FXUS65 KFGZ 051137 CCA
AFDFGZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
415 PM MST FRI DEC 04 2009

.SYNOPSIS...EXPECT INCREASING CLOUDS...COLD TEMPERATURES...AND WINDY 
CONDITIONS TODAY AND SUNDAY AHEAD OF A MAJOR WINTER STORM SYSTEM 
DEVELOPING NORTH OF ARIZONA. THIS STORM WILL AFFECT NORTHERN AND 
CENTRAL ARIZONA LATE SUNDAY NIGHT...THROUGH TUESDAY MORNING. SNOW 
LEVELS WILL RANGE FROM 5000 TO 6000 FEET WITH HEAVY SNOW 
ACCUMULATIONS ABOVE 6000 FEET...ESPECIALLY ALONG THE RIM. AT LOWER 
ELEVATIONS SOUTH OF THE RIM...EXPECT PERIODS OF MODERATE TO HEAVY 
RAINFALL.

&&

.DISCUSSION...MAJOR STORM SET TO AFFECT NORTHERN AZ...BEGINNING 
EARLY MONDAY. HOWEVER FOR TODAY...EXPECT INCREASING MID AND HIGH 
CLOUDS AS A SOUTHERN STREAM SHORT WAVE PASSES ACROSS THE AREA. 
OVERALL...TODAY WILL BE FAIR WITH HIGHS STILL A FEW DEGREES BELOW 
NORMAL. ON SUNDAY THE NEXT SHORT WAVE AHEAD OF THE MAIN TROUGH WILL 
CROSS THE AREA AND BRING A SLIGHT RISK FOR RAIN AND SNOW SHOWERS 
DURING THE DAY...BUT GIVEN HOW DRY THE AIRMASS IS RIGHT NOW...NOT 
EXPECTING MUCH IN THE WAY OF COVERAGE OR INTENSITY WITH ANY SHOWERS 
THAT DEVELOP ON SUNDAY. THE PRIMARY SHORT WAVE WITH THE STORM SYSTEM 
WILL CONTINUE TO DIG SOUTH ACROSS THE GREAT BASIN SUNDAY NIGHT AND 
MONDAY AND WILL MERGE WITH A SERIES OF SOUTHERN STREAM SHORT WAVES 
AND ASSOCIATED PACIFIC MOISTURE BEFORE CROSSING OUR AREA DURING THE 
DAY MONDAY THROUGH EARLY TUESDAY. THIS WILL SET THE STAGE FOR A 
SIGNIFICANT SNOW AND RAIN EVENT MONDAY THROUGH EARLY TUESDAY WITH 
SNOW LEVELS AROUND 5000 FEET. THE FOLLOWING SUMMARIZES CONCERNS WITH 
THIS SYSTEM:

-SNOW LEVELS AROUND 5000 FEET WITH HEAVIEST ACCUMULATIONS ABOVE 6000 FT
-GIVEN THE STRONG DYNAMICS COINCIDENT WITH MODERATE FRONTOGENESIS...AND 
 CONSIDERING UPSLOPE NATURE OF THIS EVENT...WE ARE EXPECTING 1-2 INCHES 
 OF RAINFALL FOR LOCATIONS BELOW THE SNOW LEVEL...UP TO 6 INCHES OF SNOW    
 ACCUMULATION IN THE P-TYPE TRANSITION ELEVATIONS BETWEEN 5000-6000FT
 AND AT LEAST 12-18 INCHES OF SNOW WITH ISOLATED HIGHER AMOUNTS ABOVE 6000 
 FT THROUGH TUESDAY MORNING.
-SFC WINDS WILL GRADUALLY INCREASE FROM NOW THROUGH THE EVENT. GUIDANCE 
 SHOWS 700MB WINDS PEAKING AROUND 60 KNOTS BY LATE MONDAY. CONSIDERABLE
 BLOWING AND DRIFTING OF SNOW CAN BE EXPECTED OVER THE HIGHER TERRAIN WITH
 NEAR BLIZZARD CONDITIONS DURING TIMES OF HEAVY SNOWFALL LATE MONDAY. 
 DOWNSLOPE WINDS OVER THE LCR WILL WARRANT AT LEAST A WIND ADVISORY AS WE 
 GET CLOSER TO THE EVENT.
-AFOREMENTIONED DOWNSLOPE FLOW WILL LIMIT SNOW AND RAINFALL AMOUNTS ACROSS
 THE LCR...THUS LOWER POPS FOR THAT AREA.
-STRONG SUBSIDENCE IN THE WAKE OF THE TROUGH AXIS WILL QUICKLY SHUT OFF
 HEAVY PRECIP FROM WEST TO EAST BETWEEN 08Z-12Z TUESDAY WITH LOW CLOUDS
 AND FLURRIES POSSIBLE THE REMAINDER OF THE DAY. 
-GIVEN HIGH CONFIDENCE WITH THIS EVENT...WILL ISSUE A WINTER STORM   
 WATCH WITH THIS PACKAGE FOR ELEVATIONS ABOVE 5000 FEET.  

A BREAK IN THE WEATHER IS EXPECTED MID TUESDAY THROUGH EARLY 
WEDNESDAY...THEN THE NEXT SHORT WAVE IN THE SOUTHERN STREAM WILL 
AFFECT THE SOUTHWEST THURSDAY AND FRIDAY...BRINGING THE RISK FOR 
ADDITIONAL RAIN AND SNOW. 

&&

.AVIATION...FOR THE 12Z PACKAGE...VFR CONDITIONS EXPECTED FOR THE 
FORECAST PERIOD. SOUTHWEST WINDS WILL INCREASE TO 15 TO 25 KTS WITH 
GUSTS TO 30 KTS THIS AFTERNOON. AVIATION DISCUSSION NOT UPDATED FOR 
AMENDMENTS.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...WINTER STORM WATCH FROM MONDAY 
MORNING THROUGH TUESDAY MORNING FOR ELEVATIONS ABOVE 5000 FEET. 

&&
$$

PUBLIC..................NP
AVIATION/FIRE WEATHER...DB

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