Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 301538
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
835 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...
RATHER VIGOROUS UPPER LOW CONTINUED TO TAKE AIM ON ARIZONA THIS
MORNING WITH THE LOW CENTER DRIVING SOUTH THROUGH FAR SRN NEVADA AND
SWINGING TOWARDS THE EAST AND INTO FAR WEST CENTRAL ARIZONA. BY THIS
AFTERNOON THE LOW CENTER IS PROGGED TO BE OVER WEST CENTRAL AZ WITH
ALL OF THE BEST DYNAMICS...INCLUDING MIDLEVEL Q CONVERGENCE...PVA...
UPPER DIFLUENCE AND UPPER JET SUPPORT...FOCUSING ON SOUTH CENTRAL
ARIZONA DURING THE EARLY TO MID AFTERNOON HOURS. SO FAR...AS OF 8
AM...RADAR INDICATED THAT ALL OF THE CONVECTION WAS TO THE NORTH OF
OUR AREA...OVER NRN AZ AND SRN NEVADA. CURRENT SPC MESOANALYSIS
GRAPHICS SHOWED NO MLCAPE OVER THE LOWER DESERTS...BUT AFTER 18Z WE
SHOULD START SEEING 100-250 J/KG CAPE WORKING INTO PORTIONS OF SERN
CA AND THE WESTERN DESERTS.

LATEST SUITE OF MESOSCALE MODELS...INCLUDING HRRR...WRF4KM AND SSEO
STORM SCALE ENSEMBLE OF OPPORTUNITY...INDICATED THAT CONVECTION
WOULD REALLY START BREAKING OUT ACROSS SOUTH CENTRAL AZ AFTER ABOUT
20Z THIS AFTERNOON...WITH SCATTERED SHOWERS AND EMBEDDED
THUNDERSTORMS ACROSS MUCH OF THE AREA INTO THE EVENING HOURS. LESS
CONVECTION WOULD BE FOCUSED OVER SERN CA AND FAR WESTERN AZ AS
DYNAMICS WOULD BE DECREASING BEHIND THE UPPER LOW CENTER. CURRENT
POPS HAVE BEEN TWEAKED AGAIN AND RANGE BETWEEN 20 AND 40 PERCENT
OVER SOUTH CENTRAL AZ DURING THE AFTERNOON HOURS TODAY. CAPE THIS
AFTERNOON IS NOT FORECAST TO BE EXCESSIVE...MOSTLY BELOW 400
J/KG...BUT WITH RATHER STRONG DYNAMICS IT WILL NOT TAKE AS MUCH TO
GENERATE SOME MODERATELY STRONG THUNDERSTORMS. THUS WE CAN EXPECT
SOME GUSTY WINDS OVER 40 MPH THIS AFTERNOON ALONG WITH BRIEF
MODERATE TO HEAVY RAIN. MAYBE SOME BLOWING DUST AS WELL. THIS
AFTERNOON AND EVENING MIGHT BECOME A BIT INTERESTING CONVECTIVELY
SPEAKING.

.PREVIOUS 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...
EASTERLY WINDS...VAR BETWEEN NE AND SE AT TIMES...WILL BEGIN TO VEER
TO SOUTH AND EVENTUALLY WESTERLY HEADINGS MIDDAY THRU THIS AFTERNOON.
ANOTHER STORM SYSTEM WILL TRANSITION IN FROM THE NORTHWEST AND
SUPPORT SHOWER/THUNDER DEVELOPMENT IN THE AFTERNOON ALONG WITH
WIDESPREAD BREEZINESS. PRECIP COVERAGE AT THIS TIME LOOKS TO BE
SPOTTY...SO CONTINUED VC MENTIONING IN THE 12Z TAFS. GUSTS INTO THE
20 TO 25KT RANGE WILL BE POSSIBLE...WITH MORE ERRATIC AND SLIGHTLY
STRONGER WINDS IN THE VICINITY OF SHOWERS/THUNDER. BEST WINDOW FOR
PRECIP ACTIVITY STILL LOOKS TO BE 30/22Z THROUGH 01/03Z. CLOUDS WILL
CONTINUE TO INCREASE THIS MORNING...DEVELOPING INTO SCT AND BKN MID
LEVEL COVERAGE 7 TO 9KFT OR SO.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
ELEVATED WEST WINDS TO CONTINUE FOR KIPL THROUGHOUT THE DAY...WITH
GUSTS OF 25KTS POSSIBLE. SOUTHERLY WINDS WILL TRANSITION TO
NORTHWESTERLY FOR KBLH AS ANOTHER STORM SYSTEM PASSES THROUGH THE
REGION. SHOWER/STORM CHANCES GENERALLY REMAIN EAST OF THE CO RIVER
THROUGHOUT THE DAY...BUT GUSTY STORM WINDS CANNOT BE RULED OUT FOR
KBLH.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
A WARMER AIRMASS WILL TRANSITION INTO THE AREA FROM THE WEST...WITH
HIGH TEMPERATURES PEAKING INTO THE MID TO UPPER 90S BY
WEDNESDAY AND THURSDAY FOR MANY LOWER DESERT SITES. MINIMUM
HUMIDITIES WILL DRY BELOW 15 PERCENT FOR MONDAY...BELOW 10 PERCENT
FOR TUESDAY AND WIDESPREAD SINGLE DIGIT PERCENTAGES POSSIBLE BY
MIDWEEK. OVERNIGHT RECOVERIES WILL RANGE FROM FAIR TO MODEST
THROUGHOUT THE WEEK. AFTER A FEW DAY BREAK FROM ELEVATED
WINDS...BREEZY SOUTH AND SOUTHWESTERLY WINDS IN THE WESTERN DISTRICTS
WILL RETURN AFTER WEDNESDAY AND SPREAD ACROSS THE REGION THURSDAY AND
FRIDAY AS ANOTHER LOW PRESSURE AREA APPROACHES FROM THE PACIFIC.

&&

.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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