PHOENIX AND 101F FOR YUMA/ THROUGH
THE WEEK. WITH A MORE WESTERLY COMPONENT IN THE WIND FLOW
PATTERN...MIXING RATIOS ARE FORECAST TO DROP DOWN AROUND 6-8 G/KG
RANGE FROM SOUTHEAST CALIFORNIA INTO THE CENTRAL ARIZONA DESERTS
EARLY NEXT WEEK. EVEN WITH HIGH PRESSURE IN PLACE ACROSS NORTHERN
MEXICO...THE FAVORABLE WIND FLOW AND LACK OF MOISTURE SHOULD WARD
OFF OUR CHANCES FOR ANY STORMS THAT MAY TRY TO FORM. ENSEMBLE AND
DETERMINISTIC MODELS HAVE WELL ADVERTISED THE TROUGH FEATURE SLOWLY
MOVING NORTHWARD ONLY TO BE ABSORBED IN THE LONGWAVE TROUGH PATTERN.
EVEN PAST 115 HRS BOTH ECMWF AND GFS...AND RESPECTIVE ENSEMBLE
MEMBERS...HAVE THE NEXT UPPER LEVEL DISTURBANCE WELL AGREED UPON BY
LATE WEEK THURSDAY/FRIDAY BEGINNING TO IMPACT THE WESTERN COAST.


.PREVIOUS DISCUSSION.../ISSUED 410 AM MST/PDT FRIDAY 19 SEPT/...
TODAY THROUGH SUNDAY...

MONDAY THROUGH THURSDAY...
WITH RIDGING BEGINNING TO BUILD IN MONDAY ALONG WITH SOME ADDITIONAL
DRYING...TEMPS WILL BE A BIT WARMER AND POPS WILL BE LIMITED TO LOW
END SLIGHT CHANCE OVER THE HIGHER MOUNTAINS OF SOUTH-CENTRAL
ARIZONA. LOOK FOR SLIGHT ADDITIONAL WARMING TUESDAY WITH LITTLE
CHANGE WEDNESDAY ALONG WITH  LITTLE CHANGE IN POPS. BY THURSDAY...A
PACIFIC TROUGH MOVES INLAND AND DRAWS SOME MOISTURE NORTHWARD.
SLIGHT CHANCE AREA WAS BROADENED BUT STILL CONFINED TO THE HIGHER
TERRAIN OF SOUTH-CENTRAL ARIZONA.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
SCT-BKN MID-LEVEL CLOUD DECKS AOA 8000FT TO RETURN OVERNIGHT AND
PERSIST INTO SATURDAY MORNING. STORMS FOR THE MOST PART WILL HUG THE
HIGHER TERRAIN NORTH AND EAST OF TERMINALS...BUT NORTHERLY STEERING
FLOWS COULD BRING AN ISOLATED STORM INTO THE LOWER DESERTS THIS
AFTERNOON/EVENING. OUTSIDE OF ANY WANDERING CONVECTIVE OUTFLOW
BOUNDARIES...WINDS WILL CONTINUE TO BE LIGHT AOB 10KTS WITH NO
SUDDEN UNEXPECTED WIND SHIFTS.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
MAINLY CLEAR SKIES AND LIGHT WINDS TO PREVAIL ACROSS THE AREA
THROUGH THE TAF PERIOD.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
RATHER DRY WESTERLY FLOW TO KEEP SKIES MAINLY CLEAR THROUGH THE
FORECAST PERIOD AT MOST LOCATIONS ACROSS THE REGION...WITH THE
EXCEPTION OF THE HIGHER TERRAIN OF SOUTH-CENTRAL ARIZONA...WHERE
LINGERING MOISTURE MAY ALLOW ISOLATED SHOWERS/THUNDERSTORMS TO
DEVELOP EACH AFTERNOON/EARLY EVENING. MINIMUM RELATIVE HUMIDITIES TO
FALL INTO THE 20 TO 30 PERCENT RANGE EACH AFTERNOON...WITH GOOD TO
EXCELLENT OVERNIGHT RECOVERIES. WINDS TO REMAIN MAINLY ON THE LIGHT
SIDE...MAINLY IN THE 5 TO 15 MPH RANGE...WITH THE USUAL DIURNAL
TRENDS TO PREVAIL AT MOST LOCATIONS.


&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...DEWEY
PREVIOUS DISCUSSION...AJ
AVIATION...MEYERS
FIRE WEATHER...MEYERS/PERCHA





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