Severe Thunderstorm Warning 117, NWS Tucson, AZ

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
230 AM MST TUE OCT 7 1997

A VIGOROUS PACIFIC TROUGH CONTINUES TO APPROACH ARIZONA FROM THE
WEST THIS MORNING...FINALLY SOME RELIEF FROM THE RELENTLESS ARIZONA
HEAT IS ON THE WAY. THE MAIN QUESTIONS FOR TODAY ARE TIMING OF THE
SURFACE FRONT AND HOW MUCH CLOUD COVER/PRECIP.

THE SURFACE FRONT WAS LOCATED BETWEEN YUMA AND TUCSON AT 08 UTC
MOVING TO THE EAST AND APPEARS TO BE AHEAD OF SCHEDULE. YUMA WAS
ALREADY OBSERVING NORTHWEST WINDS AT THE SURFACE AT 0500 UTC WELL IN
ADVANCE OF THE 09 TO 12 UTC WINDOW THE 00 UTC NGM MOS GUIDANCE WAS
SHOWING. THE AVN NOW APPEARS TO HAVE THE BEST TIMING IN MOVING THE
FRONT ACROSS MOST OF SOUTHEAST ARIZONA BY LATE IN THE AFTERNOON. FOR
THIS REASON HAVE LOWERED HIGHS TODAY AND LOW TEMPS TONIGHT FROM
PREVIOUS FORECASTS TO ACCOUNT FOR THE EARLIER ARRIVAL OF THE FRONT.

IN ADVANCE OF THE TROUGH MOISTURE IS BEING DRAWN INTO ARIZONA FROM
THE SOUTH BUT NOT IN GREAT QUANTITIES. WATER VAPOR IMAGERY IS
SHOWING A DECENT MID-LEVEL MOISTURE INTRUSION AND THE SOUNDER
PRECIPITABLE WATER PRODUCT IS SHOWING A PW PLUME OF .50 TO .75 INCH
ACROSS SOUTHERN ARIZONA. WITH RAPID HEIGHT FALLS AND COOLING
ASSOCIATED WITH THE APPROACHING TROUGH...500 MB HEIGHTS LOWER THAN
570 DM BY MID AFTERNOON...COUPLED WITH DAYTIME HEATING SHOULD BE
ENOUGH TO TRIGGER SHOWER ACTIVITY AND A FEW THUNDERSTORMS. THE FLOW
LOOKS MOST PROMISING OVER EXTREME SOUTHEAST ARIZONA WHERE A GOOD
SOUTHERLY FETCH IS FORMING. LOOKS LIKE MAINLY A WIND PRODUCER FROM
TUCSON WESTWARD WITH THE MAIN PRECIP ACTIVITY OVER ZONES 29...30 AND
19. AS 500 MB TROUGH AXIS SWINGS THROUGH THIS EVENING THERE WILL BE
A FEW SNOW SHOWERS IN THE HIGHEST ELEVATIONS OF THE WHITE MOUNTAINS.
TUS 220. MCCOLLUM

TUS...NONE

AZZ019-026>030-071500-
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE TUCSON AZ
500 AM MST MON OCT 6 1997

...FALL WEATHER IS FINALLY ON THE WAY FOR SOUTHEAST ARIZONA...

A VIGOROUS STORM SYSTEM WILL MOVE ACROSS ARIZONA TODAY. THE MAIN
IMPACT OF THIS STORM OVER SOUTHEAST ARIZONA WILL BE SOUTHWEST TO
WEST WINDS OF 15 TO 30 MPH DEVELOPING BY THE AFTERNOON. BLOWING DUST
WITH AREAS OF REDUCED VISIBILITIES COULD BE A PROBLEM IN SOME
LOCATIONS. THE COLD FRONT ASSOCIATED WITH THIS STORM WILL MOVE
ACROSS SOUTHEAST ARIZONA TODAY BRINGING WITH IT PARTLY TO MOSTLY
CLOUDY SKIES AND A CHANCE OF SHOWERS AND THUNDERSTORMS...ESPECIALLY
OVER EASTERN PORTIONS. AFTERNOON TEMPERATURES ARE EXPECTED TO BE
COOLER...WITH 80S IN THE DESERTS AND MAINLY 60S AT HIGHER
ELEVATIONS.

THE COLD FRONT WILL MOVE INTO NEW MEXICO OVERNIGHT WITH DIMINISHING
WINDS. IN ITS WAKE A COOL AND DRY AIR MASS WILL RESULT IN THE LOWEST
NIGHTTIME TEMPERATURES SINCE SPRING. EXPECT LOWS IN THE UPPER 40S TO
LOWER 50S IN DESERT LOCATIONS TO NEAR FREEZING AT THE HIGHEST
MOUNTAIN ELEVATIONS.

SUNNY SKIES WILL RETURN TO SOUTHEAST ARIZONA BY WEDNESDAY.
HOWEVER...TEMPERATURES WILL REMAIN ON THE COOL SIDE...GENERALLY
RANGING FROM THE 60S IN THE MOUNTAINS TO THE LOWER 80S ON THE
DESERT.

MCCOLLUM