Area Forecast Discussion
Issued by NWS Tucson, AZ

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS65 KTWC 250419
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
918 PM MST SUN AUG 24 2014

.SYNOPSIS...MOISTURE WILL WORK BACK INTO THE AREA FROM THE SOUTH
OVER THE NEXT 24 TO 48 HOURS...RESULTING IN SHOWERS AND THUNDERSTORMS
WITH POTENTIALLY HEAVY RAIN ACROSS SOUTHEAST ARIZONA...ESPECIALLY
SOUTH CENTRAL ARIZONA NEAR THE INTERNATIONAL BORDER. BELOW NORMAL
AFTERNOON TEMPERATURES THIS WEEK WILL GRADUALLY APPROACH NORMAL
LEVELS BY NEXT WEEKEND.

&&

.DISCUSSION...THE UPPER PATTERN IS DEFINED BY A CATEGORY 4 HURRICANE
NAMED MARIE POSITIONED AT 16.6N/112.8W...TRACKING WNW AT 12 MPH THRU
THE EASTERN PACIFIC...AN UPPER-LEVEL TROUGH IN THE PACIFIC NORTHWEST
TRACKING SOUTH INTO THE GREAT BASIN...AND A RIDGE IN THE CENTRAL
STATES WITH A TAIL EXTENDING ALL THE WAY ACROSS SOUTHERN ARIZONA.

A BIG SHIFT FROM THE CURRENT DRY WEATHER PATTERN WE HAVE BEEN IN THE
PAST FEW DAYS IS EXPECTED TO OCCUR OVER THE NEXT 24 TO 48 HOURS. THE
UPPER FLOW BEGINS TO OPENS UP TO MORE OF A SOUTHERLY FLOW OVER THE
NEXT 24 HOURS AS THE RIDGE AXIS WEAKENS. THIS NOT ONLY ALLOWS FOR
DEEPER MOISTURE POOLED UP IN NW MEXICO /THANKS TO HURRICANE MARIE/
TO TRACK NORTHWARD INTO THE STATE...BUT ALLOWS FOR A MID-LEVEL
DISTURBANCE TO MOVE INTO FAR SE AZ TOMORROW EVENING. DIFLUENT FLOW
AROUND THIS FEATURE AS IT INTERACTS WITH THE APPROACHING TROUGH FROM
THE PACIFIC NORTHWEST SHOULD HELP FOCUS CONVECTION ACROSS SOUTH
CENTRAL ARIZONA TOMORROW NIGHT. QUICK LOOK AT BOTH THE 00Z NAM AND
GFS RUNS INDICATES BOTH MODELS ARE TRYING TO DROP VERY HEAVY RAIN
ACROSS THE SOUTHERN TOHONO OODHAM NATION...ALTHOUGH WITH DIFFERENT
TIMING. THE NAM IS MUCH FASTER BRINGING THE MAJORITY OF THE RAINFALL
MONDAY NIGHT...AND THE GFS WAITS UNTIL TUESDAY WHEN ENHANCED UPPER
DIFFLUENCE ASSOCIATED WITH THE UPPER TROUGH MOVES ACROSS THE AREA.
REALITY PROBABLY SITS SOMEWHERE IN BETWEEN.

CONFIDENCE IS HIGH THAT WE WILL HAVE HEAVY RAINFALL ACROSS THE
FORECAST AREA RESULTING IN FLASH FLOODING...ESPECIALLY SOUTH-CENTRAL
ARIZONA NEAR THE INTERNATIONAL BORDER WHERE IT IS NOT INCONCEIVABLE
THAT ISOLATED SPOTS CAN GET AS MUCH AS 2-4 INCHES. HOWEVER...LOW
CONFIDENCE ON THE TIMING OF HEAVY RAIN. IN ANY EVENT...WILL INCREASE
POPS MONDAY NIGHT AND TUESDAY FROM PRESENT GRIDS DUE TO INCREASED
CONFIDENCE FOR MEASURABLE RAINFALL.

&&

.PREV DISCUSSION...

