FXUS65 KTWC 300920
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
215 AM MST MON NOV 30 2009

.SYNOPSIS...A LOW PRESSURE SYSTEM MOVING OVER NORTHERN MEXICO WILL 
IMPACT THE AREA THROUGH MONDAY NIGHT. THIS SYSTEM WILL BRING 
PERIODS OF VALLEY RAIN AND POTENTIALLY SIGNIFICANT 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...LOW NOW PUSHING INTO NORTHERN SONORA JUST SOUTH OF THE 
INTERNATIONAL BORDER. BANDS OF CONVECTION ROTATING AROUND THE LOW 
THROUGH SOUTHEAST ARIZONA FROM THE SOUTHEAST AND EAST. SNOW LEVELS 
AROUND 5000 FEET EARLY THIS MORNING AND FALLING...WITH LOWEST VALUES 
CLOSER TO THE LOW IN SOUTHERN AREAS. UPSLOPE AROUND THE LOW HAS BEEN 
MOST FAVORABLE FOR THE CHIRICAHUA MTNS AREA SO FAR...BUT SHOWERS ARE 
BECOMING MORE NUMEROUS AND WIDESPREAD. INHERITED FORECAST IS IN 
PRETTY GOOD SHAPE.

CUT-OFF WILL BE SLOW TO TRANSIT SONORA AND IS NOT EXPECTED TO REACH 
CHIHUAHUA UNTIL TONIGHT...SO WRAP-AROUND WILL BE A FACTOR INTO 
TUESDAY MORNING. WE WILL GO AHEAD AND EXTEND THE CURRENT SNOW 
ADVISORY ACROSS NORTHERN AREAS INTO LATER THIS AFTERNOON AND WINTER 
STORM WARNING ACROSS SOUTHERN AREAS INTO THIS EVENING...ABOUT AN 
ADDITIONAL 5 HOURS OR SO. LOWEST SNOW LEVELS ARE EXPECTED AROUND 
SUNRISE TO 9 AM...AND STILL EXPECTED TO BOTTOM OUT AROUND 4500 FEET 
NORTH AND 4000 FEET SOUTH.

GETTING ON THE COLD SIDE AS SOON AS TONIGHT AND AGAIN TUESDAY NIGHT. 
MIGHT HAVE SOME PATCHY FROST WITH RESIDUAL MOISTURE IN THE BOUNDARY 
LAYER EVEN AS WE SEE DRY NORTHERLY TO NORTHWESTERLY FLOW BEHIND THE 
LOW.

DIRTY RIDGE WITH WARMING BACK UP TO NEAR CLIMO THE REST OF THE WEEK. 
NEXT WEEK IS STARTING TO SET UP WITH SOME SIGNIFICANT SOUTHERN 
BRANCH ENERGY AND MOISTURE POINTING TOWARD A MORE ACTIVE PERIOD 
AFTER THIS COMING WEEKEND.

&&

.AVIATION...AS AN UPPER LEVEL LOW CONTINUES TO MOVE THROUGH THE 
AREA...SCT-BKN CLOUDS AT 2-5K FT AGL WITH MTN TOPS OCCASIONALLY 
OBSCURED WILL CONTINUE. PERIODS OF SHRA/SHSN DIMINISHING LATER 
TODAY. THERE WILL BE AREAS OF MVFR CONDITIONS NEAR SHOWERS WITH 
BRIEF PERIODS OF IFR CONDITIONS. WINDS ARE EXPECTED TO REMAIN 
GENERALLY LESS THAN 10KTS. AVIATION DISCUSSION NOT UPDATED FOR TAF 
AMENDMENTS.

&&

.FIRE WEATHER...NO FIRE WEATHER CONCERNS AT THIS TIME.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...

WINTER STORM WARNING THROUGH 11PM MST TONIGHT FOR ZONES 
AZZ034-035 ABOVE 4500 FEET.

WINTER WEATHER ADVISORY THROUGH 4PM MST TODAY FOR ZONES 
AZZ030-033 ABOVE 4500 FEET.  

$$

WEATHER.GOV/TUCSON