Severe Thunderstorm Warning 17, NWS Phoenix, AZ

AZZ020>028-CAZ030>033-280545-

SOUTHWEST ARIZONA/SOUTHEAST CALIFORNIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
250 PM MST SUN JUL 27 2003

.SYNOPSIS...
STRONG HIGH PRESSURE ALOFT WILL REMAIN OVER THE INTERMOUNTAIN WEST
THROUGH AT LEAST THE MIDDLE OF THIS WEEK...THEN MOVE EAST TO NEAR
THE FOUR CORNERS AREA BY FRIDAY. SO...A RATHER MOIST EASTERLY FLOW
SHOULD PERSIST OVER THE FORECAST AREA THROUGH WEDNESDAY. A LOW
PRESSURE SYSTEM WILL MOVE SLOWLY WEST ACROSS NORTHWEST MEXICO
TONIGHT AND MONDAY...BE CENTERED OVER THE NORTHERN GULF OF
CALIFORNIA BY TUESDAY MORNING...THEN WEAKEN WHILE DRIFTING SLOWLY
NORTH TUESDAY AND WEDNESDAY. AS A RESULT...THE CHANCE FOR SCATTERED
SHOWERS AND THUNDERSTORMS SHOULD BE ENHANCED...ESPECIALLY MONDAY AND
TUESDAY. EXPECT A MORE TYPICAL MONSOON PATTERN TO BECOME ESTABLISHED
TOWARD THE END OF THE WEEK AS THE UPPER HIGH MOVES TO THE FOUR
CORNERS AREA AND SOUTHEAST FLOW DEVELOPS ALOFT.

.DISCUSSION...
VERY QUIET OVER THE CENTRAL AND EASTERN RIM COUNTRY EARLY THIS
AFTERNOON...AS WELL AS OVER SOUTHEAST ARIZONA...DUE IN PART TO
DRYING/SUBSIDENCE IN ADVANCE OF UPPER LOW OVER CHIHUAHUA MEXICO
COUPLED WITH THE FACT THAT CONVECTION WAS WIDESPREAD AND QUITE
ACTIVE OVER THAT REGION YESTERDAY. SCTD THUNDERSTORMS HAVE FORMED
OVER HIGHER TERRAIN NORTHWEST OF PRESCOTT. 2 PM SFC TEMPS/DEW POINTS
WERE SIMILAR TO WHAT OCCURRED YESTERDAY OVER THE LOWER DESERT...AND
A FEW DEGREES LOWER OVER SOUTH CENTRAL AZ HIGHER TERRAIN.

