Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 221652
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
949 AM MST MON DEC 22 2014

.SYNOPSIS...
HIGH PRESSURE OFF THE WEST COAST WILL RESULT IN NEAR NORMAL
TEMPERATURES WITH VARYING AMOUNTS OF HIGH CLOUDS THROUGH THE MIDDLE
OF THE WEEK. BY THURSDAY...A FAST MOVING STORM SYSTEM WILL SWING
THROUGH THE GREAT BASIN...BRINGING SLIGHTLY COOLER TEMPERATURES AND
INCREASED CLOUDINESS THAT WILL LAST THROUGH FRIDAY. DRY...AND
POTENTIALLY MUCH COOLER...WEATHER IS EXPECTED BY THE COMING WEEKEND.

&&

.DISCUSSION...
TODAY...REGIONAL SATELLITE IMAGERY SHOWS THE HIGH CLOUDS HAVE
FINALLY THINNED OUT OVER THE SOUTHWESTERN STATES THIS MORNING...AND
THAT THE STORM TRACK ALONG THE EASTERN PERIPHERY OF THE PACIFIC
RIDGE HAS SHIFTED SLIGHTLY TO OUR EAST...BRINGING THE INFLUENCE OF
576-582DM HEIGHTS OVER SOUTHEAST CALIFORNIA. MODELS IN THE SHORT
TERM SUGGEST 850-800MB TEMPS WARM ABOUT 3-5 DEG ACROSS OUR FORECAST
AREA...AND WITH DRIER AIR AND LESS CLOUD COVER...AFTERNOON TEMPS
OVER THE LOWER DESERTS IN SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA
WILL BE 8-10 WARMER TODAY COMPARED TO THE LAST FEW DAYS...PEAKING
OUT IN MID 70S. THE INHERITED DIGITAL FORECAST GRIDS CAPTURE THE
OBSERVED TRENDS IN THE NEAR TERM...NO UPDATES NEEDED.

PREVIOUS DISCUSSION...
TUESDAY AND WEDNESDAY...BROAD AREA OF JET ENERGY AND COLD AIR WILL
BEGIN TO EXPAND INTO THE CENTRAL PART OF THE COUNTRY...TRIGGERING
THE PACIFIC RIDGE AMPLIFICATION...AND WORKING A BACK DOOR COLD FRONT
INTO THE SOUTHWEST STATES FOR TUESDAY AND WEDNESDAY. GIVEN THE
CONTINENTAL ORIGIN POINT FOR THIS FRONT...EXPECT A FAIR BIT OF SFC
DEWPOINT DRYING IN ITS WAKE. AFTN DEWPOINTS WILL DROP INTO THE
SINGLE DIGITS TO TEENS ACROSS EASTERN AND PORTIONS OF CENTRAL AZ...
WITH SLIGHTLY HIGHER VALUES HOLDING ALONG AND OVER THE CO RIVER
VALLEY. ALONG WITH THE DRIER AIR INTRUSION...ELEVATED NORTH TO
NORTHEASTERLY WINDS WILL SETTLE ACROSS THE REGION. TIGHTEST SFC
PRESSURE GRADIENTS AND SUBSEQUENT STRONGER WINDS WILL ALIGN DOWN THE
CO RIVER VALLEY AND OVER THE RIDGETOPS OF SOUTHERN GILA COUNTY WITH
15 TO 25 MPH SUSTAINED AND GUSTS NEARING 35 MPH POSSIBLE. ELSEWHERE
ACROSS THE FORECAST AREA WINDS WON`T BE AS STRONG...BUT STILL
NOTICEABLY BREEZY COMPARED TO THE CALM WINDS EXPERIENCED OVER THE
LAST WEEK OR SO. COOLER AIR WILL SLOWLY FILTER INTO THE REGION...
ALLOWING TEMPERATURES TO RETURN CLOSER TOWARDS SEASONAL NORMALS BY
TUESDAY AND CHRISTMAS EVE...LOW TO MID 60S FOR THE DESERTS AND MID
50S FOR THE FOOTHILLS/HIGHER TERRAIN.

