Expires:No;;297399
FXUS65 KTWC 271611
AFDTWC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
910 AM MST FRI NOV 27 2009
.SYNOPSIS...REMAINING WARM AND DRY TODAY. A VIGOROUS PACIFIC LOW 
PRESSURE SYSTEM WILL MOVE INTO THE AREA THIS WEEKEND AND MONDAY. 
THIS SYSTEM WILL BRING A CHANCE OF VALLEY RAIN AND MOUNTAIN SNOW AS 
WELL AS MUCH COOLER TEMPERATURES. DRY CONDITIONS BEHIND THE SYSTEM 
FOR THE MIDDLE OF THE WEEK...EVEN AS THE COOLER AIR HANGS ON WITH 
COLD OVERNIGHT LOWS.
&&
.DISCUSSION...WEAK UPPER LOW VICINITY BAJA SPUR WITH FAIRLY THICK 
MID AND HIGH-LEVEL CLOUDS JUST EAST OF THIS FORECAST AREA ACROSS SRN 
NM/FAR WEST TX. ABUNDANT SUNSHINE THIS MORNING THEN SOME INCREASE IN 
HIGH-LEVEL CLOUDS THIS AFTERNOON AS FLOW ALOFT BECOMES INCREASINGLY 
WLY/SWLY. FOCUS OF ATTENTION TO TURN TOWARD STRONG TROUGH ENTERING 
THE PACIFIC NW AT THIS TIME. UPPER LOW TO DEVELOP OVER NORTHERN 
CALIFORNIA THIS AFTERNOON THEN SYSTEM TO MOVE SEWD ACROSS SOUTHERN 
CALIFORNIA SAT...AND TOWARD NRN SONORA BY EARLY MON. 
MOISTURE MAINLY ABOVE 700 MB WILL INCREASE ACROSS THE AREA TONIGHT 
WITH LOWER-LEVEL MOISTURE TO INCREASE STARTING SAT AND ESPECIALLY 
SUN-MON. PRECIP-FREE CONDITIONS TO OCCUR TONIGHT THEN SHOWERS SHOULD 
DEVELOP BY MIDDAY SAT PARTICULARLY NEAR HIGHER TERRAIN FROM TUCSON 
NWD/EWD. PERHAPS AN ISOLATED THUNDERSTORM SAT AFTERNOON AS 
DESTABILIZATION OCCURS. INHERITED FORECASTS KEEP SNOW ACCUMULATIONS 
BELOW ADVISORY CRITERIA THRU SAT NIGHT WITH ANY ACCUMS OF SIGNIFICANCE
ACROSS THE WHITE MOUNTAINS AND THE GILA/PINALENO MOUNTAINS OF THE 
UPPER GILA RIVER VALLEY.
27/00Z GFS/ECMWF WERE IN GENERAL AGREEMENT THAT UPPER LOW WILL MOVE 
SLOWLY EWD ACROSS THE NRN BAJA/NRN GULF CALIFORNIA REGION SUN...THEN 
TOWARD NRN SONORA MIDDAY MON. RECEIPT OF 27/12Z NAM SUGGESTS THAT 
SUN AFTERNOON INTO MON WOULD BE THE PERIOD MOST SUPPORTIVE OF 
SIGNIFICANT PRECIP. ALSO...GIVEN THE PROGGED PAT OF THE SYSTEM 
ACROSS NRN SONORA...THE EMPHASIS FOR MORE SIGNIFICANT ACCUMULATING 
SNOWS WOULD BE ACROSS SERN MOUNTAINS SUCH AS THE CHIRICAHUAS AND 
HUACHUCAS OF COCHISE COUNTY. AT THIS TIME DO NOT ANTICIPATE SNOW 
LEVELS TO VALLEY FLOORS THERE. AT ANY RATE...STILL TOO EARLY FOR 
WATCHES TO BE ISSUED AND THUS WILL CONTINUE REFERENCE TO THE 
HAZARDOUS WEATHER OUTLOOK PRODUCT /AWIPS PIL PHXHWOTWC/WMO HEADER 
FLUS45 KTWC/.
BOTH GFS/ECMWF INDICATE THIS SYSTEM TO EJECT EWD MON NIGHT THEN 
WLY/NWLY FLOW ALOFT TO OCCUR TUE-THUR. STILL ENOUGH MOISTURE FOR A 
SLIGHT CHANCE OF RAIN AND MOUNTAIN SNOW SHOWERS FROM TUCSON SWD/EWD 
MON NIGHT...THEN DRY CONDITIONS TUE-THUR. ABOVE NORMAL TEMPS THIS 
AFTERNOON. COOLER SAT THEN QUITE COOL SUNDAY-TUESDAY WITH DAYTIME 
HIGH TEMPS AVERAGING ABOUT 10 DEGS OR SO BELOW NORMAL. WARMER WED 
WITH HIGH TEMPS TRENDING CLOSE TO NORMAL NEXT THUR.
&&
.AVIATION...CLEAR SKIES THRU 18Z THEN SCT-BKN CLOUDS AT OR ABOVE 20K 
FT AGL THIS AFTERNOON CONTINUING INTO SATURDAY MORNING. SURFACE 
WINDS VARIABLE IN DIRECTION GENERALLY LESS THAN 10 KTS INTO SATURDAY 
MORNING. DURING THE 18Z-23Z PERIOD SATURDAY...CLOUD BASES LOWERING 
TO AROUND 7-10K FT AGL WITH SHRA AND HIGHER TERRAIN SHSN DEVELOPING. 
SURFACE WINDS 18Z-23Z SATURDAY SLY/SWLY 12-25 KTS AND GUSTY. 
AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.
&&
.FIRE WEATHER...REMAINING DRY TODAY THOUGH LESS WIND VERSUS 
THANKSGIVING DAY. A VIGOROUS PACIFIC LOW PRESSURE SYSTEM WILL MOVE 
ACROSS SOUTHERN CALIFORNIA SATURDAY AND INTO NORTHERN SONORA MEXICO 
BY EARLY MONDAY. THIS SYSTEM WILL BRING A CHANCE OF RAIN AND 
MOUNTAIN SNOW TO THE AREA...ESPECIALLY SATURDAY AFTERNOON INTO 
MONDAY. BREEZY TO WINDY CONDITIONS ARE ALSO FORECAST SATURDAY. 
HOWEVER...CRITICAL FIRE WEATHER THRESHOLDS ARE NOT EXPECTED TO BE 
MET SINCE RELATIVE HUMIDITIES ARE FORECAST ABOVE 15 PERCENT. MUCH 
COOLER BY SUNDAY AND MONDAY.
&&
.TWC WATCHES/WARNINGS/ADVISORIES...NONE.
$$
BF
WEATHER.GOV/TUCSON