FXUS65 KTWC 252155
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
255 PM MST WED NOV 25 2009

.SYNOPSIS...HIGH PRESSURE ALOFT WILL PROVIDE DRY CONDITIONS WITH 
ABOVE NORMAL DAYTIME TEMPERATURES THROUGH FRIDAY. A PACIFIC LOW 
PRESSURE SYSTEM WILL THEN MOVE ACROSS SOUTHEAST ARIZONA THIS 
WEEKEND. THIS SYSTEM WILL BRING A CHANCE OF RAIN AND MOUNTAIN SNOW 
SHOWERS ALONG WITH MUCH COOLER TEMPERATURES. DRY CONDITIONS NEXT 
TUESDAY AND WEDNESDAY THOUGH DAYTIME TEMPERATURES REMAINING BELOW 
NORMAL.

&&

.DISCUSSION...HIGH PRESSURE RIDGE TO BUILD OVER SE AZ THRU 
THANKSGIVING DAY AS WEAK LOW PRESSURE DEVELOPS OVER THE BAJA 
CALIFORNIA REGION. MOSTLY CLEAR SKIES WITH ABOVE NORMAL DAYTIME 
TEMPS ON TAP AGAIN THUR. SURFACE PRESSURE GRADIENT TO TIGHTEN 
SUFFICIENTLY TO SUPPORT LOCAL ELY/SELY BREEZES THUR. CONTINUED WARM 
AND DRY FRI AS THE UPPER RIDGE MOVES EWD AND TROUGH MOVES ACROSS THE 
PACIFIC NW. A VIGOROUS UPPER TROUGH IS THEN EXPECTED TO MOVE ACROSS 
THE AREA THIS WEEKEND. THERE WERE DIFFERENCES BETWEEN THE 25/12Z 
GFS/ECMWF SOLUTIONS REGARDING THE EVOLUTION OF THIS SYSTEM...WITH 
THE GFS NOW DEEPER AND SLOWER WITH THE PROGRESSION OF THIS SYSTEM 
VERSUS THE ECMWF. THE 25/12Z CANADIAN SOLUTION SUPPORTED IN ESSENCE 
A BLEND OF THE GFS/ECMWF SOLUTIONS. AT ANY RATE...INCREASED POPS 
PRIMARILY DURING THE SATURDAY AFTERNOON TO MONDAY PERIOD. AT THIS 
TIME APPEARS THE BEST CHANCE OF MEASURABLE PRECIP WILL BE SATURDAY 
NIGHT INTO SUNDAY. SNOW LEVELS BY SUNDAY MORNING EXPECTED TO LOWER 
TO AROUND 5500-6000 FEET. WILL FORECAST BY SUNDAY MORNING SNOW 
ACCUMS ON MT LEMMON OF AROUND 1 INCH...2 INCHES FOR MT GRAHAM...AND 
3 INCHES FOR THE WHITE MOUNTAINS. ADDITIONAL SNOWFALL ALBEIT JUST 
BELOW ADVISORY CRITERIA IS EXPECTED SUNDAY. SLIGHT CHANCE OF RAIN 
AND MOUNTAIN SNOW SHOWERS MAINLY FROM THE TUCSON METRO AREA EWD 
STILL MERITED SUNDAY NIGHT AND MONDAY. PRECIP-FREE CONDITIONS TO 
OCCUR MON NIGHT-WED. COOLER SAT THEN DAYTIME HIGH TEMPS SUN 
AVERAGING ABOUT 10 DEGS OR SO BELOW NORMAL. STILL QUITE COOL MON 
THEN SOME WARMING TUE.

&&

.AVIATION...MOSTLY CLEAR SKIES WILL PREVAIL INTO THURSDAY WITH ANY 
CLOUDS OF SIGNIFICANCE AT OR ABOVE 20K FT AGL. SURFACE WIND ELY/SELY 
5-15 KTS TONIGHT. SURFACE WIND THURSDAY KTUS VICINITY ELY/SELY 10-20 
KTS AND GUSTY...AT KOLS/KDUG AIRFIELDS GENERALLY ELY WIND 5-15 KTS. 
AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...NO FIRE WEATHER CONCERNS THROUGH FRIDAY. A PACIFIC 
LOW PRESSURE SYSTEM WILL THEN MOVE ACROSS SOUTHEAST ARIZONA THIS 
WEEKEND. THIS SYSTEM IS EXPECTED TO BRING A CHANCE OF RAIN AND 
MOUNTAIN SNOW SHOWERS TO THE AREA...ESPECIALLY SATURDAY NIGHT AND 
SUNDAY. BREEZY CONDITIONS WILL ALSO OCCUR SATURDAY. HOWEVER... 
CRITICAL FIRE WEATHER THRESHOLDS ARE NOT EXPECTED TO BE MET AT THIS 
TIME. ALSO...COOLER TEMPERATURES ARE ON TAP SATURDAY WITH MUCH 
COOLER TEMPERATURES TO FOLLOW SUNDAY. DRY CONDITIONS RETURN NEXT 
TUESDAY AND WEDNESDAY WITH A GRADUAL WARMING TREND.

&&

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

$$

BF

WEATHER.GOV/TUCSON