Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 190942
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
240 AM MST SAT APR 19 2014

.SYNOPSIS...
A PACIFIC STORM SYSTEM WILL CONTINUE TO AFFECT THE AREA TODAY WITH
MORE EXTENSIVE CLOUDINESS AND LOCALIZED CHANCES FOR SHOWERS AND
THUNDERSTORMS. THE BEST CHANCES FOR RAINFALL WILL OCCUR ACROSS
CENTRAL AND EASTERN ARIZONA THROUGH THIS AFTERNOON. TEMPERATURES
TODAY WILL END UP NEAR SEASONAL VALUES...HOWEVER QUICKLY WARM BACK
INTO THE 90S EARLY NEXT WEEK AFTER THE STORM SYSTEM PASSES TO THE
NORTHEAST.

&&

.DISCUSSION...
TWO DISTINCT VORTICITY CENTERS CAN BE SEEN IN REGIONAL RADAR/WV
SATELLITE IMAGERY EARLY THIS MORNING ROTATING ABOUT THE LARGER SCALE
CIRCULATION CENTER/COLD CORE PROGRESSING INTO SWRN ARIZONA. THE
INITIAL VORT MAX HAS LIFTED TO NEAR LAKE HAVASU UNDERGOING
SUBSTANTIAL STRETCHING AND DEFORMATION...WHILE A SECONDARY
INTENSIFYING VORTICITY CENTER/PV ANOMALY CORE WAS LIFTING TO THE
NORTH ACROSS THE BAJA PENINSULA AHEAD OF THE COLD CORE ALOFT AND
COLLOCATED WITHIN THE CORRIDOR OF A STRONGER JET STREAK. RECENT
SATELLITE LOOPS ALSO INDICATE MODEST CLOUD TOP COOLING AHEAD OF THIS
LATTER VORTICITY CENTER WITH OBJECTIVE ANALYSIS DEPICTING INCREASING
DIFLUENCE AND ASCENT BEGINNING TO ENVELOPE THE REGION. IN FACT...A
NICE CLUSTER OF THUNDERSTORMS HAVE FORMED IN NERN SONORA WHERE JET
DYNAMICS HAVE BECOME JUXTAPOSED WITH A SMALL LOW LEVEL MOISTURE
SURGE...STEEPENING LAPSE RATES...AND RESULTANT MUCAPES AOA 500 J/KG.

WHILE PROPAGATION TRAJECTORIES WILL TAKE THIS INITIAL CLUSTER OF
STORMS ONLY THOUGH FAR SERN ARIZONA THIS MORNING...OVERALL MIDLEVEL
LAPSE RATES WILL RAPIDLY STEEPEN (AOA 7.5 C/KM) ACROSS MUCH OF THE
FORECAST AREA AS THE COLD CORE MOVES DIRECTLY OVERHEAD. COMBINED
WITH PERSISTENT UVV...SFC HEATING...AND MOISTURE ADVECTION...THE
ATMOSPHERE ACROSS THE EASTERN PARTS OF THE CWA WILL BECOME
SUPPORTIVE FOR SUSTAINED DEEP CONVECTION THROUGH THE AFTERNOON
HOURS. SREF PROBABILITIES STILL STRONGLY SHOW ARGUMENTS FOR LI/S
NEAR -2C AND SBCAPES BETWEEN 250 AND 500 J/KG BY EARLY AFTERNOON.
HIGH RESOLUTIONS MODELS ALSO FORECAST ISOLD/SCT SHOWERS AND STORMS
TO MATERIALIZE THROUGH CNTRL AND ERN ARIZONA AHEAD OF THE VORTICITY
CENTER AND WITHIN THE CYCLONIC CURVATURE REGION OF THE JET.

WHILE ALL THESE THERMODYNAMIC PARAMETERS APPEAR FAVORABLE FOR MORE
WIDESPREAD CONVECTION...BOUNDARY LAYER MOISTURE WILL STILL BE
PROBLEMATIC (PARTICULARLY AT LOWER ELEVATION LOCATIONS) WITH MIXING
RATIOS ONLY APPROACHING 7 G/KG ADVECTING INTO THE AREA. THUS...WITH
CLOUD BASES ONLY FALLING TO AROUND THE H7 LEVEL...SUBSTANTIAL
SUBCLOUD DRY AIR WILL STILL EXIST AND ONLY THE MORE WIDELY SPACED
HEAVIER SHOWERS MAY LEAD TO ACCUMULATING RAINFALL. WIDESPREAD SVR
WEATHER IS NOT EXPECTED WITH ANY STORMS THAT DO FORM AS BULK 0-6KM
SHEAR WILL BECOME ALMOST NON-EXISTENT WITHIN THE LARGER SCALE
CIRCULATION CENTER AND 0-1KM SHEAR VECTORS WILL BE SIMILARLY
WEAK...HOWEVER MUCH LIKE FRIDAY AFTERNOON EVAPORATIONAL COOLING AND
DESCENT OF RAIN COOLED AIR COULD LEAD TO VERY ISOLATED STRONGER WIND
GUSTS.

