562
FXUS65 KTWC 201720
AFDTWC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
1020 AM MST MON JUL 20 2026
SYNOPSIS
THE COMBINATION OF AMPLE MOISTURE POSITIONED ACROSS
SOUTHEAST ARIZONA AND AN UPPER-LEVEL DISTURBANCE MOVING INTO
THE AREA FROM NEW MEXICO TODAY WILL RESULT IN WIDESPREAD SHOWERS
AND THUNDERSTORMS...ESPECIALLY TO THE EAST AND SOUTH OF TUCSON.
THESE STORMS WILL BE CAPABLE OF PRODUCING HEAVY RAINFALL. A FLASH
FLOOD WATCH IS IN EFFECT FOR GRAHAM, GREENLEE, COCHISE AND SANTA
CRUZ COUNTIES THIS AFTERNOON INTO THIS EVENING. THERE IS A
POSSIBILITY THAT TUESDAY WILL ALSO BE ACTIVE ACROSS THE REGION WITH
A CONTINUED POTENTIAL FOR HEAVY RAINFALL. OTHERWISE, DAYTIME
TEMPERATURES WILL REMAIN BELOW AVERAGE BY SEVERAL DEGREES INTO
MIDWEEK INCREASING TO ABOVE NORMAL LATE THIS WEEK INTO THE
WEEKEND.
UPDATE 1015 AM
ISOLATED SHOWERS AND SPRINKLES ARE MOVING
FROM ESE TO WNW THIS MORNING. DON'T EXPECT MUCH MORE THAN A
TRACE TO A FEW HUNDREDTHS OF AN INCH OF RAIN. CLOUD DEBRIS
EXISTS FROM TUCSON/NOGALES WEST INTO THE LOWER DESERTS, WITH
CLEARING ACROSS THE REST OF SE AZ. EXPECT CLEARING TO EXPAND
THROUGH THE MORNING.
THE FLASH FLOOD WATCH IS IN GOOD SHAPE WITH CONVECTION
DEVELOPING OVER THE CHIRICAHUA MTNS AND THE MOGOLLON RIM BY
NOON, THEN MOVING W/SW INTO THE LOWER DESERTS/VALLEYS BY MID TO
LATE AFTERNOON INTO THE EVENING.
THE MAIN THREAT WILL BE VERY HEAVY RAINFALL AND FLASH FLOODING,
WITH GUSTY WINDS A SECONDARY THREAT. THERE COULD BE A LOCALIZED
GUST TO 50 KTS AS CONVECTION MOVES OFF THE TERRAIN, BUT 30-40KTS
ARE MORE LIKELY. A DEEPER DIVE INTO THE FLASH FLOOD SETUP
SHOWS ABUNDANT MOISTURE AND A SUSCEPTIBLE AREA. WIDESPREAD
0.5"+ WITH LOCALIZED AMOUNTS OF 2"+ FELL ACROSS A GOOD CHUNK OF
FAR SEAZ, ESPECIALLY COCHISE COUNTY. THIS AREA WILL BE THE MOST
VULNERABLE. IN ADDITION, CAMS SHOW WEAKLY ORGANIZED CLUSTERS
WITH THE POTENTIAL FOR CELL MERGERS AND AT LEAST SOME
TRAINING/BACKBUILDING AS FLOW REMAINS RELATIVELY WEAK.
AS THE MID/UPPER LEVEL LOW NOSES INTO SEAZ FROM NM/MX,
CONVECTION COULD GO WELL INTO THE EVENING AND PERHAPS INTO THE
OVERNIGHT. CONFIDENCE IS LOW AT THIS TIME REGARDING THE
OVERNIGHT, BUT THERE IS AT LEAST SOME SIGNAL IN THE HREF OF
HIGHER RAINFALL TOTALS ACROSS CENTRAL PIMA COUNTY. THERE IS NOT
ENOUGH CONFIDENCE TO EXPAND THE FLASH FLOOD WATCH WEST INTO
EASTERN/CENTRAL PIMA COUNTY, BUT ITS IS NOT OUT OF THE
QUESTION WE HAVE A FLASH FLOOD WARNING OR TWO THIS EVENING.
AS FOR THE TUCSON METRO, CONFIDENCE IS AGAIN LOW ON
EVOLUTION/PROPAGATION OF STORMS OFF THE RIM THIS
EVENING/OVERNIGHT. WE WILL LIKELY HAVE STORMS IN THE METRO, BUT
ONCE AGAIN FAVORING THE CATALINA FOOTHILLS, ORACLE/CATALINA, THE
FAR EAST SIDE, AND SOUTH INTO THE CORONA DE TUCSON. WE CANNOT
RULE OUT LOCALIZED FLASH FLOODING, BUT PROBABILITIES ARE RATHER
LOW. THE MORE LIKELY SCENARIO IS SEEING LIGHT TO MODERATE RAIN
SHOWERS WITH EMBEDDED STORMS LATE EVENING INTO OVERNIGHT AS THE
MID/UPPER LEVEL LOW BEGINS TO PROVIDE MORE LIFT AND ELEVATED
INSTABILITY TO THE AREA.
