Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 281025
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
325 AM MST WED JAN 28 2015

.SYNOPSIS...
SOME PATCHY FOG IS POSSIBLE THIS MORNING BUT OTHERWISE ANTICIPATE
DRY CONDITIONS WITH JUST SOME HIGH CLOUDS TODAY. ANOTHER LOW
PRESSURE SYSTEM APPROACHES THURSDAY FOR INCREASED CLOUDINESS DURING
THE DAY. RAIN CHANCES GO UP DRAMATICALLY THURSDAY NIGHT AND CONTINUE
INTO SATURDAY...MAINLY EAST OF THE LOWER COLORADO RIVER VALLEY. SNOW
LEVELS WILL REMAIN HIGH...LOWERING TO NEAR 7000 FEET BY SATURDAY
MORNING. ANTICIPATE COOLER HIGH TEMPERATURES AS WELL. DRY CONDITIONS
TAKE OVER SUNDAY THROUGH TUESDAY.

&&

.DISCUSSION...
AT 3 AM THIS MORNING...WEAK SHORT WAVE RIDGE WAS BUILDING OVER
ARIZONA BEHIND AN EXITING WAVE...AND THIS WILL ALLOW FOR WELL ABOVE
SEASONAL NORMAL HIGH TEMPS TODAY. BOUNDARY LAYER MOISTURE IN THE
WAKE OF THE PASSING SYSTEM REMAINS ELEVATED...WITH SURFACE DEWPOINTS
RANGING FROM THE MID 40S TO MID 50S...AND WITH MOSTLY CLEAR SKIES
EARLY THIS MORNING THERE MAY BE PATCHY FOG DEVELOPING MAINLY ACROSS
THE LOWER ELEVATIONS. WILL LEAVE IN THE MENTION OF PATCHY FOG ACROSS
THE CWA THAT WAS INTRODUCED BY THE PREVIOUS FORECAST SHIFT. CLEAR
SKIES WILL NOT LAST LONG THOUGH...IR IMAGERY SHOWED INCREASING HIGH
CLOUDS STARTING TO SPREAD INTO THE AREA FROM THE SOUTHWEST AND BY
AFTERNOON EXPECT TO SEE PARTLY TO MOSTLY CLOUDY SKIES...ALTHOUGH
THIN SPOTS IN THE CIRRUS ARE LIKELY.

ON THURSDAY...A VERY INTERESTING AND VERY WET WEATHER PATTERN WILL
BEGIN TO SET UP ACROSS THE WESTERN CONUS...WITH RATHER HIGH
AMPLITUDE RIDGING ACROSS THE PAC NW...WITH A DEEP AND VIGOROUS UPPER
TROF SETTING UP TO THE SOUTH AND OFF THE SRN CA AND BAJA CA COAST.
ON THURSDAY...AS THE DEVELOPING TROF APPROACHES FROM THE
SOUTHWEST...UPPER JET ROUNDING THE BASE OF THE TROF WILL START TO
SPREAD COPIOUS MOISTURE NORTHWARD...WITH CONSIDERABLE MID/HIGH
CLOUDS SPREADING INTO FAR SERN CA AND ARIZONA. IR IMAGERY THIS
MORNING SHOWED THE HIGH AMOUNTS OF MOISTURE OFF THE BAJA COAST READY
TO BE ADVECTED NORTH AND INTO OUR AREA LATER THIS WEEK. DESPITE THE
INCREASING CLOUD COVER ON THURSDAY...HIGH TEMPS WILL REMAIN ELEVATED
DUE TO SOUTHERLY FLOW AND WARM AID ADVECTION AHEAD OF THE ADVANCING
SYSTEM. EXPECT HIGHS IN THE MID 70S OVER THE CENTRAL DESERTS ON
THURSDAY.

