Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 301600
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
900 AM MST THU JUL 30 2015

.SYNOPSIS...STORM COVERAGE WILL BE LESS FOR VALLEY LOCATIONS
TODAY...OTHERWISE WE WILL CONTINUE TO HAVE ENOUGH MOISTURE FOR A
CHANCE OF SHOWERS AND THUNDERSTORMS FOR MUCH OF SOUTHEAST ARIZONA
INTO NEXT WEEK.

&&

.DISCUSSION...WATER VAPOR IMAGERY...30/12Z UPPER-AIR PLOTS AND
RECENT MODEL DATA SHOW A RIDGE CENTERED OVER THE SOUTHERN
PLAINS...WITH THE PESKY UPPER LOW STILL OFF THE WEST COAST OF THE
BAJA PENINSULA. A WEAK IMPULSE IS CURRENT LIFTING TO THE NORTH
ACROSS NORTHEAST ARIZONA. AS A RESULT...VISIBLE AND IR SATELLITE
IMAGERY SHOWS EXTENSIVE CLOUDINESS ASSOCIATED WITH THIS FEATURE THAT
EXTEND FROM SOUTHERN CALIFORNIA...ACROSS NORTHERN ARIZONA AND INTO
MUCH OF WESTERN NEW MEXICO.

THIS MORNINGS KTWC SOUNDING PAINTS A VERY DIFFERENT WEATHER PICTURE
COMPARED TO 24 HOURS AGO. IT SHOWS A DROP IN PRECIPITABLE WATER FROM
1.62 INCHES YESTERDAY MORNING TO 1.25 INCHES THIS MORNING. IN
ADDITION...THE MU CAPE HAS DECREASED FROM AROUND 1100 J/KG YESTERDAY
MORNING...TO LESS THAN 300 J/KG TODAY. THE LIFTED INDEX FROM THIS
MORNING WAS A MEAGER MINUS 1. GIVEN THAT...MIDNIGHT SHIFT ALREADY
UPDATED TODAYS FORECAST TO LOWER POPS IN THE VALLEYS AND INCREASE
HIGH TEMPS A BIT. WE WILL STILL SEE STORM DEVELOPMENT OVER THE
MOUNTAIN TOPS.

AS OF 15Z (8 AM MST)...TEMPERATURES ACROSS THE REGION RANGED FROM
THE LOWER 70S TO THE LOWER 80S...WITH THE TUCSON INTL AIRPORT
REPORTING A TEMP OF 81 DEGS...AFTER A MORNING LOW OF 74 DEGS...WHICH
WAS EXACTLY NORMAL FOR THIS DATE. THESE CURRENT READINGS SEEM TO BE
ON TRACK WITH RESPECT TO EXPECTED DAYTIME HIGHS...SO NO CHANGES ARE
PLANNED AT THIS TIME...BUT WILL CONTINUE TO MONITOR.

FOR DETAILS REGARDING THE FORECAST BEYOND TODAY...PLEASE REFER TO
THE PREVIOUS DISCUSSION BELOW.

&&

.AVIATION...VALID THRU 31/18Z.
MOSTLY SUNNY THIS MORNING AND PARTLY CLOUDY THIS AFTERNOON WITH SCT
TO BKN MID LEVEL DECKS. SCT SHRA/TSRA DEVELOPING AGAIN AFT 30/17Z
LASTING INTO THE EVENING HOURS. MVFR CONDITIONS AND VRB WIND GUSTS
TO 40 KTS POSSIBLE IN AND AROUND THE STRONGER TSRA. OUTSIDE OF STORM
INFLUENCES...SFC WINDS WILL GENERALLY BE LESS THAN 12 KTS WITH A FEW
HIGHER GUSTS IN THE AFTERNOON/EARLY EVENING HOURS. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...WE WILL KEEP ENOUGH MOISTURE FOR A CHANCE OF SHOWERS
AND THUNDERSTORMS ACROSS MUCH OF SOUTHEAST ARIZONA INTO NEXT WEEK.
WEAK DRYING IN WESTERN AREAS IS EXPECTED TO SEE LESS OF A CHANCE OF
THUNDERSTORMS WEST OF TUCSON STARTING THIS WEEKEND. STRONG WINDS ARE
EXPECTED NEAR THUNDERSTORMS WITH OUTFLOWS POSSIBLE FARTHER AWAY FROM
STORMS. OTHERWISE...20-FT WINDS WILL GENERALLY BE TERRAIN DRIVEN AND
LESS THAN 15 MPH...WITH SOME AFTERNOON AND EARLY EVENING BREEZINESS
DUE TO THE STRONG DAYTIME HEATING.

