Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 211605
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
900 AM MST THU AUG 21 2014

.SYNOPSIS...AN UPPER LOW OVER SOUTHERN CALIFORNIA WILL WEAKEN TODAY
AS IT MOVES ACROSS ARIZONA THROUGH EARLY FRIDAY.  EXPECT SCATTERED
SHOWERS AND THUNDERSTORMS INTO THIS EVENING BEFORE ACTIVITY ENDS
FROM WEST TO EAST OVERNIGHT.  DRIER AIR BEHIND THE LOW WILL LIMIT
THUNDERSTORMS TO MAINLY EAST AND SOUTH OF TUCSON FRIDAY AND THROUGH
THE WEEKEND.  AFTER A COUPLE OF COOLER THAN NORMAL DAYS HIGH
TEMPERATURES WILL WARM BACK UP TO NORMAL OVER THE WEEKEND.

&&

.DISCUSSION...MID/HIGH LEVEL MOISTURE FROM TS LOWELL HAS OVERSPREAD
THE AREA IN ADVANCE OF AN UPPER LOW ALONG THE SRN CALIFORNIA COAST
AS EVIDENCED FROM THE EXTENSIVE CLOUDS COVER OVERHEAD AND ABOVE
NORMAL PW.  PLENTY OF ECHOES ON THE RADAR THIS MORNING BUT THE
MAJORITY OF THIS ARE RETURNS FROM THE MID-LEVEL CLOUD DECKS OVER OUR
AREA WITH ONLY A COUPLE OF LOCATIONS INDICATING ANY LIGHT RAIN THUS
FAR.

THIS CLOSED UPPER LOW WILL BOTTOM OUT OVER NORTHERN BAJA BY NOON
THEN BEGIN TO THE TURN TO THE NORTHEAST.  AS IT DOES SO...INCREASED
DYNAMICS WILL WORK ON THIS MOISTURE TO INCREASE THE COVERAGE AND
INTENSITY OF THE SHOWERS.  THE "BEST" ACTIVITY WILL BE WEST AND
NORTHWEST OF OUR FORECAST AREA AS WE WILL NOT BE IN THE BEST
LOCATION WITH RESPECT TO THE LOW.  THE CLOUD COVER WILL LIMIT THE
STRENGTH OF THE CONVECTION OVER CENTRAL AREAS WHILE THE COMBINATION
OF MORE SUN AND BETTER DYNAMICS BRINGS A SMALL THREAT OF STRONG TO
POTENTIALLY SEVERE THUNDERSTORMS FAR WESTERN PIMA COUNTY.  WILL NEED
TO KEEP AN EYE ON THAT THROUGH THE DAY.  FOR THE REMAINDER OF THE
AREA CONDITIONS BEST DESCRIBED AS SCATTERED LIGHT SHOWERS WITH
ISOLATED THUNDERSTORMS WITH HEAVIER SHOWERS.  COULD BE AN
INTERESTING DAY FOR PARTS OF THE AREA SO STAY TUNED.  WITH THE
CLOUDS AND SHOWERS HIGH TEMPERATURES WILL BE SIGNIFICANTLY BELOW
NORMAL THIS AFTERNOON.

THE CLOSED LOW OPENS UP THIS EVENING AS IT MOVES NORTHEAST INTO
CENTRAL AZ BY DAYBREAK FRIDAY.  THIS WILL RESULT IN SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS CONTINUING ACROSS MOST OF THE
AREA WELL INTO THE NIGHT BEFORE DRIER AIR STARTS MOVING INTO WESTERN
AREAS RESULTING IN STORMS DIMINISHING FROM WEST TO EAST.  CERNIGLIA

PREVIOUS DISCUSSION FOLLOWS FOR LATER PERIODS.

UPPER TROF AXIS OVER THE EASTERN AREAS FRIDAY AFTERNOON. ALTHOUGH PW
VALUES WILL BE DOWN VERSUS TODAY...STILL WILL SEE ISOLATED TO
SCATTERED STORMS FRIDAY AFTERNOON. HIGHS WARMER THAN TODAY BUT STILL
BELOW NORMAL.

LOW GRADE MONSOON FORECAST FOR THE WEEKEND AS AN UPPER TROF PASSING
BY TO THE NORTH KEEPS DRIER WESTERLY FLOW OVER THE AREA. HOWEVER
WILL HAVE ENOUGH RESIDUAL MOISTURE FOR SLIGHT CHANCE OF STORMS
MAINLY SOUTH AND EAST OF TUCSON. WARMER WITH HIGHS SLIGHTLY ABOVE
NORMAL BOTH DAYS.

NEXT WEEK...WITH UNCERTAINTY ON AMOUNT OF TROPICAL MOISTURE BEING
SENT OUR WAY FROM THE NEXT PACIFIC TROPICAL STORM...WENT WITH BASIC
CLIMO POPS AREAWIDE. MODELS ARE SUGGESTING THAT WE COULD SEE LIGHT
SOUTHERLY WINDS MOVING UP THE GULF OF CALIFORNIA AS EARLY AS SUNDAY
WITH STRONGER WINDS ON MONDAY WHICH WILL BRING GULF SURGE LIKELY
MONDAY NIGHT INTO TUESDAY. HIGHS WILL REMAIN SLIGHTLY ABOVE NORMAL.

&&

.AVIATION...VALID THRU 22/18Z.
SCT-BKN CLOUDS AT 6-10K FT AGL AND BKN-OVC CLOUDS AOA 12K FT AGL.
ISOLD-SCT SHOWERS AND THUNDERSTORMS DEVELOPING DURING THE MID
MORNING HOURS AND PERSISTING THRU TONIGHT.  PRECIPITATION CHANCES
WILL BE HIGHEST WEST OF A KOLS TO KTUS TO KCGZ LINE THIS MORNING
THRU THE MID AFTERNOON HOURS...AND THEN CENTRAL AND EASTERN AREAS
LATE THIS AFTERNOON AND TONIGHT.  ISOLD MVFR VISIBILITIES AND WIND
GUSTS TO 45 KTS WILL BE POSSIBLE WITH THE STRONGEST TSRA.  OUTSIDE
OF THUNDERSTORM OUTFLOWS...SURFACE WIND WILL GENERALLY BE LESS THAN
10 KTS.  AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...AN INCREASE IN MOISTURE TODAY WILL BRING PLENTY OF
CLOUDS ALONG WITH SCATTERED SHOWERS AND THUNDERSTORMS WELL INTO THE
EVENING HOURS.  THE SHOWERS AND THUNDERSTORMS WILL BE MOVING TO THE
NORTH AROUND 20 MPH.  STRONG THUNDERSTORMS ARE POSSIBLE WEST OF
TUCSON THIS AFTERNOON.  THEN DRIER AIR WILL FILTER INTO THE REGION
FRIDAY ONWARD FOR MORE SUNSHINE...LESS CONVECTION AND WARMER
AFTERNOON TEMPERATURES INTO MONDAY.  THERE IS A CHANCE OF INCREASED
CONVECTION TUESDAY INTO THURSDAY NEXT WEEK.  OUTSIDE OF THUNDERSTORM
INFLUENCE 20 FT WINDS WILL BE DIURNALLY TERRAIN DRIVEN AND GENERALLY
LESS THAN 15 MPH.  CERNIGLIA

&&

$$

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