THURSDAY /CHRISTMAS DAY/ THROUGH THE COMING WEEKEND...
FAIR MODEL AGREEMENT IS HOLDING FOR THE LATE WEEK AND WEEKEND
FORECAST AS THE UPPER LEVEL PATTERN RETURNS TO MORE ACTIVE AND
PROGRESSIVE SET-UP. 00Z SOLUTIONS FROM THE OPERATIONAL GFS AND ECMWF
PLOT THE PASSING GREAT BASIN SHORTWAVE A BIT DEEPER AND FURTHER TO
THE SOUTH ACROSS AZ LATE THURSDAY INTO FRIDAY. BOTH THESE SOLNS EVEN
PAINT SOME THICKER CLOUDS AND VERY LIGHT QPF OVER THE EASTERN AZ
HIGHER TERRAIN...AS A NARROW BAND OF ELEVATED PWATS IS DRAWN INTO THE
REGION FROM OFF THE SO CAL COAST AND BAJA CA. FCST PWAT VALUES ATTM
AREN`T OVERLY IMPRESSIVE...MOSTLY SHY OF 0.70 INCH. UPPER SHORTWAVE
WILL QUICKLY EXIT TO THE EAST FRIDAY...AS UNSETTLED BROAD
NORTHWESTERLY FLOW REMAINS OVER MUCH OF THE WEST. CONTINUED COOL
TEMPERATURES AND PERIODS OF PASSING CLOUDS ARE POSSIBLE AS SEVERAL
SHORTWAVES TRAVERSE THE FLOW.

TOWARDS THE FAR EXTENDED PERIOD OF THE LATE WEEKEND AND EARLY NEXT
WEEK...MODELS ARE HINTING AT A DRY BUT POTENTLY COLDER SYSTEM
EXPANDING SOUTHWARD FROM CANADA LATE SUNDAY. MUCH OF THE INTERIOR
WEST COULD BE IN FOR A SPELL OF BELOW NORMAL
TEMPERATURES...RESULTING IN SOME OF OUR COOLEST NIGHTS OBSERVED SO
FAR THIS LATE IN THE CALENDAR YEAR.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
NO MAJOR AVIATION CONCERNS THROUGH TUESDAY MORNING AS THICKER CIRRUS
CLEARS DURING THE PERIOD. TIMING OF WIND SHIFTS AND PREVAILING
DIRECTIONS ARE THE PRIMARY FORECAST UNCERTAINTIES. WHILE THE TYPICAL
WESTERLY COMPONENT WILL DEVELOP THIS AFTERNOON...A STEEPENING
PRESSURE GRADIENT WILL GENERALLY SUPPORT A E/NE DIRECTION LATE
TONIGHT. HOWEVER...TERRAIN FEATURES MAY LOCALLY CAUSE PERIODS OF
VARIABLE WINDS...OR FREQUENTLY SHIFTING LIGHTS WINDS AT KPHX
OPPOSITE THE EXPECTED GRADIENT.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA...INCLUDING KIPL AND
KBLH...
NO AVIATION CONCERNS THROUGH TUESDAY MORNING WITH RAPIDLY THINNING
CIRRUS. VARIABLE SFC WINDS THIS MORNING WILL FAVOR A NW DIRECTION BY
THIS AFTERNOON. THERE IS SOME POSSIBILITY OF A FEW STRONGER GUSTS AT
KBLH. A FRONTAL BOUNDARY PASSING THROUGH THE AREA WILL CAUSE MUCH
STRONGER NLY WINDS ABOVE THE LOW LEVEL INVERSION TUESDAY
MORNING...THOUGH LIKELY FALLING SHORT OF LLWS CRITERIA.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
WEDNESDAY THROUGH SUNDAY...
WEATHER DISTURBANCES WILL REMAIN NORTH OF THE DISTRICT THROUGH THE
WEEKEND...LEAVING ONLY VERY SLIGHT CHANCES OF PRECIPITATION OVER
HIGHER TERRAIN LOCATIONS. UNDER DRY NWLY FLOW ALOFT...TEMPERATURES
WILL REMAIN NEAR AVERAGE AS LOWER ELEVATION AFTERNOON HUMIDITY
LEVELS FALLING INTO THE TEENS...WHILE HIGHER ELEVATION HUMIDITIES
ONLY FALL INTO A 20 TO 30 PERCENT RANGE. ANOTHER FRONTAL PASSAGE
FRIDAY MAY ALLOW A BRIEF PERIOD OF GUSTY NORTH WINDS...HOWEVER THE
LATTER HALF OF THE WEEK WILL MAINTAIN VERY LIMITED FIRE DANGER.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...MEYERS/NOLTE
AVIATION....MO
FIRE WEATHER...MO




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