Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 251637
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
935 AM MST SUN JAN 25 2015

.SYNOPSIS...
STRONG HIGH PRESSURE WILL PERSIST ACROSS THE WESTERN STATES
TODAY...RESULTING IN MOSTLY SUNNY SKIES AND WARM CONDITIONS. A LOW
PRESSURE SYSTEM WILL MOVE THROUGH THE AREA MONDAY...BRINGING AN
INCREASE IN MOISTURE AND LIGHT RAIN SHOWERS. IN ITS WAKE...ABOVE
NORMAL TEMPERATURES AND HIGHER THAN NORMAL HUMIDITIES WILL PREVAIL
THROUGH THE WEEK. ANOTHER LOW PRESSURE SYSTEM WILL BRING ADDITIONAL
MOISTURE AND ANOTHER CHANCE FOR PRECIPITATION LATE IN THE WEEK
THROUGH THE WEEKEND.

&&

.DISCUSSION...
UPPER LOW NEAR 26N 119W CONTINUES TO SLOWLY RETROGRADE...HOWEVER
SHOULD START MAKING THE TURN TO THE NORTH AS THE PACIFIC NW BLOCKING
HIGH IS NOW BECOMING ORIENTED TOWARDS A MORE EASTERN LATITUDE.
THICKER CIRRUS STREAMING NORTH FROM SONORA IS HITTING THE LIMITING
STREAMLINE JUST SOUTH OF THE PHOENIX AREA...AND FURTHER NORTHWARD
ADVANCEMENT WILL ONLY BE SLOW THROUGH THE REMAINDER OF THE DAY.
OTHERWISE...SOME MINOR ADJUSTMENTS WERE MADE TO REDUCE DEWPOINTS AND
FINE TUNE HOURLY TEMPERATURE TRACES...BUT ALL IN ALL A FABULOUS
WEATHER DAY REMAINS ON TAP FOR THE FORECAST AREA.

EARLY LOOK AT 12Z OPERATIONAL DATA AND VARIOUS 06Z/09Z ENSEMBLE AND
HIGH RESOLUTION MODELS INDICATES A TREND TOWARDS THE HIGHER THETA-E
PLUME AND STRONGEST ASCENT SHIFTING TO THE WEST...ONLY GRADUALLY
LIFTING INTO CNTRL ARIZONA AROUND 00Z TUESDAY. QPF ENSEMBLE MEAN
TRENDS POINT TOWARDS BETTER CHANCES FOR 0.25-0.50 INCH ACCUMULATIONS
THROUGH THE COLORADO RIVER VALLEY...AND LESSER AMOUNTS INTO THE
IMMEDIATE PHOENIX VICINITY. HAVE MADE SOME ADJUSTMENTS IN FORECAST
GRIDS TOWARDS THESE SOLUTIONS...AND WILL REEVALUATE WITH ADDITIONAL
HIGH RESOLUTION 12Z/15Z MODEL RUNS.

&&

.PREVIOUS DISCUSSION...
/440 AM MST SUN JAN 25 2015/
LATEST STREAMLINE ANALYSIS SHOWS A LARGE ANTICYCLONE ACROSS NORTHERN
CALIFORNIA BUILDING SOUTHEASTWARD. FURTHER SOUTH...A CLOSED LOW
EVIDENT ON WV IMAGERY CONTINUES TO RETROGRADE WESTWARD FROM THE BAJA
PENINSULA. A COL REGION IS ALSO EVIDENT...WHICH IS DEFLECTING DEEPER
MOISTURE ACROSS NORTHERN MEXICO BOTH TO THE WEST AND EAST...BUT WITH
LITTLE PROGRESS NORTHWARD INTO CENTRAL AZ. MOSTLY SUNNY SKIES ARE
EXPECTED TODAY WITH WELL-ABOVE NORMAL TEMPERATURES ACROSS THE
REGION. INCREASING CIRRUS IS EXPECTED LATE IN THE DAY AS THE FLOW
VEERS AND THE MID-UPPER LEVEL MOISTURE FINALLY ADVECTS NORTHWARD.
SHORT-TERM TEMPERATURES ARE WEIGHTED HEAVILY TOWARDS A BLEND OF
BIAS-CORRECTED ECMWF AND SREF...WHICH HAVE BEEN RECENT TOP
PERFORMERS. FORECAST MAX OF 79 DEGREES IN PHOENIX WOULD STILL FALL A
FEW DEGREES SHORT OF THE RECORD OF 83 DEGREES SET IN 1951.

MODELS CONTINUE TO INDICATE THAT THE AFOREMENTIONED LOW PRESSURE
SYSTEM WILL LIFT NORTHWARD BEGINNING TONIGHT...BRINGING WIDESPREAD
RAIN TO THE DESERT SOUTHWEST MONDAY AND MONDAY NIGHT. DEEP TROPICAL
MOISTURE WILL BE IN PLACE WITH PWATS BETWEEN 0.75 AND 1.25 INCHES
EQUATING TO STANDARDIZED ANOMALIES OF +2 TO +3. STRONGEST FORCING
FOR ASCENT CONTINUES TO TREND WESTWARD INTO CA. HOWEVER...ISENTROPIC
ASCENT AND MOISTURE TRANSPORT IN A MERIDIONAL FLOW WILL BE
SUFFICIENT TO PRODUCE THE HEAVIEST RAINFALL ACROSS PORTIONS OF AZ.
RAIN SHOWERS WILL GENERALLY TAPER OFF MONDAY NIGHT AS THE SYSTEM
WEAKENS AND SUBSIDENCE OVERSPREADS SOUTHERN AZ BEHIND THE TROUGH
AXIS.

