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 280543 AAA
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1045 PM MST FRI FEB 27 2015

.UPDATE...UPDATED AVIATION DISCUSSION.

.SYNOPSIS...
TODAY IS THE LAST DAY OF WARM AND DRY WEATHER...AS A STRONG COLD
LOW PRESSURE SYSTEM WILL BEGIN TO IMPACT OUR FORECAST AREA LATER
TONIGHT...BRINGING GUSTY WINDS AND WIDESPREAD RAINFALL TO THE
REGION...ALONG WITH MUCH COOLER TEMPERATURES THIS WEEKEND AND EARLY
NEXT WEEK.

&&

...A PROLONGED WET WINTER WEATHER EVENT IS IN STORE FOR THE DESERT
SOUTHWEST SATURDAY THROUGH TUESDAY...

.DISCUSSION...
THINGS ARE BEGINNING TO CHANGE WEATHERWISE ACROSS THE REGION THIS
EVENING...AS THE UPPER LOW THAT IS EXPECTED TO BRING SIGNIFICANT
RAINFALL...AND HIGHER ELEVATIONS SNOWS TO MUCH OF ARIZONA OVER THE
NEXT FEW DAYS CONTINUES TO MOVE SOUTHWARD ALONG THE WEST
COAST...WITH THE LATEST SATELLITE IMAGERY NOW SHOWING THE UPPER LOW
CENTER NOW PASSING OVER THE PORTLAND AREA. THE MAIN IMPACTS SO FAR
FOR OUR CWA HAS BEEN AN INCREASE IN MIDDLE AND HIGH CLOUDINESS AND
THE DEVELOPMENT OF GUSTY SW-LY WINDS...ESPECIALLY OVER SE CA...WHERE
WIND GUSTS AS HIGH AS 40 MPH HAVE BEEN OBSERVED. THE LATEST 00Z NAM
AND GFS MODEL SUITES CONTINUE TO SHOW A GRADUAL INCREASE IN MOISTURE
LEVELS OVER THE REGION FROM LATE TONIGHT INTO SUNDAY AND THE
DEVELOPMENT OF AT LEAST SOME SHOWER ACTIVITY ON SATURDAY AND SUNDAY
OVER SOUTH-CENTRAL ARIZONA...MAINLY OVER THE HIGHER TERRAIN NORTH
AND EAST OF PHOENIX. HOWEVER...THEY ARE ALSO CONTINUING A TREND
TOWARD A LATER ARRIVAL OF THE HEAVIER RAINFALL...A TREND THAT HAS
BEEN GOING ON OVER THE LAST FEW MODEL RUNS. THIS TREND IS DUE TO THE
FACT THAT THE MAIN UPPER LOW CENTER...AND ITS ASSOCIATED SURFACE
FRONT/MOISTURE PLUME DOES NOT REALLY BEGIN TO PROGRESS EASTWARD INTO
SE CA/AZ UNTIL AN UPSTREAM KICKER BEGINS TO APPROACH IT FROM THE
NORTH...WHICH IS NOT UNTIL EARLY MONDAY. SO...ALTHOUGH WE ARE STILL
AT RISK OF SEEING A SIGNIFICANT RAINFALL EVENT...IT NOW APPEARS THAT
IT MAY TURN OUT TO MORE FOCUSED ON SUNDAY NIGHT/MONDAY RATHER THAN
ON SUNDAY/SUNDAY NIGHT...ESPECIALLY OVER SOUTH-CENTRAL AZ. WE WILL
JUST HAVE TO AWAIT FUTURE SHIFTS/MODEL RUNS TO REFINE THE
TIMING/INTENSITY OF THIS SYSTEM. AS FAR AS THE SHORT-TERM FORECAST
IS CONCERNED...INHERITED PRODUCTS ARE HOLDING UP WELL...OTHER THAN
SOME VERY MINOR ADJUSTMENTS TO HOURLY TRENDS.

&&

.PREVIOUS DISCUSSION...
WATER VAPOR/IR SATELLITE IMAGERY AND REGIONAL UPPER AIR PLOTS SHOW
OUR NEXT POTENT UPPER LEVEL LOW SLIDING SOUTH ALONG THE BRITISH
COLUMBIA/PAC NW COAST THIS AFTERNOON. THE LOW IS SUPPORTED BY A
120-130KT 300-250MB JET THAT CONTINUES TO NOSE ACROSS SOUTHERN
NEVADA INTO NORTHERN ARIZONA. SURFACE CONDITIONS REMAIN DRY AND WARM
CWA-WIDE...WITH PHOENIX TOPPING OUT AT 78 DEGREES SO FAR THIS
AFTERNOON. MODELS ARE STILL ON TRACK THAT WINDS WILL BE ON THE
INCREASE THIS EVENING AND INTO SATURDAY OVER SOUTHEAST CALIFORNIA
AND ALONG THE LOWER COLORADO RIVER VALLEY...ALL DUE TO THE
TIGHTENING GRADIENT AHEAD OF THE LOW. WEST-SOUTHWEST WINDS WILL PEAK
TOMORROW ACROSS OUR WESTERN ZONES...WITH GUSTS OF 30-35 MPH AND SOME
AREAS OF BLOWING DUST POSSIBLE...ESPECIALLY NEAR EL CENTRO...YUMA
AND BLYTHE.

