125
FXUS65 KTWC 031607
AFDTWC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
907 AM MST THU SEP 3 2026
SYNOPSIS
EXPECT SCATTERED TO NUMEROUS THUNDERSTORMS EACH
AFTERNOON AND EVENING THROUGH THE WEEKEND AS TROPICAL MOISTURE
MOVES IN. THE MAIN THREAT WILL BE HEAVY RAINFALL LEADING TO
AREAS OF FLASH FLOODING. HIGH TEMPERATURE WILL WILL FLUCTUATE
BETWEEN NORMAL AND A FEW DEGREES BELOW NORMAL.
UPDATE
WATER VAPOR SATELLITE HAS A NOSE OF 1.4-1.6 INCHES OF PWATS
EXTENDING FROM THE GULF OF CALIFORNIA UP OVER THE CATALINAS AND
UP TO THE WHITE MOUNTAINS. THICK CLOUD COVER IN THE NORTHERN
HALF OF THE CWA WITH CLEARING SOUTH, ALONG THE INTERNATIONAL
BORDER AND OUT WEST OF TUCSON. THE AREAS WITH PLENTY OF SUNSHINE
WILL ERODE CIN AND TAP INTO THE AVAILABLE CAPE. ALL SETTING UP
TO AN EARLY START OF THUNDERSTORMS. 12Z CAM GUIDANCE SHOWS
THUNDERSTORMS AND RAIN SHOWERS FORMING BY 11 AM. IF THERE IS
MORE SURFACE HEATING IN THE EARLY HOURS, ESPECIALLY ON THE
MOUNTAIN SLOPES, IT WILL JUMP START STORMS AN HOUR EARLIER THAN
THE GUIDANCE. THESE STORMS WILL BE EFFICIENT RAINERS THROUGHOUT
THE DAY AND INTO THE NIGH DUE TO THE STREAM OF MOISTURE FROM THE
GULF. SOUTHERN PIMA COUNTY, CATALINAS AND RINCON MOUNTAINS,
SANTA CRUZ COUNTY, AND WESTERN PORTION OF COCHISE COUNTY HAS
20-70 PERCENT FOR ONE INCH OR HIGHER RAIN TOTALS. THE SANTA
RITAS, EMPIRE MOUNTAINS, PORTIONS OF CATALINAS HAVE A 10-60% FOR
2 INCHES OR HIGHER. THE HIGHEST CHANCES WILL BE IN THE SANTA
RITAS. THIS WILL BRING A SLIGHT RISK (<15%) FOR FLASH FLOODING
FOR THE REGION TODAY, ESPECIALLY FOR AREAS THAT SAW HEAVY RAIN
AND EXPERIENCED A FLASH FLOOD IN THE LAST 48 HOURS.
SEE PREVIOUS DISCUSSION BELOW FOR THE NEXT SEVEN DAYS FORECAST.
DISCUSSION
SCATTERED WEAK SHOWERS WITH ISOLATED THUNDER HAVE
FORMED OVER THE LAST HOUR BETWEEN NOGALES AND BENSON. THIS MAY
BE THE RESULT OF OUTFLOWS MOVING IN FROM SONORA FROM CONVECTION
WEDNESDAY EVENING. EXPECT SHOWER ACTIVITY TO PERSIST FOR A
FEW MORE HOURS WITH OCCASIONAL LIGHTNING.
ALOFT WE ARE IN A TRANSITIONAL MONSOON PATTERN WITH RIDGING
WELL TO THE EAST AND A CLOSED LOW OVER THE PACIFIC NORTHWEST.
PWATS HAVE INCREASED BY ABOUT A 0.25" OVER THE LAST 24 HOURS
FROM CENTRAL PIMA COUNTY EASTWARD. THIS IS IN PART DUE TO
SOUTHERLY FLOW OVER ARIZONA AND SONORA PULLING UP TROPICAL
MOISTURE FROM HURRICANE MARIE. BECAUSE OF THIS EXPECT
THUNDERSTORM COVERAGE TO EXPAND NORTHWARD COMPARED TO WEDNESDAY
WITH 30-60 POPS FROM THE TOHONO O'ODHAM NATION EASTWARD. CAMS
SHOW CONVECTION STARTING AS EARLY AS 11 AM AND CONTINUING
THROUGH THE EVENING HOURS. THE MAIN THREAT LOOKS TO BE HEAVY
RAINFALL THANKS TO THE ABOVE NORMAL PRECIPITABLE WATER. THE
03/00Z HREF PAINTS AREAS FROM SOUTHERN PINAL COUNTY DOWN TO
SANTA CRUZ COUNTY AND THE EASTERN HALF OF GRAHAM AND COCHISE
COUNTIES AS HAVING THE BEST CHANCES FOR 1" HOURLY RAINFALL
RATES THIS AFTERNOON AND EVENING. THIS COULD LEAD TO AREAS OF
FLASH FLOODING AND ALSO RISES IN AREA WASHES AND RIVERS. FRIDAY
THE BEST MOISTURE SHIFTS SLIGHTLY EAST WITH THE BEST CHANCES
FOR SCATTERED THUNDERSTORMS FROM TUCSON EASTWARD. AGAIN, THE
MAIN THREAT WILL BE HEAVY RAINFALL LEADING TO FLASH FLOODING.
