Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 020444
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
945 PM MST WED OCT 1 2014

.SYNOPSIS...
A PERSISTENT HIGH PRESSURE RIDGE BUILDING INTO THE REGION WILL LEAD
TO A WARMING TREND FOR THE REST OF THE WEEK WITH ABOVE NORMAL
TEMPERATURES PEAKING ON SATURDAY. ANTICIPATE LITTLE CHANGE IN
TEMPERATURES THURSDAY FOLLOWED BY A WARMING TREND FRIDAY AND
SATURDAY. THERE WILL BE LITTLE CHANGE IN TEMPERATURES SUNDAY.
WEAKENING HIGH PRESSURE NEXT WEEK WILL RESULT IN A VERY SLOW COOLING
TREND.

&&

.DISCUSSION...
SURFACE PRESSURE TENDENCIES ARE RISING THIS EVENING AS SURFACE HIGH
PRESSURE BUILDS OVER THE INTERIOR WEST BEHIND A DEPARTING TROUGH AND
ASSOCIATED WEAK FRONT THAT MOVED THROUGH NORTHERN ARIZONA AND THE
MOHAVE DESERT TODAY. MODELS INDICATE SOME SLIGHTLY COOLER AIR
FILTERING INTO OUR FORECAST AREA...MOST NOTICEABLY OVER THE LOWER
COLORADO RIVER VALLEY AND VICINITY. ACCORDINGLY...SOME SPOTS MAY BE
SLIGHTLY COOLER THURSDAY BUT OVERALL THE TEMPERATURE TRENDS WILL BE
MINOR FOR THE LOWER ELEVATIONS. OF MORE NOTE WILL BE THE
STRENGTHENING PRESSURE GRADIENT OVER OUR FORECAST AREA LEADING TO
PREVAILING NORTH AND NORTHEAST WINDS WITH LOCALLY BREEZY
CONDITIONS...MAINLY LOWER COLORADO RIVER VALLEY...STARTING TONIGHT.
THE WIND PATTERN WILL CONTINUE INTO SATURDAY. UPWARD TREND OF TEMPS
FOR FRIDAY AND SATURDAY STILL ON TRACK.

&&

.PREVIOUS DISCUSSION ISSUED 230 PM...
A COMPACT SHORTWAVE MOVING INTO WRN COLORADO WAS FORCING A SOUTHWARD
MOVING COLD FRONT INTO FAR NWRN ARIZONA THIS AFTERNOON...THOUGH POST
FRONTAL SFC PRESSURE RISES WERE WANING SLOWING THE FRONTAL PROGRESS.
WV IMAGERY DEPICTS SUBSTANTIAL DRYING AND SUBSIDENCE PROGRESSING
TOWARDS THE FORECAST AREA...WITH OBJECTIVELY ANALYZED WEAK HEIGHT
FALLS/MID LEVEL CAA SKIRTING INTO NORTHERN ARIZONA. HOWEVER...IN THE
WAKE OF THE SHORTWAVE AND ASSOCIATED FRONTAL PASSAGE
TONIGHT...STRONGER RIDGING ALOFT WILL RAPIDLY BUILD OVER THE SWRN
CONUS AND PERSIST AS THE PREDOMINANT FEATURE THROUGH EARLY NEXT
WEEK.

WITH THE PASSING SHORTWAVE FEATURE...UPSTREAM FLOW
AMPLIFICATION...AND RESULTING SURFACE HIGH PRESSURE EXPANSION ACROSS
MUCH OF THE GREAT BASIN...THE PRESSURE GRADIENT WILL RESULT MORE
NOTICEABLE NORTH TO NORTHEASTERLY WINDS...PARTICULARLY DOWN THE
COLORADO RIVER VALLEY AND THE MARICOPA/GILA HIGHER
TERRAIN/FOOTHILLS. LOCAL SFC WINDS 10-15 MPH ARE LIKELY WITH
ISOLATED GUSTINESS FOR THE NEXT SEVERAL DAYS. OVERNIGHT WINDS MAY
KEEP LOW TEMPERATURES MORE MILD THAN THEY HAVE BEEN THE PAST FEW
NIGHTS...BUT STILL PLEASANTLY COOL FOR EARLY OCTOBER.

