Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 262050
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
150 PM MST MON JAN 26 2015

.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL CONTINUE TO AFFECT THE REGION TONIGHT
WITH PERIODS OF LIGHT RAIN. THIS DISTURBANCE WILL MOVE NORTH OF THE
REGION TUESDAY...AND IN ITS WAKE ABOVE NORMAL TEMPERATURES AND
HIGHER THAN NORMAL HUMIDITIES WILL PREVAIL. ANOTHER LOW PRESSURE
SYSTEM WILL BRING ADDITIONAL MOISTURE AND RENEWED HIGHER CHANCES FOR
PRECIPITATION LATE IN THE WEEK AND INTO THE WEEKEND.

&&

.DISCUSSION...
A WEAKENING PV ANOMALY NEAR 31N 118W WAS LIFTING NORTH ON THE
LEEWARD SIDE OF A HIGH AMPLITUDE RIDGE DOMINATING THE WRN CONUS THIS
AFTERNOON. ASCENT IN THE FORM A BROAD ISENTROPIC LIFT AND WARM
ADVECTION WAS ACTING ON A PLUME OF HIGHER THETA-E AIR STRETCHING
FROM SERN ARIZONA THROUGH WEST CENTRAL ARIZONA. WITHIN THE OVERALL
FLOW PATTERN OF BACKED MIDTROPOSPHERIC WINDS...RADAR ECHOES INDICATE
A MESO-VORT NEAR KIPL WHICH APPEARS TO BE ENHANCING ECHOES LIFT
THROUGH SERN CALIFORNIA. ACROSS CNTRL ARIZONA...A DEEP LAYER OF DRY
AIR BELOW THE H7 LEVEL STILL PERSISTS WITH T/TD DEPRESSIONS NEAR 40F
SUGGESTING MORE DIFFICULTY WILL BE ENCOUNTERED REACHING WETBULB
TEMPERATURES AND ACCUMULATING RAINFALL REACHING THE SFC.

THE PREPONDERANCE OF HIGH RESOLUTION MODELS MATCH CURRENT RADAR
RETURNS QUITE CLOSELY SHOWING A SOLID CORRIDOR OF SHOWERS LIFTING
THROUGH WRN ARIZONA...DEVELOPING AREA OF BROKEN SHOWERS IN THE
VICINITY OF THE AFOREMENTIONED MESO-VORT...AND WEAKER ECHOES LIFTING
NORTH FROM THE TUCSON AREA. WHILE THE ENTIRE FORECAST AREA WILL
LIKELY SEE SOME MEASURE OF RAINFALL...PREFERRED HIGH RESOLUTION EMC
WRF AND NSSL WRF MEMBERS DEPICT THE INITIAL CNTRL ARIZONA RAIN BAND
STRUGGLING THIS AFTERNOON...AND MORE SCT FAST MOVING SHOWERS THIS
EVENING AND OVERNIGHT LIFTING INTO NRN ARIZONA.
EVENTUALLY...SUBSIDENT DOWNGLIDE AND DRYING (ALREADY SEEN IN WV
IMAGERY PROPAGATING UP THE BAJA PENINSULA WILL OVERSPREAD THE
REGION...DRASTICALLY LIMITING THE RAIN POTENTIAL.

DRIER AIR ALOFT WILL SURGE INTO THE FORECAST AREA TUESDAY...BUT
RESIDUAL LOW LEVEL MOISTURE WILL KEEP SOME LINGERING STRATO-CU
THROUGH AT LEAST THE EARLY AFTERNOON. HOWEVER...THERE SHOULD BE
SUFFICIENT CLOUD BREAKS DURING PEAK HEATING ALONG WITH ABNORMALLY
WARM H8 TEMPERATURES TO RESULT IN AFTERNOON HIGHS ABOVE 3F-6F ABOVE
NORMAL. SHORTWAVE RIDGING...WARM TEMPERATURES ALOFT AND NEARLY FULL
INSOLATION WILL PREVAIL THROUGH WEDNESDAY PROVIDING ANOTHER
UNUSUALLY WARM DAY WITH HIGHS SOME 5F-10F ABOVE NORMAL.