BOTH TODAY AND FRIDAY THE WPC HAS PORTIONS OF SOUTHEAST ARIZONA
UNDER A SLIGHT RISK FOR EXCESSIVE RAINFALL.
THIS WEEKEND INTO EARLY NEXT WEEK THE UPPER AIR PATTERN REMAINS
MOSTLY UNCHANGED WITH A CLOSED LOW OVER THE PACIFIC NORTHWEST
AND HIGH PRESSURE OVER THE GREAT PLAINS AND MIDWEST. THIS WILL
ALLOW TROPICAL MOISTURE TO CONTINUE TO ADVECT INTO THE REGION.
EXPECT DAILY AFTERNOON AND EVENING THUNDERSTORMS CAPABLE OF
HEAVY RAINFALL LEADING TO FLASH FLOODING. AFTER MONDAY THE
PACIFIC NORTHWEST LOW BEGINS TO MOVE INLAND, BUT IS IMMEDIATELY
REPLACED BY ANOTHER TROUGH OVER THE WEST COAST. HOWEVER THERE
ARE LARGE DIFFERENCES BETWEEN ENSEMBLE SYSTEMS IN HOW STRONG THE
SECOND UPPER LOW WILL BE. MODELS DO AGREE THOUGH THAT PWATS
WILL BE 25-50 PERCENT ABOVE NORMAL THROUGH AT LEAST NEXT WEEK
THURSDAY, SO EXPECT CONTINUED DAILY AFTERNOON AND EVENING
THUNDERSTORMS PAST MONDAY.
TEMPERATURES WILL BE NEAR OR JUST SLIGHTLY BELOW NORMAL THROUGH THE
FORECAST PERIOD.
AVIATION
VALID THROUGH 04/18Z.
EXPECT SCT-BKN CLOUDS 8-12K FT AGL THROUGH THE FORECAST PERIOD.
ISOLATED TO SCATTERED TSRA/SHRA FROM CENTRAL PIMA COUNTY
EASTWARD AFTER 03/18Z THROUGH 04/05Z. NEAR THUNDERSTORMS EXPECT
HEAVY RAINFALL AND GUSTY WINDS TO 35 KTS. OTHERWISE WINDS WILL
BE WEST SOUTHWEST 5-10 KTS THIS AFTERNOON AND EVENING, AND LIGHT
AND TERRAIN DRIVEN AT OTHER TIMES. AVIATION DISCUSSION NOT
UPDATED FOR TAF AMENDMENTS.
FIRE WEATHER
EXPECT DAILY SCATTERED THUNDERSTORMS EACH
AFTERNOON AND EVENING TODAY INTO EARLY NEXT WEEK. THERE WILL BE
SOME VARIATION IN COVERAGE DAY TO DAY, BUT EXPECT THE BULK OF
THE ACTIVITY FROM CENTRAL PIMA COUNTY EASTWARD. HEAVY RAINFALL
LEADING TO FLASH FLOODING WILL BE THE MAIN THREAT. TEMPERATURES
WILL BE AROUND NORMAL TO A FEW DEGREES BELOW NORMAL INTO EARLY
NEXT WEEK. MINIMUM RELATIVE HUMIDITY VALUES MAINLY 20 TO 45
PERCENT IN THE VALLEYS AND 30 TO 60 PERCENT IN THE MOUNTAINS
OVER THE NEXT WEEK. WINDS WILL GENERALLY REMAIN LESS THAN 15 MPH
AND TERRAIN DRIVEN THROUGH THE WEEK.
TWC WATCHES/WARNINGS/ADVISORIES
NONE.
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