THE HIGHEST RAIN TOTALS ARE EXPECTED ACROSS SOUTHWESTERN AZ WHERE
LOW-MID LEVEL THETA-E WILL BE MAXIMIZED. ACROSS YUMA COUNTY...A HALF
OF AN INCH OF RAIN IS POSSIBLE. ELSEWHERE...EXPECT GENERALLY BETWEEN
A QUARTER AND A HALF OF AN INCH OF PRECIPITATION. MODEL CONSENSUS
SUGGESTS RAIN TOTALS IN THE PHOENIX AREA WILL BE SOMEWHAT
LOWER...GENERALLY AROUND TWO TENTHS OF AN INCH.

THE LOW PRESSURE SYSTEM WILL ACCELERATE NORTHWARD TUESDAY AS THE
RIDGE DRIFTS EASTWARD INTO THE SOUTHERN PLAINS. MODEL CROSS-SECTIONS
INDICATE THAT LOW CLOUDS WILL BE PREVALENT IN THE MORNING...BEFORE
DISSIPATING IN THE AFTERNOON. LOCAL HI-RES WRFS ALSO SUGGEST THAT AN
ISOLATED SHOWER MAY BE POSSIBLE IN THE EARLY MORNING...PARTICULARLY
NORTH AND EAST OF PHOENIX.

ABOVE NORMAL TEMPERATURES AND HIGHER THAN NORMAL HUMIDITIES WILL
PREVAIL THROUGH NEXT WEEK AS A RIDGE BECOMES REESTABLISHED TO OUR
SOUTH ACROSS MEXICO. ABUNDANT MID AND HIGH CLOUDS ARE ALSO EXPECTED
THROUGH THE WEEK. GLOBAL MODELS CONTINUE TO SUGGEST THAT ANOTHER
PACIFIC LOW PRESSURE SYSTEM WILL AFFECT THE REGION LATE IN THE WEEK.
THIS SYSTEM APPEARS SLOWER THAN ITS PREDECESSOR AND HAS THE
POTENTIAL TO PRODUCE PRECIPITATION IN THE FRIDAY-SUNDAY TIME
FRAME...MAINLY ACROSS AZ. OFFICIAL FORECAST IS WEIGHTED TOWARDS THE
LATEST ECMWF...WHICH IS EXHIBITING RELATIVELY LOW ENSEMBLE SPREAD.
HOWEVER...PRECISE TIMING REMAINS UNCERTAIN AND CHANCE POPS HAVE BEEN
UTILIZED FRIDAY THROUGH SATURDAY NIGHT. THEREAFTER...MODEL CONSENSUS
SUGGESTS LOWER PROBABILITIES FOR SUNDAY.

&&

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

LITTLE TO NO AVIATION IMPACTS THROUGH EARLY MONDAY MORNING. INITIAL
CLEAR SKIES THIS MORNING WILL BECOME CLOUDY BY MONDAY MORNING AS
HIGH CLOUDS STREAM IN FROM THE SOUTH. BY 12Z MONDAY...CIGS SHOULD
LOWER TO AROUND 10K FEET. EASTERLY SFC WINDS WILL BE FAVORED FOR THE
ENTIRE PERIOD...ALTHOUGH WINDS MAY BECOME RATHER LIGHT/VARIABLE OR
EVEN LIGHT WEST LATER IN THE AFTERNOON SUNDAY...MORE SO AT KIWA THAN
KPHX.

FOR PLANNING PURPOSES...RAIN SHOWERS AND LOWERING CIGS SHOULD IMPACT
TERMINAL SITES LATER MONDAY AFTERNOON THROUGH TUESDAY MORNING. AT
THIS TIME...IT APPEARS ANY RAIN WOULD BE DELAYED UNTIL AFTER 21Z
MONDAY AND CIGS FALLING BELOW 6K FT WOULD BE FAVORED AFTER 03Z
TUESDAY. CONFIDENCE IS FAIR THAT CIGS WILL BE MAINTAINED IN A 4K-6K
FT LAYER MONDAY NIGHT THROUGH TUESDAY MORNING.

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

NO AVIATION IMPACTS THROUGH EARLY MONDAY MORNING WITH MOSTLY CLEAR
SKIES TODAY AND INCREASING CLOUDS TONIGHT. WINDS WILL REMAIN LIGHT
AND GENERALLY FAVOR A WESTERLY OR NORTHERLY DIRECTION.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...
NEAR TO SLIGHTLY ABOVE NORMAL TEMPERATURES EXPECTED THROUGH THE
PERIOD WITH WEDNESDAY AND THURSDAY BEING THE WARMEST DAYS. FAIRLY
MOIST CONDITIONS WILL EXIST AS SOUTHERLY FLOW PERSISTS ACROSS
THE DESERT SOUTHWEST. AN EXITING LOW PRESSURE SYSTEM EARLY TUESDAY
WILL BRING LINGERING RAIN CHANCES THROUGH TUESDAY AFTERNOON...WHILE
ANOTHER LOW PRESSURE SYSTEM IS FORECAST TO BRING MORE RAIN CHANCES
FOR THURSDAY NIGHT THROUGH POSSIBLY SATURDAY. THE MOIST CONDITIONS
WILL ONLY LEAD TO MINIMUM HUMIDITIES EACH AFTERNOON IN THE 25 TO 45
PERCENT RANGE. WITH THE EXCEPTION OF SOME OCCASIONAL EARLY MORNING
OR AFTERNOON BREEZINESS...WINDS WILL REMAIN LIGHT THROUGH THE ENTIRE
PERIOD.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...MO/HIRSCH
AVIATION...KUHLMAN/CB
FIRE WEATHER...KUHLMAN






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