Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 190326
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
830 PM MST FRI APR 18 2014

.SYNOPSIS...
A PACIFIC STORM SYSTEM WILL AFFECT THE AREA TONIGHT AND SATURDAY
BRINGING EXTENSIVE CLOUDS...INCREASED MOISTURE AND LOCALIZED CHANCES
FOR SHOWERS THROUGH SATURDAY AFTERNOON. BEST CHANCES FOR SHOWERS
AND THUNDERSTORMS WILL OCCUR ON SATURDAY ACROSS CENTRAL AND EASTERN
ARIZONA. DAYTIME TEMPERATURES THROUGH SATURDAY WILL END UP NEAR
SEASONAL VALUES...HOWEVER QUICKLY WARMING BACK INTO THE 90S EARLY
NEXT WEEK AFTER THE STORM SYSTEM HAS PASSED.

&&

.DISCUSSION...
THE PACIFIC LOW PRESSURE CENTER WAS LOCATED NEAR IMPERIAL CA AT 03Z
AND WILL CONTINUE TO MOVE EAST AND ACROSS CENTRAL AZ SATURDAY
AFTERNOON. ALTHOUGH THE AIRMASS MOISTURE UP A BIT FROM HIGHER PRECIP
WATER ADVECTION FRIDAY AFTERNOON...MOST DYNAMICS/UPPER LEVEL SUPPORT
FOR SHOWERS WILL BE RELEGATED TO SOUTHEAST AZ TONIGHT...MAINLY EAST
AND SOUTHEAST OF PHOENIX AND ESPECIALLY NEAR THE AZ SOUTHEAST
CORNER. THEREFORE THERE IS A MINIMAL CHANCE OF A LIGHT SHOWERS OR
SPRINKLES OVERNIGHT IN OUR FORECAST AREA.

AS THE COLD CORE OF THE UPPER LOW CENTER TRACKS ACROSS CENTRAL AZ
SATURDAY...AFTERNOON INSTABILITY COMBINED WITH CURVATURE EFFECTS OF
THE TROF SHOULD LEAD TO ANOTHER THREAT OF AFTERNOON SHOWERS AND
POSSIBLE THUNDERSTORMS...MAINLY ACROSS SOUTH CENTRAL AZ INCLUDING
PHOENIX. PARTS OF SOUTHEAST CA AND THE COLORADO RIVER VALLEY
SATURDAY AFTERNOON SHOULD BE UNDER THE STABILIZING SUBSIDENCE FIELDS
FOUND ON THE BACKSIDE OF THE TROF.

CURRENT FORECASTS LOOK OK FOR NOW. NO UPDATES NECESSARY. PREVIOUS
DISCUSSION BELOW STILL APPLIES.

.PREVIOUS DISCUSSION...118 PM MST...
THE PACIFIC LOW PRESSURE SYSTEM HAS PROGRESSED INLAND INTO SOUTHERN
CALIFORNIA SINCE THIS MORNING WITH THE LOW CENTER RIGHT OVER SAN
DIEGO. NEARLY UNIDIRECTIONAL SOUTHERLY FLOW OVER MUCH OF ARIZONA
CONTINUES TO ADVECT IN MOISTURE...MAINLY ABOVE 700MB. CURRENT WATER
VAPOR IMAGERY SHOWS AN ORGANIZED SYNOPTIC LOW STRUCTURE WITH A
BAROCLINIC LEAF STRETCHING FROM SONORA MEXICO THROUGH EASTERN AND
NORTHERN ARIZONA. BROAD ASCENT ENCOMPASSES MUCH OF ARIZONA EARLY
THIS AFTERNOON IN RESPONSE TO A REGION OF UPPER DIFLUENCE NORTH OF
AN UPPER JET MAX NOSING INTO SOUTHEAST ARIZONA. AS A RESULT...
EXTENSIVE CLOUDINESS CONTINUES TO AFFECT THE REGION AS WELL AS
ISOLATED LIGHT SHOWERS OR SPRINKLES. LATE THIS MORNING...A SMALL
CLUSTER OF LIGHT SHOWERS DEVELOPED ACROSS NORTHERN PIMA COUNTY
ASSOCIATED WITH A PV ANOMALY AND A KINK SEEN IN THE 500MB HEIGHT
FIELD. FOR THE MOST PART...ANY SHOWERS TODAY WILL HAVE A DIFFICULT
TIME REACHING THE SURFACE DUE TO DRY AIR BELOW 700MB AS SHOWN BY
AREA THE INVERTED V STRUCTURE ON FORECAST SOUNDINGS. GUSTY OUTFLOW
WINDS NEAR 40MPH ALREADY OCCURRED WITH THE FIRST CLUSTER OF SHOWERS
THAT MOVED ACROSS PHOENIX AND ANY FURTHER SHOWER ACTIVITY TODAY WILL
BRING THE POTENTIAL FOR GUSTY WINDS AND POSSIBLY BLOWING DUST.

