FXUS65 KFGZ 261027
AFDFGZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
325 AM MST SAT DEC 26 2009

.SYNOPSIS...A COLD AIRMASS BEHIND THE LARGE LOW PRESSURE SYSTEM OVER 
THE CENTRAL PART OF THE COUNTRY...WILL CONTINUE TO BRING BELOW 
NORMAL TEMPERATURES TO NORTHERN ARIZONA THROUGH THE WEEKEND. A 
TROUGH OF LOW PRESSURE IS FORECAST TO MOVE ACROSS THE SOUTHWEST 
STATES LATE MONDAY THROUGH WEDNESDAY...BRINGING UNSETTLED WEATHER TO 
NORTHERN ARIZONA.

&&
.DISCUSSION...A LARGE LOW PRESSURE SYSTEM OVER THE CENTRAL PART OF 
THE COUNTRY HAS PUSHED A COLD AIRMASS INTO THE SOUTHWEST 
STATES...BELOW NORMAL TEMPERATURES CAN BE EXPECTED THROUGH THE 
WEEKEND INTO THE FIRST HALF OF NEXT WEEK. 

A FIRST IN A SERIES OF LOW PRESSURE TROUGHS WILL MOVE INTO THE 
INTERMOUNTAIN WEST ON SUNDAY AND WEAKEN AS IT MOVES ACROSS 
ARIZONA...PRODUCING A LOW CHC FOR SNOW FLURRIES ON SUNDAY...FROM 
FLAGSTAFF NORTHWEST TO THE KAIBAB PLATEAU. A STRONGER TROUGH OF LOW 
PRESSURE IS FORECAST TO MOVE INTO THE WEST COAST STATES ON 
MONDAY...AND THEN ACROSS ARIZONA TUESDAY WITH A THIRD DISTURBANCE 
AND LAST IN THE SERIES OF LOW PRESSURE TROUGHS MOVING ACROSS 
NORTHERN ARIZONA ON WEDNESDAY. LOOK FOR AN INCREASING CHC FOR RAIN 
SHOWERS AND SNOW SHOWERS STARTING EARLY TUESDAY AND LASTING THROUGH 
THE DAY...AND AGAIN ON WEDNESDAY. THE GFS AND ECMWF ARE BECOMING 
MORE CONSISTENT WITH THIS FEATURE AND THE POSSIBILITY OF 
ACCUMULATING SNOW ABOVE 5500 TUESDAY AND AGAIN WEDNESDAY. TIMING OF 
THESE SYSTEMS STILL REMAINS SOMEWHAT IN QUESTION AT THIS POINT IN 
TIME...AND HENCE THE REASON FOR THE 20 AND 30 PERCENT CHANCE OF 
PRECIPITATION TUESDAY AND WEDNESDAY. 

THURSDAY THROUGH SATURDAY...NORTHERN ARIZONA IS FORECAST TO BE EAST 
OF A LARGE SCALE HIGH PRESSURE RIDGE WITH THE RIDGE AXIS ALONG THE 
WEST COAST. THIS POSITION OF THE HIGH PRESSURE RIDGE WILL ALLOW FOR 
WEAK DISTURBANCES TO MOVE OVER THE TOP OF THE RIDGE AND THEN INTO 
NORTHERN ARIZONA. DURING THIS TIME PERIOD HIGH TEMPERATURES ARE 
FORECAST TO MODERATE BACK CLOSER TO SEASONAL AVERAGES. 
&&

.AVIATION...FOR THE 12Z PACKAGE...VFR CONDITIONS WITH OCCASIONAL 
NORTH-NORTHEASTERLY WINDS AT 5-10KT. AVIATION DISCUSSION NOT UPDATED 
FOR AMENDMENTS.

&&

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

&&

$$

PUBLIC.........TC
AVIATION.......JVC

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