LATEST FORECAST MODELS HAVE COME INTO VERY GOOD AGREEMENT REGARDING
THE EVOLUTION...TIMING AND TRACK OF THIS UPCOMING WEATHER
SYSTEM...INCLUDING DETAILS SUCH AS PRECIPITATION AMOUNTS. GFS
ENSEMBLE MEMBERS WERE SHOWING EXCELLENT AGREEMENT AS WELL IN CALLING
FOR THIS SYSTEM TO SWING INLAND THURSDAY NIGHT...THEN MOVE SLOWLY
EASTWARD FRIDAY INTO FRIDAY NIGHT BRINGING LOCALLY MODERATE TO HEAVY
RAINS TO SOUTH CENTRAL ARIZONA. NAEFS AND SREF GUIDANCE SUGGESTED
CHANCES FOR RAIN MEASURING 0.10 INCHES WOULD BE IN EXCESS OF 70
PERCENT ACROSS SOUTH CENTRAL AZ...MAINLY AREAS FROM PHOENIX
EASTWARD...LATE THURSDAY NIGHT THROUGH THE EVENING HOURS ON FRIDAY.
ATMOSPHERIC RIVERS GUIDANCE ALSO FORECASTS AN IMPRESSIVE SURGE IN
TROPICAL MOISTURE SPREADING INTO ARIZONA FROM THE SOUTHWEST BY
FRIDAY WITH PWAT VALUES CLIMBING TO AROUND 1.2 INCHES OVER SERN AZ
AS WELL AS THE CENTRAL DESERTS. FORECAST PWAT VALUES ARE NEARLY 4
STANDARD DEVIATIONS ABOVE NORMAL...AND REPRESENT NEAR RECORD VALUES
FOR THE TUS AREA. OVERALL...AS MOISTURE SPREADS IN FROM THE SOUTH
THURSDAY NIGHT...POPS RISE INTO THE LIKELY TO CATEGORICAL BALLPARKS
FROM PHOENIX EAST...AND TO BETWEEN 15 AND 30 PERCENT OVER THE
WESTERN DESERTS. AS STRONG QG FORCING CONTINUES ON FRIDAY ACROSS THE
AREA...POPS RISE EVEN FURTHER AND BECOME CATEGORICAL ACROSS SOUTH
CENTRAL AZ...WITH SCATTERED TO NUMEROUS SHOWERS AFFECTING THE
WESTERN DESERTS AND SERN CA. MUCH COOLER HIGH TEMPS ARE EXPECTED
FRIDAY GIVEN THE CLOUD COVER AND SHOWERS...AND HIGHS WILL FALL OVER
15 DEGREES AND INTO THE UPPER 50S TO LOW 60S OVER THE CENTRAL AZ
DESERTS.

BY FRIDAY AFTERNOON PROGS ADVERTISE THE PRESENCE OF A CLOSED UPPER
LOW OVER FAR SERN CA/WESTERN AZ...AND THIS LOW WILL VERY SLOWLY
TRANSLATE TO THE EAST/SOUTHEAST FRIDAY NIGHT THROUGH THE DAY ON
SATURDAY. AS SUCH...DYNAMICS/LIFT WILL SLOWLY TAPER OFF BUT MOISTURE
WILL REMAIN QUITE ELEVATED THROUGH THE PERIOD...KEEPING CHANCES FOR
LINGERING SHOWERS ELEVATED OVER MOST OF THE AREA...ESPECIALLY ACROSS
SOUTH CENTRAL AZ. BY SATURDAY...THERE WILL STILL BE A CHANCE FOR
SHOWERS OVER THE CENTRAL DESERTS...WITH SHOWERS NUMEROUS OVER THE
HIGHER TERRAIN OF SOUTHERN GILA COUNTY. FOR THE PERIOD FROM THURSDAY
NIGHT THROUGH THE DAY ON SATURDAY...WE CAN EXPECT STORM TOTAL
RAINFALL ACCUMULATIONS FROM ONE HALF INCH TO OVER ONE INCH ACROSS
THE CENTRAL AZ DESERTS...WITH AMOUNTS AROUND ONE INCH AT
PHOENIX...AND AMOUNTS APPROACHING 2 INCHES ACROSS THE HIGHER TERRAIN
AREAS EAST OF PHOENIX.

