Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 291601
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
900 AM MST FRI APR 29 2016

.SYNOPSIS...
DRY NORTHWEST FLOW ALOFT WILL INCREASE OVER THE REGION TODAY THROUGH
SATURDAY. WARMER AFTERNOON TEMPERATURES ARE ALSO FORECAST.
HOWEVER...ANOTHER PACIFIC LOW PRESSURE SYSTEM IS EXPECTED TO MOVE
INTO THE REGION SATURDAY NIGHT AND SUNDAY...DEVELOPING BREEZY
CONDITIONS AND A THREAT FOR SHOWERS AND THUNDERSTORMS. THE BEST
CHANCE OF PRECIPITATION WILL OCCUR OVER THE SOUTH CENTRAL ARIZONA
DESERTS AND MOUNTAINS...MAINLY IN THE VICINITY OF PHOENIX. CLEARING
IS EXPECTED SUNDAY NIGHT...WITH HIGH PRESSURE AND MUCH WARMER
WEATHER NEXT WEEK.

&&

.DISCUSSION...
COOL UPPER LOW CONTINUED TO TRANSITION OFF TOWARDS THE NORTHEAST
THIS MORNING WITH THE MAIN LOW CENTER EAST/NORTHEAST OF THE FOUR
CORNERS AREA AS SEEN IN VAPOR IMAGERY AND MORNING PLOT DATA. 12Z
500MB PLOTS INDICATED CYCLONIC SHEAR/CURVATURE TO THE FLOW OVER
EASTERN ARIZONA HELPING SUPPORT WEAK UPWARD MOTION...AND WITH A WRAP
AROUND DECK OF MID LEVEL MOISTURE PRESENT FROM THE GREATER PHOENIX
AREA EASTWARD...THE UVV LED TO SOME THICK CLOUD DECKS WITH BASES 8-
10K FEET AND LIGHT SHOWERS EMANATING FROM SOME OF THEM. AS SUCH
SLIGHT CHANCES FOR LIGHT SHOWERS REMAINS IN THE FORECAST FROM
PHOENIX EASTWARD THIS MORNING INTO THE AFTERNOON HOURS.

OVERALL...THE LOW WILL CONTINUE TO SHIFT EAST TODAY AND A MORE
SUBSIDENT NORTHWEST FLOW ALOFT WILL GRADUALLY OVERSPREAD THE AREA
ALLOWING FOR A CLEARING TREND AND THE END OF SHOWERS OVER THE LOWER
ELEVATIONS. THERE WILL BE A FEW LINGERING SHOWERS OR THUNDERSTORMS
OVER HIGHER TERRAIN OF SOUTHERN GILA COUNTY THIS AFTERNOON BUT THE
LOWER DESERTS WILL SEE MOSTLY SUNNY TO PARTLY SUNNY SKIES. DUE TO
THE PROXIMITY OF THE DEPARTING LOW...TEMPS TODAY WILL CLIMB A FEW
DEGREES BUT REMAIN SEVERAL DEGREES BELOW SEASONAL NORMALS ACROSS THE
SOUTH CENTRAL DESERGTS. THE HIGH TODAY AT PHOENIX IS FORECAST TO BE
83 DEGREES COMPARED TO THE NORMAL HIGH OF 89 DEGREES. HIGHS WILL BE
A LITTLE WARMER OUT WEST...IN THE MID TO UPPER 80S. CURRENT
FORECASTS LOOK TO BE IN GOOD SHAPE AND NO SIGNIFICANT UPDATES ARE
PLANNED ATTM.

.PREVIOUS DISCUSSION...
TODAY AND SATURDAY...

THE COOL LOW PRESSURE SYSTEM THAT MOVED INTO AZ THURSDAY...AND
PROVIDED AFTERNOON TEMPERATURES ABOUT 13 DEGREES BELOW NORMAL...WAS
MOVING EAST INTO NEW MEXICO THIS MORNING. DRY NORTHWEST FLOW ALOFT
WILL DEVELOP TODAY AND SATURDAY...HOWEVER BREEZY TO WINDY CONDITIONS
WILL PICK UP AGAIN SATURDAY AFTERNOON IN RESPONSE TO A STRONGER
WEATHER SYSTEM EXPECTED SUNDAY. OTHERWISE PARTLY CLOUDY TO MOSTLY
CLEAR SKIES...AND WARMER TEMPERATURES ARE EXPECTED TODAY AND
SATURDAY.

