Severe Thunderstorm Warning 16, NWS Phoenix, AZ

AZZ020>028-CAZ030>033-232245-

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
938 AM FRI JUL 23 2004

SOUTHWEST AND SOUTH-CENTRAL ARIZONA...AND SOUTHEAST CALIFORNIA
FORECAST DISCUSSION

.SYNOPSIS...
HIGH PRESSURE ALOFT WILL MEANDER OVER ARIZONA TODAY...THEN GENERALLY
BECOME CENTERED OVER NORTHERN ARIZONA THIS WEEKEND. MEANWHILE...
LOW PRESSURE SYSTEMS MOVING WEST ACROSS MEXICO AND THE GULF OF
CALIFORNIA WILL HELP INCREASE MOISTURE THROUGH THE WEEKEND. THUS...
AN INCREASING CHANCE OF MAINLY AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS IS EXPECTED BY SATURDAY AND SUNDAY. AND...LOWER
TEMPERATURES ARE EXPECTED TODAY COMPARED WITH YESTERDAY.

&&

.DISCUSSION...
STRONG HIGH PRESSURE CONTINUES IN PLACE OVER THE DESERT SOUTHWEST
WITH THE 500MB HIGH CENTER NOW CLOSE TO PHOENIX...OVER CENTRAL
ARIZONA. QUITE A BIT OF CLOUD COVER CAN BE SEEN OVER SRN/CNTRL
AZ...MUCH OF WHICH IS DEBRIS CLOUDS THAT SPREAD INTO THE STATE FROM
A DYING MCS THAT FORMED LAST NIGHT OVER NWRN MEXICO. AT 9 AM THIS
MORNING THE MCS CONTINUES TO WEAKEN AND MOVE TO THE SW OVER THE SRN
GULF OF CA...AND THIS SYSTEM WILL CONTINUE TO SEND MOISTURE TO THE
NORTH AND UP THE LOWER CO RIVER VALLEY. A SURGE BEGAN YESTERDAY
...SPURRED BY A PREVIOUS MCS OVER MEX...AND IT WILL CONTINUE TODAY
INTO TONIGHT. SURFACE DEWPOINTS IN SERN CA AND ALONG THE RIVER ARE
NOW IN THE MID 60S TO MID 70S AS A RESULT OF THE SURGE...AND THE
ANTYCYC GYRE WILL SPREAD THIS MOISTURE BACK TO THE EAST AND OVER THE
SRN/CENTRAL DESERTS...ADDING LOW LEVEL MOISTURE TO THE AIRMASS AND
INCREASING THE THREAT FOR STORMS IN THE DAYS TO COME. THE 12Z RAOB
AT PHOENIX TODAY WAS SUBSTANTIALLY MORE MOIST AND UNSTABLE AS
COMPARED TO THURSDAY...WITH AN 850MB DEWPOINT OF 14C. AND...SURFACE
DEWPOINTS THIS MORNING IN THE PHX AREA ARE IN THE 60S FOR THE MOST
PART. A LOOK AT THE WATER VAPOR IMAGERY SHOWS A PRONOUNCED
DEFORMATION/STRETCHING ZONE BISECTING THE STATE FROM SW TO NE...AND
THIS WEAKNESS ALOFT HELPED EXPLAIN SHOWERS THAT DEVELOPED THIS
MORNING IN THE WESTERN DESERTS. MODEL WIND FORECASTS AND RAOB DATA
SUGGEST THAT THE STEERING FLOW OVER SCNTRL AZ WILL BE WEAK FROM THE
NW TO N TODAY...AND WITH THE STRONG INCREASE IN MOISTURE AND
INSTABILITY...WILL LIKELY RAISE OUR POPS FOR THIS AFTERNOON AND
EVENING TO AT LEAST 20 PERCENT...WITH HIGHER POPS OVER THE HIGHER
TERRAIN. IT APPEARS THE MOST SIGNIFICANT DIFLUENCE ALOFT AND UPPER
DIVERGENCE WILL STAY TO OUR SE TODAY/TONIGHT...GIVING THE TUS CWA
SOME BOOST TO THEIR STORM CHANCES. FAR WESTERN DESERTS/SERN CA WILL
STILL BE MOSTLY OUT OF THE WOODS...AS THE SHALLOW LAYER OF HIGH
DEWPOINTS WILL MIX OUT AND THE AIRMASS WILL REMAIN TOO DRY AND
STABLE FOR ANY SIGNIFICANT CONVECTION.