THE CONGLOMERATE OF VORTICITY MAXIMA AND OVERALL CIRCULATION CENTER
WILL WEAKEN AND LIFT NORTHEAST SUNDAY AS HEIGHT RISES AND SUBSIDENCE
SLOWLY BUILD INTO THE SWRN CONUS. ENOUGH RESIDUAL MOISTURE AND
COOLER AIR ALOFT MAY BE PRESENT OVER ERN ARIZONA TO SUPPORT SOME
ISOLD AFTERNOON SHOWERS...PRIMARILY OVER THE WHITE MOUNTAINS BUT
POTENTIALLY CLIPPING THE SAN CARLOS AREA. OTHERWISE...H5 HEIGHTS AOA
582DM WILL BECOME MAXIMIZED ON MONDAY AFTERNOON YIELDING HIGHS IN
THE MID/UPPER 90S FOR LOWER ELEVATION LOCATIONS (AND POSSIBLY
TOUCHING 100 IN PREFERRED LOCATIONS OF FAR WRN ARIZONA).

A WELL DEFINED STOUT PACIFIC WAVE WILL CRASH ASHORE TUESDAY ACROSS
THE PACIFIC NORTHWEST...EVENTUALLY PROGRESSING INTO THE CNTRL/NRN
ROCKIES. MODEL OUTPUT REMAINS VERY CONSISTENT IN KEEPING THE TROUGH
BASE LIMITED TO FAR NORTHERN ARIZONA...WITH THE ENTIRE FORECAST AREA
STUCK IN SUBSIDENT ANTI-CYCLONIC FLOW. BY FAR...THE GREATEST IMPACT
WILL BE STRONG GUSTY WINDS ALONG AND IMMEDIATELY BEHIND THE LOW
LEVEL FRONTAL BOUNDARY AS THE PRESSURE GRADIENT TIGHTENS
SUBSTANTIALLY TUESDAY AFTERNOON AND EVENING. SOUTHEAST CALIFORNIA
AND THE LOWER COLORADO RIVER VALLEY WOULD LIKELY EXPERIENCE THE MOST
PROLONGED AND FREQUENT HIGHER WIND GUSTS.

OPERATIONAL AND ENSEMBLE MODEL SPREAD IS SOMEWHAT HIGHER THAN SEEN
RECENTLY FOR THE END OF NEXT WEEK...HOWEVER STILL REMAINS RELATIVELY
SMALL IN A SEASONAL SENSE. FLAT RIDGING AND/OR QUASI-ZONAL FLOW
SHOULD PREDOMINATE THE GENERAL PATTERN FOR THE MAJORITY OF TIME WITH
H5 HEIGHTS HOVERING NOT FAR FROM 576DM. THIS MODEL AVERAGE SOLUTION
FOR HEIGHTS ALOFT IS SLIGHTLY HIGHER THAN PREVIOUS MODEL
ITERATIONS...AND CONSEQUENTLY HAVE EDGED FORECAST HIGHS SLIGHTLY
WARMER TO JUST ABOVE CLIMATOLOGICAL LEVELS. THERE IS STILL NO
EVIDENCE SUPPORTING ANY PRECIPITATION MUCH OF NEXT WEEK...WITH ONLY
VERY LIMITED OPPORTUNITY POSSIBLY ARRIVING NEXT WEEKEND.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
THROUGH 17Z SAT...BKN CLDS AOA 12 THSD AGL. ISOLATED LIGHT SHOWER.
LIGHT EAST WIND UNDER 9 KNOTS. FROM 17Z SAT TO 23Z SAT...A PACIFIC
LOW PRESSURE SYSTEM WILL TRACK ACROSS CENTRAL AZ THIS PERIOD. A
CHANCE OF A FEW AFTERNOON INSTABILITY SHOWERS AND OR THUNDERSTORMS
IS EXPECTED. LIGHT WIND UNDER 10 KNOTS EXCEPT GUSTY AND ERRATIC NEAR
SHOWERS.


SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
THROUGH 07Z SAT...SCT TO BKN CLDS AOA 12 THSD AGL. ISOLATED LIGHT
SHOWER. SOUTH WIND 5 TO 10 KNOTS. FROM 07Z SAT TO 23Z SAT...SCT CLDS
BASED NEAR 12 THSD AGL. LIGHT SOUTH TO SOUTHWEST WIND UNDER 10
KNOTS.


AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
WESTERLY FLOW ALOFT WILL BRING A WARMING AND DRYING TREND TO THE
REGION THROUGH TUESDAY AS A RIDGE OF HIGH PRESSURE ESTABLISHES OVER
THE INTERMOUNTAIN WEST. WELL ABOVE SEASONAL NORMAL HIGH TEMPERATURES
ARE EXPECTED MONDAY THROUGH TUESDAY. A COOLING TREND IS EXPECTED
WEDNESDAY AND THURSDAY AS A LOW PRESSURE SYSTEM MOVES INTO THE GREAT
BASIN AND PACIFIC NORTHWEST. THE BIGGEST IMPACT WITH THIS SYSTEM
WILL BE AN INCREASE IN WIND AREA-WIDE ON TUESDAY...WITH GUSTS UP TO
35 MPH POSSIBLE...ESPECIALLY ACROSS SOUTHEAST CALIFORNIA. BREEZY
CONDITIONS FROM THE WEST WILL PERSIST WEDNESDAY. MINIMUM HUMIDITY
LEVELS ALSO BOTTOM OUT IN THE SINGLE DIGITS...PRESENTING AN
INCREASED FIRE DANGER THREAT. CONTINUED DRY AND WARMER CONDITIONS
ARE ON TAP FOR FRIDAY AS HIGH PRESSURE ALOFT BUILDS BACK INTO THE
AREA.


&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...MO
AVIATION...VASQUEZ
FIRE WEATHER...MEYERS/CB







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