FXUS65 KTWC 262111
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
210 PM MST THU NOV 26 2009

.SYNOPSIS...HIGH PRESSURE ALOFT WILL PROVIDE WARM AND DRY CONDITIONS 
AGAIN FRIDAY. A VIGOROUS PACIFIC LOW PRESSURE SYSTEM WILL THEN MOVE 
INTO THE AREA THIS WEEKEND INTO MONDAY. THIS SYSTEM WILL BRING A 
CHANCE OF RAIN AND MOUNTAIN SNOW AS WELL AS MUCH COOLER TEMPERATURES 
SUNDAY AND MONDAY. DRY CONDITIONS TO PREVAIL TUESDAY AND WEDNESDAY 
THOUGH DAYTIME TEMPERATURES REMAINING BELOW NORMAL.

&&

.DISCUSSION...WEAK UPPER LOW OFF THE NRN BAJA CALIFORNIA COAST WITH 
RIDGE AXIS EXTENDING FROM UTAH-WEST TEXAS. FAIRLY EXTENSIVE AREA OF 
CIRROFORM CLOUDINESS EXPECTED TO MOVE NWD ACROSS THIS FORECAST AREA 
TONIGHT SUFFICIENT FOR PARTLY CLOUDY SKIES. ENOUGH MOISTURE FRI 
MAINLY ABOVE 600 MB TO JUSTIFY PARTLY CLOUDY SKIES FROM TUCSON EWD 
THOUGH MOSTLY SUNNY WRN LOCALES. 

FOCUS OF ATTENTION THEN SHIFTS TOWARD VIGOROUS LOW PRESSURE SYSTEM 
TO BE NEAR THE NRN CALIFORNIA COAST FRI AFTERNOON...THEN PROGGED TO 
MOVE SEWD TOWARD THE SWRN AZ-NRN BAJA CALIFORNIA REGION BY EARLY 
SUN. THERE WERE DIFFERENCES BETWEEN THE 26/12Z GFS/ECMWF SOLUTIONS 
REGARDING THE EVOLUTION/PROGRESSION OF THIS SYSTEM. TAKEN AT FACE 
VALUE THE GFS WOULD ARGUE FOR THE BEST CHANCE OF PRECIP TO OCCUR SAT 
NIGHT...THEN MID-LEVEL DRYING OR A SEMBLANCE OF A DRY-SLOT ON SUN. 
UPPER LOW THEN WOULD STALL OVER NRN SONORA MON FOR ANOTHER ROUND OF 
PRECIP. MEANWHILE...THE ECMWF WAS MORE-PROGRESSIVE WITH THE SEWD 
TRAJECTORY ACROSS SRN CALIFORNIA AND SRN AZ SAT-SUN...THEN UPPER LOW 
TO STALL OVER NRN SONORA MON BEFORE EJECTING EWD MON NIGHT AND TUE. 
AT ANY RATE...

HAVE OPTED FOR A CHANCE OF SHOWERS ACROSS MUCH OF THE AREA SAT NIGHT 
AND SUN MORNING. SNOW LEVELS BY SUN MORNING EXPECTED TO LOWER TO 
AROUND 6000-6500 FEET. FORECAST SNOW ACCUMULATIONS BY SUN MORNING ON 
MT LEMMON AROUND 2 INCHES...3 INCHES FOR MT GRAHAM...AND A LITTLE 
OVER 4 INCHES AT HANNAGAN MEADOW...WHICH WOULD BE LOW-END ADVISORY 
CRITERIA ABOVE 7000 FEET FOR THE WHITE MOUNTAINS. FOR NOW WILL 
REFLECT SLIGHTLY LOWER SNOW ACCUMS SUN...SUN NIGHT...AND MON THOUGH 
CHANCE-CATEGORY POPS FROM TUCSON EWD WITH LESSER CHANCES WEST. BOTH 
GFS/ECMWF INDICATE THIS SYSTEM TO EJECT EWD MON NIGHT THEN WLY/NWLY 
FLOW ALOFT TO OCCUR TUE-THUR. FOR NOW WILL REJECT THE GFS SCENARIO 
OF UPPER LOW TO MOVE ACROSS NRN AZ NEXT WED NIGHT-THUR.

ABOVE NORMAL DAYTIME TEMPS AGAIN FRI AHEAD OF THE APPROACHING STORM 
SYSTEM. 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...VARIABLE CLOUDINESS AT OR ABOVE 20K FT AGL INTO FRIDAY 
MORNING. SURFACE WIND KTUS VICINITY THRU 01Z ELY/SELY 10-20 KTS AND 
GUSTY...AT KOLS/KDUG AIRFIELDS GENERALLY ELY WIND 5-15 KTS. SURFACE 
WIND AFTER 27/01Z AND INTO FRIDAY MORNING ELY/SELY 5-15 KTS. 
AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...REMAINING DRY FRIDAY WITH MINIMUM HUMIDITIES MOSTLY 
BELOW 15 PERCENT AND LESS WIND VERSUS THANKSGIVING DAY. A VIGOROUS 
PACIFIC LOW PRESSURE SYSTEM WILL MOVE ACROSS SOUTHERN CALIFORNIA 
SATURDAY AND TOWARD 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. COOLER SATURDAY WITH MUCH 
COOLER TEMPERATURES TO OCCUR SUNDAY AND MONDAY. DRY CONDITIONS TO 
PREVAIL TUESDAY THROUGH THURSDAY.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...NONE.

$$

BF

WEATHER.GOV/TUCSON