Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 281607
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
905 AM MST THU APR 28 2016

.SYNOPSIS...
ANOTHER AREA OF LOW PRESSURE WILL DIP INTO THE AREA TODAY WITH MORE
BREEZY CONDITIONS AND A SLIGHT CHANCE OF SHOWERS AND A FEW
THUNDERSTORMS...MOST SIGNIFICANT OVER THE HIGHER TERRAIN NORTH AND
EAST OF PHOENIX THIS AFTERNOON. MORE SEASONABLY WARM WEATHER WILL
RETURN FOR SATURDAY BEFORE YET ANOTHER WEATHER DISTURBANCE IMPACTS
THE REGION SATURDAY NIGHT INTO SUNDAY. HIGH PRESSURE WILL RETURN BY
THE MIDDLE OF NEXT WEEK...SUPPORTING WARMING TEMPERATURES AND
CLEARING SKIES.

&&

.DISCUSSION...
DEEP AND UNSEASONABLY COOL PACIFIC UPPER LOW CONTINUED TO PUSH EAST
ACROSS THE DESERT SOUTHWEST THIS MORNING...AND AS SEEN IN THE 12Z
PLOT DATA AND CURRENT SATELLITE LOOPS...THE MAIN LOW CENTER WAS
MOVING INTO NORTH CENTRAL ARIZONA. SERIES OF VORT SPOKES WAS
ROTATING AROUND THE UPPER LOW...AND ONE SUCH FEATURE WILL SLIDE EAST
ACROSS THE LOWER DESERTS THIS MORNING AND INTO THE AFTERNOON
HOURS...LEADING TO A SLIGHT CHANCE...OR EVEN A CHANCE...OF SHOWERS
AND THUNDERSTORMS OVER SOUTH CENTRAL ARIZONA. AT 8 PM RADAR SHOWED
MOST OF THE SHOWERS NORTH OF THE AREA OVER THE HIGHER TERRAIN OF
NORTHERN ARIZONA...BUT AN AREA OF SHOWERS WAS DEVELOPING NORTHEAST
OF PHOENIX...OVER HIGHER TERRAIN AREAS NORTHEAST OF SCOTTSDALE. AS
THE UPPER JET CONTINUES TO SAG SOUTH TODAY AND COLD AIR ASSOCIATED
WITH THE LOW CENTER MOVES SOUTH AS WELL...DYNAMICS WILL WEAKEN A BIT
BUT THERMODYNAMICS WILL PLAY A BIGGER ROLE AS INSTABILITY
SHOWERS/STORMS DEVELOP OVER THE DESERTS.

WIND WILL CONTINUE TO BE AN ISSUE WITH THIS PASSING LOW...ESPECIALLY
OVER THE SOUTHWEST ARIZONA DESERTS...AND INTO SOUTHEAST CALIFORNIA.
LATEST EFI WIND DATA INDICATED A STRIP OF WINDS ACROSS IMPERIAL
COUNTY AND INTO YUMA COUNTY REACHING ABOVE THE 95TH PERCENTILE
SUGGESTING AN ELEVATED THREAT OF HIGH WIND THIS MORNING AND OF
COURSE...IT HAS BEEN VERY WINDY OVER IMPERIAL COUNTY. THE
OBSERVATION AT EL CENTRO AT 15Z REPORTED SUSTAINED WINDS TO 31KT
WITH GUSTS TO 37KT AND OTHER OBSERVATIONS IN THE AREA ALSO REPORTED
GUSTS REACHING ADVISORY CRITERIA. AS SUCH WE INTEND TO ISSUE A WIND
ADVISORY FOR THE WESTERN DESERTS UNTIL NOON TODAY. GRADIENTS ARE
FORECAST TO WEAKEN WITH TIME AND BY AFTERNOON WINDS SHOULD TAPER OFF
AND DROP BELOW ADVISORY CRITERIA.

CURRENT FORECASTS HAVE BEEN TWEAKED TO REFLECT SKY...POP...WX TRENDS
AND WE ADDED SOME MORNING BLOWING DUST INTO THE GRIDDS OUT WEST.