SATURDAY NIGHT AND SUNDAY...

THIS IS THE EXCITING PERIOD...AS YET ANOTHER WEATHER SYSTEM IS
FORECAST TO PLUNGE INTO THE REGION SATURDAY NIGHT AND SUNDAY FROM
THE NORTH. THIS SYSTEM IS DIFFERENT FROM THE ONE THAT PASSED ON
THURSDAY ON MANY LEVELS. FIRST...THURSDAY EVENINGS SAN DIEGO WEATHER
BALLOON SOUNDING SHOWED APPRECIABLE LOW LEVEL MOISTURE BELOW 5000
FEET...WITH ABOUT 0.63 INCHES OF PRECIPITABLE WATER. PRECIP WATER
VALUES MATCHED THOSE SEEN ON THURSDAY EVENINGS PRECIP WATER
SATELLITE IMAGERY...WITH MORE SEEN OFFSHORE. SO MORE MOISTURE WILL
BE INVOLVED WITH THIS SYSTEM.  SECOND...THE SUNDAYS DISTURBANCE WILL
MOVE IN FROM THE PACIFIC NORTHWEST...DEEPENING SOUTH INTO FAR
WESTERN AZ BY SATURDAY MIDNIGHT. FUNDAMENTALLY SPEAKING...SOUTHWARD
MOVING SYSTEMS NORMALLY INTENSIFY DUE TO THE LOSS OF PLANETARY
VORTICITY. THEREFORE...WE CAN EXPECTED A SPIN-UP IN THE SYSTEM.
THIRDLY...500 MB HEIGHT FALLS DROP 80-100 METERS OVER SOUTHERN
CA/COLORADO RIVER VALLEY BY SATURDAY EVENING. HEIGHT FALLS SEEM TO
BE ORIENTATED IN A PATTERN SUGGESTING STRONG VERTICAL MOTION IN A
TRIANGULAR AREA FROM IMPERIAL CA...NORTH TO NEEDLES CA...AND SOUTH
TO YUMA EARLY SATURDAY NIGHT. IN RESPONSE...LOW LEVEL WINDS BELOW
5000 FT BACK STRONGLY FROM THE GULF OF CA...TAPPING ADDITIONAL LOW
LEVEL MOISTURE...AND MOISTURE THAT MOVES OVER THE BAJA PENINSULA
FROM THE PACIFIC.

INCREASING MID/UPPER LEVEL DYNAMICS...AND FAVORABLE THERMODYNAMICS
WITH THE ADDITIONAL BOUNDARY LAYER MOISTURE...WILL RESULT IN THE
POTENTIAL FOR EARLY AFTERNOON THUNDERSTORMS OVER SOUTH CENTRAL
AZ...FOCUSED GENERALLY AROUND WICKENBURG...PHOENIX...CASA GRANDE...
AND THE MOUNTAINS NORTH THROUGH EAST OF PHOENIX. MODELED SOUNDINGS
HINT AT A CONVECTIVE TRIGGER TEMPERATURE OF 72 DEG F AT PHOENIX (A
HIGH TEMP OF 81 IS FORECAST)...69 DEG AT WICKENBURG (A HIGH OF 75 IS
FORECAST)...AND 60 DEGREES AT GLOBE (A HIGH OF 71 IS FORECAST). THE
ONLY CAVEAT IS...RIGHT NOW THE GREATEST THERMODYNAMIC INSTABILITY IS
BETWEEN 8AM AND 1 PM MST...WITH HINTS THAT THE ATMOSPHERE MAY SLOWLY
START TO STABILIZE AFTER THAT.  FOR SOUTHEAST CA AND THE COLORADO
RIVER ZONES...IT MAY BE TOO STABLE FOR ANY THUNDERSTORMS ON
SUNDAY...JUST A SLIGHT CHANCE OF SHOWERS.

