Severe Thunderstorm Warning 5, NWS Phoenix, AZ

AZZ020>028-CAZ030>033-032245-

SOUTHWEST ARIZONA/SOUTHEAST CALIFORNIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1015 AM MST TUE JUL 3 2001

.SYNOPSIS...
A LARGE HIGH PRESSURE SYSTEM ALOFT...CENTERED NEAR THE FOUR CORNERS
REGION...WILL DRIFT SLOWLY NORTHWARD THIS WEEK. THIS WILL RESULT IN
A CHANGE IN THE WIND PATTERN...WITH SOUTHEASTERLY WINDS BRINGING IN
MORE MOISTURE TO BOTH SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA. A
CORRESPONDING INCREASE IN THUNDERSTORM POTENTIAL CAN BE EXPECTED AS
THE AIR BECOMES MOISTURE LADEN. IT WILL...HOWEVER...TEND TO MODERATE
THE DAYTIME TEMPERATURES DOWN TO MORE NORMAL LEVELS BY MID WEEK.

.DISCUSSION...
WATER VAPOR IMAGERY AND PLOT DATA SHOW WESTERN U.S. ANTICYCLONE HAS
A NUMBER OF FEATURES AROUND ITS PERIPHERY. ON ITS SOUTHEAST FLANK IS
A BIG INVERTED TROUGH CENTERED JUST SOUTHEAST OF CHIHUAHUA
MEXICO...WITH A DEFORMATION ZONE IN BETWEEN. THERE ARE ALSO MINOR
PERTURBATIONS EXTENDING FROM THE TEXAS PANHANDLE TO THE FAR NORTHERN
SEA OF CORTEZ. ON THE SOUTHWEST FLANK OF THE HIGH IS ANOTHER
CYCLONIC CIRCULATION WELL WEST OF NORTHERN BAJA. THERE IS ALSO A
WEAKENING SHORT WAVE APPROACHING THE PAC NORTHWEST COAST AND ANOTHER
SHORT WAVE OVER THE NORTHERN HIGH PLAINS. HIGHER 850 AND 700 MB DEW
POINTS APPEAR TO BE HEADED THIS WAY IN CONNECTION WITH WESTWARD
ADVANCING INVERTED TROUGH. LOWER DEW POINT VALUES ARE APPARENT ON
THE EAST SIDE OF THE INVERTED TROUGH.

A MIXED BAG OF 24 HOUR CHANGES ON THIS MORNINGS RAOBS. TUS AND PSR A
BIT COOLER BELOW 700 MB. 1Y7 AND TUS BOTH GAINED ABOUT .2 INCHES
PWATER...1Y7 BELOW 550 MB AND TUS ABOVE 600 MB...WHEREAS NKX LOST
ABOUT .2 INCHES PWATER. MORE DISTINCT EASTERLY FLOW ON THE PSR
SOUNDING. THE SOUNDINGS STILL HAVE MOIST MID LEVELS AND RELATIVELY
DRY LOW LEVELS...PROFILES CONDUCIVE TO DOWNBURSTS. THIS IS
CONSISTENT WITH SPC SLIGHT RISK.

12Z PROGS SHOW A PERTUBATION OVER NEW MEXICO MOVING INTO SOUTHERN
ARIZONA TODAY...AVN A BIT SLOWER AND FURTHER SOUTH THAN ETA. IF THIS
WERE TO PAN OUT...WE SHOULD BE MORE ACTIVE OVER THE LOW DESERTS THIS
EVENING GIVEN MORE FAVORABLE STEERING FLOW AND BETTER MID LEVEL
MOISTURE OVER SOUTHEAST ARIZONA. BY WEDNESDAY MORNING...INVERTED
TROUGH AXIS TO REACH EASTERN SONORA. FLOW BECOMES SOUTHEASTERLY ON
WEDNESDAY. THIS WOULD SUGGEST DEEPER MOISTURE WILL BE MOVING IN
REGION-WIDE. HOWEVER...BOTH ETA AND AVN SHOW LOWER 850 MB DEW POINTS
MOVING INTO SOUTHEAST ARIZONA AND HIGHER VALUES MOVING INTO
SOUTHWEST ARIZONA AND SOUTHEAST CALIFORNIA. BY THURSDAY...THE 850 MB
MOISTURE AXIS SHIFTS EASTWARD INTO CENTRAL ARIZONA. THIS IS
ASSOCIATED WITH AN EASTWARD SHIFT OOF THE RIDGE POSITION. THE SHORT
OF IT ALL IS THAT STORM ACTIVITY WILL BE ON THE UPSWING. THE
CHARACTER OF THE STORMS WILL ALSO BE CHANGING DURING THIS TIME AS WE
CHANGE THE MOISTURE PROFILES.

JAMISON