DUE TO EXPECTED HIGH SNOW LEVELS...MOSTLY AOA 7000 FEET...WE DO NOT
EXPECT SNOW TO BE AN ISSUE WITH THIS WEATHER SYSTEM. ANY SNOW THAT
FALLS WILL BE OVER THE HIGHEST PEAKS ONLY.

ON SATURDAY NIGHT...AS THE LOW/TROF CONTINUE TO SAG TO THE SOUTHEAST
AND THE TROF AXIS PUSH SOUTHEAST OF OUR AREA...HIGHER PRESSURE WILL
STEADILY BUILD IN FROM THE NORTHWEST LEADING TO A DRYING TREND.
THERE WILL BE A LINGERING SLIGHT CHANCE FOR MAINLY EVENING SHOWERS
OVER SOUTH CENTRAL AZ...AND A CHANCE FOR SHOWERS OVER THE HIGHER
TERRAIN EAST OF PHOENIX.

SUNDAY THROUGH TUESDAY...
SUNDAY LOOKS TO BE A DRY DAY EXCEPT FOR A FEW LINGERING SHOWERS OVER
SOUTHERN GILA COUNTY...WITH TEMPERATURES RISING BACK TO NEAR NORMAL
AS AN UPPER LEVEL RIDGE MOVES IN ACROSS THE STATE. WITH THE UPPER
RIDGE TAKING OVER FOR EARLY NEXT WEEK...WILL LIKELY SEE CONTINUED
DRY CONDITIONS AND HIGH TEMPERATURES BACK INTO THE 70S.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...
MID LEVEL CLOUDS HAVE EXITED THE REGION AND ONLY SOME HIGH LEVEL
CEILINGS ARE REMAINING. THESE WILL LIKELY CLEAR OUT AFTER 06-09Z
YIELDING SEVERAL HOURS WHERE FOG COULD FORM. FEEL THE BEST LOCATION
WOULD BE KIWA OR KSDL GIVEN THEIR COOLER TEMPERATURES BUT CONFIDENCE
TOO LOW TO GO WITH MUCH LOWER THAN 6SM AT THIS POINT. OTHERWISE
AVIATION IMPACTS THROUGH LATE WEDNESDAY APPEAR MINIMAL. EXPECT
LIGHT/DIURNALLY DRIVEN WINDS AT ALL SITES.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
JUST SOME HIGH CLOUDS LEFT TO CONTEND WITH ACROSS SE CA. SREF VSBY
PROBABILITIES SUGGEST MVFR CONDITIONS ARE POSSIBLE AT BLH AND I WILL
MAKE SLIGHT DOWNWARD ADJUSTMENTS TO THEIR VSBY FORECAST IN THE 06Z
TAF. IPL CHANCES APPEAR LOWER PER 21Z SREF BUT DEWPOINT DEPRESSIONS
ARE ALREADY NARROWING AND I WILL ALSO MENTION MVFR THERE AS WELL.
CONDITIONS SHOULD IMPROVE RAPIDLY AFTER 16Z WITH INCREASED BL MIXING
AND HEATING. AS FOR WINDS...LIGHT/DIURNALLY DRIVEN AT BOTH SITES.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
ABOVE NORMAL TEMPERATURES AND RELATIVELY MOIST CONDITIONS WILL
PREVAIL THURSDAY AS A RIDGE PREDOMINATES ACROSS MEXICO. ANOTHER LOW
PRESSURE SYSTEM WILL RESULT IN INCREASING RAIN CHANCES AND
COOLER TEMPERATURES THURSDAY NIGHT THROUGH SATURDAY. A WARMING AND
DRYING TREND IS EXPECTED SUNDAY/MONDAY AS A RIDGE BUILDS ACROSS
CALIFORNIA.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...CB
AVIATION...LEINS
FIRE WEATHER...HIRSCH







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