MOIST AIR WILL BEGIN SURGING INTO AZ. SATELLITE IMAGERY SHOWS THE 2
INCH PRECIP WATER VALUES ARE ROUGHLY 200 MILES SOUTH OF THE
BORDER...AND HEADING THIS WAY. HIGHER RES MODELS ARE MORE BULLISH ON
PRECIP CHANCES FOR MONDAY THAN I PREVIOUSLY EXPECTED. FORECAST
SOUNDINGS SHOW COOLER AIR IN THE MID LEVELS MOVING IN STARTING LATE
TONIGHT...WITH 500 MB TEMPS FALLING BY A DEGREE OR SO BY MONDAY
AFTERNOON...WITH ADDITIONAL COOLING EXPECTED THROUGH TUESDAY.
COMBINED WITH THE MOIST ADVECTION AND POTENTIAL BOUNDARY
INTERACTIONS FROM DYING STORMS IN MEXICO...DECIDED TO INCREASE POPS
ON MONDAY.

IR SATELLITE IMAGERY SHOWS A FEW CONVECTIVE BANDS WELL AHEAD OF
HURRICANE MARIE MOVING THIS DIRECTION...SO THINKING THE ACTIVITY
MONDAY THROUGH TUESDAY WILL FOLLOW A SIMILAR PATTERN WITH PERIODS OF
MODERATE TO HEAVY RAIN...FOLLOWED BY SHORT BREAKS BEFORE THE NEXT
WAVE MOVES IN.

MODELS STILL HITTING THE MOISTURE HARD ON TUESDAY. BUFKIT NAM
PROFILES PUSH THE PRECIP WATER VALUES UP TO 2 INCHES EARLY TUES
MORNING...WHICH IS NEAR THE CLIMATOLOGICAL MAX FOR THIS TIME OF
YEAR. THE GFS SLIGHTLY LESS MOIST. MODELS ARE ALSO HITTING THE
PRECIP CHANCES HARD FOR OVERNIGHT MONDAY INTO TUESDAY MORNING. MAIN
CONCERN OVER THE NEXT 48 HOURS WILL BE THE FLOOD THREAT. WE SHOULD
HAVE STRONGER STEERING FLOW THAN TYPICAL MONSOON DAYS...SO THE FLOOD
THREAT WILL COME FROM EFFICIENT RAIN PROCESSES AND TRAINING STORMS.

TUESDAY WILL BE CLOUDY AND RELATIVELY COOL AS WELL. HIGH TEMPS WILL
BE 5 DEGREES OR MORE BELOW CLIMATOLOGY WITH ALL THE CLOUD COVER IN
PLACE.

BY WEDNESDAY...THE MOISTURE RETREATS QUICKLY AND WE SHOULD START A
DRYING TREND THROUGH NEXT WEEKEND. TEMPS WILL REBOUND TO CLIMATOLOGY
AND MAYBE A FEW DEGREES WARMER BY NEXT WEEKEND.

JJB

&&

.AVIATION...VALID THRU 26/06Z. SCATTERED CLOUDS AT 12-14KFT MSL WITH
BROKEN CIRRUS 20-25KFT MSL OVERNIGHT. BIGGEST CONCERN IS FOR
THUNDERSTORMS /SCT-BKN 8-10KFT MSL/ MONDAY...BEGINNING AS EARLY AS
18Z...BUT THE BETTER CHANCES WILL OCCUR AFTER 22Z AND INCREASING
INTO THE EVENING. CONFIDENCE IS INCREASING FOR STORMS TO IMPACT ALL
TERMINALS AT SOME POINT MONDAY AFTERNOON THROUGH TUESDAY. WILL
CONTINUE TO FINE TUNE THOSE DETAILS WITH LATER TAF ISSUANCES.
OTHERWISE...WINDS SHOULD REMAIN LIGHT. AVIATION DISCUSSION NOT
UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...MOISTURE IS ON THE WAY UP OVER THE NEXT 24 TO 48
HOURS. IN FACT...SHOWERS AND THUNDERSTORMS CAN BEGIN AS EARLY AS
MIDDAY MONDAY...WITH SIGNIFICANTLY INCREASING CHANCES INTO MONDAY
EVENING. BEST CHANCE FOR WETTING RAINS WILL BE MONDAY NIGHT INTO
TUESDAY EVENING AS DEEPER MOISTURE ASSOCIATED FROM HURRICANE MARIE
MOVES INTO THE AREA.

&&

$$

VISIT US ON FACEBOOK...TWITTER...YOUTUBE...AND AT WEATHER.GOV/TUCSON












USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.