Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 301004
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
305 AM MST SAT APR 30 2016

.SYNOPSIS...
A NEW LOW PRESSURE SYSTEM WILL MOVE INTO THE REGION FROM THE NORTH
TODAY AND SUNDAY. THIS WILL PROVIDE BREEZY CONDITIONS...MORE
COOLING...AND A CHANCE OF AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS...PARTICULARLY OVER NORTHERN AND CENTRAL ARIZONA.
CLEARING IS EXPECTED SUNDAY NIGHT...WITH DRY AND MUCH WARMER WEATHER
DEVELOPING NEXT WEEK. HOT WEATHER IS EXPECTED NEXT WEEK WITH DESERT
TEMPERATURES WARMING INTO THE MID TO UPPER 90S. THERE ARE HINTS OF
ANOTHER PACIFIC WEATHER SYSTEM MOVING INTO THE REGION BY NEXT
WEEKEND.

&&

.DISCUSSION...

TODAY AND SUNDAY...

THE FLUID DYNAMICS OF THE EVOLVING WEATHER SYSTEM OVER THE SOUTHWEST
U.S. CHANGED FRIDAY EVENING AS A NUMBER OF NEW AND SMALLER
DISTURBANCES HAVE UNEXPECTEDLY SPUN UP UNDER A STRONG NORTHERLY JET
STREAM OVER THE PACIFIC NORTHWEST. THIS IS BEST SEEN IN THE 300/250
MB 00Z SAT PLOT DATA ACROSS WA/OR/ID.  IN OTHER WORDS...WHAT WAS ONCE
THOUGHT TO BE ONE VERY CLEAN AND UNILATERAL SYSTEM MOVING SOUTH AND
PIVOTING OUT OF SOUTHERN CA SATURDAY NIGHT...AND EXPOSING SOUTH
CENTRAL AZ INCLUDING PHOENIX TO A CHANCE OF THUNDERSTORMS SUNDAY...
HAS NOW CHANGED.

THE INITIAL DISTURBANCE...CLEARLY SEEN IN IR SATELLITE IMAGERY OVER
SOUTHERN NEVADA AND PRODUCING THUNDERSTORMS AT MIDNIGHT...WILL NOW
BE DRIVEN INTO CENTRAL AZ BY EVENING. STRONG 500/300MB HEIGHT
FALLS...MID LEVEL DYNAMICS...AND IMPORTED MOISTURE FROM NEVADA WILL
RESULT IN A CHANCE OF SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND
EVENING...GENERALLY FROM THE COLORADO RIVER VALLEY NEAR BLYTHE...EAST
TO WICKENBURG...PHOENIX...AND SURROUNDING DESERTS AND MOUNTAINS.

MODELED SOUNDINGS NOW SUGGEST THE CONVECTIVE TRIGGER TEMP AT PHOENIX
IS 75 DEG F (A HIGH TEMP OF 84 IS FORECAST)...66 DEG AT WICKENBURG
(A HIGH OF 75 IS FCST)...61 DEG AT GLOBE (A HIGH OF 75 IS FCST)...
AND 75 AT BLYTHE (A HIGH OF 82 IS FCST). THESE CONVECTIVE TRIGGER
TEMPS WILL GENERALLY DEVELOP BETWEEN NOON AND 2 PM.  ALSO...MODELED
SOUNDINGS DEPICT CONVECTIVE CLOUD BASES ON THE HIGH SIDE...ROUGHLY
12-14 THSD FT SUGGESTING THE POSSIBILITY OF MODERATELY STRONG
DOWNBURST WINDS AND EVERYTHING THAT COMES WITH IT INCLUDING LOCALLY
DENSE BLOWING DUST.

THE CHANCE OF SHOWERS AND THUNDERSTORMS WILL DIMINISH THIS EVENING
WITH THE LOSS OF DAYTIME HEATING...BUT CONTINUE AGAIN SUNDAY OVER
PORTIONS OF SOUTH CENTRAL AZ FROM PHOENIX NORTH AND EAST...
PARTICULARLY OVER THE MOUNTAINS AS A SECOND AND WEAKER DISTURBANCE
ROTATES INTO THE REGION FROM THE NORTH.

