FXUS65 KTWC 290917
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
215 AM MST SUN NOV 29 2009

.SYNOPSIS...A VIGOROUS LOW PRESSURE SYSTEM ACROSS THE LOWER COLORADO 
RIVER VALLEY THIS MORNING WILL MOVE INTO FAR NORTHERN MEXICO AND 
IMPACT THE AREA THROUGH MONDAY. 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...ISOLATED TO SCATTERED CONVECTIVE BANDS SPREADING 
ACROSS THE AREA THIS MORNING. MOISTURE WAS SLOW TO INCREASE BUT 
FINALLY SEEING MEASURABLE PRECIPITATION ACROSS THE AREA AS LOWER 
LEVELS HAVE MOISTENED SUFFICIENTLY. FORCING DIMINISHING ACROSS 
SOUTHERN PORTIONS OF THE WHITE MOUNTAINS AND RIM COUNTRY. AN EARLIER 
CONVECTIVE BAND BROUGHT ABOUT 1 INCH TO HANNAGAN MEADOW A COUPLE OF 
HOURS AGO. WE HAVE ELECTED TO CANCEL THE SNOW ADVISORY FOR THE 
REMAINDER OF THE MORNING WHILE STILL EXPECTING AN ADDITIONAL 1 TO 3 
INCHES.

STRONG LOW NOW PUSHING INTO THE YUMA AREA TRACKING TOWARD THE 
NORTHERN GULF OF CALIFORNIA AND NORTHERN SONORA. TRACK WILL BE JUST 
SOUTH OF THE BORDER. GOOD DYNAMICS AND MOISTURE UNDER AN UPPER LEVEL 
DIFFLUENT PATTERN NORTHEAST OF THE LOW LATER TODAY AND ESPECIALLY 
TONIGHT. STILL ON TRACK FOR SIGNIFICANT PRECIP TONIGHT INTO 
MONDAY...WITH SNOW LEVELS AS LOW AS 4K FEET. WE HAVE ADJUSTED THE 
WINTER STORM WATCH FROM 5K FEET DOWN TO 4.5K FEET TO ADD SUCH 
LOCATIONS AS SIERRA VISTA...TOMBSTONE AND SONOITA IN ADDITION TO 
BISBEE FOR SUNDAY NIGHT AND MONDAY.

SOME WRAP-AROUND FROM THE EAST MONDAY NIGHT INTO TUESDAY 
MORNING...MAINLY FOR EASTERN AREAS INCLUDING GRAHAM AND ESPECIALLY 
COCHISE COUNTY. IF THE WINTER STORM WATCH IS CONVERTED TO A WARNING 
(CURRENTLY LEANING THAT DIRECTION) THEN A TEMPORAL EXTENSION INTO 
MONDAY NIGHT NOT OUT OF THE QUESTION FOR THOSE AREAS.

DIRTY RIDGE BY WEDNESDAY AND THURSDAY...SOME WARMING BUT MORNINGS 
STILL COLD AND EVEN AFTERNOON HIGHS AT OR BELOW CLIMO.

&&

.AVIATION...AS AN UPPER LEVEL LOW EDGES CLOSER TO SOUTHEAST 
ARIZONA...SCT-BKN CLOUDS AT 4-7K FT AGL WITH MTN TOPS OCCASIONALLY 
OBSCURED WILL CONTINUE. SHRA COVERAGE WILL INCREASE TO 
SCATTERED...MORE NUMEROUS NEAR MOUNTAINS. OTHERWISE...LOCALIZED MVFR 
CONDITIONS ARE POSSIBLE DUE TO LOWER CIGS IN SHRA WITH INCREASING 
CHANCES OF MVFR CONDITIONS TONIGHT AND MONDAY. LIGHTER WINDS 
TODAY...GENERALLY LESS THAN 10KTS. AVIATION DISCUSSION NOT UPDATED 
FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...A STRONG PACIFIC LOW PRESSURE SYSTEM CURRENTLY OVER 
THE LOWER COLORADO RIVER VALLEY WILL CONTINUE SOUTHWARD TOWARD 
NORTHERN SONORA MEXICO. THIS SYSTEM WILL BRING PERIODS OF RAIN AND 
MOUNTAIN SNOW TO THE AREA THROUGH MONDAY AND PERHAPS MONDAY NIGHT. 
MUCH COOLER TEMPERATURES ARE EXPECTED SUNDAY AND MONDAY. DRY 
CONDITIONS WILL RETURN BY WEDNESDAY THOUGH TEMPERATURES WILL REMAIN 
COOL.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...

WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY AFTERNOON FOR 
AZZ030-033>035 ABOVE 4500 FEET.  

$$

WEATHER.GOV/TUCSON