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