IN SUMMARY...PERHAPS THE BEST CHANCE OF SHOWERS AND THUNDERSTORMS
WITH GUSTY WINDS WILL BE THIS AFTERNOON AND EVENING...NOT SUNDAY.

CLEARING SKIES ARE FORECAST FOR SUNDAY NIGHT.


MONDAY THROUGH THURSDAY...

DRY WESTERLY FLOW WILL DEVELOP MONDAY...FOLLOWED BY A BUILDING HIGH
PRESSURE SYSTEM TUE...WED...AND MOST OF THURSDAY. THIS WILL RESULT
IN MOSTLY CLEAR SKIES AND MUCH WARMER TEMPERATURES.


THURSDAY NIGHT AND FRIDAY...

MODELS HAVE BEEN FORECASTING ANOTHER PACIFIC WEATHER SYSTEM TO
APPROACH SOUTHERN CA LATE THURSDAY AND FRIDAY. ENSEMBLE SPREAD
CONTINUES BO BE WIDE WITH RESPECT TO TIMING AND INTENSITY. HOWEVER
ITS A NEAR CERTAINTY THAT ANOTHER PACIFIC SYSTEM WILL MOVE INTO THE
REGION BY THE END OF NEXT WEEK AND WEEKEND FOR MORE COOLING...
WIND...AND A THREAT OF SHOWERS. FOR NOW WE FEEL COMFORTABLE
INTRODUCING JUST A SLIGHT CHANCE OF SHOWERS AREA-WIDE FRIDAY AND
SATURDAY WITH NO SPECIFICS NOR RESOLUTION.


&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...
TYPICAL EARLY EVENING BREEZINESS WILL SUBSIDE OVERNIGHT...ULTIMATELY
GIVING WAY TO DOWNSLOPE EASTERLY FLOW BETWEEN 08Z AND 10Z. LATEST
MODEL GUIDANCE INDICATES INSTABILITY WILL INCREASE SATURDAY
AFTERNOON...RESULTING IN WIDESPREAD BREEZINESS AND A CHANCE OF
CONVECTION. GUSTS WILL GENERALLY REACH 25 KT...EXCEPT HIGHER IN THE
VICINITY OF SHOWERS AND THUNDERSTORMS. STORMS ARE MOST LIKELY IN A
PERIOD FROM AROUND 23Z SATURDAY TO 03Z SUNDAY.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
WINDS WILL SUBSIDE LATER ON THIS EVENING AT KIPL/KBLH...BEFORE
INCREASING ONCE AGAIN DURING THE MORNING. MAIN AVIATION WEATHER
CONCERN APPEARS TO BE A CHANCE OF THUNDERSTORMS...GENERALLY FROM KBLH
EASTWARD SATURDAY AFTERNOON. ANY STORMS THAT DEVELOP WILL BE CAPABLE
OF PRODUCING WIND GUSTS TO 40 KT.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...

A DRIER AND WARMER AIRMASS WILL STEADILY MOVE INTO THE REGION WITH
BELOW NORMAL HIGH TEMPS ON MONDAY WARMING TO ABOVE NORMAL ON TUESDAY
AND WELL ABOVE NORMAL ON WEDNESDAY WHEN HIGHS IN THE UPPER 90S...
AND ELEVATED FIRE WEATHER DANGER...IS EXPECTED. MINIMUM HUMIDITIES
IN THE MID TEENS TO LOWER 20S PERCENT RANGE ON MONDAY WILL BECOME
EVEN DRIER BY WEDNESDAY WHEN THEY WILL FALL TO THE SINGLE DIGITS.
EXPECT FAIR TO GOOD OVERNIGHT RECOVERIES ON MONDAY TO BECOME FAIR BY
TUESDAY WITH SOME IMPROVEMENT POSSIBLE ON FRIDAY. BREEZY SOUTH AND
SOUTHWESTERLY WINDS IN THE WESTERN ZONES ARE IN STORE FOR WEDNESDAY
AND IN CENTRAL AND EASTERN ZONES ON THURSDAY AND FRIDAY.

&&

.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...VASQUEZ
AVIATION...HIRSCH
FIRE WEATHER...SAWTELLE



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