Heavy Snow in California, February 15 to 16, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1000 PM MST WED FEB 15 2012

.SYNOPSIS...
STRONG LOW PRESSURE WILL AFFECT THE REGION TONIGHT AND TOMORROW.
SCATTERED TO NUMEROUS SHOWERS...WITH SNOW AS LOW AS 3000 FEET...CAN
BE EXPECTED ACROSS SOUTHEAST CALIFORNIA TONIGHT AND EXPANDING INTO
SOUTHWEST ARIZONA. PRECIPITATION CHANCES WILL SPREAD INTO
SOUTH-CENTRAL ARIZONA THURSDAY BUT WILL BE SLIGHT. TEMPERATURES WILL
REMAIN BELOW NORMAL UNDER MOSTLY CLOUDY SKIES. CONDITIONS WILL BEGIN
TO IMPROVE FRIDAY WITH TEMPERATURES MAKING A SLOWLY RECOVERY FOR THE
WEEKEND. ANOTHER STORM SYSTEM WILL RETURN UNSETTLED CONDITIONS TO
THE REGION SUNDAY AND INTO EARLY NEXT WEEK.

&&

.DISCUSSION...
PRECIP ECHOES HAVE OVERSPREAD MOST OF OUR SOUTHEAST CALIFORNIA ZONES
WITH SOME WEAK ECHOES HAVING BEEN IN LA PAZ COUNTY OFF AND ON FOR
SEVERAL HOURS. COLD FRONT PASSED THROUGH BLH AND IPL A LITTLE BEFORE
04Z AS IS EVIDENT IN THE WIND SHIFT. IR IMAGERY HAS SHOWN A
PERSISTENT AREA OF COLDER CLOUD TOPS OVER SAN BERNARDINO COUNTY AND
WESTERN JOSHUA TREE NATIONAL PARK. THIS IS INDICATIVE OF MORE
SUBSTANTIAL PRECIP. HOWEVER...SURFACE OBSERVATIONS...THOUGH
LIMITED...HAVE NOT INDICATED A LOT OF PRECIP IN THAT AREA.
IRONICALLY THE RADAR THAT HAS THE BEST COVERAGE OF THAT
AREA...KEYX...IS NOT AVAILABLE THIS WEEK DUE TO ONGOING WORK TO
CONVERT IT TO DUAL POLARIZATION CAPABILITY. SNOW HAS LIKELY BEGUN TO
FALL IN OUR ADVISORY AREA AREA...JTNP ABOVE 4000FT ELEVATIONS. IT
WILL PROBABLY START STICKING SOON IN CONJUNCTION WITH THE TIMING OF
THE ADVISORY. STRONG WINDS HAVE NOT BEEN PERSISTENT AND MAY NOT
DEVELOP UNTIL MORNING. 00Z NAM AND GFS CONTINUE TO SHOW PRECIP
CONTINUING OVERNIGHT AND INTO THE DAY THURSDAY OVER SOUTHEAST
CALIFORNIA AND SOUTHWEST ARIZONA BUT THEY ARE RELUCTANT TO PUT QPF
OVER THE PHOENIX AREA...THOUGH SOME WRAP AROUND IS ADVERTISED FOR
SOUTHERN GILA AND NORTHERN PINAL THURSDAY AFTERNOON AND EVENING.
WILL HOLD OFF ON CURTAILING POPS OVER EASTERN MARICOPA/NORTHERN
PINAL/SOUTHERN GILA FOR TONIGHT AND THURSDAY MORNING SINCE THERE IS
STILL SOME GOOD DIV Q FORCING AS WELL AS SOME ISENTROPIC ASCENT THAT
CONTINUES TO BE ADVERTISED BY MODELS. POPS MAY NEED TO BE ENDED
SOONER THAN WE CURRENTLY SHOW. BUT OVERALL...CURRENT FORECASTS ARE
IN LINE WITH LATEST MODELS.