.PREVIOUS DISCUSSION...
TODAY AND FRIDAY...
VERY TRANSIENT PATTERN STILL IN PLACE OVER THE ENTIRE CONUS...WITH
UPPER LEVEL FEATURES ONLY STAYING IN RESIDENCE ACROSS THE WEST FOR
1-2 DAYS BEFORE SHIFTING EAST OF THE REGION. THIS GOES FOR BOTH
POSITIVE AND NEGATIVE HEIGHT ANOMALIES...SHORTWAVE RIDGES AND
TROUGHING. SHOWER AND THUNDERSTORM ACTIVITY IS CONTINUING ACROSS
SOUTHERN NV AND PORTIONS OF NORTHERN AZ THIS EARLY MORNING...ENHANCED
ALONG THE LATEST VORT MAX INTRUSION AND ML OMEGA POCKET TRAVELING
ALONG WITH AN UL LOW ANCHORED OVER THE SIERRA/EASTERN NV. SKIES
ACROSS MUCH OF THE CWA WERE CLEAR AT TIME OF WRITING...WITH SOME CU
FIELDS ALONG THE NORTHERN CWA BOUNDARY AND OVER THE HIGHER TERRAIN
EAST OF PHOENIX. INITIAL UL JET INTRUSION AND VORT LOBE PASSAGE
THROUGH LATE MORNING MAY SUPPORT SOME LIGHT SHOWER ACTIVITY ACROSS
NORTHERN PORTIONS OF LA PAZ AND MARICOPA COUNTIES...WITH EVEN SOME
ACCAS AND VIRGA/SPRINKLES OVER THE PHOENIX METRO IN THE AM. HI-RES
MODELS SUPPORT THE IDEA OF LIGHT SHOWERS AND MAYBE AN ISOLATED
THUNDERSHOWER IN THE EARLY AM BEFORE THE MAIN VORT BAND AND JET
STREAK BEGIN TO SINK SOUTH OF THE AREA BY THE AFTERNOON. BREEZY
CONDITIONS FROM THE WEST WILL RETURN TODAY...BUT NOT TO THE TUNE OF
SPEEDS WE SAW EARLIER IN THE WEEK. COOLER TEMPERATURES WILL RESULT
AGAIN AFTER YESTERDAY`S 80S...WITH HIGH TEMPERATURES COOLING 5 TO 10
DEGREES OR SO. MAIN CIRC CENTER WILL CLEAR INTO THE FOUR CORNERS
OVERNIGHT...WITH A FEW TRAILING SHORTWAVES THAT COULD GEN UP AN
ADDITIONAL ROUND OF CU/LIGHT SHOWERS/SPRINKLES BY THE LATE
AFTERNOON/EVENING ACROSS CENTRAL AZ. RAINFALL AMOUNTS THROUGHOUT OUR
CWA WILL BE ON THE LIGHT SIDE...GENERALLY LESS THAN 0.05 INCHES.
FRIDAY WILL FIND THE FORECAST AREA UNDER SUBSIDENT NORTHWESTERLY FLOW
AS THE LATEST LOW EXITS INTO THE PLAINS...WITH ANOTHER SYSTEM QUICK
ON ITS HEELS FOR SATURDAY.

SATURDAY THROUGH MONDAY...
UL SYSTEM FOR SATURDAY QUICKLY TRANSITIONS INTO THE AREA FROM THE
NORTH...WHILE OPENING UP ACROSS THE WEST AS BROAD NEGATIVE HEIGHT
ANOMALIES OVERTAKE MUCH OF THE CONUS. ANOTHER ROUND OF BREEZES AND A
TEMPERATURE COOL DOWN WILL RESULT...WITH PORTIONS OF THE SOUTH-
CENTRAL AZ DESERTS UNDER SLIGHT CHANCES FOR ADDITIONAL SHOWER
ACTIVITY LATE SATURDAY INTO SUNDAY. AS WITH THE LAST FEW SYSTEMS TO
BREEZE THROUGH THE REGION...RAINFALL AMOUNTS WILL BE ON THE LIGHTER
SIDE AND FAVOR AREAS MAINLY NORTH OF THE CWA. THE MAJORITY OF THE
SOUTHERN HALF OF THE FORECAST AREA /SOUTHEAST CA...YUMA...SW MARICOPA
AND NW PINAL/ ARE LIKELY TO MISS OUT ON ANY PRECIP AND EVEN CLOUD
COVER TO SOME EXTENT FOR SATURDAY AND SUNDAY. UL JET STREAK AND
TROUGH HEIGHTS WILL BEGIN TO WEAKEN OVER THE SOUTHWEST...WITH PACIFIC
RIDGING TRANSITIONING INTO THE AREA ALLOWING FOR DRY CONDITIONS AND
WARMER TEMPERATURES TO RETURN FOR THE NEW WORK WEEK.

