000
FXUS65 KPSR 190452
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
940 PM MST THU MAR 18 2010
.SYNOPSIS...
A FAST MOVING COLD FRONT WILL MOVE THROUGH THE REGION FRIDAY...
BRINGING COOLER TEMPERATURES...BREEZY CONDITIONS...ALONG WITH A
SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS NORTH AND EAST OF
PHOENIX. HIGH PRESSURE WILL RETURN EARLY NEXT WEEK BRINGING DRY
WEATHER AND WARMER TEMPERATURES. ANOTHER FAST MOVING PACIFIC WEATHER
SYSTEM WILL BRING A SLIGHT CHANCE OF SHOWERS TO ARIZONA NEXT
TUESDAY INTO WEDNESDAY...ALONG WITH COOLER TEMPERATURES.
&&
.DISCUSSION...
WV IMAGERY CLEARLY SHOWS THE UPPER LEVEL TROF RAPIDLY DROPPING SOUTH
THROUGH NEVADA...AND THE ASSOCIATED FRONTAL BAND WITH SOME EMBEDDED
LIGHTNING STRIKES STRETCHING FROM DAGGETT CA...OFF TO THE NE ACROSS
NW AZ AND INTO SOUTHEAST UTAH. THIS RAPIDLY DEEPENING SYSTEM WILL
CONTINUE TO TIGHTENING MID AND LOW LEVEL GRADIENTS ACROSS SE CA
OVERNIGHT...AND WILL SERVE TO GENERATE STRONG GUSTY NORTHERLY WINDS
OVER THE LOWER COLORADO RIVER VALLEY LATE FRIDAY MORNING/AFTERNOON.
THE PREVIOUS SHIFT ISSUED A WIND ADVISORY FOR OUR RIVER ZONES FROM 8
AM UNTIL 5 PM MST/PST FRIDAY...AND THIS WILL REMAIN IN EFFECT.
EVEN THOUGH MOISTURE IS LIMITED WITH THIS SYSTEM...MODELS ADVERTISE
A RESPECTABLE CORE OF HEIGHT FALLS...AROUND 80 METERS...AND -22C
500MB TEMPS THAT MOVE OVER THE CENTRAL DESERTS AND HIGHER TERRAIN OF
SOUTH-CENTRAL ARIZONA FRIDAY. AS SUCH...LAPSE RATES STEEPEN AND
THERE WILL BE A PERIOD OF INSTABILITY/INTENSE VERTICAL MOTION AS THE
FRONT TRANSITIONS THROUGH THE AREA. EVEN THE GFSBUFR MODEL SOUNDINGS
HINT AT A SMALL WINDOW OF NEG LIFTED INDICIES EAST OF THE COLORADO
RIVER THROUGH THE DAY. ELECTED TO INTRODUCE A SLIGHT CHANCE OF
THUNDERSTORMS TO THE FORECAST FRIDAY...MAINLY FOCUSING NORTH AND
EAST OF PHOENIX. IMPORTANT TO KEEP IN MIND THAT IF THESE STORMS
FORM...THEY WILL BE HIGH-BASED DRIER STORMS...AND WILL HAVE THE
POTENTIAL TO PRODUCE STRONG GUSTY WINDS AND LITTLE RAIN.
NO OTHER ADJUSTMENTS/CHANGES MADE TO THE REMAINDER OF THE SHORT TERM
DIGITAL GRIDS/FORECAST. PREVIOUS DISCUSSION STILL APPLIES.
PREVIOUS DISCUSSION...
THE TROUGH...AND ASSOCIATED COLD FRONT...SHOULD BE ROLLING THROUGH
WEST AND CENTRAL ARIZONA AROUND MID DAY FRIDAY. NORTH WINDS WILL
SPREAD ACROSS THE CWA AS THIS SYSTEM RAPIDLY MOVES THROUGH DURING
THE DAY. WINDS SHOULD BE BREEZY ACROSS AREAS EAST OF THE COLORADO
RIVER VALLEY BUT ARE NOT EXPECTED TO REACH THE ADVISORY LEVELS THAT
WILL BE SEEN ALONG THE COLORADO RIVER VALLEY.
BOTH THE GFS AND ECMWF SEEMED TO SPEED UP THE SYSTEM AND ACCORDINGLY
LED TO A DROP IN ANTICIPATED HIGH TEMPS FOR FRIDAY. THEREFORE WE
DROPPED THE HIGHS ABOUT 5 DEGREES...WITH NOW EXPECTING ONLY 74 FOR
PHOENIX...A 5 DEGREE DROP FROM THE PREVIOUS FORECAST PACKAGE. ALSO
RAISED THE POPS JUST A BIT ACROSS NORTH AND EAST EXTREMES OF THE CWA
BUT STILL ONLY IN THE SLIGHT CHANCE FOR THE HIGHER TERRAIN AND
SOUTHERN GILA COUNTY.