STILL RECEIVING MIXED SIGNALS REGARDING WHAT WILL HAPPEN TONIGHT.
ATMOSPHERE NOT AS UNSTABLE AS WAS THE CASE YESTERDAY. HOWEVER...
UPPER FORCING WILL BE ON THE INCREASE TONIGHT AS UPPER LOW AND
INVERTED TROF MOVE OVER THE EASTERN HALF OF THE CWA. ASSOCIATED
INCREASE IN VERTICAL SHEAR...ASSOCIATED WITH STRENGTHENING 700-400
MB LAYER EAST TO NORTHEAST WINDS...WOULD INCREASE POTENTIAL FOR ANY
STORMS WHICH FORM TONIGHT TO BECOME SEVERE...WITH HIGH WIND THE
GREATEST THREAT. OVER OUR CWA...BEST CHANCE FOR STORMS THIS EVENING
APPEARS TO BE OVER THE WESTERN THIRD OF CWA...ALONG OR NEAR THE
LOWER COLORADO RIVER VALLEY (LA PAZ/E RIVERSIDE/E IMPERIAL/YUMA
COUNTIES)...WHERE GFS FORECASTS STRONGEST UPPER DIVERGENCE...
UPSTREAM CONVECTION IS CURRENTLY MOST VIGOROUS...AND BOUNDARY LAYER
IS WARMER AND MORE MOIST THAN WAS THE CASE YESTERDAY. STRONG/SEVERE
STORMS WITH SIGNIFICANT RAIN WILL ALSO OCCUR WELL SOUTH OF OUR
CWA...VERY CLOSE TO THE INTERNATIONAL BORDER...CLOSE TO THE TRACK OF
THE UPPER LOW WHERE DYNAMICS AND INSTABILITY ARE MUCH MORE FAVORABLY
CORRELATED. SO...WILL GO WITH SLIGHT CHANCE FOR STORMS SOUTH CENTRAL
AZ TONIGHT...WHILE RETAINING CHANCE WORDING OVER WESTERN HALF OF
CWA. MONDAY SHOULD BE AN UP DAY/NIGHT OVER MOST OF OUR FORECAST
AREA...WITH DECENT POTENTIAL FOR ORGANIZED SEVERE COMPLEXES OF
STORMS TO DEVELOP AND PROPAGATE TOWARD THE SW. SHOULD SEE INCREASED
MOISTURE OVERSPREAD MUCH OF OUR CWA BY MONDAY DUE TO OUTFLOW FROM
STORMS TO OUR SOUTH...AND A GULF SEEP OR SURGE IS NOT OUT OF THE
QUESTION. WILL KEEP IT UNSETTLED THROUGH MUCH OF THE WEEK AS UPPER
HIGH MOVES FROM NEVADA TO NEAR THE FOUR CORNERS BY FRIDAY...BUT
HIGHEST POPS IN THIS FORECAST PACKAGE WILL BE IN THE FIRST COUPLE OF
DAYS UPCOMING WEEKEND FORECAST IS PROBLEMATIC IN THAT MEDIUM RANGE
MODELS DISAGREE ON POSITION OF UPPER HIGH AND ORIENTATION OF UPPER
FLOW OVER OUR CWA. FOR NOW...WILL STICK WITH A LOW GRADE MONSOON
FORECAST THIS WEEKEND...WITH EXPECTATION OF SOUTHEASTERLY FLOW
ALOFT. DG
 I
.PSR...NONE.

AZZ020>028-CAZ030>033-280100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
600 AM MST SUN JUL 27 2003

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

.DAY ONE...TODAY

THUNDERSTORMS WILL BE ON THE INCREASE TODAY AND TONIGHT ESPECIALLY
OVER SOUTH CENTRAL ARIZONA. THE MOST ACTIVE TIME WILL BE THE EVENING
HOURS. SOME OF THESE STORMS MAY PRODUCE BRIEF HEAVY RAINS AND
POSSIBLY STRONG DAMAGING WINDS. AREAS OF REDUCED VISIBILITIES IN
BLOWING DUST WILL ALSO BE POSSIBLE IN THE DESERT REGIONS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX, AZ
101 PM MST SUN JUL 27 2003

TIME(MST)  .....CITY LOCATION.....STATE   ...EVENT/REMARKS...
           ....COUNTY LOCATION....

0705 PM    PUNKIN CENTER             AZ   60 MPH TSTM WIND GUST
07/26/03   GILA                           COOPERATIVE OBSERVER
                                          REPORTED FOURTEEN INCH
                                          DIAMETER TREE LIMB AND
                                          NUMEROUS SMALL LIMBS DOWN.
                                          POWER WAS LOST FOR FIVE
                                          HOURS. BOAT COVERS
                                          DESTROYED AT BOAT STORAGE
                                          SITE. REPORTED BY CO-OP
                                          OBSERVERS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX, AZ
104 PM MST SUN JUL 27 2003

TIME(MST)  .....CITY LOCATION.....STATE   ...EVENT/REMARKS...
           ....COUNTY LOCATION....

0705 PM    PUNKIN CENTER             AZ   60 MPH TSTM WIND GUST
07/26/03   GILA                           COOPERATIVE OBSERVER
                                          REPORTED FOURTEEN INCH
                                          DIAMETER TREE LIMB AND
                                          NUMEROUS SMALL LIMBS DOWN.
                                          POWER WAS LOST FOR FIVE
                                          HOURS. BOAT COVERS
                                          DESTROYED AT BOAT STORAGE
                                          SITE. REPORTED BY CO-OP
                                          OBSERVERS