FOR SATURDAY INTO THE WEEKEND...MODELS CONTINUE TO WANT TO SHIFT THE
UPPER HIGH TO THE NORTHWEST...AND PUT IT OVER SRN NV OR NW AZ. THIS
GIVES A MORE NLY TO NELY STEERING FLOW WHICH IS A GOOD DIRECTION FOR
BRINGING STORMS FROM THE RIM DOWN INTO OUR DESERTS. WE SHOULD HAVE
ENOUGH LOW LEVEL MOISTURE BY THE WEEKEND TO SUPPORT CONTINUED STORM
DEVELOPMENT AS THEY WORK INTO OUR AREA...SO THE CHANCE POPS THAT ARE
IN THE FORECAST RIGHT NOW LOOK OK. THERE IS A PRONOUNCED INVERTED
TROF OVER W TEXAS/NW MEXICO THAT WILL PUSH TO THE WEST TONIGHT
THROUGH SATURDAY...AND IT WILL GIVE SIGNIFICANT LIFT/DIFLUENCE ALOFT
TO PART OF AZ HELPING TO INCREASE STORM CHANCES. HOWEVER IT APPEARS
THAT THIS FEATURE MAY SKIRT OUR AREA TO THE SOUTHEAST FOR THE MOST
PART...AND MAINLY BE A PLAYER FOR THE TUS CWA AGAIN. ONE THING OF
INTEREST IN THE 12Z ETA RUN...AS THE HIGH MIGRATES TO THE NORTHWEST
IT STARTS TO BUILD...WITH A 594 CENTER FORECAST BY SUNDAY AFTERNOON.
IN TURN THE AIRMASS TO OUR NORTH AND WEST DRIES OUT...WITH LOW MEAN
RH AND 850MB DEWPOINTS FORECAST. THUS AS WE MOVE INTO THE WEEKEND
THERE MIGHT NOT BE QUITE AS MUCH CONVECTION DEVELOPING ALONG THE
CENTRAL/WESTERN RIM AS WE THOUGHT...AND THUS LESS WEATHER AVAILABLE
TO ADVECT SOUTHWARD WITH THE NLY/NELY STEERING FLOW. THIS WOULD THEN
LIMIT THE POTENTIAL FOR STORMS IN OUR AZ ZONES SAT INTO SUNDAY. THIS
WILL HAVE TO BE LOOKED AT IN MORE DETAIL WHEN THE GFS RUN FINISHES
COMING IN THIS MORNING. CURRENT FORECAST FOR TODAY LOOKS PRETTY GOOD
BUT MAY NEED TO UPDATE AND RAISE POPS SOMEWHAT FOR THIS AFTERNOON.

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.

&&

11

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
1048 AM MST FRI JUL 23 2004

AZZ024-240500-
SOUTHERN GILA/TONTO NF FOOTHILLS-
1048 AM MST FRI JUL 23 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTH CENTRAL ARIZONA.

.DAY ONE...TODAY

ISOLATED TO SCATTERED THUNDERSTORMS MAY CAUSE HEAVY RAINS AND
MINOR FLOODING OF POOR DRAINAGE AND LOW LYING AREAS. WASHES MAY BEGIN
FLOWING.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE IS AN CHANCE FOR THUNDERSTORMS SATURDAY THROUGH NEXT FRIDAY
WITH THE BEST THREAT FOR HEAVY RAINS...FLOODING...AND GUSTY
WINDS...EXPECTED SATURDAY THROUGH TUESDAY.

.SPOTTER CALL TO ACTION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED TODAY THROUGH THURSDAY.

&&

FOR ADDITIONAL WEATHER INFORMATION...CHECK OUR WEB SITE AT
HTTP://WWW.WRH.NOAA.GOV/PHOENIX (IN SMALL LETTERS)

AZZ021>023-026>028-240500-
GREATER PHOENIX AREA-NORTHWEST AND NORTH CENTRAL PINAL COUNTY-
NORTHWEST MARICOPA COUNTY-SOUTHWEST DESERTS-
SOUTHWEST MARICOPA COUNTY-WEST CENTRAL DESERTS-
1048 AM MST FRI JUL 23 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHWEST AND SOUTH CENTRAL
ARIZONA.

.DAY ONE...TODAY

THERE IS A SLIGHT CHANCE FOR THUNDERSTORMS TODAY...BUT THEY WILL
LIKELY NOT PRODUCE SEVERE WINDS...HEAVY RAIN OR FLOODING. GUSTY WINDS
TO 40 MPH...ALONG WITH BRIEF HEAVY RAIN AND SOME BLOWING DUST ARE
POSSIBLE WITH ANY STORMS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE IS AN INCREASING CHANCE FOR THUNDERSTORMS SATURDAY THROUGH
TUESDAY...AND THEY MAY PRODUCE LOCALLY HEAVY RAINFALL...MINOR
FLOODING OF ROADS AND WASHES...AND STRONG GUSTY WINDS LEADING TO
BLOWING DUST. THE THREAT FOR THUNDERSTORMS IS EXPECTED TO DECREASE
FROM THE WEST WEDNESDAY THROUGH FRIDAY.

.SPOTTER CALL TO ACTION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED SATURDAY THROUGH TUESDAY.

&&

FOR ADDITIONAL WEATHER INFORMATION...CHECK OUR WEB SITE AT
HTTP://WWW.WRH.NOAA.GOV/PHOENIX (IN SMALL LETTERS)

AZZ020-025-CAZ030>033-240500-
IMPERIAL COUNTY-JOSHUA TREE NATIONAL PARK-
LOWER COLORADO RIVER VALLEY AZ-LOWER COLORADO RIVER VALLEY CA-
RIVERSIDE COUNTY/EASTERN DESERTS-YUMA/MARTINEZ LAKE AND VICINITY-
1048 AM MST FRI JUL 23 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST CALIFORNIA AND THE
LOWER COLORADO RIVER VALLEY.

.DAY ONE...TODAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE IS A SLIGHT CHANCE FOR THUNDERSTORMS SATURDAY THROUGH
TUESDAY...MAINLY IN THE EVENING HOURS. THEY MAY PRODUCE GUSTY WINDS
TO OVER 40 MPH...ALONG WITH BRIEF HEAVY RAIN AND BLOWING DUST. THE
THREAT FOR THUNDERSTORMS WILL DECREASE FROM THE WEST BEGINNING
WEDNESDAY.

.SPOTTER CALL TO ACTION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED SATURDAY THROUGH TUESDAY.

&&

FOR ADDITIONAL WEATHER INFORMATION...CHECK OUR WEB SITE AT
HTTP://WWW.WRH.NOAA.GOV/PHOENIX (IN SMALL LETTERS)