Area Forecast Discussion
Issued by NWS Phoenix, AZ

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS65 KPSR 271209 AAA
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
509 AM MST SAT DEC 27 2014

.UPDATE...UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS.

&&

.SYNOPSIS...
BELOW NORMAL TEMPERATURES ARE EXPECTED THIS WEEKEND AND EARLY NEXT
WEEK WITH OCCASIONAL HIGH CLOUDS. ANOTHER COLD AND POSSIBLY WET LOW
PRESSURE SYSTEM WILL MOVE INTO THE REGION BY MIDWEEK...WITH THE
POTENTIAL FOR DESERT RAIN AND MOUNTAIN SNOW. DRY BUT COOL WEATHER IS
EXPECTED TO RETURN BY NEXT WEEKEND.

&&

.DISCUSSION...
TODAY THROUGH TUESDAY...
CLEAR SKIES AND COLD TEMPERATURES WERE NOTED THIS MORNING. THIS WILL
BE THE COLDEST MORNING WITH READINGS A FEW DEGREES HIGHER SUNDAY
MORNING DUE TO INCREASING HIGH CLOUDS LATE NIGHT. OTHERWISE DRY
WESTERLY FLOW ALOFT WITH SLOWLY WARMING TEMPERATURES...AND
OCCASIONAL HIGH CLOUDS ARE EXPECTED THROUGH TUESDAY.

TUESDAY NIGHT THROUGH THURSDAY...
THIS PERIOD GETS EXCITING BUT COMPLICATED AS THE NEXT VERY COLD
WESTERN CANADIAN TROF MOVES SOUTH OVER THE FAR WESTERN STATES TOWARD
AZ. IN GENERAL...THIS SYSTEM BRIEFLY RETROGRADES OFFSHORE FROM SAN
FRANCISCO AND LOS ANGELES TO PICK UP COPIOUS AMOUNTS OF BOUNDARY
LAYER FRONTAL BAND MOISTURE...WITH THE POTENTIAL FOR WIDE-SPREAD
RAIN AND SNOW IN AZ WED AND THU...PARTICULARLY OVER PHOENIX AND THE
SURROUNDING MOUNTAINS. LET US EXPLAIN.

YESTERDAY THE MODELS WERE GENERALLY SHOWING THE ABOVE SCENARIO...
HOWEVER THERE WERE MODEL TIMING ISSUES AS THE SYSTEM MOVED TOWARD
AZ. THE GFS WAS FASTER AND EUROPEAN MODEL SLOWER...AND...THE GFS
NEVER SWUNG THE SYSTEM OFFSHORE LIKE THE EURO. NOW THE MODELS ARE IN
AGREEMENT WHICH IS A BLEND OF YESTERDAYS RUNS.

BOTH THE GFS AND EURO MODELS PARTIALLY SWING THE VERY COLD CANADIAN
AIRMASS OFF THE SAN FRANCISCO AND LOS ANGELES COASTS TUESDAY
AFTERNOON THROUGH WEDNESDAY AFTERNOON. OFFSHORE LOW LEVEL PRESSURE
GRADIENTS INCREASE DRAMATICALLY TO THE POINT THAT NEAR GALE FORCE
SURFACE WINDS MECHANICALLY AND THERMODYNAMICALLY INJECT COPIOUS
AMOUNTS OF BOUNDARY LAYER MOISTURE INTO THE FRONTAL ZONE. THIS LONG
FETCH OF BUILDING FRONTAL BAND MOISTURE SWINGS INLAND AND UPSLOPE
INTO SOUTHERN CA...AND EVENTUALLY INTO SOUTHWEST AND SOUTH CENTRAL
ARIZONA. AND...THE CANADIAN AIRMASS IS SO COLD THAT CLOUD PHYSICS
PRECIP GROWTH BECOMES VERY EFFICIENT IN THE LOWER ATMOSPHERE
RESULTING IN THE POTENTIAL FOR WIDE-SPREAD RAIN AND MOUNTAIN SNOW.

A GOOD CHANCE OF PRECIPITATION BEGINS TUESDAY EVENING OVER OUR
SOUTHEAST CA ZONES...ESPECIALLY JOSHUA TREE NATIONAL PARK ZONE 30.
SNOW LEVELS FALL TO NEAR 4000 FEET TUESDAY EVENING...THEN TO NEAR
2900 FEET BY EARLY WEDNESDAY MORNING. SNOW LEVELS WILL CONTINUE TO
FALL TO NEAR 2000 FEET ON WEDNESDAY.

COPIOUS AMOUNTS OF FRONTAL BAND MOISTURE FINALLY MOVES EAST INTO
SOUTH CENTRAL ARIZONA INCLUDING PHOENIX AND VICINITY BY WEDNESDAY
AFTERNOON. UPSLOPE PRECIP BECOMES VERY EFFICIENT IN SOUTH CENTRAL
ARIZONA DUE TO THE VERY COLD AIR ALOFT...HOWEVER SNOW LEVELS BECOME
ARTIFICIALLY HIGH WEDNESDAY/WEDNESDAY NIGHT DUE TO THE WARM MOIST
FRONTAL BAND MOVING UPSLOPE. LOWER SNOW LEVELS ARE EXPECTED
THURSDAY. ITS TOO EARLY TO PREDICT PRECIP AND SNOW AMOUNTS...BUT
THERE IS POTENTIAL FOR RELATIVELY HIGH AMOUNTS ON THE LOWER DESERTS
NEAR PHOENIX AND SURROUNDING MOUNTAINS...ESPECIALLY SOUTHERN GILA
COUNTY.

FRIDAY THROUGH SUNDAY...
CLEARING AND COLDER AS THE CANADIAN SYSTEM SLOWLY EXITS THE STATE.


.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...KSDL...AND SOUTHEAST
CALIFORNIA/SOUTHWEST ARIZONA...INCLUDING KIPL AND KBLH...

EXPECT MOSTLY CLEAR SKIES AND LIGHT SURFACE WINDS ACROSS THE REGION
THROUGH AT LEAST 12Z SUNDAY MORNING...ALTHOUGH LOCAL GUSTY WINDS ARE
POSSIBLE ALONG PORTIONS OF THE LOWER COLORADO RIVER VALLEY AND NEAR
KBLH UNTIL 22Z THIS AFTERNOON.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
DRY AND ABNORMALLY COOL WEATHER WILL PREVAIL MONDAY...WITH LIGHT
WINDS AND PERIODS OF HIGH CLOUDS. TUESDAY...ANOTHER STRONG LOW
PRESSURE SYSTEM QUICKLY DROPS SOUTH OUT OF CANADA AND CARVES OUT A
LARGE COLD TROUGH OVER THE WESTERN UNITED STATES...INCREASING THE
POTENTIAL FOR STRONGER WINDS ACROSS SOUTHEAST CALIFORNIA AND THE
LOWER COLORADO RIVER VALLEY...BUT ALSO THE CHANCES FOR MOUNTAIN SNOW
AND VALLEY RAIN SHOWERS TO AFFECT THE DISTRICTS INTO FRIDAY NEXT
WEEK.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...FREEZE WARNING THROUGH TO 8 AM MST THIS MORNING
     AZZ021>023-026>028.

CA...NONE.

&&

$$

VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX

DISCUSSION...VASQUEZ
AVIATION....MEYERS
FIRE WEATHER...MEYERS




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.