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000
FXUS65 KPSR 070420
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
920 PM MST FRI DEC 6 2013

.SYNOPSIS...
A LARGE AND COLD LOW PRESSURE SYSTEM WILL CONTINUE TO COVER THE
WESTERN STATES THROUGH EARLY NEXT WEEK. A COUPLE OF WEATHER
DISTURBANCES IN THE BROAD TROUGH WILL BRING A CHANCE OF VALLEY RAIN
AND MOUNTAIN SNOW LATE SATURDAY AND SATURDAY NIGHT. RATHER COLD
NIGHT-TIME TEMPERATURES ARE EXPECTED THROUGH TUESDAY MORNING...WITH
CLEAR SKIES AND A WARMING TREND BY THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...
NO WEATHER ISSUES THIS EVENING AS ARIZONA WAS UNDER THE INFLUENCE OF
VERY WEAK UPPER RIDGING...ACTUALLY MORE OF A DRY WESTERLY FLOW
ALOFT...WHICH LED TO GENLY SUNNY SKIES DURING THE DAY. H5 PLOTS THIS
EVENING SHOWED 20-60M HEIGHT RISES WHICH FOLLOWED 100M RISES SHOWN
ON THE EARLIER 12Z PLOTS. THE FLAT RIDGING IS AHEAD OF ANOTHER COLD
PACIFIC STORM SYSTEM NOW TAKING SHAPE ALONG THE PAC NORTHWEST
COAST...AND THIS NEXT SYSTEM WILL DIVE SOUTHEAST AND INTO MAINLY
NORTHERN ARIZONA LATER SATURDAY AND INTO SATURDAY NIGHT...BRINGING A
CHANCE OF SHOWERS ALONG WITH COOLER AIR. AT 8 PM...IR IMAGERY SHOWED
MOSTLY CLEAR SKIES ACROSS THE AREA...AND CLEARLY DEPICTED THE UPPER
SYSTEM DEVELOPING TO OUR NORTHWEST. SURFACE DEWPOINTS OVER THE LOWER
DESERTS AT 8 PM WERE ON THE DRY SIDE...MOSTLY RUNNING IN THE 20S.
FOR THE REST OF TONIGHT...EXPECT MOSTLY CLEAR SKIES WITH SOME MAINLY
HIGH CLOUDS STARTING TO INCREASE FROM THE WEST AFTER MIDNIGHT.
OTHERWISE WINDS WILL BE LIGHT AND OVERNIGHT TEMPS WILL BE ON THE
COOL SIDE. FORECASTS ARE IN GOOD SHAPE AND NO UPDATES ARE NEEDED.

.PREVIOUS DISCUSSION...
MODELS REMAIN IN GOOD AGREEMENT AS TO A LARGE COLD TROUGH REMAINING
IN PLACE OVER THE WESTERN STATES THROUGH EARLY NEXT WEEK. A COUPLE
SHORT WAVE DISTURBANCES WILL ROTATE THROUGH THE BROAD TROUGH...THE
FIRST DISTURBANCE SATURDAY...AND A SECOND WEAK ONE ON MONDAY. IN THE
NEAR TERM...THE COLD AIR THAT BROUGHT FREEZING TEMPERATURES TO THE
DESERTS TODAY WILL REMAIN IN PLACE AND CONDITIONS ARE FAVORABLE FOR
ANOTHER CHILLY MORNING SATURDAY. WHETHER FREEZING TEMPERATURES WILL
BE REALIZED TOMORROW MORNING DEPENDS ON THE AMOUNT OF CLOUD COVER
THAT OVERSPREADS THE AREA TONIGHT. CURRENT IR/WATER VAPOR SATELLITE
IMAGERY HAS THE NEXT UPPER LEVEL DISTURBANCE SPINNING OVER THE
PACIFIC NORTHWEST THIS AFTERNOON...AND MODELS CONTINUE TO ROTATE
THIS WAVE SOUTH AND EAST THROUGH CENTRAL CALIFORNIA AND NORTHERN
ARIZONA BY TOMORROW AFTERNOON.

THIS SYSTEM BRINGS ANOTHER DOSE OF COLD AIR...AND IT TAPS INTO A
MODEST AMOUNT OF LOW LEVEL MOISTURE OFF THE PACIFIC. SOME OF THIS
MOISTURE WILL MAKE IT INLAND...AND WITH GOOD ISENTROPIC LIFT/COLD
AIR IN PLACE...THERE IS A GOOD POTENTIAL FOR RAIN/SNOW SHOWERS...THE
BEST CHANCES OVER THE HIGHER TERRAIN OF JOSHUA TREE NP...PORTIONS OF
RIVERSIDE COUNTY...AND LA PAZ COUNTY WELL AWAY WELL FROM RAIN SHADOW
AREAS DUE TO THE COASTAL MOUNTAIN RANGES.

