Heavy Snow in Arizona, December 11 to 12, 2001

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
235 AM MST TUE DEC 11 2001

.SYNOPSIS...A STORM SYSTEM WILL MOVE ACROSS SOUTHERN ARIZONA TODAY
BRINGING MUCH COOLER TEMPERATURES AND VALLEY RAIN AND MOUNTAIN SNOW
TO SOUTHEAST ARIZONA. TWO OTHER DISTURBANCES WILL MOVE INTO
SOUTHERN ARIZONA...ONE TONIGHT AND THE OTHER WEDNESDAY...CONTINUING
THE CHANCE OF VALLEY SHOWERS AND MOUNTAIN SNOW SHOWERS. A COOL
NORTHWEST FLOW ALOFT WILL BE OVER THE AREA FOR THE REMAINDER OF THE
WEEK...KEEPING TEMPERATURE BELOW NORMAL. WARMER TEMPERATURES ARE
THEN EXPECTED OVER THE UPCOMING WEEKEND.

.DISCUSSION...STORM SYSTEM CURRENTLY CENTERED NEAR YUMA..WITH AREA
OF PRECIPITATION OUT AHEAD OF IT OVER PORTIONS OF WESTERN AND
CENTRAL PIMA COUNTY. SOME LIGHTNING STRIKES ALSO NOTED WITH THIS
AREA OF PRECIPITATION. THIS SYSTEM HAS INCORPORATED SOME LOW LEVEL
MOISTURE INTO IT AS INDICATED BY SAN DIEGOS 00Z SOUNDING...WHICH
SHOWS A MARINE LAYER DEPTH TO NEAR 8000 FEET. IN ADDITION...GOOD
LIFT AND VERY COLD TEMPERATURES ALOFT WILL HELP WRING OUT ALL
AVAILABLE MOISTURE AS IT TRACKS EAST ACROSS SOUTHERN ARIZONA TODAY.
THICKNESS SUPPORT SNOW LEVELS DOWN TO 4500 FEET TODAY. WILL CONTINUE
SNOW ADVISORY TODAY FOR ALL ZONES EXCEPT FAR WESTERN PIMA COUNTY
ABOVE 4500 FEET.

ANOTHER VORT MAX WILL SLIDE SOUTHEAST INTO SOUTHERN ARIZONA TONIGHT
IN NORTHWEST FLOW ALOFT. WITH MOISTURE ALREADY IN PLACE...WILL
CONTINUE THE A CHANCE OF VALLEY SHOWERS AND MOUNTAIN SNOW SHOWERS
FOR MUCH OF THE CWA...THE EXCEPTION BEING FAR WESTERN PIMA COUNTY
WHICH WILL BE ON THE BACK SIDE OF THE VORT MAX. WILL KEEP SNOW
LEVELS AT 4500 FEET...HOWEVER SNOW MAY BRIEFLY COME DOWN AS LOW AS
4000 FEET BEFORE TAPERING OFF. QPF AMOUNTS SHOULD BE AROUND ONE
THIRD OF AN INCH IN THE VALLEYS AND THE FORECAST OF 3 TO 8 INCHES IN
THE MOUNTAINS ABOVE 4500 FEET LOOKS GOOD EVERYWHERE EXCEPT THE WHITE
MOUNTAINS WHERE I WILL BUMP UP 24 HOUR TOTAL AMOUNTS INTO THE 5 TO
10 INCH RANGE.

YET ANOTHER DISTURBANCE MOVES INTO SOUTHERN ARIZONA WEDNESDAY.
ALTHOUGH THE MODELS ARE IN GENERAL AGREEMENT WITH THE TIMING AND
POSITION OF THIS DISTURBANCE...THE MODELS DIFFER ON THE AMOUNT OF
AVAILABLE MOISTURE...WITH ETA BEING MUCH DRIER THAN THE AVN. HOWEVER
WITH GOOD DYNAMICS...WILL ADD SLIGHT CHANCE WORDING TO WEDNESDAYS
FORECAST. WITH COLDER OVERNIGHT LOWS TONIGHT AND WEDNESDAY NIGHT...
AREAS OF FROST WILL BE POSSIBLE.

FOR THE LATTER FORECAST PERIODS...COOL NORTHWEST FLOW CONTINUES INTO
THE WEEKEND...WITH TEMPERATURES REMAINING BELOW SEASONAL NORMS.
MODELS CONTINUE TO FLIP FLOP ON TIMING AND STRENGTH OF THE TROUGH
EXPECTED OVER THE WEEKEND...THEREFORE HAVE KEEP CURRENT EXTENDED
FORECAST IN PLACE.  ZELL

.TWC...SNOW ADVISORY TODAY ABOVE 4500 FEET ALL ZONES XCPT ZONE 31.