FURTHER WEST NEAR THE LOW CENTER...COOLER MID LEVELS AND STEEPER
LAPSE RATES REPRESENT A SLIGHTLY MORE UNSTABLE ENVIRONMENT WHICH MAY
GIVE RISE TO ISOLATED SHOWERS AND POSSIBLY A THUNDERSTORM OR TWO BY
MID AFTERNOON ACROSS SOUTHEAST CALIFORNIA. EARLY MORNING RUNS OF THE
HI-RES HRRR AND LOCAL HI-RES MODELS SHOWED CELLS BLOSSOMING BY
AROUND 21Z THIS AFTERNOON ACROSS SOUTHEAST CALIFORNIA...BUT UPDATED
MODEL RUNS HAVE BACKED OFF ON COVERAGE. STILL THINKING 10-15 POPS IN
THIS AREA FOR THIS AFTERNOON AND EARLY EVENING IS A GOOD BET...BUT
WITH THE FAIRLY DRY AIR BELOW 700MB...RAINFALL AMOUNTS SHOULD MAINLY
BE IN THE TRACE TO A COUPLE HUNDREDTH OF AN INCH CATEGORY.

TONIGHT THOUGH SATURDAY AFTERNOON...THE COLD CORE ALOFT PULLS TO THE
EAST OF THE SHORTWAVE AND BECOMES BETTER ALIGNED WITH THE PV ANOMALY
AS THE BULK OF THE ENTIRE WAVE LIFTS AND EJECTS OVER ARIZONA. DURING
THIS TRANSITION...RENEWED VORTICITY ADVECTION AND ASCENT WILL ROTATE
THROUGH THE TROUGH WHILE LAPSE RATES STEEPEN IN THE PRESENCE OF
RESIDUAL MOISTURE. A FEW HIGH RESOLUTION MODELS AND SREF
PROBABILITIES SUGGEST THE FIRST WAVE OF UVV/SHOWERS ROTATING NORTH
INTO CNTRL ARIZONA AS EARLY AS SUNRISE SATURDAY. SFC HEATING UNDER
THE COLD CORE DURING THE DAY MAY VERY WELL LEAD TO SUBSTANTIAL
INSTABILITY (SBCAPE AOA 250 J/KG AND LI/S AOB -2)...ESPECIALLY OVER
HIGHER TERRAIN. CONCEPTUALLY AND EVIDENTIALLY THROUGH MODEL
OUTPUT...POPS WERE INCREASED SIGNIFICANTLY FOR POINTS EAST OF
PHOENIX SATURDAY AFTERNOON.

THE AFOREMENTIONED WAVE WILL RAPIDLY WEAKEN AND LIFT INTO THE CNTRL
ROCKIES/PLAINS ON SUNDAY...ALLOWING RIDGING TO QUICKLY REBUILD OVER
THE FORECAST AREA. H5 HEIGHTS AOA 582DM WILL BECOME MAXIMIZED ON
MONDAY AFTERNOON YIELDING HIGHS IN THE MID/UPPER 90S FOR LOWER
ELEVATION LOCATIONS. THE NEXT PROGRESSIVE PACIFIC WAVE WILL MOVE
ONSHORE TUESDAY AFTERNOON...THOUGH MODEL OUTPUT AND TRENDS KEEP THE
VAST MAJORITY OF JET ENERGY AND MOISTURE FROM CNTRL CALIFORNIA
NORTHWARD. IF ANYTHING...THE FORWARD SPEED AND ARRIVAL INTO THE WRN
CONUS MAY BE A BIT SLOWER...AND HAVE DELAYED THE LOCAL ONSET OF
FROPA AND COOLING TO BEYOND TUESDAY. THE GREATEST IMPACT OF THIS
SYSTEM FOR ARIZONA MAY BE GUSTY WINDS ALONG AND IMMEDIATELY BEHIND
THE FRONTAL BOUNDARY AS THE PRESSURE GRADIENT TIGHTENS TUESDAY
AFTERNOON AND EVENING. SOUTHEAST CALIFORNIA AND THE LOWER COLORADO
RIVER VALLEY WOULD LIKELY EXPERIENCE THE MOST PROLONGED AND FREQUENT
HIGHER GUSTS.

WHILE HEIGHTS ALOFT WILL BE TEMPERED BACK INTO A 570-576DM RANGE FOR
THE REMAINDER OF THE WEEK UNDER QUASI-ZONAL FLOW...FEEL THE NET
EFFECT ON TEMPERATURES WILL ONLY BE LIMITED TO KEEPING DAILY
READINGS NEAR CLIMATOLOGY. ENSEMBLE SPREAD IS RELATIVELY LOW IN THE
DAY 5-8 RANGE...SO FORECAST CONFIDENCE IS SOMEWHAT HIGHER THAN
AVERAGE. AT THIS TIME...PRECIPITATION CHANCES APPEAR ALMOST
NON-EXISTENT FOR PRETTY MUCH THE ENTIRETY OF NEXT WEEK.

&&

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









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