SUNDAY NIGHT AND MONDAY...

SUNDAYS WEATHER SYSTEM WILL BE A QUICK MOVER...SHIFTING INTO NEW
MEXICO SUNDAY NIGHT...WITH VERY STABLE WEATHER FOLLOWING FOR MONDAY.
A WARMER AFTERNOON IS EXPECTED MONDAY.

TUESDAY THROUGH THURSDAY...

A HIGH PRESSURE SYSTEM WILL BUILD INTO THE REGION THIS PERIOD FOR
MOSTLY CLEAR SKIES AND MUCH WARMER TEMPERATURES. IN OTHER WORDS...
BACK TO NORMAL SPRING-TIME WEATHER...WITH OUCH...DESERT TEMPERATURES
IN THE 90S AGAIN. ITS ALSO CONCEIVABLE THAT PHOENIX CAN REACH ITS
FIRST 100 DEG TEMP OF THE YEAR THURSDAY UNDER SOUTH WINDS/WARM
ADVECTION.

&&

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

MID-LEVEL MORNING STRATUS DECKS MOVING IN FROM THE NORTH WILL
DISSIPATE DURING THE MORNING...WITH ENOUGH MOISTURE AROUND TO
MAINTAIN SOME FEW TO SCT CLOUDS GNLY 8 TO 10KFT INTO THE AFTN/EARLY
EVE. MORNING SFC WINDS WILL HOLD ONTO SOME WESTERLY DRIFT WITH
PERIODS OF LIGHT AND VARIABLE OBSERVATIONS POSSIBLE. IF THE CLOUD
DECKS BEGIN TO CLEAR OVER PHX BUT HOLD OVER THE EASTERN MOUNTAINS
DURING THE LATE MORNING...SOME EASTERLY DRIFTS MAY DEVELOP INTO KPHX
BUT NOT LOOKING FOR THAT TO HAPPEN AT THIS TIME. ELEVATED WEST WINDS
TO RETURN FOR THE AFTERNOON WITH SUSTAINED SPEEDS PUSHING 12KTS AND
GUSTS INTO THE 20KT RANGE.

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

WEST WINDS TO CONTINUE FOR KIPL THROUGH THE TAF PERIOD WHILE WINDS
WILL BEGIN TO TRANSITION SOUTHWEST TO SOUTH FOR KBLH BY THIS EVENING.
AFTERNOON GUSTINESS 15 TO 20 KTS POSSIBLE WITH MOSTLY CLEAR SKIES.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...
ANOTHER UPPER LOW WILL CONTINUE TO APPROACH AND TRAVEL THROUGH THE
REGION SUNDAY...THIS TIME DRAWING IN SOME MOISTURE OFF THE PACIFIC TO
WARRANT SOME SLIGHT CHANCES FOR SHOWERS AND THUNDERSTORMS ACROSS THE
REGION. CHANCES FOR WETTING RAINS ARE VERY LOW TO NIL FOR THE
MAJORITY OF THE DISTRICTS BUT ANOTHER ROUND OF COOLER TEMPERATURES
AND SLIGHTLY INCREASING DEWPOINTS WILL LEAD TO DAYTIME HUMIDITIES IN
THE 20 TO 30 PERCENT RANGE. HIGH PRESSURE WILL TRANSITION INTO THE
AREA BEGINNING MONDAY ALLOWING FOR TEMPERATURES TO RETURN TO AND THEN
QUICKLY WARM ABOVE NORMAL WITH DAYTIME HUMIDITIES DRYING BELOW 10
PERCENT BY MIDWEEK. WINDS WILL BE ON THE LIGHTER SIDE...WITH
SOUTHERLY BREEZES PICKING UP MIDWEEK ACROSS SOUTHEAST CALIFORNIA.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&

$$

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

DISCUSSION...CB
PREVIOUS DISCUSSION...VASQUEZ
AVIATION...NOLTE
FIRE WEATHER...NOLTE



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