Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 240432
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
930 PM MST SUN AUG 23 2015

.SYNOPSIS...SOME SHOWERS AND THUNDERSTORMS WILL LINGER
OVERNIGHT...THEN ANOTHER GOOD CHANCE OF SHOWERS AND THUNDERSTORMS
ACROSS THE AREA LATER MONDAY AND MONDAY EVENING. SOME STORMS WILL
GENERATE STRONG WINDS AND HEAVY RAIN. FOR THE SECOND HALF OF THE
WEEK...BUILDING HIGH PRESSURE WILL TEND TO SUPPRESS THUNDERSTORM
COVERAGE WHILE BRINGING HOTTER TEMPERATURES TO THE AREA. NEAR RECORD
HIGHS ARE POSSIBLE NEXT WEEKEND.

&&

.DISCUSSION...THE 00Z KTWC SOUNDING SHOWED THAT THE GREATER TUCSON
AREA WAS JUST WAITING FOR THE RIGHT PROMPTING...AND FINALLY GOT IT
IN THE FORM OF MULTIPLE MERGING OUTFLOWS. AREAS OF RAIN AROUND METRO
TUCSON WITH THE STRONGEST STORM NEAR MARANA AND NORTHWEST TUCSON.
HEAVY RAIN IN AREAS OF THE TOHONO O`ODHAM NATION EARLIER...BETWEEN 1
AND 3 INCHES FEEDING INTO BOTH THE VAMORI WASH AND SANTA ROSA WASH
WITH SMALL STREAM FLOOD ADVISORIES IN THOSE AREAS.

WITH ALL THE RESIDUAL OUTFLOW ACTIVITY WE`LL KEEP A FEW SHOWERS WITH
ISOLATED EMBEDDED THUNDERSTORMS IN THE FORECAST INTO THE EARLY
MORNING HOURS. AS FOR MONDAY...BIG PICTURE CONDITIONS ARE FAVORABLE
AS DESCRIBED IN THE PREVIOUS DISCUSSION BELOW...HOWEVER WE`LL HAVE
TO SEE HOW LONG WE HOLD ON TO DEBRIS CLOUDS AND SHOWERS TO TRY TO
JUDGE ANY LIMITING IMPACTS FOR TOMORROW`S CHANCES AND TIMING. FIRST
GUESS IS ANOTHER SLOW TO DEVELOP DAY THAT TURNS OUT ABOVE AVERAGE BY
EARLY EVENING HOURS.

&&

.AVIATION...VALID THRU 25/06Z.
SCTD TO LCLY BKN 8-12KFT AGL WITH SCTD/ISOLD -SHRA/TSRA TIL
24/08Z...THEN DIMINISHING DEBRIS CLOUDS THRU 24/17Z. AFTR 24/19Z
ISOLD/SCTD SHRA/TS DVLPG...ESPECIALLY NR HIER TERRAIN. BRIEF MVFR
CONDS...ALG WITH STRONG GUSTY WINDS POSSIBLE IN AN AROUND SHRA/TSRA.
WINDS AWAY FROM STORMS GENERALLY BE LIGHT AND TERRAIN DRIVEN.
AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...SCATTERED SHOWERS AND THUNDERSTORMS THIS EVENING AND
ONCE AGAIN MONDAY AFTERNOON AND EVENING. DECENT STORM CHANCES REMAIN
TUESDAY INTO WEDNESDAY DUE TO PLENTY OF MOISTURE LINGERING OVER THE
REGION. AN UPPER RIDGE WILL BUILD OVER THE AREA LATE IN THE WEEK
INTO NEXT WEEKEND RESULTING IN A SIGNIFICANT DECREASE IN SHOWERS AND
THUNDERSTORMS WITH TEMPERATURES RISING TO NEAR RECORD LEVELS FRIDAY
AND SATURDAY. OUTSIDE OF THUNDERSTORM WINDS...WINDS WILL BE TYPICAL
FOR MID AUGUST AND GENERALLY LESS THAN 15 MPH WITH AFTERNOON
GUSTINESS.

