Heavy Snow in Arizona, February 14, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
533 AM MST TUE FEB 14 2012

.UPDATE...UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS.

&&

.SYNOPSIS...
A STRONGER AND COLDER WEATHER DISTURBANCE WILL MOVE INTO THE REGION
TODAY. A THREAT OF SHOWERS WILL DEVELOP AREA-WIDE TODAY...ESPECIALLY
OVER SOUTH CENTRAL ARIZONA. MUCH COLDER TEMPERATURES ARE ALSO
EXPECTED TODAY. IMPROVING CONDITIONS ARE EXPECTED LATE TONIGHT AND
WEDNESDAY...FOLLOWED BY ANOTHER WEATHER DISTURBANCE WEDNESDAY NIGHT
AND THURSDAY. A SLIGHT CHANCE OF SHOWERS WILL DEVELOP ON THE DESERTS
BY THURSDAY MORNING. MOSTLY CLEAR AND WARMER WEATHER IS EXPECTED
FRIDAY INTO THE WEEKEND.

&&

.DISCUSSION...
RATHER COLD...VIGOROUS...BUT SOMEWHAT MOISTURE STARVED PACIFIC LOW
IS NOW MOVING INTO ARIZONA AND IT WILL BRING MUCH COOLER HIGH
TEMPERATURES ALONG WITH A GOOD CHANCE FOR MAINLY LIGHT SHOWERS
ACROSS SOUTH CENTRAL ARIZONA. CORE TEMPS NEAR THE LOW CENTER ARE
NEAR MINUS 26C...AND 500MB  HEIGHT FALLS NEAR 120M WERE NOTED OVER
SRN NEVADA LAST EVENING. MAIN LOW CENTER IS NOW MOVING INTO FAR NWRN
AZ...AND AS THE LOW TRACKS EAST ACROSS THE STATE TODAY A PAIR OF
VORT LOBES WILL PIVOT EAST AND ACROSS SRN AZ. ONE OF THESE VORT
LOBES/MAXES CAN BE SEEN ALONG THE SERN CA COAST AT 2 AM...NEAR SAN
DIEGO. VERY GOOD DYNAMICS WILL BE ASSOCIATED WITH THIS SYSTEM...PVA
AND MID LEVEL Q CONVERGENCE FIELDS ARE IMPRESSIVE...SO LOW/MID LEVEL
LIFT WILL BE RATHER STRONG. UNFORTUNATELY MOISTURE WILL BE LIMITED.
PWAT VALUES WERE AROUND ONE HALF INCH ON THE SAN DIEGO SOUNDING LAST
EVENING...THE MARINE LAYER WAS ONLY UP TO 800MB AND IR IMAGERY DOES
NOT SHOW A SIGNIFICANT SUBTROPICAL MOISTURE TAP. THUS WE ARE CALLING
FOR A GOOD CHANCE FOR MOSTLY LIGHT SHOWERS OVER SOUTH CENTRAL AZ
TODAY...WITH POPS LIKELY OR HIGHER OVER THE HIGHER TERRAIN EAST OF
PHOENIX. QPF VALUES WILL BE ON THE LIGHT SIDE MOST PLACES AND MOST
DESERT LOCALES WILL PROBABLY SEE LESS THAN ONE OR TWO TENTHS OF AN
INCH WITH THIS SYSTEM. STILL LOOKING FOR THICKNESSES TO FALL 120M OR
MORE...AND FORECAST SOUNDINGS/MOS NUMBERS AND BEST PERFORMING
GRIDDED GUIDANCE ALL CALL FOR HIGHS TODAY TO FALL INTO THE LOW 60S
OR UPPER 50S OVER THE COOLER DESERTS. GREATER PHOENIX AREA SHOULD
DROP TO NEAR 60. SHOULD SUFFICIENT RAIN SHOWERS/CLOUDS DEVELOP TODAY
HIGHS COULD STAY IN THE 50S OVER MUCH OF THE CENTRAL DESERTS.

WITH THE LOW CENTER TRACKING TO OUR NORTH...THE GREATEST INSTABILITY
WILL STAY NORTH OF OUR AREA AND THUS THUNDERSTORMS WILL NOT BE
MENTIONED IN THE FORECAST AT THIS TIME. NOT OUT OF THE REALM OF
POSSIBILITY THAT A STRAY LIGHTNING STRIKE COULD BE SEEN IN OUR AREA
TODAY HOWEVER.

