Area Forecast Discussion
Issued by NWS Tucson, AZ

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 202220
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
320 PM MST SAT SEP 20 2014

.SYNOPSIS...EXPECT SCATTERED MAINLY AFTERNOON AND EVENING SHOWERS
AND THUNDERSTORMS THROUGH MONDAY. DRIER CONDITIONS WILL THEN LEAD TO
REDUCED COVERAGE OF SHOWERS AND THUNDERSTORMS TUESDAY AND WEDNESDAY.
THEREAFTER...THE CHANCES FOR SHOWERS AND THUNDERSTORMS WILL INCREASE
DURING THE LATTER PART OF THE UPCOMING WEEK. NEAR NORMAL DAYTIME
TEMPERATURES WILL PREVAIL INTO THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...LATEST 500 MB ANALYSIS REVEALS 590 DM HIGH ROUGHLY
OVER SW TEXAS AND A CUTOFF LOW HUGGING THE SOUTHERN CALIFORNIA
COAST. IN BETWEEN THESE TWO SYSTEMS...SOUTHERLY MIDLEVEL FLOW IS
ACTING TO KEEP SOME MONSOONAL MOISTURE IN PLACE ACROSS SOUTHERN
ARIZONA THIS AFTERNOON. THE 12Z KTWC SOUNDING SHOWS A BASICALLY
UNCHANGED PWAT VALUE FROM 12 AND 24 HOURS AGO OF 1.63 INCHES...WHICH
IS A LITTLE LESS THAN 2 SD ABOVE NORMAL FOR THIS TIME OF YEAR. 24-HR
COOLING BETWEEN THE 600 AND 500 MB LAYER OF ABOUT 3C...COMBINED WITH
SFC DEWPOINTS IN THE MID TO UPPER 60S...HAS RESULTED IN DECENT
INSTABILITY WITH SBCAPE VALUES AROUND 1500-2000 J/KG THIS AFTERNOON.

AS A RESULT...SCATTERED SHOWERS/TSTMS HAVE BEEN IMPACTING PORTIONS
OF THE CWA SINCE EARLIER THIS MORNING. GIVEN THE LEVEL OF AVAILABLE
MOISTURE...SOME OF THESE SHOWERS/STORMS HAVE PRODUCED RAINFALL RATES
UP TO 1.5-2 IN/HR. WITH GENERALLY WEAK MIDLEVEL FLOW AND THE BRUNT
OF THE UPPER LEVEL ENERGY FROM THE CUTOFF LOW REMAINING NORTH AND
WEST OF OUR AREA...ANTICIPATE COVERAGE OF CONVECTION TO WANE WITH
LOSS OF DAYTIME HEATING THIS EVENING. THIS IDEA IS SUPPORTED BY
VARIOUS HIGH-RES GUIDANCE SUCH AS RECENT UOFA WRF/HRRR/NSSL WRF RUNS.

SUNDAY AND MONDAY...AS THE AFOREMENTIONED UPPER LOW ROTATES INTO THE
NORTHERN GREAT BASIN...SOME DRIER AIR WILL BE DRIVEN INTO THE REGION
ON WESTERLY/SOUTHWESTERLY MIDLEVEL FLOW. WE SHOULD STILL HOLD ON TO
SOME MOISTURE IN OUR EASTERN ZONES...ENOUGH FOR ISOLATED TO
SCATTERED SHOWERS/TSTMS DURING THE AFTERNOON/EVENING HOURS.

TUESDAY AND WEDNESDAY...12Z GFS/ECMWF BOTH IN GOOD AGREEMENT THAT
THE MIDLEVEL HIGH CENTER WILL SHIFT WEST INTO SOUTHERN CALIFORNIA ON
TUESDAY. WITH DRIER AIR IN PLACE...TUESDAY AND WEDNESDAY BOTH LOOK
TO BE RELATIVELY QUIET WEATHER DAYS ACROSS THE REGION. AT THIS POINT
IT APPEARS THAT JUST ENOUGH MOISTURE WILL LINGER FOR ISOLATED
SHOWERS/TSTMS MAINLY NEAR THE HIGHER TERRAIN EAST OF TUCSON.

THURSDAY THROUGH SATURDAY...EXPECT RAIN CHANCES TO INCREASE AS A
POWERFUL PACIFIC UPPER TROUGH APPROACHES THE WEST COAST. SOME TIMING
DIFFERENCES BETWEEN THE GFS/ECMWF/CMC RUNS AT THIS POINT...BUT
REGARDLESS...LOOKS LIKE SHOWERS AND THUNDERSTORMS SHOULD BECOME MORE
PROLIFIC AS MOISTURE INCREASES ACROSS THE AREA.

&&

.AVIATION...VALID THRU 22/00Z.
EXPECT SCATTERED -SHRA/-TSRA THIS EVENING...THEN ISOLATED TO
SCATTERED -SHRA NORTH-TO-EAST OF KTUS LATE TONIGHT AND SUNDAY
MORNING. SCATTERED -SHRA/-TSRA WILL THEN OCCUR FROM KTUS VICINITY
EASTWARD AND SOUTHWARD SUNDAY AFTERNOON. MVFR CONDITIONS AND BRIEF
WIND GUSTS TO AROUND 30 KTS WILL OCCUR WITH SHRA/TSRA. OTHERWISE...
SURFACE WIND WILL BE MAINLY LESS THAN 10 KTS THRU SUNDAY AFTERNOON.
AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...SCATTERED MAINLY AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS WILL OCCUR ESPECIALLY FROM TUCSON EASTWARD AND
SOUTHWARD SUNDAY AND MONDAY. SOMEWHAT DRIER CONDITIONS WILL PRODUCE
LESS COVERAGE OF SHOWERS AND THUNDERSTORMS TUESDAY AND WEDNESDAY.
INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS WILL THEN PREVAIL
THURSDAY THROUGH SATURDAY. BRIEF GUSTY OUTFLOWS WILL OCCUR WITH THE
STRONGER THUNDERSTORMS. OTHERWISE...20-FOOT WINDS WILL GENERALLY BE
LESS THAN 15 MPH INTO THE UPCOMING WEEK.

&&

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

&&

$$

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

DISCUSSION...CARLAW
AVIATION/FIRE WEATHER...FRANCIS




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