&&

.PREV DISCUSSION...NOT QUITE AS MUCH MOISTURE AROUND BUT STILL
ENOUGH FOR STORMS. THE MAIN PROBLEM IS THE 12Z KTUS SOUNDING. WHAT
AN UGLY PROFILE FOR THUNDERSTORM CHANCES. WE WERE EXPECTING LESS
FAVORABLE CONDITIONS FOR VALLEY THUNDERSTORMS TODAY...BUT NOT THAT
MUCH LESS. WE UPDATED THE FORECAST TO REDUCE THUNDERSTORM COVERAGE
THIS AFTERNOON IN GENERAL. FAVORED LOCATIONS INCLUDE MOUNTAINS AS
WELL AS AREAS SOUTHWEST...SOUTH AND EAST OF TUCSON (TOHONO O`ODHAM
NATION...SANTA CRUZ COUNTY...COCHISE COUNTY). WE ALSO TWEAKED
FORECAST HIGHS UP A DEGREE OR SO. MORE ROOM FOR SURFACE DEW POINTS
TO MIX LOWER THIS AFTERNOON AS WELL.

LESS DEBRIS CLOUD THIS MORNING WITH MUCH OF IT NORTH AND NORTHEAST
OF TUCSON ASSOCIATED WITH AN IMPULSE LIFTING INTO NORTHEAST ARIZONA.
WE MAY HAVE TO WORK WITH WHAT WE HAVE FOR A BIT WITH THE WEAK FLOW
NO LONGER REINFORCING OUR MOISTURE SUPPLY. THAT WILL BE EVIDENT WITH
AFTERNOON MIXING OF SURFACE DEW POINTS DOWN INTO THE 50S IN MANY
VALLEY LOCATIONS TODAY (WE HELD ONTO OUR 60S THROUGH THE DAY
YESTERDAY). IN ADDITION...BY THIS AFTERNOON WE MAY SEE A TEMPORARY
MODEST WARMING TREND IN MID LEVELS AS A SECONDARY MID LEVEL HIGH
CENTER CONSOLIDATES CLOSER TO NEW MEXICO DURING THE DAY. THAT WILL
MAKE FOR EASY MOUNTAIN DEVELOPMENT AND ABOVE AVERAGE COVERAGE IN THE
MOUNTAINS...BUT LESS SUPPORT IN GENERAL FOR VALLEY STORMS. ONLY
AVERAGE TO MAYBE BELOW AVERAGE COVERAGE IN VALLEYS.

THE FLOW...THOUGH WEAK...REMAINS FAVORABLE INTO THE WEEKEND. AN
EMBEDDED IMPULSE IN THE FLOW CURRENTLY JUST SOUTH OF CHIHUAHUA WOULD
BE A NICE ASSIST FOR STORMS FRIDAY AFTERNOON AND
EVENING...ESPECIALLY FROM TUCSON SOUTH AND WESTWARD.

AFTER THAT THERE IS LESS TO FOCUS ON IN THE FLOW THAT WILL GENERALLY
MAINTAIN WEAK SOUTHERLY AND EASTERLY COMPONENTS. MEDIUM RANGE MODELS
INITIALLY MAINTAIN FAVORABLE H7 THETA-E TRENDS...SO WE WILL KEEP
THUNDERSTORM COVERAGE NEAR SEASONAL AVERAGES OVER THE WEEKEND INTO
EARLY NEXT WEEK. AS ALWAYS...MUCH DEPENDS ON THE ORIENTATION AND
LOCATION OF THE RIDGE. SOMETHING TO WATCH IS A NEW TREND WITH THE
ECMWF REBUILDING THE RIDGE INTO A BLOCKING POSITION EARLY NEXT
WEEK...WHICH WOULD REDUCE AVAILABLE MOISTURE AND THUNDERSTORM
COVERAGE.

&&

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

&&

$$

CURRENT DISCUSSION...MOLLERE
PREVIOUS DISCUSSION...MEYER/RASMUSSEN

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



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