Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 010355
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
855 PM MST SAT APR 30 2016

.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL MOVE INTO THE REGION FROM THE NORTH
TONIGHT INTO SUNDAY. THIS WILL RESULT IN A CHANCE OF AFTERNOON AND
EVENING SHOWERS AND THUNDERSTORMS...PARTICULARLY OVER THE MOUNTAINS
OF EASTERN ARIZONA SUNDAY. 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 LATE NEXT WEEK OR NEXT WEEKEND.

&&

.DISCUSSION...
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WERE PREVALENT THIS
AFTERNOON ACROSS PORTIONS OF THE AZ LOWER DESERTS...INCLUDING THE
PHOENIX AREA. THE STORMS DEVELOPED IN AN AREA CHARACTERIZED BY VERY
STRONG ASCENT AHEAD OF TIGHT VORT MAX ACROSS THE WESTERN AZ DESERTS.
LATEST WV IMAGERY AND STREAMLINE ANALYSIS SHOWS THE VORT SHEARING OUT
AS IT TRANSLATES EASTWARD ACROSS CENTRAL AZ. THE LOSS OF LARGER
SCALE ASCENT AND DIABATIC HEATING HAS CONSEQUENTLY RESULTED IN A
RAPID DECREASE IN INSTABILITY AND COVERAGE OF SHOWERS AND STORMS THIS
EVENING. LATEST HI-RES GUIDANCE INCLUDING THE HRRR CONTINUE TO SHOW
THE EXISTING ACTIVITY...MAINLY CONCENTRATED EAST OF THE PHOENIX AREA
DISSIPATING OVERNIGHT. CURRENT FORECAST HANDLES THIS WELL...THOUGH
SOME ADJUSTMENTS WERE MADE TO THE SHORT-TERM TEMPERATURES TO ACCOUNT
FOR THE RAIN-COOLED AIR EARLY THIS EVENING.

&&

.PREVIOUS DISCUSSION...
AT 2 PM A VIGOROUS UPPER LEVEL LOW PRESSURE SYSTEM WAS MOVING INTO
ARIZONA...WITH THE LOW CENTER PUSHING EASTWARD AND INTO WEST CENTRAL
AZ. BEST AREA OF PVA/DIFLUENCE AND Q-CONVERGENCE WAS FOCUSED ACROSS
WEST-CENTRAL AND SOUTH-CENTRAL ARIZONA EARLY THIS AFTERNOON AND
LATEST SPC MESOANALYSIS GRAPHIC INDICATED THAT BEST INSTABILITY WAS
ALSO IN THAT AREA WITH OVER 500 J/KG OF MLCAPE PRESENT AT 1 PM. WITH
PWAT VALUES APPROACHING THREE QUARTERS OF AN INCH OUT WEST WE HAVE A
GOOD COMBINATION OF MOISTURE...INSTABILITY AND LIFT AND NOT
SURPRISINGLY...SCATTERED SHOWERS AND THUNDERSTORMS HAVE DEVELOPED
AHEAD OF THE LOW...ACROSS EASTERN LA PAZ AND YUMA COUNTIES AND
WESTERN MARICOPA COUNTY. SOME OF THE STRONGEST CELLS ARE IN THE
PRIME DIFLUENT AREA AHEAD OF THE LOW CENTER OVER NERN LA PAZ COUNTY.
SO FAR STORMS HAVE BEEN SUB SEVERE AND WE HAVE COVERED THEM WITH
SIGNIFICANT WEATHER ADVISORIES AND SOCIAL MEDIA POSTS. FOR THE REST
OF THE AFTERNOON AND INTO THE EVENING THERE WILL CONTINUE TO BE A
CHANCE OF SHOWERS AND THUNDERSTORMS ACROSS SOUTH CENTRAL
ARIZONA...WITH SLIGHT CHANCES FURTHER WEST IN THE AREAS BEHIND THE
PASSING UPPER LOW. HIGH TEMPERATURES TODAY WILL BE ON THE COOL SIDE
AS THE UPPER LOW AND ASSOCIATED CLOUD COVER MOVES ACROSS THE
AREA...WITH MOST READINGS IN THE UPPER 70S TO LOW 80S OVER THE LOWER
DESERTS. SCATTERED SHOWERS/STORMS WILL CONTINUE TO INCREASE ACROSS
THE GREATER PHOENIX AREA DURING THE MID TO LATE AFTERNOON...THEN
CONTINUE INTO THE EVENING HOURS BEFORE STARTING TO DISSIPATE.

