FXUS65 KPSR 300333
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
830 PM MST SUN NOV 29 2009
.SYNOPSIS...
A STRONG LOW PRESSURE SYSTEM MOVING EAST ACROSS NORTHWEST MEXICO
WILL BRING COOL UNSETTLED WEATHER THROUGH MONDAY OVER SOUTH CENTRAL
ARIZONA. MOSTLY CLEAR SKIES ARE EXPECTED ACROSS SOUTHEAST CALIFORNIA
AND SOUTHWEST ARIZONA TONIGHT AND MONDAY. THE BEST THREAT FOR
PRECIPITATION WILL OCCUR EAST OF PHOENIX...WITH SNOW FORECAST IN THE
MOUNTAINS. GENERAL CLEARING IS EXPECTED TUESDAY THROUGH SATURDAY...
WITH NEAR NORMAL TEMPERATURES THE REST OF THE WEEK.
&&
.DISCUSSION...
A CUTOFF LOW PRESSURE SYSTEM THAT MOVED INTO THE REGION SATURDAY WAS
NOW CENTERED OVER THE NORTHERN GULF OF CA...ABOUT 200 MILES SOUTH-
SOUTHEAST OF YUMA AZ AT 03Z. JUDGING FROM THE 12Z SUNDAY GUAYMAS
BALLOON SOUNDING...A SIGNIFICANT AMOUNT OF LOW LEVEL MOISTURE WAS
INJECTED INTO THE STORM CIRCULATION AND SPREAD NORTH INTO SOUTHEAST
AZ...BUT MOSTLY SOUTHWEST NEW MEXICO. THIS RESULTED IN A FEW SHOWERS
AND THUNDERSTORMS ACROSS MAINLY THE SOUTHEAST QUARTER OF AZ. A FEW
THUNDERSTORMS WITH SMALL HAIL AND GUSTS TO 35 MPH ALSO DEVELOPED IN
AND AROUND THE GREATER PHOENIX AREA...SOUTH TO NEAR CASA GRANDE.
AT 03Z THIS EVENING THUNDERSTORMS HAD ENDED...BUT A FEW SHOWERS ARE
STILL EXPECTED TO CONTINUE OVERNIGHT ACROSS PARTS OF SOUTH CENTRAL
AZ...INCLUDING PHOENIX. SHOWERS ARE EXPECTED TO BE MORE NUMEROUS
TONIGHT AND MONDAY OVER THE MOUNTAINS OF SOUTHERN GILA COUNTY ZONE
24. SNOWFALL MAY INCREASE A LITTLE OVER THE UPSLOPE AREAS...SOUTH
AND EAST FACING SLOPES OF THE SAN CARLOS INDIAN RESERVATION ABOVE
5000 FEET LATE TONIGHT/MONDAY MORNING. CURRENT FORECAST FOR A FEW
INCHES OF SNOW TONIGHT IN SOUTHERN GILA COUNTY ABOVE 5000 FEET STILL
LOOKS OK.
OTHERWISE FORECASTS LOOK IN GOOD SHAPE...INCLUDING CLEARING MONDAY
NIGHT IN SOUTHERN GILA COUNTY. NO UPDATES PLANNED. PREVIOUS
DISCUSSION BELOW WILL APPLIES.
PREVIOUS DISCUSSION...
MODELS CONTINUE TO SHOW GOOD AGREEMENT ON THE TRACK AND INTENSITY OF
THE CLOSED LOW THROUGH MONDAY...GRADUALLY MOVING EAST ACROSS NRN
MEXICO AND INTO WEST TEXAS TUESDAY. BASED ON THE SLOW MOVEMENT OF
THE LOW...WRAP-AROUND MOISTURE WILL REMAIN INTACT OVER THE HIGHER
TERRAIN OF ZONE 24/SOUTHERN GILA COUNTY TONIGHT AND MONDAY...AND
WITH THE COLD AIRMASS...RAIN WILL CHANGE TO SNOW ABOVE 5000 FEET
WITH ONE TO TWO INCHES ACCUMULATION POSSIBLE AFTER MIDNIGHT. THE
SNOW LEVEL WILL LOWER TO 4500 EARLY MONDAY AS THE STORM CENTER MOVES
FARTHER AWAY FROM THE AREA. THUS...LITTLE OR NO ADDITIONAL SNOW
ACCUMULATION IS EXPECTED MONDAY.
BY MONDAY MORNING...LESS CLOUD COVER OVER OUR WESTERN ZONES WILL
LEAD TO BETTER RADIATIONAL COOLING TO MAXIMIZE THE COLD AIR MASS.
SOME ENHANCED WINDS ON THE BACK SIDE OF THE LOW WILL KEEP LOW TEMPS
IN CHECK AND ABOVE FREEZING...TUESDAY MORNING WILL LIKELY BE THE
COLDEST DAY...IN THE ABSENCE OF MUCH CLOUD COVER.
TUESDAY THROUGH FRIDAY...THE LOW PRESSURE SYSTEM SWEEPS ACROSS TEXAS
AND THE UPPER RIDGE REMAINS PERCHED OFF THE WEST COAST WITH LITTLE A
GRADUAL INCREASE IN HEIGHTS/THICKNESSES. THE RESULT...A DRIER NWLY
FLOW ALOFT THAT WILL LEAD TO MOSTLY SUNNY SKIES AND A SLOW WARMING
TREND FOR THE WORK WEEK...WITH DAYTIME HIGHS BACK IN THE LOW 70S.
BY THE WEEKEND...THE ERN PAC RIDGE BECOMES MORE AMPLIFIED...ALLOWING
FOR A SERIES OF SHORT WAVES TO SLIDE DOWN THE EAST SIDE OF THE RIDGE
INTO THE PAC NORTHWEST. THIS WILL AMPLIFY THE TROF PATTERN OVER THE
NORTHERN ROCKIES...BRINGING INCREASED WINDS AND SLIGHTLY COOLER
TEMPERATURES TO OUR FORECAST AREA.
&&
AVIATION...
SOUTH CENTRAL AZ...INCLUDING KPHX AND KIWA...
THROUGH 18Z MON...SCT-BKN CLOUDS 8 TO 10 THSD FT MSL WITH ISOLATED
SHOWERS. NORTHEAST WIND UNDER 10 KNOTS. 18Z MON TO 02Z TUE...SCT
CLOUDS 8 TO 10 THSD FT MSL. LIGHT WIND.
SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KIPL AND KBLH...
CLEAR SKIES AND LIGHT WIND THROUGH 23Z MON.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...
WEAK HIGH PRESSURE AND MOSTLY CLEAR SKIES ARE EXPECTED TUESDAY AND
WEDNESDAY...WITH WARMER AND DRIER WEATHER. MODELS ARE SHOWING
VARYING SOLUTIONS BEYOND MID WEEK...WITH THE ECMWF FAVORING A FAST
MOVING...DRY...SHORTWAVE DISTURBANCE TO ROTATE THROUGH THE AREA
THURSDAY/EARLY FRIDAY TIME FRAME. THE MAIN IMPACT /IF THIS PANS OUT/
WILL BE INCREASING WINDS. BOTH MODELS INDICATE RIDING TO ONCE AGAIN
PREVAIL LATE FRIDAY INTO THE WEEKEND.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...VASQUEZ/MEYERS
AVIATION...VASQUEZ
FIRE WEATHER...WANEK