THE MOISTURE WILL ALSO BEGIN RAMPING UP LATER THIS EVENING INTO
SATURDAY...IMPORTED INTO THE REGION ON 35-40KT WEST-SOUTHWESTERLY
850MB LLJ... WITH PWATS EXPECTED TO RISE FROM ROUGHLY 0.3 INCHES
TODAY TO AROUND 1.0 INCH...WITH INTEGRATED WATER VAPOR TRANSPORT
VALUES APPROACHING THE 99TH PERCENTILE AT TIMES THIS WEEKEND. ONCE
THE THE ATMOSPHERE MOISTENS UP SATURDAY INTO SUNDAY...THE COLD CORE
TEMPS AND DYNAMICS OF THE LOW WILL BE IN PLACE TO GENERATE PERIODS
OF SCATTERED TO WIDESPREAD SHOWERS...PEAK TIME STARTING SUNDAY
MORNING AND CONTINUING THROUGH MONDAY AFTERNOON...AND POSSIBLY A FEW
ISOLATED T-STORMS ACROSS MOST OF OUR FORECAST AREA EARLY MONDAY
AFTERNOON.

THE MOST CURRENT RUN OF THE GFS NOW PLACES THE BEST PLUME OF
MOISTURE/P-WATER VALUES CLOSE TO 1.0IN MAINLY THROUGH CENTRAL
ARIZONA IN THIS TIME FRAME...AND WITH TOTAL PRECIPITATION AMOUNTS OF
AROUND 1.5 INCHES FOR THE WEST CENTRAL DESERTS AND UP TO 3.0 INCHES
OR MORE EXPECTED IN THE HIGHER TERRAIN AREAS NORTH/EAST OF PHOENIX
THERE ARE CONCERNS FOR ELEVATED FLOWS IN WASHES AND CREEKS...
ESPECIALLY ON THE TONTO CREEK NEAR PUNKIN CENTER IN SOUTHERN GILA
COUNTY...AND ALONG THE AGUA FRIA/NEW RIVER AND CAVE CREEK DRAINAGES
NEAR NEW RIVER/ANTHEM IN NORTHERN MARICOPA COUNTY. SOME CONCERN
EXISTS FOR HEAVIER RAINFALL TO IMPACT THE SYCAMORE CREEK AREA NEAR
SUNFLOWER...AND EVEN THE CENTENNIAL WASH OUT BY THE COMMUNITY OF
WENDEN IN LA PAZ COUNTY WEST OF PHOENIX. THE EXPECTED RAINFALL
AMOUNTS FOR THESE DESCRIBED AREAS ABOVE HAVE PROMPTED THE ISSUANCE
OF A FLOOD WATCH THAT IS NOW IN EFFECT FROM EARLY SUNDAY MORNING
THROUGH MONDAY AFTERNOON.

NAM/GFS/ECMWF REMAIN IN GOOD AGREEMENT AND CONTINUE TO INDICATE THE
MID LEVEL CIRCULATION OF THE LOW WILL MOVE THROUGH THE AREA MONDAY
MORNING WITH A FRONTAL BAND OF SHOWERS AFFECTING THE LOWER DESERTS
AROUND 12Z MONDAY. THE BEST Q CONVERGENCE AND ISENTROPIC ASCENT IS
INDICATED DURING THIS PERIOD AND THE ENSEMBLES ALSO INDICATE
ELEVATED POPS DURING THIS TIMEFRAME. ALSO DREW IN THE HIGHEST QPF
DURING THE DAY MONDAY WITH PRECIP RAPIDLY SHIFTING EAST OF PHOENIX
BY MONDAY EVENING. MEANWHILE...SNOW LEVELS WILL FALL IMMEDIATELY
BEHIND THE FRONTAL BAND AND THERE SHOULD BE A RAIN/SNOW MIX EAST OF
PHOENIX LATE MONDAY NIGHT. WITH SNOW LEVELS EXPECTED TO FALL TO
AROUND 6000FT MONDAY NIGHT...ONLY THE HIGHEST PEAKS WOULD SEE
ACCUMULATING SNOWFALL....MAYBE 1-3 INCHES TOTAL.