MODELS HAVE PRETTY MUCH LOCKED IN ON THE IDEA OF ANOTHER CLOSED LOW
MOVING INTO THE DESERT SOUTHWEST WEDNESDAY INTO WEDNESDAY NIGHT. LOW
CENTER WILL MOVE FROM NRN CA NEARLY STRAIGHT SOUTH DURING THE DAY
WEDNESDAY WITH THE CENTER MOVING INTO FAR SERN CA BY WED EVENING.
LOW CENTER THEN SHIFTS INTO FAR NRN BAJA BY 12Z THURSDAY. AS SUCH WE
ARE CALLING FOR A CHANCE OF SHOWERS OVER SERN CA AND PORTIONS OF THE
FAR WESTERN AZ DESERTS WED NIGHT. THIS SYSTEM APPEARS TO HAVE EVEN
BETTER DYNAMICS THAN THE TUESDAY LOW...SO WE MAY BE RAISING POPS
EVEN FURTHER AS THE SYSTEM APPROACHES. LOW WILL SWING EAST INTO NWRN
MEXICO THURSDAY TAKING THE BULK OF THE FORCING SOUTH OF OUR AREA.
THERE WILL STILL BE AT LEAST A SLIGHT CHANCE FOR SHOWERS OVER ALL OF
OUR AREA AS MOISTURE WILL WRAP AROUND THE LOW AND INTO THE SRN
DESERTS...BUT THE HIGHEST POPS WILL STAY CLOSER TO THE LOW CENTER
AND OVER ZONES 25 AND 26. TEMPS WILL FALL OFF THURSDAY...ESPECIALLY
OVER THE WESTERN CWA...WITH COOLER DESERTS LOWERING INTO THE LOW 60S
OR EVEN UPPER 50S.

IMPROVING CONDITIONS ARE EXPECTED FRIDAY AS THE LOW EXITS TO THE
EAST...AND MOSTLY SUNNY SKIES ALONG WITH WARMER HIGH TEMPS ARE ON
TAP.

FOR THE WEEKEND INTO EARLY NEXT WEEK...ANOTHER LARGE AREA OF LOW
PRESSURE IS FORECAST TO DEVELOP OVER THE WESTERN CONUS AS THE UPPER
RIDGE BUILDS OFF THE WEST COAST. ATTM IT LOOKS LIKE RELATIVELY DRY
NORTHWEST FLOW ALOFT WILL BE SITUATED OVER THE SERN CA AND SRN AZ
DESERTS DURING THE PERIOD AS THE DISTURBANCES MOVING THRU THE
DEVELOPING TROF STAY TO OUR NORTH. AS SUCH POPS WILL STAY ON THE LOW
SIDE AND GENERALLY NEAR CLIMO. HIGH TEMPS WILL STAY NEAR SEASONAL
NORMALS OVER THE WEEKEND...AND FALL OFF SLIGHTLY NEXT MONDAY.

&&

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

UPPER LEVEL LOW PRESSURE SYSTEM SLATED TO MOVE EAST ACROSS THE STATE
TODAY. ASSOCIATED COLD FRONT CURRENTLY PUSHING INTO THE EASTERN HALF
OF THE STATE...WITH SOME PARTIAL CLEARING OVER WESTERN TAF SITES.
EXPECT LOW-MID CLOUDS TO INCREASE WITH SCATTERED LIGHT SHOWERS AND
CIGS LOWERING TO AROUND 5500 FEET AT TIMES ACROSS SOUTH-CENTRAL
ARIZONA...NEAR KIWA AND KPHX THROUGH 17Z. SHOWERS WILL FOCUS MORE
OVER HIGHER TERRAIN NORTH/EAST OF KPHX AND KIWA. SURFACE WINDS ARE
EXPECTED TO REMAIN SOUTHWEST AND WEST THROUGH THE DAY WITH GUSTS TO
NEAR 20KT AT TIMES. CLOUD DECKS THIN LATE AFTN/EVENING...WITH LIGHT
DIURNAL WINDS OVERNIGHT INTO WEDNESDAY MORNING.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
COOLER TEMPERATURES AND HIGHER HUMIDITY LEVELS AREA EXPECTED
THURSDAY AS THE LAST OF SEVERAL LOW PRESSURE SYSTEMS EXITS THE
REGION...AND THE WEATHER PATTERN WILL REMAIN UNSETTLED...WITH
PRECIPITATION CHANCES LINGERING INTO FRIDAY...ESPECIALLY OVER
SOUTHEAST ARIZONA. DRIER CONDITIONS AND A SLOW GRADUAL WARMING TREND
WILL TAKE PLACE ACROSS SOUTHEAST CALIFORNIA AND THE SOUTHWEST
DESERTS OF ARIZONA INTO THE WEEKEND. EARLY NEXT WEEK...MODELS HINT
THAT ANOTHER LOW PRESSURE SYSTEM WILL TAKE SHAPE OVER THE GREAT
BASIN AND BRING INCREASED WINDS TO THE REGION.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...CB
AVIATION...MEYERS
FIRE WEATHER...MEYERS