000 
FXUS65 KPSR 060441
AFDPSR
AZZ020>028-CAZ030>033-061045-

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX ARIZONA
940 PM MST SUN OCT 5 2003

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

.SYNOPSIS...
A LOW PRESSURE SYSTEM NEAR THE CALIFORNIA COAST WILL CONTINUE MOVING 
SOUTH-SOUTHEAST TO NEAR THE NORTHERN BAJA CALIFORNIA COAST. AT THE 
SAME TIME...ABUNDANT TROPICAL MOISTURE SHED OFF HURRICANE NORA WILL 
BRING COOLER WEATHER AND THE LIKELIHOOD OF SHOWERS AND THUNDERSTORMS 
LATE MONDAY INTO TUESDAY...DECREASING TO A SLIGHT CHANCE OF SHOWERS 
BY WEDNESDAY. THE LOW PRESSURE SYSTEM IS EXPECTED TO MOVE BACK NORTH 
TOWARD THE SOUTHWESTERN UNITED STATES WITH THE CHANCE OF SHOWERS AND 
THUNDERSTORMS INCREASING AGAIN FRIDAY.

&&

.DISCUSSION...
UPPER LEVEL SHORT WAVE RIDGE NOW SITTING OVER AZ...SHOWN NICELY IN 
THE LATEST 500MB PLOT DATA...WITH 10-20M HGTS RISES SEEN ACROSS THE 
DESERT SW. SKIES OVER THE CWA WERE GENLY CLEAR AT 9 PM...ALTHOUGH 
SOME HIGH CLOUDINESS WAS THICKENING UP TO THE WEST AHEAD OF A LOW 
DROPPING SEWD DOWN THE CA COAST. THIS LOW...WELL DEFINED IN THE 
WATER VAPOR IMAGERY...IS STILL FORECAST TO MOVE DOWN AND CLOSE OFF 
ALONG THE SRN CA/NRN BAJA COAST...WITH THE LOW CENTER NR 120W 30N BY 
MON AFTERNOON. LATEST ETA/GFS AGAIN IS CONSISTENT IN THE SHORT TERM 
ABOUT THE TIMING/TRACK OF THE LOW. HURRICANE NORA...NOW 335M SW OFF 
THE SRN TIP OF BAJA...IS SHEDDING MOISTURE TO THE NORTH...AND THE 
UPPER LOW IS FORECAST TO TAP MUCH OF THIS MOISTURE OVER THE NEXT FEW 
DAYS AND BRING A THREAT FOR SHOWERS/STORMS AND HEAVY RAIN TO OUR CWA 
BEGINNING MONDAY NIGHT AND CONTINUING THRU TUESDAY. GOES PWAT 
IMAGERY SHOWS RATHER DRY AIR OVER AZ...GENLY LESS THAN 0.75 
INCHES...BUT VALUES INCREASE MARKEDLY AS YOU GO SOUTH TOWARDS 
NORA...WITH PWAT VALUES AROUND OR ABOVE 2 INCHES OVER THE FAR SRN 
GULF OF CA. ALTHOUGH LATEST ETA/GFS AGREE NICELY WITH THE TIMING AND 
TRACK OF THE LOW THRU THE NEXT 24-48 HOURS...THE ETA CONTINUES TO BE 
A BIT TOO AGRESSIVE BRINGING MID LEVEL MOISTURE UP INTO SRN AZ LATER 
TONIGHT AND MONDAY...GIVEN SATELLITE AND GOEW PWAT IMAGERY. PREFER 
GFS HANDLING OF MOISTURE ADVECTION. BOTH PROGS AGREE THAT MAIN 
THREAT FOR HEAVY RAIN WILL BEGIN MONDAY NIGHT...MAINLY OVER 
SOUTH-CENTRAL ARIZONA WHERE THE DEEPEST MOISTURE WILL MESH WITH THE 
STRONGEST UVVS. IN FACT...CURRENT FORECAST HAS SHOWERS LIKELY SCNTRL 
AFTER MIDNIGHT MONDAY NIGHT...WITH SHOWERS LIKELY THRU TUE 
AFTERNOON. LESSER CHANCES ARE OUT WEST WHERE MOISTURE AND DYNAMICS 
ARE PROGGED TO BE LESS.

OVER THE PAST COUPLE OF DAYS...AT LEAST...THE MFR AND GFS HAVE DONE 
A VERY POOR JOB HANDLING THE FORECAST TIMING AND TRACK OF THE UPPER 
LOW...DOING HUGE FLIP FLOPS ON THE TRACK. ONE MRF RUN KEEPS THE 
UPPER LOW SPINNING WELL OFF THE SRN CA COAST THRU 240 HOURS...THE 
NEXT KICKS IT INLAND AND MOVES IT THRU THE STATE BY WED/THU TIME 
FRAME. THE GFS HAS SIMILAR PROBLEMS. NOW THE LATEST COUPLE OF GFS 
RUNS KEEP THE LOW SPINNING OFF THE NRN BAJA COAST THRU AT LEAST 
FRI...WITH ONLY MODEST UVVS/DYNAMICS OVER THE STATE AT ANY 
TIME...AND DECENT MOISTURE CONTINUING. ALSO...TROPICAL STORM OLAF IS 
ALSO DOWN OFF THE MEXICAN COAST NEAR NORA...AND ITS MOISTURE MAY 
EVENTUALLY BE PULLED UP INTO AZ LATER IN THE WEEK...DEPENDING ON HOW 
LONG THE LOW ACTUALLY STAYS OFF THE CA/BAJA COAST. FOR NOW FORECASTS 
HAVE A SLIGHT CHANCE FOR SHOWERS OR STORMS TUE NIGHT THRU 
THURSDAY...THEN INCREASE UP TO A CHANCE FRI AS THE LOW IS EXPECTED 
TO START MOVING INLAND AND TAPPING OLAF MOISTURE. DUE TO THE 
UNCERTAINTY SHOWN BY PAST MODEL RUNS...WILL NOT MAKE ANY CHANGES TO 
FORECAST ON THIS SHIFT OUTSIDE OF TONIGHT INTO MONDAY...AND WILL LET 
MID SHIFT EVALUATE NEXT MRF RUN BEFORE MAKING ANY MAJOR CHANGES TO 
THE PACKAGE. 

&&

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

&&

$$

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