TUESDAY THROUGH LATE NEXT WEEK...
DETERMINISTIC AND ENSEMBLE MODEL AGREEMENT IS FAIRLY GOOD FOR THE
MEDIUM TO EXTENDED RANGE PERIOD WITH HIGH AMPLITUDE RIDGING
OVERTAKING MUCH OF THE INTERMOUNTAIN WEST/ROCKIES EARLY TUESDAY AND
LINGERING THROUGH THURSDAY. INCREASING THICKNESSES AND RECOVERING
ATMO THERMAL PROFILE WILL ALLOW FOR NEAR TO ABOVE AVERAGE
TEMPERATURES WITH MANY LOWER DESERT SITES RETURNING TO THE 90S BY
TUESDAY. 500MB HEIGHTS HEAD INTO THE LOW 580 DAM RANGE EASILY PEAKING
SURFACE TEMPERATURES INTO THE MID-90S BY THE MIDDLE PORTION OF THE
WEEK. SOME OF THE WARMEST DESERT LOCALES...SUCH AS TACNA AND EL
CENTRO...COULD FLIRT WITH THE TRIPLE-DIGIT READINGS...BUT THE CLIMATE
STATIONS OF PHOENIX AND YUMA STILL ARE IN THE CLEAR WITH THE LATEST
GUIDANCE. LATE WEDNESDAY INTO THURSDAY THE UPPER RIDGE WILL CLEAR
EAST OF THE AREA AS A PACIFIC TROUGH APPROACHES THE WEST COAST. MORE
OCEANIC TRACK AND SOUTHERLY REACHES OF THIS TROUGH COULD SPELL
INCREASING HUMIDITIES INTO THE REGION ALONG WITH A COOLING TREND FOR
TEMPERATURES FOR THE WEEKEND AFTER NEXT.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...
TIMING WIND SHIFTS WILL BE THE PRIMARY AVIATION CHALLENGE THROUGH
FRIDAY MORNING...THOUGH A PERIOD OF CIGS NEAR 7K FT AND THE OUTSIDE
CHANCE OF A BRIEF SPRINKLE MAY AFFECT TERMINALS THIS EVENING. WIND
DIRECTIONS MAY OSCILLATE BETWEEN SOUTHEAST AND SOUTHWEST FOR A TIME
THIS MORNING...THOUGH WILL BECOME PREDOMINANTLY SOUTHWEST BY LATE
MORNING (AND INCLUDE SOME GUSTS UP TO 20KT INTO THE AFTERNOON).
CONFIDENCE IN MODERATE THAT SOME CIGS WILL SPREAD INTO THE AREA THIS
EVENING...AND A SPRINKLE IS NOT OUT OF THE QUESTION THOUGH WITH
LITTLE TO NO IMPACT.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
GUSTY SOUTHWEST WINDS WILL BE THE PRIMARY AVIATION IMPACT THROUGH
FRIDAY MORNING. PERIODIC GUSTS UP TO 30KT WILL BE LIKELY AT KIPL
THROUGH THIS EVENING BEFORE DECOUPLING. SPEEDS WILL BE SOMEWHAT LESS
AT KBLH THOUGH WITH THE SAME TREND. A PERIOD OF SOME CIGS AOA 7K FT
MAY BE POSSIBLE THIS AFTERNOON...THOUGH CLEARING WILL RAPIDLY SPREAD
INTO SOUTHEAST CALIFORNIA AFTER SUNSET.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
SOMEWHAT COOLER THAN NORMAL TEMPERATURES ASSOCIATED WITH A PASSING
LOW PRESSURE SYSTEM THROUGH THE WEEKEND WILL REBOUND MARKEDLY BY THE
MIDDLE OF NEXT WEEK. WITH THE STORM SYSTEM...WINDS WILL BECOME
SOMEWHAT GUSTY DURING THE AFTERNOON AND EVENING HOURS. HOWEVER...THE
ENVIRONMENT WILL BE SEASONABLY MOIST AS COMPARED TO NORMAL AND
MINIMUM HUMIDITY LEVELS ONLY FALLING TO AROUND A 15 TO 25 PERCENT
RANGE. OVERNIGHT RECOVERY WILL BE GOOD. SHOWER AND THUNDERSTORM
CHANCES WILL BE RELEGATED PRIMARILY TO NORTHERN ARIZONA...BUT AN
ISOLATED SHOWER COULD SNEAK INTO THE FOOTHILLS NORTH AND EAST OF
PHOENIX ON SUNDAY.

&&

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION IS NOT EXPECTED.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...WIND ADVISORY UNTIL NOON FOR AZZ020...025...026.

CA...WIND ADVISORY UNTIL NOON FOR CAZ031...033.

&&

$$

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

DISCUSSION...CB
PREVIOUS DISCUSSION...NOLTE
AVIATION...MO
FIRE WEATHER...MO/CB


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