PREVIOUS DISCUSSION...
TODAY AND TOMORROW FOR SOUTHEAST CALIFORNIA AND THE COLORADO RIVER
VALLEY...LARGE AREA OF LOW PRESSURE ON APPROACH INTO SOUTHERN
CALIFORNIA THIS AFTERNOON WITH CIRCULATION CENTER OVER SOUTHERN
NEVADA PER VIS/IR SATELLITE IMAGERY. AHEAD OF IT CUMULUS CLOUDS AND
INCREASED STRONG SOUTHERLY WINDS HAVE DEVELOPED OVER THE AREA. THESE
WINDS WILL CONTINUE THROUGH THE EVENING AS SHOWERS BEGIN TO DEVELOP
AHEAD OF AN APPROACHING SURFACE COLD FRONT. FAIRLY UNSTABLE AIRMASS
MOVING IN WITH THIS FEATURE...FORECAST MODELS SHOWING DECENT LAPSE
RATES AND A NICE QG FORCING COUPLET. THERE HAS ALREADY BEEN SOME
LIGHTNING STRIKES UPSTREAM OVER SOUTHERN NEVADA WITH THE SHOWERS. AS
SUCH...ADDED MENTION OF SLIGHT CHANCE OF THUNDER THROUGH THE EVENING
FOR SOUTHEAST CALIFORNIA. SNOW LEVELS WILL DROP THROUGH THE
EVENING...DOWN NEAR 3000 TO 3500 FT AS THE LOW CENTER CONTINUE IT/S
SOUTHWARD TRACK. ACCUMULATING SNOWFALL /ONE TO THREE INCHES/ WILL BE
POSSIBLE ACROSS PORTIONS OF JOSHUA TREE NATIONAL PARK THROUGH THE
EARLY MORNING. ALSO...INCREASED WINDS COMBINED WITH ALREADY COLD
TEMPERATURES AND SNOWFALL WILL CREATE WIND CHILL READINGS DOWN IN THE
LOW TEENS IN THE EARLY MORNING. GIVEN THOSE WINTER WEATHER
IMPACTS...A WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR ELEVATIONS
ABOVE 4000FT IN JOSHUA TREE.

STORM TOTAL PRECIPITATION POSSIBLE UP TO ONE QUARTER OF AN INCH FROM
JOSHUA TREE NATIONAL PARK AND EAST TO THE LOWER COLORADO RIVER
VALLEY. OTHER LOCATIONS HAVE THE POTENTIAL TO SEE LIGHTER RAINFALL
AMOUNTS...POTENTIALLY AT OR SLIGHTLY ABOVE ONE TENTH OF AN INCH FROM
THE SHOWER ACTIVITY. TEMPERATURES WILL REMAIN COOL FOR ANOTHER
DAY...WITH FORECAST HIGHS INTO WARMING INTO THE MID 60S.
PRECIPITATION WILL SLOWLY DIMINISH THROUGH THE DAY AS THE LOW DRIFTS
FURTHER TO OUR SOUTH DOWN INTO BAJA MEXICO.

TODAY AND TOMORROW FOR THE CENTRAL ARIZONA DESERTS...LARGE AREA OF
LOW PRESSURE MOVING THROUGH SOUTHERN NEVADA AND CALIFORNIA THIS
EVENING WILL INCREASE MID TO HIGH CLOUDS AND GENERATE LIGHT SHOWER
ACTIVITY...MOSTLY ACROSS YUMA AND LA PAZ COUNTIES. STORM TRACK HAS
THIS SYSTEM MOVING SOUTH OVER THE BAJA PENINSULA...INTRODUCING
SOUTHERLY FLOW TONIGHT AND BRINGING SOME ADDITIONAL MOISTURE IN FROM
THE BAJA WATERS. SHOWER ACTIVITY WILL INCREASE AND SLOWLY SPREAD EAST
THROUGH THURSDAY MORNING...WITH MOST OF THE HEAVIEST PRECIPITATION
EXPECTED ALONG THE COLORADO RIVER CORRIDOR. CAN/T RULE OUT SOME LIGHT
SHOWER ACTIVITY CLOSER TOWARDS PHOENIX...BUT MODELS HAVE RECENTLY
STAY CONSISTENT WITH PRECIP PLACEMENT ONLY REACHING THE WESTERN
PORTIONS OF MARICOPA COUNTY. BY LATE AFTERNOON THE DISTURBANCE IS
WELL TO OUR SOUTH...LEAVING SOMEWHAT DRIER EASTERLY FLOW ACROSS THE
REGION. TEMPERATURES FOR THURSDAY WILL REMAIN COOL...BEFORE MAKING A
SLOW RECOVERY TOWARDS WARMER VALUES FOR FRIDAY AND SATURDAY.