WITH H5 HEIGHTS REACHING A 588-591DM RANGE...TEMPERATURES WILL PEAK
ON SATURDAY...AND CANNOT RULE OUT SOME SOUTH-CENTRAL DESERT
LOCALES...INCLUDING PHOENIX...HITTING THE CENTURY MARK ALONG WITH
THE ALREADY WARM WESTERN AZ/SOUTHEAST CA DESERTS. THE AVERAGE LAST
100F HIGH TEMPERATURE OVER THE LAST NORMAL PERIOD OF 1981-2010 IN
PHOENIX HAS BEEN OCT 3RD...AND OCT 5TH FOR YUMA. BY EARLY NEXT
WEEK...HIGH PRESSURE OVER THE WEST WILL BEGIN WEAKEN AND RIDGE
HEIGHTS WILL GRADUALLY LOWER AS ANOTHER WEATHER DISTURBANCE DEVELOPS
DOWN THE WEST COAST. THE COMBINATION OF LOWER HEIGHTS...SOME PASSING
HIGH LEVEL CLOUDS AND A SUBTLE RETURN OF SOME ELEVATED HUMIDITIES
WILL SUPPORT A SLOW COOLING TREND OF AFTERNOON TEMPERATURES.

&&

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

A WEAK DRY COLD FRONT WILL SLOWLY SAG SOUTHWARD INTO SOUTHERN
ARIZONA AND FAR SOUTHEAST CALIFORNIA TONIGHT AND THURSDAY.
HOWEVER...STRENGTHENING HIGH PRESSURE TO THE NORTH WILL LEAD TO A
TIGHTENING PRESSURE GRADIENT FAVORING NORTH AND NORTHEAST
WINDS...MOST NOTICEABLY AFTER 16Z. SURFACE WIND WILL BE STRONGEST
OVER THE LOWER COLORADO RIVER VALLEY AND NEAR FOOTHILL LOCATIONS ON
THE EDGES OF THE PHOENIX METRO AREA WITH GUSTS OF 20-25 KTS. LOWER
LEVEL WINDS ABOVE THE INVERSION WILL STRENGTHEN TO 20-25 KTS AFTER
08Z AND WEAKEN CONSIDERABLY AFTER 14Z. LOCATIONS WITH CALM SURFACE
WINDS OR WINDS WITH A SOUTHERLY COMPONENT BETWEEN 09Z-13Z MIGHT
EXPERIENCE SOME LOW LEVEL WIND SHEAR. CONFIDENCE TOO LOW IN STRENGTH
OF NEAR SURFACE WINDS TO REFLECT LLWS IN THE TAFS. OTHERWISE...CLEAR
SKIES.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
A RIDGE OF HIGH PRESSURE WILL BE THE PREDOMINANT WEATHER FEATURE
ACROSS THE SOUTHWEST THROUGH THE MIDDLE NEXT WEEK. DRIER THAN NORMAL
CONDITIONS WILL PREVAIL AND NO PRECIPITATION IS EXPECTED.
TEMPERATURES WILL BE ABOVE AVERAGE THROUGH SUNDAY...FOLLOWED BY A
SLIGHT COOLING TREND EARLY NEXT WEEK AS HIGH PRESSURE WEAKENS AND
MEAGER MOISTURE RETURNS TO THE AREA. MINIMUM HUMIDITIES WILL FALL
INTO THE SINGLE DIGITS AND TEENS OVER THE WEEKEND...BEFORE TRENDING
UP VERY SLIGHTLY NEXT WEEK. WINDS WILL REMAIN UNUSUALLY LIGHT...WITH
ONLY OCCASIONAL UPSLOPE GUSTINESS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

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





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