FXUS65 KFGZ 271629
AFDFGZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
930 AM MST FRI NOV 27 2009

.SYNOPSIS...HIGH PRESSURE WILL BRING ONE MORE DAY OF MOSTLY SUNNY 
SKIES AND MILD HIGH TEMPERATURES. A STRONG LOW PRESSURE SYSTEM 
WILL IMPACT NORTHERN ARIZONA SATURDAY AND SUNDAY WITH COLDER 
TEMPERATURES...BREEZY CONDITIONS...MOUNTAIN SNOW AND VALLEY RAIN.

&&

.DISCUSSION...IT WAS CLEAR OVER MOST OF NORTHERN ARIZONA THIS 
MORNING WITH ONLY A FEW CLOUDS OVER THE WHITE MOUNTAINS. 
HOWEVER...THERE IS A LARGE BAND OF MID TO UPPER LEVEL CLOUDS MOVING 
EASTWARD ACROSS CALIFORNIA...NEVADA...AND UTAH. THIS BAND OF CLOUDS 
SHOULD ENTER THE WESTERN EDGE OF YAVAPAI AND COCONINO COUNTY BETWEEN 
20Z AND 22Z (100 TO 300 PM MST). WILL ADJUST GRIDS TO REFLECT THIS. 
SHORT TERM FORECAST IN GOOD SHAPE. MAY NEED TO INCREASE POPS/QPF 
OVER NORTHEAST ZONES (10-11) FOR SATURDAY NIGHT AND SUNDAY WITH 
AFTERNOON PACKAGE. 

&&

.PREV DISCUSSION /330 AM MST/...VERY DRY AIR IN PLACE OVER THE 
INTERMOUNTAIN WEST AND OVER THE ROCKIES. THE HIGH PRESSURE RIDGE 
THAT HAS RESIDED OVER THE WESTERN U.S. WILL BEGIN TO MOVE EAST 
TODAY...MAKING ROOM FOR AN APPROACHING UPPER LEVEL LOW PRESSURE 
SYSTEM THAT IS FORECAST TO DROP SOUTH THROUGH CALIFORNIA SATURDAY 
AND THEN INTO BAJA SUNDAY AND THE REST OF NORTHERN MEXICO ON MONDAY. 
BOTH THE GFS AND THE ECMWF HAVE BEEN CONSISTENT ON THE TRACK OF THE 
LOW OVER THE LAST SEVERAL MODEL RUNS. GOES SOUNDER DPI SHOWING SOME 
WEAK ADVECTION OF MOISTURE INTO EXTREME SOUTHEAST ARIZONA...WITH THE 
REST OF THE STATE AND THE INTERMOUNTAIN WEST AND ROCKIES REMAINING 
EXTREMELY DRY. THE DRY AIR WILL PLAY A ROLL IN LOWERING SNOW LEVELS 
ON SATURDAY OVER WHAT IS INDICATED BY THE GFS...WARMER WITH HIGHER 
SNOW LEVELS. MIDLEVEL MOISTURE AND QPF PRESENTED BY THE MODELS WILL 
GO INTO MOISTENING THE LOWER LEVELS. SO QPF AMOUNTS ON SATURDAY AS 
ADVERTISED BY THE MODELS CAN BE CUT BACK AND SNOW LEVELS WERE 
LOWERED CONSIDERABLY OVER PREVIOUS FORECAST FOR CONSIDERATION OF WET 
BULB FACTORS OF PRECIP INTO DRY AIR.

THE CLOSEST THE UPPER LOW WILL GET TO ARIZONA WILL BE LATE SATURDAY 
AFTERNOON AND EVENING...BEFORE DROPPING SOUTH INTO MEXICO. CURRENT 
THINKING IS FOR THE BEST CHANCES OF PRECIPITATION TO OCCUR WILL BE 
LATE SATURDAY INTO EARLY SUNDAY MORNING. ONCE THE LOW BEGINS TO DROP 
SOUTH INTO MEXICO THE FLOW WILL BECOME EAST NORTHEAST...THUS 
ADVECTING THE DRY LOW TO MID-LEVEL AIR FROM OVER UTAH AND COLORADO 
BACK INTO AREAS NORTH OF THE MOGOLLON RIM.  THE 00Z GFS WAS 
INDICATING THE DRY ADVECTION INTO AREAS NORTH OF THE MOGOLLON RIM ON 
SUNDAY...AND CHC'S OF PRECIP WERE LOWERED FROM THE MOGOLLON RIM 
NORTH. AGAIN SNOW LEVELS SHOULD BE LOWER THAN ADVERTISED BY THE GFS 
DUE TO THE INFLUENCES OF THE DRY ADVECTION AND WET BULBING AS THE 
PRECIPITATION FALLS THROUGH DRIER AIR. 

BY MONDAY MORNING THE UPPER LOW IS FORECAST TO BE NEAR GUAYMAS AND 
IS FORECAST TO MOVE EAST - SOUTHEAST ACROSS MEXICO WITH THE BEST 
MOISTURE AND LIFT FOR NORTHERN ARIZONA NOW CONFINED TO THE EASTERN 
RIM SOUTH INTO NORTHERN GILA AND THE WHITE MOUNTAINS. THE LOW EXITS 
OFF TO THE SOUTHEAST LATE MONDAY WITH A STRONG HIGH PRESSURE RIDGE 
ALOFT BUILDING INTO THE SOUTHWEST U.S. BY TUESDAY MORNING. IT 
APPEARS THAT THE BEST SNOW ACCUMULATION WILL BE OVER THE WHITE 
MOUNTAINS WITH POSSIBLE 3 DAY TOTALS (SATURDAY THROUGH MONDAY) OF 
AROUND 6 TO 8 INCHES WITH 1 TO 2 INCHES OR LESS OVER THE ELEVATION 
AREAS ABOVE 5500 FEET FOR NORTHERN ARIZONA. 

FOR THE REMAINDER OF THE WEEK NORTHERN ARIZONA WILL RESIDE IN 
NORTHERLY FLOW WITH THE HIGH PRESSURE RIDGE TO OUR WEST AND THE LOW 
PRESSURE TROUGH OVER THE CENTRAL U.S. THIS WILL BRING DRY CONDITIONS 
WITH NEAR SEASONABLE HIGH TEMPERATURES FOR THIS TIME OF THE YEAR.
BEYOND MONDAY MODEL CONSISTENCY OF BOTH THE GFS AND ECMWF IS LOW 
WITH MAJOR CHANGES FROM TROUGH TO RIDGES WITH EACH MODEL RUN. THE 
ECMWF APPEARS TO BE MORE STABLE THAN THE GFS BEYOND MONDAY AND THAT 
IS WHAT THE REST OF THE DIGITAL FORECAST REFLECTS.

&&
.AVIATION...FOR THE 18Z PACKAGE...EXPECT VFR CONDITIONS UNTIL 06Z 
SATURDAY. FROM 28/06Z TO 28/18Z...INCREASING LOW LEVEL CLOUD COVER 
WILL PRODUCE LOCAL MVFR CIGS ALONG THE MOGOLLON RIM WITH CHANCES FOR 
MVFR CIGS AND VSBY IN WIDELY SCATTERED RAIN AND SNOW SHOWERS NEAR 
THE 28/18Z TIME PERIOD. AVIATION DISCUSSION NOT UPDATED FOR 
AMENDMENTS.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...NONE. 

&&

$$

PUBLIC.................TC/MAS
AVIATION...............RB

VISIT WEATHER.GOV/FLAGSTAFF FOR NORTHERN ARIZONA WEATHER 
INFORMATION.