FRIDAY AND INTO NEXT WEEKEND...IMPROVING CONDITIONS FROM THE WEST
ALONG WITH SOME WARMING CAN BE EXPECTED FRIDAY AFTERNOON INTO
SATURDAY AS FLAT HIGH PRESSURE BUILDS INTO THE AREA.

CONTINUED COOLER AND MORE UNSETTLED WEATHER IS ON TAP FOR SUNDAY
INTO EARLY NEXT WEEK AS GUIDANCE CONTINUES TO CALL FOR A BROAD AREA
OF LOW PRESSURE TO DEVELOP OVER THE WEST. A SERIES OF SHORTWAVES
WILL THEN MOVE SOUTHEAST OUT OF THE PACIFIC NORTHWEST AND PUSH
ACROSS ARIZONA BRINGING ADDITIONAL SHOTS OF COOL AIR AS WELL AS
SLIGHT CHANCES FOR SHOWERS. ONE SIGNIFICANT SHORT WAVE WILL MOVE
EAST ACROSS ARIZONA SUNDAY INTO SUNDAY NIGHT...AND THICKNESS VALUES
ARE PROGGED TO BE LOWER THAN THOSE SEEN WITH THE TUESDAY OR THURSDAY
LOWS. HIGHS WILL FALL INTO THE LOW TO MID 60S OVER THE COOLER
DESERTS SUNDAY...THEN FALL A FEW DEGREES LOWER MONDAY. ALSO WE
RAISED POPS SUNDAY AND SUNDAY NIGHT...MAINLY ACROSS SOUTH CENTRAL
AZ...INTO THE 20-30 PERCENT RANGE. BREEZY TO WINDY CONDITIONS AREA
WIDE ARE ALSO IN THE FORECAST...BUT AT THIS TIME WE FEEL WINDS WILL
STAY A BIT SHY OF WIND ADVISORY CRITERIA.

&&

.AVIATION...

SOUTH CENTRAL AZ...INCLUDING KPHX AND KIWA...
FEW TO SCT LOW CLOUDS AND SCT MID-HIGH CLOUDS...OCCASIONALLY BKN AOA
10 KFT. PRECIP POTENTIAL TOO MEAGER TO MENTION IN TAFS AT THIS
POINT. OTHERWISE...WINDS WILL FAVOR AN EASTERLY COMPONENT THE REST
OF THE NIGHT AND THROUGH THE DAY THURSDAY.

SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KIPL AND KBLH...COLD FRONT
PASSED THROUGH KIPL AND KBLH SHORTLY BEFORE 04Z. NORTHWEST AND NORTH
WINDS EXPECTED THE REST OF THE NIGHT THROUGH THE DAY
TOMORROW...STRENGTHENING AFTER 16Z WITH GUSTS OF 20-30 KTS.
SCATTERED-NMRS SHWRS WILL CONTINUE OVER SERN CAL AND EXPAND INTO
SWRN AZ OVERNIGHT ATTENDED BY CIGS OF 4-6 KFT MSL...HIGHER MOUNTAINS
OBSCURED. CLOUDS/SHOWERS WILL DECLINE FROM NORTH TO SOUTH THURSDAY
AFTERNOON.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
FRIDAY THROUGH TUESDAY...
BELOW NORMAL HIGH TEMPERATURES ARE EXPECTED OVER SOUTH-CENTRAL
ARIZONA WITH HUMIDITIES IN THE MID TEENS TO UPPER TWENTIES...WITH
GOOD TO EXCELLENT OVERNIGHT RECOVERIES. EXPECT BREEZY CONDITIONS TO
DEVELOP OVER SOUTHEAST CALIFORNIA AND SOUTH-CENTRAL ARIZONA ON
SUNDAY THROUGH EARLY MONDAY. HUMIDITIES ARE ALSO EXPECTED TO
INCREASE OVER GILA COUNTY ON SUNDAY.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 10 AM PST
     THURSDAY ABOVE 4000 FEET FOR CAZ030.

&&

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...AJ/NOLTE/CB
AVIATION....AJ
FIRE WEATHER...SAWTELLE