Area Forecast Discussion
Issued by NWS Phoenix, AZ

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
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 022155 AAA
AFDPSR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PHOENIX AZ
255 PM MST TUE SEP 2 2014

.UPDATE...
UPDATED AVIATION AND FIRE WEATHER SECTIONS.

&&

.SYNOPSIS...
MOISTURE WILL GRADUALLY RETURN TO THE REGION BEGINNING
THURSDAY...WITH A MUCH MORE HUMID AIRMASS OVERSPREADING THE AREA BY
THE WEEKEND. THUNDERSTORM CHANCES WILL FIRST START OVER SOUTHEAST
ARIZONA AND THE HIGHER TERRAIN TO THE NORTH AND EAST THURSDAY...BUT
INCREASE SIGNIFICANTLY OVER THE REMAINDER OF THE AREA BY THE
WEEKEND. WITH THE INCREASING MOISTURE...TEMPERATURE WILL EVENTUALLY
FALL BACK OR SLIGHTLY BELOW AVERAGE BY EARLY NEXT WEEK.

&&

.DISCUSSION...
A SPRAWLING HIGH PRESSURE RIDGE WITH H5 HEIGHTS NEAR 592DM CONTINUES
TO ENVELOP AN AREA FROM THE SOUTHERN PLAINS THROUGH SWRN CONUS THIS
AFTERNOON (AS HAS BEEN THE CASE FOR THE PAST SEVERAL DAYS).
SUBTROPICAL MOISTURE REMAINS TRAPPED THROUGH CNTRL/SRN
SONORA/CHIHUAHUA WITH 12Z KTWC/KPSR SOUNDING DATA SAMPLING PWATS
UNDER 0.75 INCHES AND SFC-H7 MIXING RATIOS ONLY IN THE 5-6 G/KG
RANGE. MEANWHILE...A PROGRESSIVE WAVE ACROSS THE PACIFIC NORTHWEST
AND NRN/CNTRL ROCKIES WILL ACTUALLY BECOME THE IMPETUS TO SHIFT THE
CENTER OF THE AFOREMENTIONED SUBTROPICAL HIGH EASTWARD...ALLOWING A
DEEPER SOUTHERLY MONSOON WIND COMPONENT AND MOISTURE SURGE BACK INTO
THE SOUTHWEST LATE THIS WEEK INTO EARLY NEXT WEEK.

THOUGH TOMORROW NIGHT...THERE WILL BE LITTLE CHANGE IN THE
THERMODYNAMIC STRUCTURE OF THE ATMOSPHERE OVER THE ENTIRE FORECAST
AREA...AND HAVE CONTINUED TO FOLLOW A NEAR PERSISTENCE FORECAST. THE
FIRST INKLINGS OF MOISTURE RETURN WILL COMMENCE THURSDAY
MORNING...PRIMARILY IN THE MIDLEVELS AND POTENTIALLY LOOSELY TIED TO
DISTANT OUTFLOWS FROM NRN MEXICO/FAR SERN ARIZONA. HAVE ALMOST
COMPLETELY DISCOUNTED THE RECENT OVERZEALOUS GFS QPF FIELDS FORECAST
FOR THURSDAY MORNING GIVEN GOOD AGREEMENT OF SUBSTANTIAL DRY AIR
STILL RESIDING IN THE SFC-H7 LAYER. THUS WHILE VIRGA AND SOME HIGHER
ELEVATION SPRINKLES ARE POSSIBLE DURING THE MORNING HOURS...HAVE
HEDGED CLOSER TO A SREF/ECMWF BLEND FOCUSING FAR BETTER CONVECTIVE
INITIATION CHANCES DURING AFTERNOON PEAK HEATING OVER HIGHER TERRAIN
FEATURES. LOWER ELEVATIONS MAY STILL BE A TAD TOO DRY THURSDAY
EVENING WITH BOUNDARY LAYER MIXING RATIOS ONLY SNIFFING 10
G/KG...HOWEVER STRONGER OUTFLOWS WITH BLOWING DUST WILL STILL BE A
THREAT GIVEN DEEP INVERTED-V SOUNDING PROFILES.