LOW LEVEL MOISTURE WILL CONTINUE TO QUICKLY SPREAD INTO SOUTH
CENTRAL ARIZONA AND THE MOUNTAINS NORTH AND EAST OF PHOENIX.
HOWEVER...THE CURRENT TRAJECTORY OF THIS DISTURBANCE IS A BIT
FARTHER NORTH THAT PREVIOUS MODEL RUNS. THIS WILL KEEP SOME OF THE
BEST LIFT OVER THE HIGH TERRAIN...SO A FEW HUNDREDTHS OF AN INCH OF
PRECIPITATION IS POSSIBLE OVER THE GREATER PHOENIX AREA AND
SURROUNDING DESERTS SATURDAY EVENING. AS SNOW LEVELS CONTINUE TO
DROP FROM 5000 TO AROUND 3500 FEET LATE SATURDAY NIGHT...1-3 INCHES
OF DRY SNOW WILL BE POSSIBLE IN SOUTHERLY GILA COUNTY ABOVE 4000
FEET.

SUNDAY AND SUNDAY NIGHT...
SINCE THE LOW LEVEL MOISTURE PLUME AND CHANCE OF PRECIP WILL MOVE
QUICKLY ACROSS THE AREA...ONLY LINGERING RAIN/SNOW SHOWERS ARE
EXPECTED IN SOUTHERN GILA COUNTY THROUGH EARLY AFTERNOON. OTHERWISE
CLEARING SKIES ARE EXPECTED ACROSS THE ENTIRE FORECAST AREA SUNDAY
AFTERNOON AND NIGHT.

MONDAY AND TUESDAY...
MONDAY MORNING TEMPERATURES WILL BE COLD AGAIN UNDER CLEAR SKIES AND
MUCH DRIER AIR. IN OTHER WORDS...STRONG RADIATIONAL COOLING. HOWEVER
TUESDAY MORNINGS LOW TEMPERATURES WILL BE A LITTLE TRICKY DUE TO A
VERY SHALLOW INVERSION AND INCREASED NORTHEAST WINDS JUST ABOVE THE
INVERSION. IN OTHER WORDS...PERIODIC WIND MIXING IN THE SHALLOW
INVERSION COULD RESULT IN WARMER NIGHT-TIME TEMPERATURES.

WEDNESDAY THROUGH FRIDAY.
MOSTLY CLEAR SKIES WITH TEMPERATURES FINALLY APPROACHING NORMAL.

&&

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

CLEAR SKIES AND LIGHT DIURNAL WINDS EXPECTED AT ALL SITES THROUGH
SATURDAY EARLY MORNING. CIGS WILL GRADUALLY THICKEN AND LOWER DURING
THE DAY SATURDAY AS A FRONT APPROACHES THE AREA BUT NOT EXPECTING
ANY PRECIP OR AVIATION IMPACTS THROUGH 00Z SUNDAY. HOWEVER...MAY SEE
SOME CIGS START TO FALL BELOW 6K FEET AFTER 8 PM OR SO SAT EVENING
ACROSS THE CENTRAL DESERTS...AND THEY MAY AFFECT THE TAF SITES
INCLUDING KPHX. SHOWERS ARE EXPECTED TO DEVELOP BY THE MIDDLE OF THE
EVENING SATURDAY ACROSS SOUTH CENTRAL AZ AND WHILE THEY SHOULD
MAINLY STAY TO THE NORTH AND EAST OF PHOENIX AND OVER HIGHER TERRAIN
IT IS POSSIBLE THAT A FEW OF THEM MAY IMPACT THE TAF SITES. ATTM
WILL NOT MENTION PRECIP IN THE UPCOMING 06Z TAF PACKAGE DUE TO LOW
CONFIDENCE.

WINDS TO BE QUITE LIGHT AND SOMEWHAT DIURNAL AT THE TAF SITES THRU
MID MORNING SATURDAY...THEN EXPECT GRADUALLY INCREASING WIND DURING
THE AFTERNOON...MAINLY OUT WEST. GUSTY SOUTHWEST TO WEST WINDS WILL
LIKELY IMPACT THE WESTERN DESERTS INCLUDING KIPL AND KBLH AND GUSTS
MAY EXCEED 25KT AFTER 3 PM SATURDAY...STAYING BREEZY OR LOCALLY
WINDY THRU MID EVENING AT LEAST. LESS WIND EXPECTED ACROSS CENTRAL
AZ...MAINLY FAVORING THE SOUTHWEST 10-15KT THRU THE EVENING HOURS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
NORTH AND NORTHEAST BREEZY TO WINDY CONDITIONS WILL BE IN PLACE
MONDAY AND TUESDAY. CONDITIONS WILL FLIRT WITH CRITICAL THRESHOLDS
MONDAY AFTERNOON OVER THE LOWER COLORADO RIVER VALLEY AND PORTIONS
OF SOUTHEAST CALIFORNIA. WINDS WILL BE CONSIDERABLY LIGHTER
WEDNESDAY AND THURSDAY. HUMIDITIES WILL TREND DOWN SUNDAY THROUGH
TUESDAY BEFORE STARTING TO REBOUND WEDNESDAY AND THURSDAY...MAINLY
OVER SOUTH-CENTRAL ARIZONA. ANTICIPATE LITTLE CHANGE IN TEMPERATURES
SUNDAY THROUGH TUESDAY BEFORE A MODEST WARMING TREND BEGINS
WEDNESDAY.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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DISCUSSION...CB
PREVIOUS DISCUSSION...MEYERS/VASQUEZ
AVIATION...CB/LEINS
FIRE WEATHER...LEINS/AJ