STILL SOME UNCERTAINTY WITH RESPECT TO A POST-FRONTAL SHORTWAVE
TROUGH AND ITS IMPACTS ON TUESDAY. IF ENOUGH MOISTURE LINGERS ACROSS
THE AREA...THERE COULD CERTAINLY BE ADDITIONAL SHOWERS MAINLY
NORTH/EAST OF PHOENIX TUESDAY. SNOW LEVELS WILL BE A TAD LOWER...
5500FT BY THIS TIME...SO COULD BE LIGHT ACCUMS AS WELL ALTHOUGH
CONFIDENCE IS WAY TOO LOW TO PIN DOWN EXACT SNOWFALL AMOUNTS AT THIS
TIME. PRECIP CHANCES SHOULD BEGIN TO WANE QUICKLY ON WEDNESDAY AS
DRY NORTHWESTERLY FLOW TAKES HOLD ACROSS THE WESTERN CONUS.

AS FOR TEMPERATURES...BELOW NORMAL TEMPERATURES ARE EXPECTED FROM
SATURDAY THROUGH MUCH OF THE UPCOMING WEEK. SUNDAY AND MONDAY WILL
BE PARTICULARLY COOL WITH HIGHS BARELY GETTING OUT OF THE LOWER 60S
IN MOST LOCATIONS. SOME MODERATION WILL TAKE PLACE BY MID WEEK AS
DRIER AIR MOVES IN FROM THE NORTHWEST.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...

AN APPROACHING WEATHER SYSTEM IS EXPECTED TO TIGHTEN THE PRESSURE
GRADIENT OVER THE REGION OVER THE NEXT 24 HOURS. THE MAIN IMPACTS TO
THE PHX AREA TERMINALS WILL BE TO ENHANCE THE NORMAL SE-LY DRAINAGE
WINDS TONIGHT...WITH SUSTAINED WIND SPEEDS AS HIGH AS 15KT POSSIBLE
BY DAYBREAK ON SATURDAY. ONCE THE WINDS SWITCH TO WESTERLY SAT
AFTERNOON...SUSTAINED WINDS AROUND 15KTS WITH GUSTS TO 25KTS CAN BE
EXPECTED. LOW LEVEL MOISTURE WILL START INCREASING LATE TONIGHT AS
WELL...WHICH SHOULD ALLOW FOR SOME LOWER SCT CLOUD LAYERS TO DEVELOP
AT AROUND 5-6K FEET FOR A TIME ON SATURDAY MORNING...WITH THESE
CLOUDS LIKELY BEING MIXED OUT FOR A TIME ON SAT AFTERNOON BEFORE
REDEVELOPING SAT EVENING. THERE IS AN OUTSIDE RISK OF FEW-SCT
SHOWERS DEVELOPING AS WELL ON SAT...BUT CONFIDENCE IS TOO LOW TO
INCLUDE IN THE TAFS AT THIS TIME...EXCEPT FOR VCSH AT KSDL.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...

LOW PRESSURE APPROACHING FROM THE NORTHWEST IS EXPECTED TO KEEP
GUSTY WESTERLY WINDS GOING AT KIPL AND SOUTHWESTERLY WINDS AT KBLH
THROUGH THE ENTIRE TAF PERIOD...WITH GUSTS AS HIGH AS 35KT...AND
EVEN AN OUTSIDE CHANCE OF BLOWING DUST POSSIBLE FOR A TIME ON SAT AT
BOTH TAF SITES. INCREASING MOISTURE LEVELS THROUGH THE COLUMN WILL
ALLOW CIGS TO GRADUALLY LOWER THROUGH THE TAF PERIOD...WITH CLOUD
BASES DROPPING AS LOW AS 5K FT ON SAT.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...
COOL AND WET CONDITIONS WILL BE PRESENT THROUGH THE FIRST PART OF
THE PERIOD WITH THE BEST CHANCES FOR WIDESPREAD RAINS ON SUNDAY AND
MONDAY. THERE WILL BE A CHANCE OF A FEW THUNDERSTORMS ON MONDAY AND
POTENTIALLY TUESDAY. HUMIDITIES WILL BE WELL ABOVE TYPICAL VALUES
THROUGH TUESDAY BEFORE MINIMUM VALUES FALL BACK TO AROUND 20 PERCENT
ON THURSDAY AFTERNOON. PERIODS OF BREEZY SOUTHWESTERLY WINDS CAN BE
EXPECTED ON MONDAY AND TUESDAY. HIGH TEMPERATURES ACROSS THE DESERTS
WILL ONLY REACH INTO THE 60S SUNDAY THROUGH WEDNESDAY. HIGH PRESSURE
AND DRIER WEATHER SHOULD MOVE IN STARTING LATER WEDNESDAY AND SHOULD
PERSIST THROUGH THE END OF THE WEEK.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...FLOOD WATCH FROM EARLY SUNDAY MORNING THROUGH MONDAY AFTERNOON
     AZZ022>024.

     FLOOD WATCH FROM EARLY SUNDAY MORNING THROUGH SUNDAY EVENING
     AZZ021.

CA...NONE.

&&

$$

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

DISCUSSION...PERCHA/MEYERS/LEINS
AVIATION...PERCHA
FIRE WEATHER...KUHLMAN





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