244 
FXUS65 KPSR 152043 CCA
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
145 PM MST SUN JAN 15 2012

.UPDATE...AVIATION DISCUSSION UPDATED.

&&

.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL MOVE INTO THE DESERT SOUTHWEST 
TONIGHT...BRINGING A CHANCE OF RAIN SHOWERS TO SOUTH-CENTRAL 
ARIZONA. PRECIPITATION WILL LINGER ACROSS THE AREA EARLY 
MONDAY...BUT WILL SHIFT TO EASTERN GILA COUNTY DURING THE AFTERNOON. 
DRY CONDITIONS ALONG WITH A WARMING TREND ARE EXPECTED FROM TUESDAY 
THROUGH THE END OF THE WEEK.

&&

.DISCUSSION...
MOISTURE PLUME AHEAD OF UPPER LOW CENTERED WEST OF BAJA WILL BE 
SPREADING ISOLATED TO SCATTERED LIGHT SHOWERS/SPRINKLES OVER THE 
FORECAST AREA TODAY. THUS MADE AN UPDATE FOR THE TODAY PERIOD IN THE 
GRIDS AND TEXT FORECASTS. BEST OPPORTUNITY FOR PRECIP DURING THE 
DAYTIME TODAY WITHIN OUR FORECAST AREA WILL BE OVER SOUTHWEST 
ARIZONA. AMOUNTS WILL BE RATHER LIGHT AND NOT WIDESPREAD...SO KEPT 
POPS BELOW 50 PERCENT. 12Z MODELS INDICATE THAT THE BEST TIMING AND 
LOCATION FOR PRECIP WILL BE TONIGHT OVER SOUTHEAST ARIZONA...OUTSIDE 
OF OUR FORECAST AREA. HOWEVER...SUFFICIENT MOISTURE AND LIFT SHOULD 
BE AVAILABLE FOR AT LEAST A SLIGHT CHANCE OF LIGHT SHOWERS ACROSS 
THE FORECAST AREA WITH BEST CHANCES OVER SOUTH-CENTRAL 
ARIZONA...ESPECIALLY ZONE 24...AND THIS IS DEPICTED IN EXISTING 
FORECASTS. MADE SOME TWEAKS TO HIGH TEMPS FOR TODAY AS WELL...MAINLY 
TO NUDGE DOWN HIGHS OVER SOUTHWEST ARIZONA AND SOUTHEAST CALIFORNIA 
WHERE CLOUD COVER WILL BE THICKER. OTHERWISE...NO CHANGES AT THIS 
TIME. MORE LATER.

PREVIOUS DISCUSSION...
CYCLONIC FEATURE OFF THE CA COAST HAS BECOME MORE DIFFUSE AS 
EXPECTED. MEANWHILE...LATEST WV IMAGERY SHOWS A PLUME OF DEEPER 
MOISTURE OFF THE BAJA COAST WITH ITS SIGHTS SET ON SE AZ. EXPECT 
MORE CLOUDS THAN SUN TODAY...WITH HIGH TEMPERATURES GENERALLY IN THE 
UPPER 60S AND A FEW DEGREES COOLER THAN YESTERDAY ACROSS 
SOUTH-CENTRAL AZ. 

MODELS HAVE COME INTO BETTER AGREEMENT WITH REGARD TO THE TIMING OF 
THE LOW AS IT MOVES TOWARDS SAN DIEGO TONIGHT. ECMWF HAS BEEN 
SUGGESTING A SLOWER ONSET OF THE PRECIP AND THE LATEST TRENDS 
CONTINUE TO POINT IN THAT DIRECTION. POPS WERE LOWERED FURTHER FOR 
TODAY AND SIT AT LESS THAN 5 PERCENT. GFS/ECMWF MOISTURE FLUX 
MAGNITUDES ARE MAXIMIZED ALONG A CORRIDOR FROM CASA GRANDE TO 
GLOBE AFTER MIDNIGHT AND INTO MONDAY MORNING. THIS IS ALSO REFLECTED 
IN THE LATEST LOCAL RUNS OF THE WRF...WHICH SUGGEST PRECIP WILL 
DEVELOP IN THE AFOREMENTIONED AREAS...BEFORE POSSIBLY BACKBUILDING 
INTO THE NORTHERN AND EASTERN PORTIONS OF THE PHOENIX METRO AREA. 
THIS SHIFT TO THE EAST HAS RESULTED IN A DECREASE IN POPS OF ROUGHLY 
10 PERCENT ACROSS NORTHERN MARICOPA COUNTY BUT AN INCREASE OF 10 TO 
20 PERCENT NEAR ARIZONA CITY.

