Severe Thunderstorm Warning 120, NWS Tucson, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
915 AM MST THU OCT 6 2005

.SYNOPSIS...AN INCREASE IN MOISTURE WILL RESULT IN A SLIGHT CHANCE
OF THUNDERSTORMS FOR AREAS EAST OF TUCSON THROUGH THE DAY...WITH DRY
CONDITIONS ELSEWHERE. EXPECT DRY WEATHER ON FRIDAY AS A WEAK RIDGE
MOVES ACROSS THE AREA. A STRONG LOW PRESSURE SYSTEM WILL THEN
DEVELOP OVER THE DESERT SOUTHWEST...AND BRING A CHANCE OF SHOWERS BY
SATURDAY NIGHT INTO SUNDAY. COOLER TEMPERATURES WILL OCCUR
SUNDAY...THEN DRY AGAIN BY NEXT TUESDAY WITH A WARMING TREND.

&&

.DISCUSSION...KEMX WSR-88D DETECTED SCATTERED MOSTLY LESS THAN 35
DBZ ECHOES ACROSS GREENLEE AND SRN GRAHAM COUNTIES...AS WELL AS
CENTRAL/WRN COCHISE COUNTIES AT 1610Z. CELLS WERE MOVING EWD ABOUT
10 KTS. THE REST OF SE AZ WAS VOID OF PRECIP ECHOES. SATELLITE
IMAGERY INDICATED GENERALLY CLEAR SKIES ACROSS SE PINAL/PIMA/SANTA
CRUZ COUNTIES...WITH SCATTERED-BROKEN MAINLY CUMULOFORM CLOUDS ERN
SECTIONS.

DEWPOINTS VALID 16Z WERE IN THE 40S-LOWER 50S WEST...BUT WERE IN THE
MID-UPPER 50S. BELIEVE COLD FRONT WAS NEAR THE SE AZ/SW NM AT THIS
TIME GIVEN THE NEARLY 15 DEG TEMP DIFFERENCE BETWEEN KDUG AND KDMN.
ELY SURFACE WIND GUSTING OVER 20 KTS AT KSAD AND KDUG AS WELL.
06/12Z KTUS SOUNDING REFLECTED AN INCREASE IN MOISTURE VERSUS 24
HOURS AGO...MAINLY IN THE MID-LEVELS...WITH PRECIP WATER VALUE NEAR
1.05 INCHES. FAIRLY STABLE PROFILE THOUGH WITH LIFTED INDEX NEAR
ZERO AND UNMODIFIED SURFACE-BASED CAPE OF ONLY 298 J/KG. ANALYSES OF
06/12Z UPPER AIR PLOTS INDICATED SHORTWAVE TROUGH/MID-LEVEL TROUGH
AXIS FROM WRN UTAH-WRN AZ. UPPER LOW WAS CENTERED OVER NRN MINNESOTA
AS WELL AS WRN FL. SHORTWAVE RIDGE AXIS WAS OVER THE PACIFIC NW AND
LIGHT WLY/SWLY FLOW PREVAILED OVER SRN AZ.

AGREE WITH SWODY1 THAT CONVERGENCE ASSOCIATED WITH QUASI-STATIONARY
FRONTAL BOUNDARY WITH OROGRAPHIC FORCING...IN COMBINATION WITH
ALBEIT SPARSE BOUNDARY LAYER MOISTURE...WILL PRODUCE SCATTERED
AFTERNOON TSTMS ERN SECTIONS. MIDNIGHT SHIFT MADE EXCELLENT DECISION
WITH REGARD TO SHORT-TERM FORECAST WHICH IS QUITE ADEQUATE...
ESPECIALLY GIVEN 06/12Z PROGGED ETA/NAM LIFTED INDEX VALUES OF AT
LEAST MINUS 2 ERN SECTIONS THIS AFTERNOON. DRY AREAWIDE TONIGHT INTO
FRI AS SHORTWAVE RIDGE TRANSITIONS ACROSS THE AREA.

SIGNIFICANT CHANGES OCCUR THIS WEEKEND...PARTICULARLY LATE IN THE
WEEKEND...AS LOW PRESSURE DEEPENS OVER THE SWRN CONUS. FAIRLY DECENT
RUN-TO-RUN CONSISTENCY AMONGST THE VARIOUS GFS SOLUTIONS THOUGH THE
GFS IS STARTING TO BECOME MORE PROGRESSIVE WITH APPROACHING UPPER
LOW.

WILL OPT FOR SLIGHT CHANCE OF SHOWERS/TSTMS SAT...AND MAINLY DURING
THE AFTERNOON WHEN PROGGED MOISTURE INCREASE IS MOST PRONOUNCED.
APPEARS THAT THE BEST CHANCE OF MEASURABLE PRECIP TUCSON VICINITY
WILL BE ABOUT A 12-HOUR PERIOD...MOST LIKELY SAT NIGHT...THOUGH THE
EXACT TIMING IS STILL NOT TOTALLY CERTAIN. SURFACE WIND ASSOCIATED
WITH SYSTEM MAY VERY WELL BE MORE SIGNIFICANT THAN PRECIP HOWEVER.

GIVEN PROGRESSIVE NATURE OF PAST 2-3 GFS SOLUTIONS...MAY OPT FOR SOME
ADJUSTMENTS TO POP/WEATHER FIELDS FOR THE SUN-MON PERIOD. WILL
ADDRESS THIS NOTION FURTHER DURING THE AFTERNOON DISCUSSION. FOR NOW
WILL OPT FOR NO CHANGES TO INHERITED FORECASTS.

&&

.AVIATION...TAF AND TWEBS ADEQUATELY COVER ALL SIGNIFICANT WEATHER
AT KTUS.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...NONE.

&&

BF

WEATHER.GOV/TUCSON