Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 201003
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
303 AM MST WED AUG 20 2014

.SYNOPSIS...SCATTERED MAINLY AFTERNOON AND EVENING THUNDERSTORMS
WILL CONTINUE THROUGH FRIDAY. SOME STORMS WILL PRODUCE HEAVY
RAINFALL AND GUSTY WINDS. A GRADUAL DRYING IS EXPECTED TO OCCUR
THIS WEEKEND INTO EARLY NEXT WEEK. HOWEVER...ENOUGH MOISTURE WILL
REMAIN FOR ISOLATED TO SCATTERED THUNDERSTORMS. BELOW NORMAL DAYTIME
TEMPERATURES WILL PREVAIL THROUGH FRIDAY FOLLOWED BY A WARMING TREND
THIS WEEKEND.

&&

.DISCUSSION...DEBRIS CLOUDS CONTINUE ACROSS EASTERN HALF OF FORECAST
AREA WITH RADAR SHOWING LITTLE TO NO ACTIVITY WITH THESE CLOUDS.
WATER VAPOR IMAGERY PLACED CLOSED UPPER LOW OFF SRN CA CST WITH MUCH
DRIER AIR OVER MOST OF THE STATE VERSUS 24 HOURS AGO. THIS LOW HAS
STARTED TO TAP INTO MAINLY HIGH LEVEL MOISTURE FROM THE OUTER EDGE
OF TROPICAL STORM LOWELL...WHICH AS OF THE LATEST ADVISORY WAS
LOCATED 775 MILES WSW OF THE BAJA CALIFORNIA TIP. AS FOR THE CLOSED
UPPER LOW...MODELS ARE IN PRETTY GOOD AGREEMENT ON MEANDERING IT
NEAR THE SRN CA CST TODAY. ALTHOUGH MOISTURE VALUES ARE STILL
RELATIVELY HIGH...THE DRIER SW FLOW ALOFT ALONG WITH A COOL BOUNDARY
LAYER WILL LIMIT THUNDERSTORMS TODAY MOSTLY TO THE HIGHER TERRAIN.
CAN`T RULE OUT A FEW GETTING INTO THE VALLEYS. HAVE THUS LOWERED
POPS ACROSS THE BOARD TODAY WITH VALUES CLOSE TO MOS GUIDANCE. HIGHS
TODAY FROM TUCSON WEST WILL BE NEAR TUESDAY HIGHS WHILE AREAS TO THE
EAST WILL BE MUCH WARMER VERSUS RATHER CLOUDY/SHOWERY TUESDAY.

TONIGHT...MODEL CROSS SECTIONS INDICATE THAT A BIT MORE MID-LEVEL
MOISTURE WILL BE PULL FROM THE OUTER EDGE OF TS LOWELL INTO SW AZ AS
THE CLOSED LOW SLOWLY MOVES INLAND OVER SAN DIEGO. COULD SEE A FEW
STORMS DEVELOP OVER OUR WESTERN DESERTS LATE TONIGHT INTO THURSDAY
MORNING.

THURSDAY LOOKS AT RATHER ACTIVE AS CLOSED LOW OPENS UP AS IT MOVES
INTO WESTERN ARIZONA. THUS EXPECT A RETURN TO SCATTERED AFTERNOON
AND EVENING SHOWERS AND THUNDERSTORMS. HIGHS SIMILAR TO WHAT IS
FORECAST FOR TODAY WHICH CONTINUES TO BE BELOW NORMAL.

FRIDAY...TROF AXIS WILL BE MOVING INTO WESTERN NEW MEXICO WITH DRIER
AIR FILTERING ACROSS THE AREA FROM THE WEST. PRECIPITABLE WATER
VALUES ARE PROGGED TO BE LESS THAN ONE INCH IN THE WHITES TO NEAR
1.50" ALONG THE INTNL BORDER. THIS WILL LIMIT THUNDERSTORM ACTIVITY
TO THE MOUNTAINS EAST OF TUCSON AND ALONG THE INTERNATIONAL BORDER
FROM NOGALES EAST. BELOW NORMAL HIGHS CONTINUE FOR ONE MORE DAY.

SATURDAY...THE PACIFIC UPPER TROF THAT KICKS OUR CURRENT LOW THRU
THE STATE ON FRIDAY WILL BE PASSING BY TO OUR NORTH. RATHER DRY
WESTERLY FLOW ALOFT WITH PRECIPITABLE WATER VALUES PROGGED TO RANGE
FROM 0.75"-1.25" DRIEST IN THE WHITES. THUNDERSTORM COVERAGE LESS
THAN FRIDAY BUT PRETTY MUCH IN THE SAME AREAS. WARMER WITH HIGHS
EDGING CLOSER TO NORMAL.

SUNDAY...TROFINESS REMAINING TO OUR NORTH WILL LIMIT ANY
THUNDERSTORM ACTIVITY TO MAINLY THE HIGHER TERRAIN E AND S OF
TUCSON. HIGHS WILL BE AT OR SLIGHTLY ABOVE NORMAL.

MONDAY AND TUESDAY...WILL MAINTAIN LOW GRADE MONSOON FORECAST AS
UPPER LEVEL TROFINESS REMAINS CLOSE TO THE STATE.

DEEPER MOISTURE MAY RETURN TO THE AREA THANKS TO A TROPICAL SYSTEM
MOVING CLOSE ENOUGH TO THE GULF OF CA TO SEND A SURGE OF MOISTURE
NORTH INTO THE STATE. TIME WILL TELL.

&&

.AVIATION...VALID THRU 21/12Z.
EXPECT ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS DEVELOPING
THIS AFTERNOON...PERSISTING INTO THE EVENING HOURS TONIGHT. MVFR
VISIBILITIES AND WIND GUSTS TO 45 KTS WILL OCCUR WITH THE STRONGER
TSRA. A FEW CLOUDS-SKC CONDITIONS EXPECTED THRU MID MORNING WEST OF
A KOLS TO KCGZ LINE...WITH SCT-BKN CLOUDS AT 8-14K FT AGL EAST OF
THIS LINE. SCT-BKN CLOUDS AREAWIDE THIS AFTERNOON AND EVENING AT
6-11K FT AGL...SLOWLY DIMINISHING AFT 21/04Z TONIGHT. OUTSIDE OF
THUNDERSTORM OUTFLOWS...SURFACE WIND WILL GENERALLY BE LESS THAN 10
KTS. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...ISOLATED TO SCATTERED MAINLY AFTERNOON AND EVENING
THUNDERSTORMS ARE EXPECTED THROUGH EARLY NEXT WEEK. THE STRONGER
THUNDERSTORMS WILL PRODUCE STRONG...GUSTY AND ERRATIC WINDS. OUTSIDE
OF THE THUNDERSTORM OUTFLOWS...20-FOOT WINDS WILL EXHIBIT NORMAL
DIURNAL TRENDS AND WILL BE MOSTLY LESS THAN 15 MPH.

&&

$$

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