Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 250457
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
955 PM MST WED DEC 24 2014

.SYNOPSIS...
HIGH PRESSURE WILL MOVE TO THE EAST ALLOWING INCREASING HIGH CLOUDS
AHEAD OF A SOMEWHAT DRY LOW PRESSURE SYSTEM POISED TO SLIDE THROUGH
THE FOUR CORNERS REGION ON THURSDAY. THIS SYSTEM WILL BRING COOLER
AND BREEZY CONDITIONS FOR THURSDAY ALONG WITH A CHANCE OF SOME LIGHT
SHOWERS...AND POSSIBLY A LIGHT DUSTING OF SNOW...OVER THE HIGHER
TERRAIN OF SOUTH-CENTRAL ARIZONA THURSDAY EVENING INTO FRIDAY. A DRY
AND COOL WEATHER PATTERN WILL PERSIST FROM SATURDAY THROUGH EARLY
NEXT WEEK.

&&

.DISCUSSION...
A LOW PRESSURE SYSTEM HAS PUSHED WELL INTO THE WESTERN STATES AND
THE ASSOCIATED COLD FRONT EXTENDS FROM IDAHO SOUTHWESTWARD THROUGH
CALIFORNIA THIS EVENING AND IS APPROACHING THE L.A. BASIN. METARS
FROM CALIFORNIA INDICATE THAT PRECIP ON THE LOWER ELEVATIONS HAS
BEEN MODEST. THIS IS DESPITE VERY IMPRESSIVE 500 MB HEIGHT FALLS.
HOWEVER...PRECIPITABLE WATER VALUES NOT OVERLY IMPRESSIVE WITH
PRECIPITABLE WATER VALUES OVER CALIFORNIA AND OFFSHORE OF ABOUT
THREE QUARTERS OF AN INCH. LATEST MODELS INDICATE THAT THE SOUTHERN
END OF THE FRONT WILL MOVE ACROSS SOUTHEAST CALIFORNIA LATER
TONIGHT REACHING THE LOWER COLORADO RIVER ROUGHLY BY 11Z-12Z AND
THEN THE PHOENIX AREA BY 17-18Z...THE UPPER LOW CENTERED NEAR SLC
ABOUT THAT TIME. AS IS OFTEN THE CASE THERE WILL BE SOME RAIN
SHADOWING FROM THE CALIFORNIA MOUNTAINS BUT WITH SOME MOISTURE
RECOVERY OVER SOUTHEAST ARIZONA IN THE AFTERNOON AS SOME PACIFIC
MOISTURE FUNNELS THROUGH SOME GAPS IN THE BAJA MOUNTAINS AND ALONG
WITH SOME CONTRIBUTION FROM SEA OF CORTEZ AS WELL. IN FACT...BOTH
GFS AND NAM DEPICT SOME VERY MODEST CAPE THURSDAY AFTERNOON OVER TWC
FORECAST AREA. DIV Q FIELDS NOT VERY IMPRESSIVE FOR OUR AREA...
THOUGH HEIGHT FALLS ARE. THERE WILL A BIT OF ISENTROPIC ASCENT AS
WELL. PRECIP CHANCES OVER OUR FORECAST AREA WILL BE CONFINED TO
EASTERN AREAS PRIMARILY EAST OF A LINE FROM CAVE CREEK TO
FLORENCE...BUT THERE WILL BE A SLIGHT CHANCE OVER NORTHERN AND
EASTERN FRINGES OF THE PHOENIX METRO WITH THE PASSAGE OF THE FRONTAL
ZONE. BREEZY TO WINDY CONDITIONS CAN BE EXPECTED BEHIND THE
FRONT...MAINLY OVER SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA. COOL
ADVECTION NOT VERY IMPRESSIVE BUT SUBSEQUENT REINFORCEMENT OF THE
TROUGH WILL LEAD TO MORE NOTICEABLY COOL CONDITIONS FRIDAY. MADE
SOME EARLIER UPWARD ADJUSTMENTS TO THE WIND GRIDS AND SOME MINOR
ADJUSTMENTS TO DEW POINTS.