A RIDGE WILL MOVE OVER THE AREA SATURDAY AND SUNDAY LEADING TO SOME
WARMING AND DRY WEATHER FOR THE WEEKEND. BOTH THE GFS AND ECMWF
INDICATE THE NEXT SYSTEM TO START TO IMPACT THE REGION BY TUESDAY.
THE GFS IS AGGRESSIVELY DEVELOPING A CUTOFF LOW MOVING OVER NORTHERN
BAJA CALIFORNIA WHEREAS THE ECMWF SHOWS IT MORE AS A SHORT WAVE OFF
OF A LARGER TROUGH CENTERED OVER THE IDAHO VICINITY. ECMWF PASSES
THE TROUGH OVER ARIZONA QUICKLY WITH NOT MUCH WEATHER IMPACT WHEREAS
THE GFS DROPS THE CUTOFF LOW SOUTHEAST OVER SONORA MEXICO.
CURIOUSLY...THE TWO MODELS CONVERGE LATER IN TIME...ON
WEDNESDAY...AGREEING WITH DEVELOPMENT OF ANOTHER LARGER SCALE GREAT
BASIN LOW...THIS ONE CENTERED OVER THE FOUR CORNERS BY WEDNESDAY.
MOST OF THE ENERGY ASSOCIATED WITH THIS SYSTEM LOOKS TO BE CENTERED
TO THE NORTH AND EAST OF OUR CWA. ACCORDINGLY...ATTM NOT EXPECTING A
LOT OF WEATHER WITH THIS SYSTEM OTHER THAN THE TYPICAL GUSTY
WINDS...PRIMARILY ON WEDNESDAY.
&&
.AVIATION...
KIPL...KBLH...AND SURROUNDING AIRFIELDS...
WIND SPEEDS WILL INCREASE OUT OF THE WEST-NORTHWEST WITH APPROACHING
COLD FRONT DURING OVERNIGHT HOURS. FROPA EXPECTED BY 12Z FRIDAY...
BRINGING GUSTY NORTH WINDS 20-30 KTS WITH OCNL GUSTS TO 40 KTS
MAINLY NEAR KBLH...WITH LESSER WIND NEAR KIPL. GUSTY WINDS EXPECTED
TO CONTINUE INTO THE AFTERNOON...AND DIMINISH OVER THE AREA AFTER
SUNSET.
KPHX...KIWA...AND SURROUNDING AIRFIELDS...
EXPECT MOSTLY CLEAR SKIES AND LIGHT WINDS FAVORING EAST/SOUTHEAST
THROUGH 15Z FRIDAY. WINDS INCREASE OUT OF THE WEST...GUSTS UP TO
20KTS AS THE UPPER TROF/COLD FRONT MOVE THROUGH THE AREA AFTER 18Z.
IN CONJUNCTION WITH THE FRONTAL PASSAGE...THERE IS A SLIGHT CHANCE
OF THUNDERSTORMS--LESS THAN 20 PCT...THAT COULD IMPACT KIWA/KPHX.
STORMS THAT FORM WILL BE HIGH-BASED/DRIER...AND WILL HAVE THE
POTENTIAL TO PRODUCE STRONG GUSTY OUTFLOW WINDS.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
A DRY AIRMASS ASSOCIATED WITH ANOTHER HIGH PRESSURE SYSTEM SETTLES
OVER THE REGION SATURDAY...BEHIND THE DEPARTED COLD FRONT...WHICH
WILL CAUSE MINIMUM RELATIVE HUMIDITIES TO DIP INTO THE SINGLE DIGITS
ACROSS LOWER DESERT LOCATIONS THROUGH MONDAY. BREEZY NORTHERLY WINDS
WILL SLOWLY DIMINISH SATURDAY. LIGHTER WINDS AND A WARMING TREND ARE
ANTICIPATED SUNDAY INTO MONDAY...BEFORE ANOTHER LOW PRESSURE SYSTEM
TRACKS ACROSS THE REGION TUESDAY INTO WEDNESDAY PROVIDING THE AREA
WITH A SLIGHT CHANCE OF PRECIPITATION.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...WIND ADVISORY FROM 8 AM TO 5 PM MST FRIDAY FOR AZZ020-025.
CA...WIND ADVISORY FROM 8 AM TO 5 PM PDT FRIDAY FOR CAZ031.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...MEYERS/WATERS
AVIATION...MEYERS
FIRE WEATHER...PADDOCK
