690
FXUS65 KPSR 130406
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
905 PM MST MON AUG 12 2013
.SYNOPSIS...
DRY WEATHER WILL CONTINUE FOR THE LOWER DESERTS FOR MOST...IF NOT
ALL OF THE WEEK. AFTERNOON AND EVENING THUNDERSTORM CHANCES WILL
REMAIN CONFINED TO THE EASTERN PORTIONS OF THE ARIZONA HIGH TERRAIN.
HIGH PRESSURE WILL GRADUALLY BEGIN TO REBUILD INTO THE SOUTHWEST
STATES...LEADING TO SLOWLY RISING TEMPERATURES AND CONTINUED STORM
CHANCES OVER HIGHER TERRAIN...WITH LITTLE CHANCE FOR RAINFALL OVER
LOWER DESERT COMMUNITIES.
&&
.DISCUSSION...
LITTLE CHANGE IN THE WEATHER PATTERN AGAIN TODAY...AS UPPER TROFFING
TO OUR WEST HAS KEPT A DRY SOUTHWEST FLOW IN PLACE ACROSS SERN CA
AND MOST OF ARIZONA. AS A RESULT VERY DRY AIR REMAINS ACROSS ALL OF
OUR CWA WITH THE EXCEPTION OF ZONE 24 WHERE ISOLATED SHOWERS AND
THUNDERSTORMS DEVELOPED AGAIN THIS AFTERNOON...MAINLY EAST OF GLOBE.
LOW LEVEL MOISTURE BOUNDARY...OR A SORT OF DRYLINE...REMAINS OVER
FAR EASTERN AZ...GRADUALLY PUSHING WESTWARD THEN RETREATING BACK TO
THE EAST DURING THE EVENING HOURS AS DRIER WESTERLY FLOW SETS UP
ACROSS THE DESERTS. EARLY THIS AFTERNOON SURFACE DEWPOINTS AT
PHOENIX WERE IN THE MID 50S AS SURFACE WINDS GUSTED A BIT FROM THE
SOUTHEAST. AT 9 PM DEWPOINTS FELL TO 29 AS WEST WINDS TO 15KT MIXED
TO THE SURFACE AND PUSHED THE MOISTURE BACK TO THE EAST. AT 830 PM
STORMS HAD MOSTLY ENDED ACROSS ZONE 24...AND ALL OF ARIZONA FOR THAT
MATTER...WITH SKIES RAPIDLY CLEARING EAST OF PHOENIX. IR IMAGERY
SHOWED CLEAR SKIES FROM PHOENIX WESTWARD. EXPECT GENLY CLEAR SKIES
REST OF TONIGHT...EXCEPT FOR A FEW LINGERING MID LEVEL DEBRIS CLOUDS
OVER THE HIGHER TERRAIN...AND MOSTLY LIGHT WINDS. FORECASTS IN FINE
SHAPE AND NO UPDATES ARE NEEDED.
.PREVIOUS DISCUSSION...
DESPITE AN INCREASE IN PWATS PER 12Z SOUNDING DATA...BOTH SYNOPTIC
AND MESOSCALE CONDITIONS APPEAR UNFAVORABLE FOR ORGANIZED AND
PERSISTENT DEEP CONVECTION THIS AFTERNOON/EVENING (AND FOR THE NEXT
COUPLE DAYS FOR THAT MATTER). MUCH OF THE INCREASED MOISTURE WAS
SAMPLED IN A 600-700MB LAYER...AS WELL AS IN THE SHALLOW BOUNDARY
LAYER AT LOWER ELEVATIONS WHERE THE MOISTURE GRADIENT/DRYLINE TYPE
BOUNDARY HAS SLOSHED WESTWARD WITH THE OVERNIGHT DRAINAGE
WIND/PRESSURE COMPONENT. HOWEVER...THIS NARROW CORRIDOR OF MOISTURE
ALOFT ABOVE 700MB HAS BEEN JUST SUFFICIENT TO SUPPORT ISOLD PULSE
TYPE CONVECTION OVER SOUTHERN GILA COUNTY IN AN ENVIRONMENT OF
MLCAPE AOA 500 J/KG WITH AMPLE SHEAR...YET LACKING LAPSE RATES IN
THE UNSTABLE LAYER. GIVEN UNSEASONABLY STRONG SWLY 850-300MB FLOW
VECTORS AROUND 20KT AND AN INCREASINGLY HOSTILE ENVIRONMENT FOR
SUSTAINED UPDRAFTS...MOST ACTIVITY SHOULD HAVE WANED OR PROPAGATED
OUT OF THE FORECAST AREA BY THIS EVENING.
RIDGING WILL RETROGRADE FROM THE SOUTHERN PLAINS AND AMPLIFY OVER
THE SWRN CONUS FOR THE REMAINDER OF THE WEEK. DURING THIS TRANSITION
PHASE DURING THE MIDWEEK TIME FRAME...WINDS IN THE H7-H5 LAYER WILL
BACK TO A MORE PRONOUNCED S/SE DIRECTION ALLOWING MIXING RATIOS
ALOFT TO INCREASE TOWARDS A 5-7 G/KG RANGE ACROSS THE ENTIRE REGION.