&&

.PREVIOUS DISCUSSION ISSUED 220 PM MST/120 PM PST...
UPPER LEVEL RIDGE AXIS CURRENTLY OVERHEAD WILL QUICKLY PUSH EASTWARD
TONIGHT WITH INCREASING HIGH CLOUDS BLANKETING MUCH OF THE REGION.
OVERNIGHT LOWS TONIGHT SHOULD BE A FEW DEGREES WARMER IN MOST SPOTS
DUE THE CLOUD COVER. THE NEXT WEATHER SYSTEM...WHICH IS CURRENTLY
ENTERING NORTHERN CALIFORNIA...WILL SLIDE SOUTHEASTWARD OVER THE
NEXT COUPLE DAYS WHILE ALSO DEEPENING INTO A CLOSED LOW AS IT ENTERS
NORTHERN ARIZONA AND SOUTHERN UTAH THURSDAY AFTERNOON. THICKNESSES
WILL QUICKLY FALL STARTING IN OUR WESTERN ZONES THURSDAY MORNING
WITH A SURFACE COLD FRONT SURGING SOUTHWARD DOWN THE COLORADO RIVER
VALLEY THURSDAY AFTERNOON. THIS COLD FRONT WILL CONTINUE TO MARCH
THROUGH OUR CWA THURSDAY EVENING...REACHING OUR FAR EASTERN ZONES BY
AROUND MIDNIGHT. WINDS WILL INCREASE BEHIND THE FRONT WITH GUSTS UP
TO 30 MPH POSSIBLE ACROSS SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA
THURSDAY AFTERNOON.

GIVEN THE DRY TRAJECTORY OF THIS LOW PRESSURE SYSTEM AND DRY
CONDITIONS ALREADY IN PLACE...AM EXPECTING ONLY MARGINAL MOISTURE
LEVELS FOR THURSDAY AND FRIDAY. FORECAST PRECIPITABLE WATER VALUES
INCREASE ON THURSDAY TO ANYWHERE FROM A THIRD TO A HALF AN INCH WITH
THE BULK OF THE MOISTURE IN A SMALL LAYER BETWEEN 850-700MB. GIVEN
THE LIMITED MOISTURE...BUT SOME DECENT VERTICAL LIFT MOVING THROUGH
FROM STRONG DYNAMICS ALOFT...CAN EXPECT SOME SHOWER DEVELOPMENT OVER
MAINLY HIGH TERRAIN AREAS STARTING THURSDAY AFTERNOON AND LASTING
THROUGH AROUND MIDNIGHT NORTH OF PHOENIX AND UNTIL SUNRISE FRIDAY
OVER GILA COUNTY. QPF AMOUNTS OF UP AN A TENTH OF AN INCH IS
EXPECTED...BUT MOST LOCATIONS WILL ONLY SEE A HUNDREDTH OR TWO. SNOW
LEVELS QUICKLY DROP DURING THE DAY THURSDAY...REACHING 4500-5000
FEET MIDNIGHT THURSDAY. PEAKS IN GILA COUNTY MAY SEE UP TO AN INCH
OR TWO OF SNOW WITH ONLY TRACES DOWN TO 5000 FEET DURING THE
NIGHTTIME HOURS THURSDAY NIGHT.

THE UPPER TROUGH WILL BE SLOW TO MOVE OUT OF THE REGION AS IT
LINGERS OVER THE FOUR CORNERS REGION THROUGH FRIDAY. SKIES ARE
EXPECTED TO BECOME MOSTLY CLEAR THURSDAY NIGHT GIVING WAY TO CHILLY
OVERNIGHT LOWS...BUT ELEVATED WINDS SHOULD KEEP TEMPERATURES FROM
GETTING NEAR FREEZING AT ALL BUT A FEW LOWER DESERT SPOTS. FRIDAY
WILL BE RATHER COLD WITH MANY LOWER DESERT SPOTS ONLY REACHING INTO
THE LOW TO MID 50S. FRIDAY NIGHT HAS THE POTENTIAL TO BRING FREEZING
TEMPERATURES TO NORTHERN PINAL COUNTY...INCLUDING THE FAR SOUTHEAST
PHOENIX METRO AREA...AS WELL AS RURAL AREAS OF SOUTHWEST ARIZONA.
HIGH TEMPERATURES FOR THE WEEKEND COULD STRUGGLE TO BREAK INTO THE
60S ACROSS MANY OF THE LOWER DESERT LOCALES...WHILE OVERNIGHT LOWS
WILL CONTINUE TO DIP INTO THE 30S IN MOST SPOTS.

