Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 301706
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
1005 AM MST SUN AUG 30 2015

.SYNOPSIS...ANOTHER GOOD CHANCE OF SHOWERS AND THUNDERSTORMS THIS
AFTERNOON AND MONDAY. SOME STORMS WILL GENERATE STRONG WINDS AND
LOCALLY HEAVY RAINFALL...WITH AREAS OF BLOWING DUST POSSIBLE. A SLOW
DRYING TREND WILL THEN LIMIT THUNDERSTORMS TO EAST OF TUCSON THE
SECOND HALF OF THE WEEK. HOTTER THAN AVERAGE TEMPERATURES WILL FALL
TO NEAR AVERAGE AROUND THE MIDDLE OF THE WEEK.

&&

.DISCUSSION...CURRENT FORECAST LOOKED ON TRACK WITH SHOWERS AND
THUNDERSTORMS REDEVELOPING THIS AFTERNOON THROUGH THIS EVENING.
ANOTHER DAY OF HIGH TEMPERATURES SEVERAL DEGREES ABOVE NORMAL BEFORE
STARTING TO LOWER TO NEAR SEASONABLE READINGS THIS COMING WORK WEEK.
PLEASE REFER TO THE ADDITIONAL SECTIONS FOR MORE DETAILS.

&&

.AVIATION...VALID THRU 31/18Z. CLOUDS WILL THEN BE ON THE INCREASE
LATE THIS MORNING THROUGH THE AFTERNOON WITH ANOTHER ROUND OF SCT
SHRA/TSRA IN STORE. SIMILAR TO SATURDAY...SHRA/TSRA AREAL COVERAGE
WILL BE RELATIVELY WIDESPREAD AND CONTINUE INTO THE EARLY EVENING
HOURS. BRIEF MVFR CONDITIONS AND GUSTY WINDS TO 45 KTS WILL BE
POSSIBLE IN AND AROUND THE STRONGER STORMS. OUTSIDE OF THUNDERSTORM
INFLUENCE SURFACE WINDS WILL GENERALLY BE UNDER 10 KTS. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...ANOTHER ROUND OF SCATTERED SHOWERS AND THUNDERSTORMS
TODAY...WITH RELATIVELY SIMILAR COVERAGE TO SATURDAY...ONLY LESS
ACTIVITY OVER THE FAR WESTERN ZONES. PRIME CONCERN TODAY IS STRONG
WINDS AND HEAVY RAIN DUE TO SLOW MOTIONS.  THIS BASIC IDEA WILL
CONTINUE EARLY THIS WEEK...WITH DAILY AFTERNOON AND EVENING STORMS
EXPECTED.  STARTING MONDAY STORMS WILL TEND TO BE MORE FOCUSED OVER
EASTERN ZONES...WITH SIGNIFICANTLY DIMINISHED THUNDERSTORM ACTIVITY
FROM WEDNESDAY ON.  THUNDERSTORMS ARE EXPECTED TO BE WET AND AS IS
TYPICAL MAY PRODUCE STRONG...GUSTY AND ERRATIC WINDS WITH THE
STRONGER THUNDERSTORMS.

OUTSIDE OF THUNDERSTORMS GENERALLY LIGHT TERRAIN DRIVEN WINDS ARE
EXPECTED. FROM MONDAY ONWARD A WEST TO SOUTHWEST FLOW WILL GRADUALLY
DEVELOP ACROSS ARIZONA.  THE STRONGEST WINDS WILL BE ACROSS ZONE
150...PEAKING IN THE 15-20 MPH RANGE.  THIS FLOW WILL ALSO STEADILY
PUSH THE MOISTURE OUT OF THE REGION FOR DECREASING CHANCES OF
THUNDERSTORMS WEDNESDAY THROUGH FRIDAY.

&&

.CLIMATE...YESTERDAY WAS THE 81ST STRAIGHT DAY IN WHICH THE LOW
TEMPERATURE WAS 70 DEGREES OR WARMER. THE PREVIOUS 81 DAY STREAK
OCCURRED IN 2013. THE OFFICIAL NWS FORECAST HAS THIS RECORD BEING
BROKEN ON TODAY. UNLESS THE AIRPORT GETS HIT WITH A STRONG
THUNDERSTORM...THIS RECORD WILL LIKELY CONTINUE TO ADD DAYS INTO
NEXT WEEKEND.