&&

.PREV DISCUSSION...WE HAD ENOUGH SHOWER AND THUNDERSTORM ACTIVITY
YESTERDAY TO FLIP THE ATMOSPHERE ON A LARGE ENOUGH SCALE TO STILL
HAVE PLENTY OF RESIDUAL CONVECTIVE INHIBITION ALONG WITH MORE STABLE
CONDITIONS ON THE 12Z KTWC SOUNDING THIS MORNING. AN 18Z SOUNDING
REVEALED A RECOVERING ATMOSPHERE THAT GENERALLY STILL DID NOT
SUPPORT WIDESPREAD CONVECTIVE INITIATION IN VALLEY LOCATIONS...BUT
DID SHOW PROMISE ONCE YOU HELP THINGS ALONG WITH A CONVECTIVE
OUTFLOW FROM MOUNTAINS STORMS. WE`VE SEEN THE DELAYED DEVELOPMENT IN
VALLEY LOCATIONS PART OF THE FORECAST...NOW LETS SEE THE OUTFLOWS.
AS EXPECTED OUR INITIAL DEVELOPMENT HAS BEEN IN THE MOUNTAINS EARLY
THIS AFTERNOON...BUT THE DEVELOPMENT ALONG THE MOGOLLON RIM NORTH OF
SAFFORD HAS BEEN A BIT MORE FRAGMENTED THAN EXPECTED SO FAR.

UA WRF-GFS AND LOCAL WRF RUNS CONTINUE TO SHOW OUTFLOWS FROM BOTH
GRAHAM COUNTY AND SANTA CRUZ COUNTY BECOMING A FACTOR IN EASTERN
PIMA COUNTY WEATHER AFTER 4 OR 5 PM. OUR CURRENT FORECAST TRENDS
WILL STAND PAT WITH THAT SCENARIO FOR NOW...BUT WE`VE MIXED OUT A
BIT MORE BOUNDARY LAYER MOISTURE THAN I WOULD HAVE LIKED. OUTFLOWS
SHOULD BE ABLE TO PUSH STRONG CONVECTION DEEP INTO LOWER DESERTS AS
WELL WITH COVERAGE EXPECTED TO INCREASE AREA-WIDE IN THE LATE
AFTERNOON AND EARLY EVENING HOURS.

LARGE SCALE FEATURES REMAIN FAVORABLE FOR ELEVATED THUNDERSTORM
COVERAGE AND ORGANIZATION MONDAY WITH THE RIDGE STRENGTHENING
IMMEDIATELY DOWNSTREAM IN NEW MEXICO. AND POSSIBLE IMPULSE EMBEDDED
IN THE FLOW WRAPPING UNDER THIS FEATURE INTO SOUTHEAST ARIZONA FROM
CHIHUAHUA OVER THE NEXT 12 TO 24 HOURS.

THEN THE RIDGE IS EXPECTED TO GRADUALLY REORIENT INTO A BLOCKING
POSITION LATE IN THE WEEK AS A STRONG LOW DIGS DOWN THE BRITISH
COLUMBIA AND PACIFIC NORTHWEST COASTS. BY THURSDAY AND FRIDAY...THE
RESULTING WEEK FLOW...SLOW DRYING AND MODEST SUBSIDENCE UNDER
BUILDING HIGH PRESSURE WILL START TO SHUT DOWN THUNDERSTORM ACTIVITY.

AS THIS HAPPENS MOS ISN`T GOING TOO CRAZY WITH THE TEMPERATURES FOR
FRIDAY THROUGH SUNDAY...HOWEVER THICKNESS REGRESSIONS FOR BOTH GFS
AND ECMWF SUPPORT AFTERNOON HIGHS FROM 107 TO 109 FOR TUCSON. AS
USUAL WE WILL FACTOR THIS INTO THE FORECAST WITH MODEL OUTPUT SLOW
TO RESPOND AT DAY 5 AND 6 WITH TEMPERATURE EXTREMES. THE PATTERN
CHANGE LOOKS SOUND WITH GOOD ENSEMBLE MEAN AGREEMENT AND HIGH
RELATIVE MEASURE OF PREDICTABILITY.

&&

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

&&

$$

MEYER/LADER/CARLAW

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


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