FXUS65 KTWC 291629
AFDTWC

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

.SYNOPSIS...A LOW PRESSURE SYSTEM MOVING INTO NORTHERN MEXICO TODAY 
WILL IMPACT THE AREA THROUGH MONDAY EVENING. 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...THE LOW PRESSURE SYSTEM RESPONSIBLE FOR WIND 
YESTERDAY AND SHOWERS LAST NIGHT THROUGH THIS MORNING WAS NOW 
CENTERED OVER NORTHERN BAJA. RECENT RADAR IMAGERY INDICATED ISOLATED 
SHOWER AND THUNDERSTORM ACTIVITY ACROSS PARTS OF SOUTHEAST 
ARIZONA...MAINLY IN GRAHAM AND COCHISE COUNTIES AT 9AM MST. AS THE 
COLD CORE OF THE UPPER LOW REMAINS FAIRLY CLOSE TO SOUTHEAST 
ARIZONA...STILL EXPECTING INSTABILITY SHOWERS AND A FEW 
THUNDERSTORMS THIS AFTERNOON. SATELLITE IMAGERY WAS SHOWING SOME 
CLEARING GENERALLY FROM TUCSON WESTWARD...BUT EXPECTING THIS AREA TO 
FILL IN WITH CLOUDINESS AND SCATTERED SHOWERS AND A FEW 
THUNDERSTORMS THIS AFTERNOON. THUS...THE SHORT TERM FORECAST STILL 
LOOKED GOOD. 

THE LAST TWO MODEL RUNS TRACK THE UPPER LOW A BIT FARTHER SOUTH OVER 
NORTHERN MEXICO THAN WHAT WAS DEPICTED YESTERDAY...BUT THE TIMING 
REMAINED CONSISTENT. THIS SLIGHTLY FARTHER SOUTH TRACK WILL MAINLY 
IMPACT THE LOCATION OF THE HEAVIEST SNOWFALL AND RAIN...WITH COCHISE 
AND SOUTHERN GRAHAM COUNTIES BEING THE MAIN CONCERN. THIS WILL 
ESPECIALLY BE THE CASE IF SNOW LEVELS DROP AS LOW AS WHAT WAS BEING 
PROJECTED FOR LATE TONIGHT AND EARLY MONDAY. AT THIS TIME...WILL 
KEEP THE WINTER STORM WATCH GOING FOR THE SAME LOCATIONS AND MAKE 
FINAL DISCUSSIONS ON THE AFTERNOON FORECAST PACKAGE ON WHETHER 
SWITCH OVER TO ADVISORIES OR WARNINGS. PLEASE REFER TO THE 
ADDITIONAL SECTIONS BELOW FOR MORE INFORMATION.   

&&

.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 LOW PRESSURE SYSTEM MOVING INTO NORTHERN MEXICO 
TODAY WILL IMPACT THE REGION THROUGH MONDAY. THIS SYSTEM WILL BRING 
PERIODS OF RAIN AND MOUNTAIN SNOW TO THE AREA THROUGH MONDAY AND 
PERHAPS MONDAY NIGHT. MUCH COOLER TEMPERATURES ARE EXPECTED TODAY 
AND MONDAY. DRY CONDITIONS WILL RETURN BY WEDNESDAY THOUGH 
TEMPERATURES WILL REMAIN COOL.

&&

.PREV 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.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...

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

$$

WEATHER.GOV/TUCSON