&&

.PREV DISCUSSION...THE LARGE SCALE PATTERN SHOWS A WEAKENING RIDGE
OVER THE DESERT SOUTHWEST...CAUGHT IN A SQUEEZE PLAY BETWEEN THE
REGIONAL TROUGH NORTHWEST AND NORTH OF OUR AREA...AND A DECENT LOW
NEAR CENTRAL AND SOUTHWEST TEXAS. THE 300MB INFLECTION OF THESE
FEATURES PUT A HIGH CENTER JUST SOUTH OF US WITH THE LOW OVER
SOUTHWEST TEXAS SHOWING UP VERY WELL AT H3 RELATIVELY WELL STACKED.
THE RESULTING UPPER LEVEL FLOW SHOWS GOOD DIVERGENCE OVER SOUTHEAST
ARIZONA THIS AFTERNOON. THAT WILL HELP ORGANIZE SOME STORMS OVER THE
AREA...WITH THE RESULTING ORGANIZATION HELPING TO DEVELOP STRONG
OUTFLOWS AGAIN THIS AFTERNOON. THIS WILL BE IMPORTANT SINCE THE MID
LEVEL AND STORM LEVEL FLOWS REMAIN SO WEAK. THE H7 THETA-E RIDGE
THAT WE SAW WEST OF TUCSON YESTERDAY WILL ALSO SHIFT FURTHER EAST TO
A POSITION OVER EASTERN PIMA AND SANTA CRUZ COUNTIES THIS AFTERNOON.
THESE TWO FEATURES WILL TEND TO FOCUS OUR BEST ACTIVITY INITIALLY
FROM EASTERN PIMA AND SANTA CRUZ COUNTIES EASTWARD THIS
AFTERNOON...WITH AN OUTFLOW ASSIST INTO PORTIONS OF THE TOHONO
O`ODHAM NATION AND SOUTH CENTRAL PINAL COUNTY LATER.

FOR MONDAY...BOTH OF THESE FEATURES (THE H7 THETA-E RIDGE AND
FAVORABLE UPPER LEVEL DIFFLUENT AREA) SHIFT EASTWARD AS THE
SOUTHWESTERLY FLOW SLOWLY INCREASES ACROSS WESTERN PORTIONS OF THE
STATE. THAT WILL PUT OUR AREA OF FOCUS MAINLY FROM TUCSON EASTWARD.

BY TUESDAY AND WEDNESDAY THE SOUTHWESTERLY FLOW WILL SLOWLY START TO
TAKE IT`S TOLL ON OUR MOISTURE. THERE`S ONLY SO LONG THE DEEPER
MOISTURE CAN HOLD ON IMMEDIATELY TO OUR WEST. DIMINISHING ACTIVITY
FOR MUCH OF OUR AREA TUESDAY AFTERNOON WITH MOST OF THE STORMS EAST
OF TUCSON.

THE REMNANTS OF THE RIDGE WILL BASICALLY HAVE FILLED BY THEN. WE
PROBABLY WON`T HAVE COMPLETELY DRIED OUT FOR THE SIMPLE FACT THE
FLOW AT OUR LATITUDE WON`T BE STRONG ENOUGH TO SCOUR US OUT. THE
THUNDERSTORM COVERAGE HOWEVER WILL BE BELOW AVERAGE AT BEST BY
FRIDAY.

THE LARGE SCALE FLOW ISN`T FAVORABLE FOR MONSOON ACTIVITY NEXT
WEEK...HOWEVER THE EASTERN PACIFIC TROPICS ARE GETTING BUSY AGAIN
AND WITH THIS MEAN TROUGH POSITION HANGING ON THROUGH THE NORTHERN
AND CENTRAL GREAT BASIN...WE MIGHT BE ABLE TO COAX SOME PERIPHERAL
TROPICAL INFLUENCES IN OUR GENERAL DIRECTION BY THEN.

&&

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

&&

$$

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