THE FORECAST FOR FRIDAY IS A BIT TRICKIER...AS BETTER LOW LEVEL
MOISTURE PROFILES SHOULD SPREAD NORTH BUT THE MAGNITUDE AND
POSITIONING OF UPPER LEVEL SUPPORT REMAINS IN QUESTION. ONE LARGER
WILD CARD IS THE CIRCULATION REMNANTS OF TROPICAL SYSTEM DOLLY FROM
THE GULF OF MEXICO CROSSING WEST OVER THE MEXICAN PENINSULA. WHILE
GLOBAL MODELS START LOSING ANY DEFINED CIRCULATION OVER THE
MOUNTAINS...THERE IS SOME EVIDENCE OF A LINGERING INVERTED TROUGHING
AND DIFLUENCE HEADING INTO CHIHUAHUA/SONORA LATE FRIDAY. MADE SOME
MODEST INCREASES TO POPS FRIDAY EVENING...THOUGH HOLDING OFF THE
MORE APPRECIABLE RAINFALL CHANCES UNTIL THE WEEKEND.

SATURDAY INTO EARLY NEXT WEEK...SOME MEASURE OF TROPICAL INFLUENCE
IS LOOKING MORE POSSIBLE AS THE COMBINATION OF STRONGER UPPER
DIFLUENCE (SOME INPUT FROM TS DOLLY) AND DEEPER TROPICAL MOISTURE
INFLUX FROM EAST PACIFIC TROPICAL SYSTEM NORBERT MAY MEET OVER THE
FORECAST AREA. HOWEVER...THE LATEST 12Z AND 18Z HURRICANE CENTER
CONSENSUS MODEL TRACKS KEEP THE CENTER OF NORBERT WELL TO THE
SOUTHWEST OF THE BAJA PENINSULA...AND MOISTURE INFLUENCE MAY BE MORE
LIMITED OR SECONDARY THAN PREVIOUS GLOBAL SCALE MODELS MAY HAVE
PRESUMED. REGARDLESS...PRECIP CHANCES WERE FURTHER INCREASED GIVEN
OVERWHELMING OPERATIONAL AND ENSEMBLE MODEL CONSENSUS ON MOISTURE
AND CAPE/OMEGA FIELDS SUNDAY AND MONDAY. HOWEVER GIVEN THE TIME
FRAME 5 TO 6 DAYS OUT...KEPT POPS CAPPED AROUND 50 PERCENT FEELING
ONE OF THESE DAYS WILL BE VERY CONVECTIVE ACTIVE AND OTHER
POTENTIALLY NOT SO ACTIVE.

SOME DISCREPANCIES REMAIN IN MOISTURE PLACEMENT AND INFLUENCE OF DRY
AIR INTRUDING FROM A TROUGH TO OUR NW BY THE MIDDLE OF NEXT WEEK.
MANY 12Z OPERATIONAL MODELS DEPICT RATHER RAPID DRYING IN NWLY FLOW
AS EARLY AS TUESDAY...THOUGH CERTAINLY NOT ALL ENSEMBLE MEMBERS
SUPPORT SUCH AN IDEA OF STRONGER TROUGHING AND NORTHWEST FLOW.
NEVERTHELESS...WITH THE UPTICK IN STORM ACTIVITY AND EXPECTATION OF
MOSTLY TO CONSIDERABLY CLOUDY SKIES...A COOL DOWN OF WELCOME
PROPORTIONS WILL RESULT FOR THE WEEKEND...WITH SEVERAL BEST
PERFORMING AND CONSENSUS TEMPERATURE FORECASTS COOLING MUCH OF THE
FORECAST AREA BELOW 100F BY MONDAY AND BEYOND.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...AND
SOUTHWEST ARIZONA AND SOUTHEAST CALIFORNIA INCLUDING KIPL AND KBLH...

EXPECT CLEAR SKIES TONIGHT FOLLOWED BY SOME CUMULUS DEVELOPMENT
WEDNESDAY AFTERNOON. LIGHT DIURNAL WIND PATTERNS WILL CONTINUE.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
FRIDAY THROUGH TUESDAY...
MONSOON MOISTURE WILL CONTINUE TO INCREASE AND SPREAD WESTWARD
REACHING THE LOWER DESERTS OF SOUTHEAST CALIFORNIA BY SATURDAY.
STORM CHANCES CONTINUE THROUGH MONDAY BEFORE TRENDING DOWNWARD
TUESDAY. HUMIDITIES WILL FOLLOW A SIMILAR TREND.
MEANWHILE...TEMPERATURES TREND DOWNWARD. WINDS WILL FOLLOW FAMILIAR
SUMMERTIME SLOPE-VALLEY PATTERNS BUT WITH SIGNIFICANT DISRUPTIONS
DUE TO THUNDERSTORM ACTIVITY.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...MO/NOLTE
AVIATION...AJ
FIRE WEATHER...AJ






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