ANOTHER UPPER LOW EMANATING FROM THE EAST PACIFIC WILL MOVE INTO THE
REGION WEDNESDAY NIGHT...INITIALLY AS AN OPEN WAVE HOWEVER TAPPING A
WEALTH OF SUBTROPICAL MOISTURE WITH A DEEP FETCH OF MERIDIONAL FLOW.
WHILE THE MAGNITUDE OF SUBTROPICAL MOISTURE REMAINS IN
QUESTION...SUBJECTIVE PATTERN RECOGNITION AND MODEL TRENDS SUPPORT A
MORE SIGNIFICANT SURGE THAN PREVIOUSLY FORECAST BY GLOBAL MODELS.
FOR NOW...BEST RAINFALL CHANCES WERE HEDGED ACROSS CENTRAL AND
EASTERN ARIZONA. EXACT TIMING OF THE RAIN IS HARD TO NAIL DOWN AT
THIS POINT...BUT FEEL BEST CHANCES WILL BE DURING THE DAYTIME HOURS
FRIDAY. WOULD NOT BE SURPRISED IF LINGERING SHOWERS PERSIST THROUGH
MUCH OF SATURDAY AS THE UPPER LOW COULD BECOME QUASI-STATIONARY OVER
THE REGION FOR A DAY OR SO. HAVE SELECTIVELY DECREASED HIGHS BY A
FEW DEGREES ON FRIDAY GIVEN THE HIGHER CONFIDENCE OF RAIN AND
MAINTAINED A NEAR PERSISTENCE FORECAST FOR SATURDAY.

CONFIDENCE FOR THIS COMING WEEKEND IS STILL FAIRLY LOW AS MODELS
HAVE HAD SOME DIFFICULTY OVER THE PAST FEW MODEL RUNS...BUT IN
GENERAL IT WOULD SEEM THINGS MAY DRY OUT BY SATURDAY NIGHT OR EARLY
SUNDAY. SLIGHT CHANCE POPS REMAIN IN THE FORECAST INTO SATURDAY
NIGHT...BUT HAVE TRIMMED POPS ON SUNDAY WITH THE ONLY SLIGHT CHANCE
POPS NOW OVER THE HIGHER TERRAIN EAST OF PHOENIX.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...
A LOW PRESSURE SYSTEM IS STILL ON TRACK TO BRING INCREASING MOISTURE
AND LIGHT RAIN TO THE PHOENIX TERMINALS FROM LATE THIS AFTERNOON
INTO TONIGHT. HOWEVER...LATEST HI-RES MODEL OUTPUT AND FORECAST
SOUNDINGS ARE TRENDING A BIT DRIER THAN EARLIER RUNS. THUS...CURRENT
THINKING NOW IS THAT BKN-OVC CLOUD LAYERS WILL LIKELY REMAIN AOA 6K
FT THROUGH MUCH OF THE EVENING RUSH...WITH JUST SOME SCT (AT WORST)
LAYERS AROUND 6K FT PERHAPS BRIEFLY FORMING THIS EVENING ONCE THE
LIGHT RAIN/SHOWERS DO MOVE IN THE REGION.

CIGS IN THE 4-6K FT ARE MORE LIKELY TO OCCUR LATE TONIGHT AS
ADDITIONAL SHOWER ACTIVITY MOVES ACROSS THE PHX AREA AND SOUTHERLY
FLOW ALOFT PUSHES ADDITIONAL LOW-LEVEL MOISTURE INTO THE
REGION...WITH THESE CIGS LINGERING UNTIL AROUND MIDDAY ON TUE BEFORE
CLEARING ON TUE AFTERNOON AS HIGH PRESSURE BEGINS TO BUILD NORTHWARD
BACK INTO THE REGION. WINDS ARE EXPECTED TO REMAIN QUITE LIGHT
THROUGH THE TAF PERIOD...REVERTING TO AN EASTERLY DIRECTION BY LATE
TONIGHT.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
LIGHT SHOWERS TO BRING CIGS DOWN INTO THE 3-5K FT RANGE AT BOTH KIPL
AND KBLH LATE THIS AFTERNOON THROUGH THIS EVENING. ALTHOUGH THESE
SHOWERS ARE FORECAST TO END BY MIDNIGHT...LIGHT WINDS AND A RATHER
MOIST AIRMASS ARE EXPECTED TO ALLOW SCT TO BKN CIGS IN THE 3-6K FT
RANGE TO LINGER INTO TUE MORNING BEFORE SLOWLY CLEARING ON TE
AFTERNOON.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
WEDNESDAY THROUGH SUNDAY...
ABOVE NORMAL TEMPERATURES AND RELATIVELY MOIST CONDITIONS WILL
PREVAIL WEDNESDAY-THURSDAY AS A RIDGE PREDOMINATES ACROSS MEXICO.
ANOTHER LOW PRESSURE SYSTEM WILL RESULT IN INCREASING RAIN CHANCES
AND COOLER TEMPERATURES FRIDAY AND SATURDAY. A WARMING AND DRYING
TREND IS EXPECTED SUNDAY 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...MO/KUHLMAN
AVIATION...PERCHA
FIRE WEATHER...HIRSCH





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