HOWEVER...SFC DEWPOINTS LOOK TO ONLY SLOWLY RESPOND IN KIND AND
WITHOUT AN EVIDENT WELL DEFINED FORCING MECHANISM (I.E. INVERTED
TROUGH OR PERSISTENT UPPER LEVEL DIFLUENCE)...RAINFALL CHANCES LOOK
NO MORE THAN A CLIMATOLOGICAL PROBABILITY. OPERATIONAL MODELS HAVE
CONTINUED THE TREND OF PORTRAYING LITTLE TO NO QPF...WHILE ENSEMBLE
MEMBERS ONLY TARGET THURSDAY AS APPROACHING CLIMATOLOGICAL ODDS.
FOR THE LATE WEEK TO EARLY WEEKEND...OPERATIONAL AND ENSEMBLE
FORECAST MEMBERS AGREE ON THE GENERAL IDEA OF THE 500MB RIDGE CENTER
SHIFTING WESTWARD ENOUGH TO BE NEARLY OVERHEAD BY THURSDAY. RIDGE
HEIGHTS START PUSHING 595DM PLUS WITH 1000-500MB THICKNESSES SLIGHTLY
INCREASING EACH AFTERNOON. WARM AND ABOVE NORMAL AFTERNOON
TEMPERATURES WILL PERSIST THROUGH THE WEEK...WITH SOME OF THE LOWER
ELEVATION LOCALES CLOSER TOWARDS THE COLORADO RIVER POTENTIALLY
SEEING 110 PLUS READINGS. AT THE SAME TIME...MORNING LOWS WILL BEGIN
A GRADUAL WARMING TREND DUE TO THE WARMER AFTERNOONS AND RETURN OF
ELEVATED DEWPOINT READINGS TRYING TO RETURN TO MORE MONSOON-LIKE
READINGS. GFS/ECMWF/GEM BEGIN TO DIVERGE ON ACTUAL RIDGE POSITIONING
AND SUBSEQUENT ORIENTATION OF THE FLOW OVER AND INTO THE REGION.
EXTENDED POP FORECAST STILL DEPICTS A SLIGHTLY LOW-GRADE /AND BELOW
CLIMO/ MONSOON PATTERN...WITH TYPICAL AFTERNOON/EVENING SLIGHT
CHANCES FOR THE ARIZONA HIGH TERRAIN AND MOSTLY SINGLE DIGIT POPS
ACROSS THE LOWER DESERTS.
&&
.AVIATION...
SOUTH-CENTRAL ARIZONA...INCLUDING KPHX...KIWA AND KSDL...AND
SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KIPL AND KBLH...
NO CHANGE IN THE WEATHER PATTERN EXPECTED FOR THE NEXT 24 HOURS AT
LEAST AS DRY SOUTHWEST/WEST FLOW ALOFT WILL KEEP DRY AIR IN
PLACE...LEADING TO SUNNY DAYS AND CLEAR NIGHTS. MAY SEE A FEW HIGH
BASED CU FROM PHOENIX EASTWARD TUESDAY AFTERNOON AND EARLY EVENING
OTHERWISE EXPECT CLEAR SKIES. THUNDERSTORMS WILL STAY OVER HIGHER
TERRAIN WELL TO THE EAST OF PHOENIX AND NO OUTFLOWS ARE EXPECTED TO
REACH INTO THE LOWER DESERTS THRU TUE EVENING. WINDS WILL CONTINUE
TO FOLLOW NORMAL DIURNAL SPEEDS AND DIRECTIONS AT THE TAF SITE AND
MAY EXHIBIT SOME LOCAL GUSTINESS DURING THE AFTERNOON AND EVENING
HOURS. HAVE PLAYED LARGELY A PERSISTENCE FORECAST WITH THE WINDS AT
ALL TAF SITES. NO AVIATION CONCERNS THRU TUESDAY EVENING.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
OVERALL...DRY AIR WILL DOMINATE ALL BUT FAR EASTERN ARIZONA THROUGH
THE PERIOD WITH SLIGHTLY ABOVE NORMAL TEMPERATURES. MODEST MONSOON
MOISTURE ACROSS SOUTHERN GILA COUNTY WILL ALLOW FOR A CONTINUED
SLIGHT CHANCE OF AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS.
MINIMUM HUMIDITIES WILL GENERALLY BE IN THE 10-15 PERCENT RANGE
ACROSS THE LOWER DESERTS. WEAK SYNOPTIC GRADIENT FLOW WILL ALLOW FOR
TYPICAL MOUNTAIN VALLEY DIURNAL WINDS TO PREVAIL THROUGH THE PERIOD.
$$
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&
$$
VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX
DISCUSSION...CB
PREVIOUS DISCUSSION...MO/NOLTE
AVIATION...CB
FIRE WEATHER...KUHLMAN