FOR LATE SUNDAY INTO NEXT WEEK...LARGE SPREAD IN OPERATIONAL AND
ENSEMBLES SOLNS FROM ALL MODEL SUITES...GFS/ECMWF/NAEFS/CMC...HAS
DEVELOPED FOR THE LATE WEEKEND AND EARLY NEXT WEEK. EVOLUTION OF THE
WAVE PATTERN AND HOW/WHERE DISTURBANCES WILL BREAK IN THAT PATTERN
HAS INTRODUCED SIGNIFICANT PHASING IN THE UPPER LEVEL PATTERN FOR
NEXT WEEK. TAKING A BROAD BRUSH APPROACH...MOSTLY DRY AND COOL
NORTHWEST FLOW WITH EMBEDDED SHORTWAVES WILL HOLD OVER THE REGION
FOR EARLY NEXT WEEK...KEEPING TEMPERATURES AT OR BELOW SEASONAL
NORMALS WHILE PERIODICALLY BRINGING CLOUDS INTO THE REGION. MORNING
LOWS WILL BE PARTICULARLY COOL AS VERY LITTLE CHANGE IN AIRMASS
TEMPERATURE IS HIGHLIGHTED ATTM...WITH THE POTENTIAL FOR LOW TO
UPPER 30S POSSIBLE ACROSS THE LOWER DESERTS BY NEW YEARS.

&&

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

A COLD FRONT MOVING THROUGH CALIFORNIA AND NEVADA TONIGHT WILL REACH
THE LOWER COLORADO RIVER VALLEY BETWEEN 11Z-13Z TUESDAY THEN REACH
THE PHOENIX METRO AREA BETWEEN 16Z-18Z. EXPECT SURFACE WINDS TO BE
STRONGEST BEHIND THE FRONT...GUSTING 20-30 KTS OVER SOUTHEAST
CALIFORNIA AND LOWER COLORADO RIVER VALLEY AND 15-25 KTS OVER
SOUTH-CENTRAL ARIZONA INCLUDING PHOENIX METRO. THE CLOUD BAND WITH
THE FRONT WILL BE BROKEN UP TO SOME DEGREE AS IT PASSES OVER THE
CALIFORNIA MOUNTAINS BUT THERE COULD BE JUST ENOUGH MOISTURE FOR SCT
CUMULUS TO BECOME TEMPORARILY BROKEN OR OVERCAST IN THE 5-7 KFT MSL
RANGE WITH/BEHIND THE FRONTAL PASSAGE. ANTICIPATE HIGHER DESERT
MOUNTAINS TO HAVE OSBCURATIONS AS THE FRONTAL ZONE PASSES WITH
LONGER LIVED CEILINGS OVER HIGHER TERRAIN NORTH AND EAST OF PHOENIX
AREA.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
FRIDAY THROUGH TUESDAY...
A WEATHER DISTURBANCES MOVING THROUGH THE FOUR CORNERS AREA FRIDAY
MAY BRING SOME LIGHT RAIN AND SNOW SHOWERS TO HIGHER TERRAIN
LOCATIONS OF EASTERN ARIZONA. HOWEVER...THE LARGER FIRE WEATHER
IMPACT MAY BE GUSTY NORTH WINDS ONCE AGAIN RETURNING TO THE COLORADO
RIVER VALLEY. HOWEVER AS WITH THE MOST RECENT SYSTEMS...HUMIDITY
VALUES ONLY FALLING TO NEAR 20 PERCENT WILL LIMIT THE OVERALL FIRE
DANGER. MORE TRANQUIL...DRY AND COOL WEATHER WILL PREVAIL OVER THE
WEEKEND AS AFTERNOON HUMIDITY LEVELS FALL INTO A 20 TO 30 PERCENT
RANGE WITH GOOD TO EXCELLENT OVERNIGHT RECOVERY. THE POTENTIAL
EXISTS FOR ANOTHER WIND PRODUCING SYSTEM AFFECTING THE DISTRICT BY
THE MIDDLE OF NEXT WEEK.
&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

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






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