FXUS65 KTWC 062157
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
255 PM MST SUN DEC 6 2009

.SYNOPSIS...A STRONG WINTER STORM SYSTEM WILL APPROACH THE AREA FROM 
THE NORTHWEST ON MONDAY. THIS SYSTEM WILL BRING WIDESPREAD VALLEY 
RAIN AND SIGNIFICANT MOUNTAIN SNOW TO SOUTHEAST ARIZONA MONDAY NIGHT 
INTO MIDDAY TUESDAY. DRIER CONDITIONS WEDNESDAY FOLLOWED BY ANOTHER 
CHANCE OF VALLEY RAIN AND MOUNTAIN SNOW THURSDAY INTO FRIDAY.

&&

.DISCUSSION...WRN CONUS TROUGH TO CONTINUE TO DEEPEN TONIGHT AND 
MON. ASIDE FROM A SLIGHT CHANCE OF SNOW SHOWERS WHITE MOUNTAINS...
REMAINING PRECIP-FREE TONIGHT UNDER MOSTLY CLOUDY SKIES. MID-LEVEL 
GRADIENT TO BE SUFFICIENTLY TIGHT FOR BREEZY CONDITIONS PORTIONS OF 
SANTA CRUZ/COCHISE COUNTIES TONIGHT...THEN BREEZY TO WINDY 
CONDITIONS AREAWIDE MON AFTERNOON AND CONTINUING INTO TUE. MAY 
EVENTUALLY NEED A WIND ADVISORY FROM THE TUCSON METRO AREA EWD/SWD 
FOR SOME PORTION OF MON AFTERNOON-TUE. ALSO...MOISTURE WILL INCREASE 
ACROSS THE AREA TO SUPPORT A CHANCE OF VALLEY RAIN AND MOUNTAIN SNOW 
MAINLY NORTH AND WEST OF TUCSON BY MON AFTERNOON. 

06/12Z GFS/NAM/ECMWF SOLUTIONS REMAIN IN GOOD AGREEMENT AND CONTINUE 
TO DEPICT DEEPER-LAYER MOISTURE ACROSS SE AZ MON NIGHT-TUE MORNING. 
THIS PERIOD IS ALSO COINCIDENT WITH SYNOPTIC-SCALE ASCENT AS PER 
700-300 MB NEGATIVE DIV-Q FIELDS. PRECIP SHOULD TAPER FROM WEST-EAST 
TUE AFTERNOON AS DEEPER MOISTURE IS SHUNTED WELL NEWD. PER COORD 
WITH WFO/S PSR/FGZ AND HIGH CONFIDENCE IN SCENARIO...OPTED TO 
UPGRADE WINTER STORM WATCH TO WINTER STORM WARNING FOR HEAVY SNOW 
FROM 5 PM MON TO NOON MST TUE FROM TUCSON EWD/SWD ABOVE 6000 FEET. 
SNOW ACCUMULATIONS OF 6-12 INCHES BETWEEN 6000-7000 FEET ARE 
EXPECTED BY TUE EVENING...WITH THE POTENTIAL FOR 12-18 INCHES ABOVE 
7000 FEET. 

SHORTWAVE RIDGE ALONG THE CALIFORNIA COAST WED WILL FLATTEN AND MOVE 
EWD ACROSS THE AREA WED NIGHT. RIDGE TO BE FAIRLY DIRTY WITH MID AND 
HIGH-LEVEL MOISTURE TO MOVE ACROSS THE AREA. THE NEXT SHORTWAVE 
TROUGH CONTINUES TO BE PROGGED TO MOVE ACROSS THE GREAT BASIN REGION 
LATE THUR AND FRI. THIS SYSTEM WILL BRING ANOTHER CHANCE OF VALLEY 
RAIN AND MOUNTAIN SNOW SHOWERS PARTICULARLY FROM TUCSON EWD. TRENDED 
POPS DOWNWARD FOR SAT-SUN AS STORM TRACK SHIFTS SOMEWHAT NWD. 
HOWEVER...PERHAPS ENOUGH MOISTURE FOR LOW-GRADE POPS ACROSS THE 
HIGHER TERRAIN NE OF TUCSON SAT. 

NEAR-NORMAL DAYTIME TEMPS MON. QUITE COOL TUE THEN WARMER WED WITH 
HIGH TEMPS THUR-SUN TRENDING EITHER CLOSE TO NORMAL OR PERHAPS A FEW 
DEGS BELOW NORMAL.

&&

.AVIATION...SCATTERED TO OCCASIONALLY BROKEN CLOUDS WITH BASES 
AROUND 6-8K FT AGL WILL OCCUR INTO MONDAY MORNING. SURFACE WINDS 
KTUS THRU 02Z SLY/SWLY 8-18 KTS AND GUSTY THEN DECREASING MOST 
SECTIONS TO 5-15 KTS AND CONTINUING INTO MONDAY MORNING. 
THEREAFTER...DETERIORATING CONDITIONS WITH SCATTERED SHRA/HIGHER 
TERRAIN SHSN AND GUSTY SLY/SWLY WINDS DURING THE 18Z-23Z PERIOD 
MONDAY. AREAS OF MVFR CONDITIONS DUE TO SHRA/HIGHER TERRAIN SHSN 
MONDAY NIGHT AND TUESDAY MORNING. AVIATION DISCUSSION NOT UPDATED 
FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...A STRONG STORM SYSTEM WILL APPROACH SOUTHEAST 
ARIZONA FROM THE NORTHWEST MONDAY. THIS SYSTEM WILL BRING WIDESPREAD 
VALLEY RAIN AND MOUNTAIN SNOW PARTICULARLY MONDAY NIGHT THROUGH 
MIDDAY TUESDAY. BREEZY TO WINDY CONDITIONS WILL ALSO ACCOMPANY THIS 
SYSTEM. DRIER CONDITIONS WILL OCCUR WEDNESDAY. ENOUGH MOISTURE FOR A 
CHANCE OF RAIN AND MOUNTAIN SNOW THURSDAY INTO SATURDAY AS A SERIES 
OF DISTURBANCES MOVE ACROSS THE AREA. BREEZY TO OCCASIONALLY WINDY 
CONDITIONS MAY ALSO ACCOMPANY THESE SYSTEMS.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...WINTER STORM WARNING IN EFFECT
      FROM 5 PM MONDAY TO NOON MST TUESDAY ABOVE 6000 FEET 
      AZZ019-030-033>035.

$$

BF

WEATHER.GOV/TUCSON