DISCUSSION
TO BE SUCCINCT: SOUTHEAST ARIZONA IS POISED FOR
AN ACTIVE START TO THE WORK WEEK. THE COMBINATION OF AMPLE
MOISTURE ACROSS THE REGION AND AN UPPER-LEVEL DISTURBANCE MOVING
INTO THE AREA FROM NEW MEXICO WILL RESULT IN WIDESPREAD SHOWERS
AND THUNDERSTORMS...ESPECIALLY EAST AND SOUTH OF TUCSON. THESE
STORMS WILL BE CAPABLE OF PRODUCING HEAVY RAINFALL, WITH
LOCALIZED RAINFALL AMOUNTS BETWEEN 1 AND 3 INCHES. GIVEN HOW
SATURATED SOILS ARE ACROSS THE AREA FROM STORMS OVER THE PAST
WEEK, THERE IS AN INCREASED POTENTIAL FOR RAINFALL RUNOFF TO
PRODUCE FLASH FLOODING. THEREFORE, A FLASH FLOOD WATCH IS IN
EFFECT FOR PORTIONS OF SOUTHEAST ARIZONA (INCLUDING GRAHAM,
GREENLEE, COCHISE AND SANTA CRUZ COUNTIES) FROM NOON MST TODAY
THROUGH MIDNIGHT MST TONIGHT.
THE UPPER PATTERN THIS MORNING CONTINUES TO BE DEFINED WITH AN
UPPER TROUGH OF LOW PRESSURE ALONG THE RIO GRANDE IN FAR WEST
TEXAS AND AN ANOMALOUSLY STRONG E/W ORIENTED RIDGE OF HIGH
PRESSURE CENTERED OVER THE COLORADO ROCKIES. THINGS USUALLY GET
ACTIVE WHEN FEATURES ARE ON THE MOVE, AND THAT IS WHAT WE WILL
SEE THE NEXT FEW DAYS. THAT UPPER-LOW WILL NUDGE INTO THE
EASTERN PORTIONS OF SOUTHEAST ARIZONA TODAY AS THE UPPER HIGH
CENTER BEGINS TO MOVE INTO WRN KS. THE UPPER-LOW THEN THEN
THROUGH NORTHERN ARIZONA TUESDAY AS THE HIGH CENTER TRACKS INTO
OKLAHOMA. PLENTY OF MOISTURE AVAILABLE EAST AND SOUTH OF TUCSON
TODAY AS PWATS ARE GENERALLY HOVERING BETWEEN 1.25 AND 1.50
INCHES. THE AREA OF BEST LIFT/DYNAMICS DUE TO DEFORMATION OF THE
FLOW ALOFT AS THE UPPER-LOW MOVES INTO OUR NECK OF THE WOODS
WILL BEGIN IN THE WHITES AND ALONG THE SOUTHERN PORTIONS OF THE
MOGOLLON RIM THAT EXTENDS INTO NM EARLY THIS AFTERNOON AND
SPREADS ACROSS COCHISE AND INTO SANTA CRUZ COUNTY AS THE DAY
PROGRESSES. THE COMBINATION OF BOTH THESE ELEMENTS WILL RESULT
IN AN INCREASED POTENTIAL FOR HEAVY RAINFALL RATES TO THE EAST
AND SOUTH OF TUCSON TODAY. THIS IS SUPPORTED BY THE 20/00Z HREF
WHICH SHOWS A WIDESPREAD NEIGHBORHOOD PROBABILITY 70-90% FOR
STORMS TO PRODUCE IN EXCESS OF AN INCH OF RAIN ACROSS THE
AFOREMENTIONED AREAS BETWEEN 20/21Z AND 21/03Z AND EVEN A 10%
PROBABILITY FOR RAINFALL IN EXCESS OF 3 INCHES ACROSS COCHISE
AND SANTA CRUZ COUNTIES. PER COORDINATION WITH THE WEATHER
PREDICTION CENTER (WPC), THEY EXPANDED THE SLIGHT RISK FOR FLASH
FLOODING ON THEIR DAY 1 EXCESSIVE RAINFALL OUTLOOK (ERO) TODAY
TO INCLUDE SANTA CRUZ COUNTY TO BETTER SUPPORT OUR FLASH FLOOD
POTENTIAL.
IN ADDITION TO THE RAINFALL, THERE IS A SIMILAR SETUP AS TO
YESTERDAY WITH THE DRIER AIRMASS RESIDING IN WEST-CENTRAL NEW
MEXICO GETTING ENTRAINED INTO THE STORMS AS THEY MOVE OFF THE
TERRAIN INTO THE GILA RIVER VALLEY...INCREASING THE LIKELIHOOD
FOR GUSTY OUTFLOW WINDS TO 40-45 MPH/BLOWING DUST TO IMPACT THE
GILA RIVER VALLEY AND SAN SIMON VALLEY AGAIN TODAY.
