Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 202149 CCA
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
240 PM MST WED AUG 20 2014

.CORRECTED...CORRECTED THE TIME.

.SYNOPSIS...AN UPPER LOW OVER SOUTHERN CALIFORNIA WILL MOVE ACROSS
NORTHERN ARIZONA LATE THURSDAY NIGHT AND EARLY FRIDAY WITH SCATTERED
SHOWERS AND THUNDERSTORMS EXPECTED THURSDAY AFTERNOON AND NIGHT.
DRIER AIR BEHIND THE LOW WILL LIMIT CONVECTION TO MAINLY EASTERN AND
SOUTHERN AREAS FRIDAY THROUGH THE WEEKEND.  AFTER A COUPLE OF COOLER
THAN NORMAL DAYS...HIGH TEMPERATURES WILL WARM BACK UP TO NORMAL
OVER THE WEEKEND.

&&

.DISCUSSION...SOMEWHAT INTERESTING WEATHER THE NEXT 36 HOURS AS THE
UPPER LOW MOVING OVER SOUTHERN CALIFORNIA OPENS UP AND MOVES
NORTHEAST ACROSS CENTRAL/NORTHERN ARIZONA LATER THURSDAY NIGHT INTO
FRIDAY MORNING.  WATER VAPOR LOOP SHOWING HIGH LEVEL MOISTURE FROM
TS LOWELL BEGINNING TO MOVE NORTH OVER SOUTHERN AZ WITH THE MID
LEVEL MOISTURE EXPECTED LATE TONIGHT INTO THURSDAY WHICH WILL
MOISTEN UP THE ATMOSPHERE SOME.  WHILE THE TIMING OF THE SYSTEM IS
NOT IDEAL (A BIT LATE) IT SHOULD BE GOOD ENOUGH TO HELP FIRE OFF
CONVECTION THURSDAY AFTERNOON INTO THURSDAY NIGHT WITH SOMEWHAT OF A
FOCUS OVER CENTRAL/WESTERN PIMA COUNTY.  VARIETY OF HI RES MODELS
INDICATE PLENTY OF MID AND HIGH LEVEL CLOUDS AROUND WITH SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS.  I HAVE TWEAKED POPS UP SOME
FROM WHAT WE HAD...ESPECIALLY WEST FOR THE AFTERNOON AND EVENING
HOURS.  AS A RESULT OF THE ANTICIPATED INCREASE IN CLOUDS AND
SHOWERS WE WILL HAVE ANOTHER COOLER THAN NORMAL DAY.

FOR FRIDAY...THE UPPER LOW...ACTUALLY AN OPEN TROUGH BY THIS POINT
WILL MOVE NE OF THE AREA WITH SOMEWHAT DRIER AIR MOVING OVER THE
REGION AT THE MID AND HIGH LEVELS WITH THE EXCEPTION OF ALONG THE
ITRNL BORDER WHICH WILL DIMINISH THE SHOWER AND THUNDERSTORM THREAT
AREAS FROM TUCSON NORTH AND WEST.  ANOTHER COOLER THAN NORMAL DAY
THANKS TO A BOTTOMING OUT OF HEIGHTS AND THICKNESS WITH THE PASSING
TROUGH.

FOR THE WEEKEND THROUGH MONDAY THERE WILL BE WESTERLY FLOW ACROSS
THE REGION LIMITING THE ATMOSPHERIC MOISTURE TO SLIGHTLY BELOW
NORMAL LEVELS.  STILL ENOUGH FOR ISOLATED TO SCATTERED CONVECTION
BUT PRIMARILY OVER SOUTH AND EAST OF TUCSON.  WITH FEWER CLOUDS AND
REBOUNDING THICKNESS VALUES HIGH TEMPERATURES ARE EXPECTED TO
REBOUND TO NORMAL LEVELS.

FOR THE MIDDLE OF NEXT WEEK SOME QUESTIONS ARISE DUE TO A POTENTIAL
TROPICAL SYSTEM OVER THE EASTERN PACIFIC.  THE QUESTION RELATES TO
HOW MUCH MOISTURE MAY BE TOSSED OUR WAY AND WHEN AS THE SYSTEM HEADS
OUT TO SEA.  IF LITTLE TO NONE OF THIS TROPICAL MOISTURE MAKES IT
THIS FAR NORTH WE WILL CONTINUE TO HAVE LESS THAN NORMAL CONVECTION
ACROSS THE AREA.  IF IT MANAGES TO MAKE IT HERE IT WILL BE MORE
ACTIVE.  WITHOUT A CLEAR SIGNAL AT THIS TIME I HAVE LEFT THE
FORECAST AS IS WHICH IS A LOW GRADE MONSOON FORECAST WITH NEAR
NORMAL TEMPERATURES.  CERNIGLIA

&&

.AVIATION...VALID THRU 21/12Z.
EXPECT ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS THROUGH ABOUT
04Z. HOWEVER...CONFIDENCE IS CURRENTLY TOO LOW TO INSERT TS REMARKS
AT ANY TAF SITE. FELT MOST CONFIDENT IN STORMS IMPACTING KOLS TODAY
SO HAVE MENTIONED VCSH IN THAT CASE. OTHERWISE...WINDS WILL
GENERALLY REMAIN LIGHT AND LESS THAN 10 KTS. THUNDERSTORMS WOULD
PROMOTE GUSTY AND ERRATIC WINDS OF COURSE. VFR CONDITIONS EXPECTED
AS WELL THROUGH THE 18Z TAF PERIOD.

&&

.FIRE WEATHER...ISOLATED TO SCATTERED MAINLY AFTERNOON AND EVENING
THUNDERSTORMS ARE EXPECTED THROUGH EARLY NEXT WEEK. HOWEVER...THE
OVERALL TREND IN THUNDERSTORM ACTIVITY WILL BE DIMINISHED FROM
RECENT WEEKS. THE STRONGER THUNDERSTORMS WILL STILL 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. ALSO...RELATIVE HUMIDITY VALUES WILL
FALL A BIT LOWER THAN RECENT WEEKS DUE TO SOME DRYING IN THE
ATMOSPHERE...BUT WE WILL REMAIN ABOVE CRITIC RELATIVE HUMIDITY
THRESHOLDS THROUGH EARLY NEXT WEEK.

&&

$$

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