AFDFLG
NORTHERN ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
320 PM MST SUN SEP 21 2003
.SYNOPSIS...HIGH PRESSURE WILL DOMINATE THE WEATHER PATTERN OVER
NORTHERN ARIZONA THROUGH TUESDAY. EXPECT MOSTLY CLEAR SKIES...WARM
DAYS...AND COOL NIGHTS. TROPICAL MOISTURE WILL BEGIN TO INCREASE BY
WEDNESDAY BRINGING CLOUDS AND A CHANCE OF RAIN THURSDAY INTO FRIDAY.
SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DECREASE OVER THE
WEEKEND.
.DISCUSSION...500 MB HIGH PRESSURE ALONG THE CALIFORNIA COAST WILL
SHIFT EAST OVER SOUTHERN NEVADA/NORTHERN ARIZONA BY TUESDAY...
KEEPING SKIES CLEAR AND DAYTIME HIGHS SLIGHTLY ABOVE NORMAL.
MEAN WHILE THE REMNANT CIRCULATION AND MOISTURE FROM MARTY WILL MOVE
NORTHWARD INTO THE SOUTHERN GULF OF CALIFORNIA...NORTHWEST MEXICO
AND SOUTHERN HALF OF ARIZONA BY LATE TUESDAY. HIGH PRESSURE WILL
REMAIN OVER SOUTHERN UTAH AND INTO NORTHERN NEW MEXICO. DRY AIR
ACROSS THIS AREA WILL BE PULLED SOUTHWARD INTO THE NORTH SIDE OF THE
LOW. A DEFORMATION AXIS SETS UP ALONG SOUTHERN PORTION OF THE
FORECAST AREA ON WEDNESDAY. BY THURSDAY AS THE CIRCULATION FROM
MARTY WEAKENS THE MID-LEVEL FLOW BEGINS TO BECOME SOUTHEASTERLY
ALLOWING DEEPER MOISTURE TO FLOW UP ON TO THE MOGOLLON RIM. THIS
WILL BRING AN UP SWING IN SHOWER AND THUNDERSTORM ACTIVITY THURSDAY
AND FRIDAY...MAINLY FROM THE MOGOLLON RIM SOUTH INTO NORTHERN GILA
AND YAVAPAI COUNTIES. AS FOR SATURDAY INTO SUNDAY THE ENSEMBLES AND
VARIOUS MEDIUM RANGE MODELS HAVE VARIOUS RENDITIONS OF WHERE THE
TROPICAL SYSTEM WILL MOVE ALONG WITH ITS MOISTURE. GFS/MRF PULLS THE
MOISTURE WESTWARD TOWARD A CUTOFF LOW OFF THE CALIFORNIA COAST AND
THEN BRINGS IT BACK ACROSS THE AREA OVER THE WEEKEND AS THE LOW GETS
CAUGHT IN THE WESTERLIES. DUE TO THE UNCERTAINTY DAYS 6 AND 7,
(SATURDAY AND SUNDAY) WE WILL LEAVE THE DRYING TREND FOR NEXT
WEEKEND AS IS...FOR NOW.
Dennis
