Flash Flood Warning 51, NWS Tucson, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
210 PM MST SUN AUG 19 2007

.SYNOPSIS...A VERY GRADUAL DRYING TREND WILL OCCUR THROUGH THE
MIDDLE OF THE WEEK...WITH ONLY A SLIGHT CHANCE OF MAINLY AFTERNOON
AND EVENING THUNDERSTORMS EXPECTED. A FAVORABLE EASTERLY FLOW WILL
RETURN TOWARD THE END OF THE WEEK AND ESPECIALLY NEXT WEEKEND...
BRINGING AN INCREASED CHANCE OF THUNDERSTORMS TO SOUTHEAST ARIZONA.
DAYTIME HIGH TEMPERATURES WILL REMAIN ABOVE NORMAL THIS WEEK.

&&

.DISCUSSION...KEMX WSR-88D DETECTED SCATTERED MAINLY 35-55 DBZ
ECHOES ADJACENT THE MOUNTAINS OF CENTRAL/ERN PIMA...SANTA CRUZ AND
WRN COCHISE COUNTIES AT 2105Z. ECHOES WERE EXHIBITING A VERY SLOW
NWD DRIFT OR WERE STATIONARY. THE REST OF SE AZ WAS VOID OF PRECIP
ECHOES. ABUNDANT LOW-LEVEL MOISTURE EXISTS THOUGH LARGE-SCALE
FORCING MECHANISM LACKING THIS AFTERNOON AND EVENING FOR WIDESPREAD
CONVECTIVE EVENT. THUS WILL REFLECT 20 PERCENT CHANCE OF SHOWERS/
TSTMS THIS EVENING EXCEPT ACROSS THE NATION AS WELL AS SANTA CRUZ/
COCHISE COUNTIES WHERE SOMEWHAT HIGHER POPS WARRANTED. BELIEVE BULK
OF ACTIVITY WILL END BY MIDNIGHT AS PER 19/18Z NAM12 SOLUTION.

APPEARS DOWNWARD TREND IN CONVECTIVE ACTIVITY ON TAP STARTING MONDAY
AND CONTINUING INTO MIDWEEK AS UPPER HIGH PRESENTLY OVER SRN NM
SHIFTS WWD IN RESPONSE TO TROUGH MOVING ACROSS THE NRN STATES. STILL
WILL BE AMPLE MOISTURE TO JUSTIFY LOW-GRADE POPS TUCSON VICINITY EWD
MAINLY DURING THE AFTERNOONS AND EVENINGS. PER COORD WITH WFO PSR
HAVE OPTED FOR DRY SCENARIO TUE-WED NIGHT ACROSS SE PINAL AND THE
NATION...WITH DRY CONDITIONS FAR WRN PIMA COUNTY DURING THE TUE-FRI
NIGHT PERIOD.

19/12Z GFS TRENDED DOWNWARD VERSUS PREVIOUS SOLUTIONS ON UPSWING IN
CONVECTIVE ACTIVITY DURING THE FRI-SUN PERIOD. FOR INSTANCE...THIS
SOLUTION PROGGED ANY SEMBLANCE OF INVERTED TROUGHS AND MID-LEVEL
IMPULSES MOVING WWD AROUND PERIPHERY OF SRN CONUS HIGH...SUCH AS
POSSIBLE TROPICAL SYSTEM DEAN REMNANTS...FURTHER SOUTH THAN PREVIOUS
SOLUTIONS. HOWEVER...DID NOT COMPLETELY BUY INTO THIS NOTION BUT
RATHER ADJUSTED INHERITED GRIDDED DATA POP VALUES DOWNWARD SLIGHTLY.
AT ANY RATE...WILL STILL REFLECT CHANCE-TYPE POPS WHICH WOULD
TRANSLATE INTO SCATTERED SHOWERS/TSTMS FRI-SUN.

DAYTIME HIGH TEMPS AT A COUPLE OF LOCALES IN THIS FORECAST AREA MON
INTO WED MAY APPROACH RECORD HIGHS. GIVEN THAT MOST FORECAST POINTS
ARE EXPECTED TO BE MORE THAN 3 DEGS FROM RECORD TEMPS HOWEVER...WILL
NOT ISSUE HEADLINE OF RECORD OR NEAR-RECORD MAX TEMPS WITH THE
PUBLIC ZONE FORECASTS. STILL...DAYTIME HIGH TEMPS TO REMAIN ABOVE
NORMAL THROUGH MUCH OF THIS WEEK.

&&

.AVIATION...WDLY SCT TSRA WILL OCCUR ACROSS MUCH OF SE AZ THIS
EVENING...WITH MUCH OF THE ACTIVITY EXPECTED TO END AROUND BY 20/06Z
OF SO. HOWEVER...SCT TSRA IS FORECAST MAINLY SOUTH AND WEST OF KTUS.
CEILINGS FROM TSRA MOSTLY AT OR ABOVE 7KFT AGL...THOUGH CIGS AS LOW
AS 2-3 KFT AGL AND VSBYS AS LOW AS 1-3SM WITH THE STRONGEST TSTMS.
CONVECTIVE DEBRIS CLOUDS AFTER 20/06Z WITH CIGS AT OR ABOVE 12KFT
AGL...BECOMING MOSTLY CLEAR MONDAY MORNING. AVIATION DISCUSSION NOT
UPDATED FOR TAF AND TWEB AMENDMENTS.

&&

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

WEATHER.GOV/TUCSON