OTHERWISE, THE UPPER-LOW EVENTUALLY MAKES IT INTO OUR ERN CWA
BY 21/12Z TUESDAY MORNING...THEN RAPIDLY EJECTS NNW INTO NORTH
CENTRAL AZ TUESDAY EVENING. THE PROBABILITIES FOR EXCESSIVE
RAINFALL WITH BOTH THE 20/00Z HREF AND REFS REMAIN IMPRESSIVE
FOR HEAVY RAINFALL ACROSS THE EASTERN HALF OF THE FORECAST AREA
TUESDAY. MY CONCERN IS THAT MY OWN EXPERIENCE TELLS ME THAT IF
AN AREA GETS HIT HARD WITH ADDITIONAL NOCTURNAL CONVECTION
UNDER THE UPPER-LOW LIKE IS EXPECTED TONIGHT, THEN TUESDAY WILL
LIKELY BE A DOWN DAY AS THE ATMOSPHERE IS WORKED OVER. IN
ADDITION, I DON'T LIKE THE POSITION OF THE UPPER-LOW BEING TO
OUR NORTH DURING THE DAY. THAT LEAVES SOUTHEAST ARIZONA IN THE
SUBSIDENT WAKE OF THE FEATURE. IT IS POSSIBLE THAT THERE IS JUST
ENOUGH MOISTURE AND INSTABILITY WITHIN THE LOWER-LEVELS TO
SUPPORT WIDESPREAD SHOWERS AND THUNDERSTORMS...BUT I DON'T KNOW
ABOUT THE INTENSITY OF THE DOWNPOURS. IT IS POSSIBLE THAT IN THE
WAKE ANOTHER DISTURBANCE FROM SONORA MEXICO FOLLOWS IN BEHIND
AND MOVES ACROSS THE AREA TO SUPPORT STRONGER MORE INTENSE
STORMS...BUT THAT IS A BIG IF. IT WOULD BE JUST AS LIKELY FOR
THIS FEATURE TO MOVE ACROSS SUPPORTING NOCTURNAL CONVECTION
TUESDAY NIGHT INTO WEDNESDAY MORNING. AT THIS TIME, THE WPC
STILL HAS A LARGE AREA OF SOUTHEAST ARIZONA IN THE 'SLIGHT RISK'
ON THEIR DAY-2 ERO FOR TUESDAY, BUT THERE IS JUST TOO MUCH
UNCERTAINTY FOR ME AT THIS TIME TO MESSAGE ANOTHER BIG DAY
TUESDAY.
AVIATION /15Z MONDAY THROUGH 15Z TUESDAY/
VALID THROUGH 21/12Z. SCT 6-8K FT AGL BKN-OVC 8-12K
FT AGL WITH WIDELY SCATTERED -SHRA/EMBEDDED -TSRA MOVING WEST
THRU AREAS FROM TUCSON AND SOUTH THROUGH 20/14Z THIS MORNING.
OTHERWISE, SCT-BKN CLOUDS 6-8K FT AGL BKN-OVC 8-12K FT AGL
AFTER 19/20Z THIS AFTERNOON WITH WIDESPREAD SHOWERS AND
THUNDERSTORMS WITH MOUNTAIN OBSCURATIONS POSSIBLE ACROSS
COCHISE, SANTA CRUZ, GRAHAM AND GREENLEE COUNTIES WITH 3-5SM IN
HEAVY RAIN. BLDU WILL ALSO BE POSSIBLE IN THE GILA RIVER AND SAN
SIMON VALLEYS AS STORMS THERE WILL BE CAPABLE OF PRODUCING
ERRATIC STRONG WIND GUSTS OF 35-40 KTS. OUTSIDE OF THUNDERSTORMS,
SURFACE WINDS GENERALLY UNDER 10 KTS. AVIATION DISCUSSION NOT
UPDATED FOR TAF AMENDMENTS.
FIRE WEATHER
DAILY CHANCES FOR THUNDERSTORMS WILL CONTINUE
EACH AFTERNOON AND EVENING THROUGH THE NEXT 7 DAYS WITH DAY TO
DAY VARIABILITY. WIDESPREAD SHOWERS AND THUNDERSTORMS ARE
EXPECTED EAST AND SOUTH OF TUCSON TODAY, AND POSSIBLY AGAIN
TUESDAY. THESE STORMS WILL BE CAPABLE OF PRODUCING HEAVY
RAINFALL WITH THE POTENTIAL FOR FLASH FLOODING. A FLASH FLOOD
WATCH IS IN EFFECT TODAY FOR THE EASTERN PORTIONS OF SOUTHEAST
ARIZONA. MINIMUM RELATIVE HUMIDITY 25-30 PERCENT IN THE LOWER
DESERT LOCATIONS AND ABOVE 40 PERCENT IN THE MOUNTAINS THIS
WEEK. WINDS THIS WEEK WILL REMAIN MAINLY LIGHT AND UNDER 15 MPH,
THOUGH STRONG AND ERRATIC WINDS WILL BE POSSIBLE WITH ANY
THUNDERSTORM.
TWC WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH FROM NOON MST TODAY THROUGH THIS EVENING FOR
AZZ503-507>513.
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