HIGHER POP WEIGHTING WAS ASSIGNED TO THE RELIABILITY ADJUSTED MAV 
GUIDANCE...RESULTING IN FINAL OFFICIAL POPS UP TO 40 PERCENT FOR 
TONIGHT FROM CASA GRANDE TO GLOBE AND AROUND 20 PERCENT FOR PHOENIX. 
PRECIP IS EXPECTED TO LINGER THROUGH THE MONDAY 
MORNING...PARTICULARLY ACROSS EASTERN GILA COUNTY. BEST ESTIMATE OF 
STORM TOTAL PRECIP IS AROUND ONE HUNDREDTH OF AN INCH FOR 
PHOENIX...FIVE HUNDREDTHS OF AN INCH FOR CASA GRANDE...FIFTEEN 
HUNDREDTHS OF AN INCH FOR GLOBE AND UP TO A QUARTER OF AN INCH 
ACROSS EXTREME EASTERN GILA COUNTY.

COOLING TREND WILL CONTINUE MONDAY AND WILL BE MOST PRONOUNCED 
ACROSS EASTERN GILA COUNTY...WHERE PRECIPITATION WILL LINGER INTO 
THE AFTERNOON. HOWEVER...SNOW LEVELS WILL BE RELATIVELY 
HIGH...GENERALLY AROUND 6500 FT...AND NO SNOW ACCUMULATION IS 
EXPECTED...EVEN ACROSS THE HIGHEST PEAKS. 

FLOW WILL BECOME ZONAL TUESDAY...RESULTING IN LITTLE CHANGE IN 
TEMPERATURES. WARMING TREND WILL BEGIN WEDNESDAY AS A RIDGE BUILDS 
ACROSS THE WESTERN CONUS. ABOVE AVERAGE TEMPS WILL CONTINUE INTO AT 
LEAST SATURDAY. POPS REMAIN NEGLIGIBLE THROUGH FRIDAY...BUT WERE 
INCREASED TOWARDS CLIMO FROM FRIDAY NIGHT ONWARD AS A BROAD TROUGH 
MOVES TOWARDS THE WEST COAST. 

&&

AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX AND KIWA...
INCREASING MID AND HIGH LEVEL CLOUDS THROUGHOUT THE DAY INTO THE 
OVERNIGHT HOURS TONIGHT. CEILINGS WILL GRADUALLY LOWER OVERNIGHT TO 
NEAR 8K FT. WINDS WILL BE MOSTLY LIGHT AND DIURNAL GENERALLY LESS 
THAN12KTS. INTRODUCED VCSH FROM THE AFTERNOON THROUGH OVERNIGHT 
HOURS TO ACCOUNT FOR SHOWERS AT NEAR BY TAF SITES DUE TO UPSLOPE 
FLOW AS THE LOW PRESSURE SYSTEM SWEEPS THROUGH. 

SOUTHWEST ARIZONA AND SOUTHEAST CALIFORNIA INCLUDING KIPL AND KBLH...
MID TO HIGH LEVEL CLOUD DECKS INCREASING TODAY THROUGH OVERNIGHT 
TONIGHT AS THE LOW PRESSURE SYSTEM MOVES ACROSS SOUTHERN CALIFORNIA. 
MOSTLY LIGHT AND DIURNAL WINDS...10-12KT IN THE AFTERNOON BUT THE 
CHANCE FOR POSSIBLE GUSTS UP TO 20KT NOT OUT OF THE QUESTION. AS THE 
LOW MOVES THROUGH RIDGE TOPS WILL SEE STRONGEST WINDS AND WILL 
TRANSFER TO DOWNSLOPE CONDITIONS ESPECIALLY AT KIPL. OVERNIGHT 
CEILINGS MAY LOWER NEAR 8K FT AND MOST OF THE PRECIP CHANCES WILL 
REMAIN OVER CENTRAL ARIZONA. 

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. 

&&

.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...
LINGERING CLOUDINESS AND SOME LIGHT SHOWERS OVER EASTERN ARIZONA 
WILL REMAIN BEHIND MONDAY/S WEATHER SYSTEM AS IT MAKES A QUICK EXIT 
TO THE EAST. DRY AND ZONAL FLOW SETS UP OVER THE AREA AND REMAINS 
THROUGH SATURDAY. TEMPERATURES WILL SLOWLY WARM ABOVE SEASONAL 
NORMALS /POTENTIALLY WARMING INTO THE MID TO UPPER 70S BY END OF THE 
WEEK/ AS DEWPOINTS SLOWLY DRY OUT AND STABILIZE INTO THE UPPER 
20S/30S WITH MODEST OVERNIGHT HUMIDITY RECOVERIES EXPECTED. WINDS 
WILL BE LIGHT AND DIURNALLY DRIVEN WITH MOSTLY CLEAR SKIES AS WELL. 

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...AJ/HIRSCH
AVIATION...DEWEY/NOLTE
FIRE WEATHER...NOLTE