Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 221138
AFDPSR

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

...UPDATED AVIATION AND FIRE WEATHER...

.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 THROUGH WEDNESDAY...
HIGH LEVEL CLOUDS OF VARYING COVERAGE AND THICKNESSES CONTINUE TO
STREAM ACROSS THE REGION FROM THE NORTH WITH PARTLY TO MOSTLY CLOUDY
SKIES PERSISTING FROM LAST EVENING. CLOUDS WILL GRADUALLY BREAK IN
COVERAGE AND THIN AS DRIER AIR EXPANDS DOWN FROM THE GREAT BASIN
ALONG THE EASTERN PERIPHERY OF STRONG PACIFIC RIDGING...CENTERED
AROUND 130W/30N THIS MORNING. SUBTLE WARMING THROUGH THE LOWER ATMO
COLUMN...ABOUT 5 C OR SO...AND LESS CLOUD COVER DURING THE DAYTIME
WILL LEAD TO A WARMER AFTERNOON THAN THOSE OVER THE WEEKEND. THE
GREATEST AMOUNT OF PROFILE CHANGE IS EXPECTED ACROSS THE WESTERN
FORECAST AREA WHERE TEMPERATURES COULD BE 8 TO 10 DEGREES WARMER THAN
THOSE OBSERVED SUNDAY. LOW 580DM RIDGE HEIGHTS WILL HOLD OVER
SOUTHERN CA THROUGH THE EARLY WEEK WHILE THE RIDGE AMPLIFIES AND
EVENTUALLY EXPANDS INTO WESTERN CANADA/PAC NW BY TUESDAY.

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 SOCAL 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...NOLTE
AVIATION....MO
FIRE WEATHER...MO






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