Area Forecast Discussion
Issued by NWS Phoenix, AZ

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS65 KPSR 182018
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
118 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 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...
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...

INCREASING CLOUDS...MOISTURE AND INSTABILITY ACROSS THE AREA WITH
THE APPROACH OF A PACIFIC LOW PRESSURE SYSTEM OFF THE SOUTHERN
CALIFORNIA COAST. WINDS WILL FAVOR THE SOUTH OR SOUTHEAST THROUGH
THE AFTERNOON ...WITH OCCASIONAL GUSTS OVER 25KT...OCCASIONALLY
VEERING TO THE SOUTHWEST...ALONG WITH BROKEN CLOUD DECKS GENERALLY
AOB 12KFT AND LOCAL CIGS DOWN TO 10KFT AT TIMES. DRIER NATURE OF THE
ATMOSPHERE WILL LEAD TO VIRGA/ISOLATED AFTN THUNDERSTORMS WITH
STRONG GUSTY DOWNDRAFTS IN EXCESS OF 30KT POSSIBLE NEAR
KPHX/KIWA/KSDL. OUTFLOW HAS POTENTIAL TO GENERATE BLOWING DUST
ACROSS LOWER DESERTS AND LOWER VISIBILITY DOWN TO 4SM...BUT NOT
PLACING ANY REDUCTIONS IN TAFS THIS TIME. SHOWER AND THUNDERSTORM
ACTIVITY TAPERS OFF OVER WESTERN TAF SITES KBLH/KIPL OVERNIGHT...BUT
WILL LINGER ACROSS SOUTH-CENTRAL ARIZONA INTO SATURDAY MORNING.

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





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.