LATER TONIGHT INTO SUNDAY...AS THE EVENING WEARS ON AND WE MOVE INTO
SUNDAY...THE MAIN UPPER LOW CONTINUES TO SHIFT OFF TO THE
EAST/NORTHEAST AND THE DYNAMICAL FORCING BECOMES MINIMAL WITH TIME.
MID LEVEL Q CONVERGENCE BULLSEYE MOVES INTO NEW MEXICO OVERNIGHT
WITH A MORE SUBSIDENT AREA OF Q DIVERGENCE MOVING INTO THE LOWER
CENTRAL DESERTS. NVA/DVV OVERSPREAD THE AREA FROM THE WEST...AND THE
MAIN UPPER JET AXIS MOVES WELL OFF TO THE EAST AND OFFERS NO SUPPORT
FOR UVV. PRETTY MUCH...BY LATE NIGHT TONIGHT AND SUNDAY WE ARE LEFT
WITH THERMODYNAMIC SUPPORT FOR SHOWERS/CONVECTION AS COOL AIR ALOFT
REMAINS IN PLACE OVER AN AREA OF ELEVATED LOW LEVEL MOISTURE.
FORECAST CAPE VALUES HOWEVER ARE LOW COMPARED TO THIS
AFTERNOON...MOSTLY LESS THAN 200 J/KG AND THE BEST CAPE STAYS ACROSS
HIGH TERRAIN AREAS NORTH AND EAST OF PHOENIX. WE WILL CONTINUE TO
KEEP A CHANCE OF SHOWERS OR STORMS GOING OVER SRN GILA COUNTY
THROUGH THE DAY ON SUNDAY BUT LOWER POPS TO THE 15-20 PERCENT
BALLPARK OVER THE LOWER CENTRAL DESERTS WITH TIME...WITH POPS OVER
THE FAR WESTERN DESERTS AND SERN CA LOWERING INTO THE SINGLE DIGITS.
WE SHOULD SEE SOME COOLING ON SUNDAY...GIVEN THE NATURE OF THE COLD
POOL ALOFT MOVING ACROSS THE AREA AND THE CLOUD COVER...MOST
SIGNIFICANT OVER SOUTH CENTRAL AZ...AND WE WILL LOWER OUR HIGHS A
COUPLE DEGREES WITH PHOENIX DROPPING TO A HIGH OF JUST 80 ON SUNDAY.
ACTUALLY...WOULD NOT BE SURPRISED IF THE HIGH IN PHOENIX SUNDAY
REMAINS IN THE 70S.

ALTHOUGH THE MAIN LOW WILL CONTINUE TO PUSH OFF TO THE EAST SUNDAY
NIGHT...ONE MORE WEAK BAGGY TROF OVER SRN CA/SRN NV WILL SLIDE EAST
AND INTO NORTHERN ARIZONA KEEPING A SLIGHT CHANCE OF EVENING SHOWERS
IN PLAY OVER THE HIGHER TERRAIN OF JOSHUA TREE NP AS WELL AS AREAS
NORTH AND EAST OF PHOENIX. OTHERWISE EXPECT POPS IN THE SINGLE
DIGITS OVER THE LOWER AZ AND CA DESERTS.

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 THROUGH SATURDAY...

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...

WITH A LOW PRESSURE STORM SYSTEM SWEEPING THROUGH THE REGION ON
SATURDAY AFTERNOON AND EVENING EXPECT SOME SCATTERED RAIN SHOWERS
AND THUNDERSTORMS AND VERY BREEZY SOUTH TO SOUTHWEST WINDS WITH
PERIODIC GUSTS OF 20 TO 25KTS. THROUGH ABOUT 03Z. EXPECT THE LOWEST
CIGS TO VARY FROM 7K TO 11K FT. EXPECT WEST TO SOUTHWEST WINDS TO
TAPER OFF TO 7 TO 10KTS. TONIGHT WITH BROKEN CIGS AT ABOUT 9K FT.
LIGHT EASTERLY COMPONENT WINDS WILL BE FAVORED BEGINNING LATE
SATURDAY NIGHT AND EARLY SUNDAY MORNING.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

VERY BREEZY TO WINDY NORTHERLY COMPONENT WINDS WITH SOME GUSTS TO
20KTS. ARE EXPECTED FOR KBLH ALONG WITH RAIN SHOWERS AND
THUNDERSTORMS IN THE VICINITY THROUGH EARLY EVENING. BROKEN TO
OVERCAST CIGS FROM 7 TO 11K FT. ARE ALSO LIKELY THROUGH THIS
EVENING. WINDY WEST AND NORTHWESTERLY WINDS WITH GUSTS OF 25 TO
30KTS ARE EXPECTED FOR KIPL WITH CLEAR TO PARTLY CLOUDY SKIES.
LIGHTER WESTERLY TO NORTHWESTERLY WINDS ARE EXPECTED FOR BOTH SITES
BY 03 TO 04Z.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...

WITH A DRIER AND WARMER AIRMASS IN PLACE EXPECT ABOVE NORMAL
TEMPERATURES THROUGH THURSDAY WITH THE HOTTEST DAY ON WEDNESDAY
REACHING INTO THE MID TO UPPER 90S IN THE LOWER DESERTS. EXPECT
ELEVATED FIRE DANGER ON WEDNESDAY AND THURSDAY WITH MINIMUM
HUMIDITIES FALLING TO THE 6 TO 11 PERCENT RANGE AND BREEZY SOUTHERLY
TO SOUTHWESTERLY WINDS SPREADING THROUGH THE LOWER DESERTS.
CONDITIONS WILL IMPROVE ON FRIDAY AND SATURDAY WHEN THE NEXT STORM
SYSTEM WILL COOL HIGH TEMPERATURES TO THE LOW TO MID 80S WITH
MINIMUM HUMIDITIES IN THE MID TEEN TO MID 20 PERCENT RANGE BY
SATURDAY.

&&

.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...HIRSCH
PREVIOUS DISCUSSION...CB/VASQUEZ
AVIATION...SAWTELLE
FIRE WEATHER...SAWTELLE



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