FXUS65 KPSR 090931
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
230 AM MST WED DEC 9 2009
.SYNOPSIS...
A SERIES OF FAST MOVING BUT WEAK AREAS OF LOW PRESSURE WILL MOVE
ACROSS THE REGION THE NEXT SEVERAL DAYS...BRINGING A MIX OF CLOUDS
AND SLIGHT CHANCES FOR LIGHT RAIN. THE LAST AND STRONGEST SYSTEM
WILL MOVE THROUGH LATE SATURDAY INTO SUNDAY AND BRING A BETTER
CHANCE FOR RAIN. SNOW LEVELS WILL BE NEAR 7000 FEET. COOL
TEMPERATURES WILL CONTINUE THROUGH THE WEEKEND WITH A WARM UP
EXPECTED NEXT WEEK.
&&
.DISCUSSION...
COOLER AIR REMAINS OVER THE FORECAST AREA THIS MORNING IN THE WAKE
OF OUR STRONG WINTER SYSTEM. BL WILL SHOW SOME MODEST WARMING TODAY
COMPARED TO YESTERDAY WITH MAX TEMPS RUNNING ABOUT 2-4 DEGREES
WARMER. LARGE BATCH OF HIGH CLOUDS TO THE WEST WILL BE FILTERING IN
THROUGH THE DAY AS WELL.
GFS/ECMWF IN FAIRLY GOOD AGREEMENT AND ALIGN WELL WITH THE GENS ON
THE WEATHER PATTERN THE NEXT SEVERAL DAYS. SOUTHERN BRANCH OF JET
STREAM WILL REMAIN RATHER ACTIVE...SENDING QUICK-MOVING WEAK SHORT
WAVE TROUGHS ACROSS OUR AREA. FIRST ONE COMES THROUGH THURSDAY NIGHT
INTO FRIDAY. FORCING WITH THIS TROUGH IS VERY WEAK. ANOTHER COUPLE
OF VERY WEAK SHORT WAVE TROUGHS WILL MOVE THROUGH FRIDAY NIGHT INTO
SATURDAY...AGAIN WITH VERY LITTLE IN WAY OF FORCING. WHAT WILL BE
OCCURRING WITH THESE SEVERAL WEAK SYSTEMS IS A CONTINUAL
RE-MOISTENING OF THE BL. WE/LL INCLUDE A SLIGHT CHANCE FOR LIGHT
RAIN IN THE FORECAST FRIDAY INTO SATURDAY AS THE BL MAY BE
SATURATING ENOUGH AT THIS TIME FOR SOME RAIN TO MAKE IT TO THE
GROUND.
MOST SIGNIFICANT SHORT WAVE TROUGH WILL MOVE IN SOMETIME SATURDAY
NIGHT INTO SUNDAY. THERE IS ABOUT A 12 HR PHASE DIFFERENCE BETWEEN
THE GFS AND ECMWF...WITH THE ECMWF BEING A LITTLE SLOWER. THIS
SYSTEM WILL HAVE SOME MORE ENERGY TO WORK WITH AS ASCENT ON THE NOSE
OF A 120KT INCOMING JET STREAK HELPS DEEPEN THE SYSTEM. DECENT SW/NE
ORIENTATION WILL ALLOW SOME PAC MOISTURE TO MOVE OVER THE MOUNTAINS
INTO WHAT WILL LIKELY BE ALREADY WELL-MOISTENED DESERT AREAS.
ISENTROPIC LIFT AND MOISTURE ADVECTION INCREASE NICELY AS THE SYSTEM
TRAVERSES OUR FORECAST AREA. POPS ARE HIGHEST AT THIS POINT FOR THE
WEEK...WOULD HAVE GONE HIGHER BUT UNCERTAINTY ON THE TIMING REQUIRED
THE POPS TO BE A BIT MORE SPREAD OUT OVER A 24 HOUR PERIOD /WITH
WHAT WILL BE A 12 HOUR AT BEST EVENT/. GIVEN THE TROPICAL ORIGIN OF
THE AIRMASS...WET BULB ZERO HEIGHTS QUICKLY SHOOT UP AHEAD OF THE
SYSTEM...PUSHING SNOW LEVELS ABOVE EVEN THE HIGHEST PEAKS IN OUR CWA
/7000-8000 FEET/.
BEHIND THIS TROUGH A LOW-AMPLITUDE AND BROAD RIDGE WILL DEVELOP OVER
THE SOUTHWEST...WHICH WILL BRING AN END TO PRECIP CHANCES AND WARMER
TEMPERATURES.
&&
AVIATION...
NO AVIATION CONCERNS EXPECTED UNDER INCREASING MID AND HIGH LEVEL
CLOUDS...WITH WEAK HIGH PRESSURE IN PLACE.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
AN UNSETTLED WEATHER PATTERN AS A SERIES OF WEATHER DISTURBANCES
MOVE ACROSS THE REGION. ANTICIPATE COOLER TEMPERATURES...LIGHT WINDS
AND ELEVATED HUMIDITY LEVELS THROUGH THE PERIOD...WITH ANOTHER SHOT
AT PRECIPITATION ACROSS THE AREA CONTINUING INTO THE WEEKEND.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...INIGUEZ
AVIATION...WANEK
FIRE WEATHER...MEYERS
