Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 120409
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
908 PM MST THU SEP 11 2014

.SYNOPSIS...MOISTURE MOVING INTO THE AREA FROM THE EAST WILL RESULT
IN INCREASE IN THUNDERSTORM COVERAGE FRIDAY...ESPECIALLY EAST OF
TUCSON. GUSTY EAST WINDS SATURDAY...THEN A REDUCED CHANCE OF STORMS
THIS WEEKEND. THE CHANCE FOR THUNDERSTORMS WILL INCREASE AGAIN EARLY
NEXT WEEK AS MOISTURE INCREASES ACROSS THE AREA FROM THE SOUTH.

&&

.DISCUSSION...THE UPPER PATTERN IS DEFINED BY AN AMPLIFIED RIDGE IN
THE EASTERN PACIFIC/WEST COAST...A SURFACE HIGH PRESSURE AREA DIVING
SOUTH THROUGH THE ROCKIES...AND A TROPICAL STORM NAMED ODILE
POSITIONED AT 15.5N 104.7W MOVING WNW AT 2 KTS.

A FEW STORMS WERE ABLE TO DEVELOP OVER THE HIGHER TERRAIN SE AND E
OF TUCSON THIS AFTERNOON. ALTHOUGH THESE STORMS WERE RELATIVELY
WEAK...ONE STORM IN THE EXTREME SE CORNER OF THE STATE WAS ABLE TO
PRODUCE AN ELEVATED OUTFLOW ACROSS SOUTHERN COCHISE COUNTY...AS SEEN
ON THE IR SAT IMAGERY. SURFACE HIGH DIVING SOUTH ALONG THE ROCKIES
WILL RESULT IN AN EASTERLY FLOW DEVELOPING ACROSS THE AREA TOMORROW
AND INCREASING SATURDAY. IN FACT...SATURDAY MAY BE QUITE BREEZY TO
LOCALLY WINDY IN SOME SPOTS. OTHERWISE...THIS FLOW WILL HELP IMPORT
INCREASED MOISTURE TO AREAS EAST OF TUCSON TOMORROW...RESULTING IN
SCATTERED STORMS TOMORROW AFTERNOON AND EVENING. THIS SCENARIO IS
DEFINED IN CURRENT FORECAST GRIDS.

&&

.PREV DISCUSSION...THE COVERAGE OF SHOWERS/TSTMS WILL EXPAND WWD FRI
IN RESPONSE TO AN INCREASED LOWER AND MID-LEVEL ELY FLOW REGIME.
THUS...HAVE CONTINUED WITH SCATTERED SHOWERS/TSTMS ACROSS ERN
SECTIONS FRI AFTERNOON/ EVENING...AND ISOLATED SHOWERS/TSTMS FOR THE
TUCSON METRO AREA WWD INTO THE TOHONO O`ODHAM NATION. DRY CONDITIONS
SHOULD CONTINUE ACROSS WRN PIMA COUNTY. THE CHANCES FOR
SHOWERS/TSTMS ARE EXPECTED TO GENERALLY DECREASE ACROSS SE AZ THIS
WEEKEND AS THE MID-LEVEL FLOW BECOMES INCREASINGLY SELY/SLY. THIS
FLOW REGIME TENDS TO FAVOR THE WHITE MOUNTAINS AS WELL AS LOCALES
SOUTH-TO-SOUTHWEST OF TUCSON FOR PRECIP CHANCES.

GUSTY EAST WINDS ARE FORECAST TO START ACROSS THE TUCSON METRO AREA
FRI NIGHT AND CONTINUE SAT IN RESPONSE TO A VERY TIGHT SURFACE
PRESSURE GRADIENT. WIND SPEEDS VIA THE 11/12Z NAM DEPICT WIND
ADVISORY CRITERIA BEING ACHIEVED FOR A FEW HOURS EARLY SAT MORNING.
AT THIS TIME...BELIEVE THE NAM WIND SPEEDS WILL BE MORE INDICATIVE
OF GUST SPEEDS AT KTUS VERSUS SUSTAINED WIND SPEEDS. LESS WIND
SHOULD OCCUR SUN AS THE SURFACE PRESSURE GRADIENT LOOSENS.

MOISTURE IS PROGGED TO SPREAD NWD ACROSS SONORA AND INTO SE AZ MON
AS TROPICAL SYSTEM ODILE MOVES TO THE WEST OF SRN BAJA CALIFORNIA.
THERE WERE FAIRLY SUBSTANTIAL DIFFERENCES BETWEEN THE GFS/ECMWF FOR
TUE-WED REGARDING PRECIP POTENTIAL ACROSS SE AZ. IN ESSENCE...THE
GFS DEPICTED MARKEDLY MORE ROBUST QPF/S VERSUS THE ECMWF...SINCE THE
GFS BRINGS THE CENTER OF ODILE SOMEWHAT CLOSER TO THE BAJA
CALIFORNIA SPUR VERSUS THE ECMWF. AT ANY RATE...HAVE FAVORED TUE
WITH THE HIGHEST POPS THAT DEPICT GENERALLY SCATTERED COVERAGE OF
SHOWERS/TSTMS ACROSS THE AREA. ISOLATED TO SCATTERED AFTERNOON/
EVENING SHOWERS/TSTMS ARE EXPECTED TO PREVAIL NEXT THUR.

HIGH TEMPS FRI SHOULD BE GENERALLY A FEW DEGS WARMER VERSUS TEMPS
ACHIEVED THIS AFTERNOON. DAYTIME TEMPS SAT WILL AVERAGE ABOUT
5 DEGS F COOLER VERSUS FRI...THEN ONLY VERY MINOR DAILY TEMP CHANGES
ARE FORECAST TO OCCUR SUN-THUR.

&&

.AVIATION...VALID THRU 12/23Z.
RESIDUAL MID-LEVEL CLOUDS /11-14K FT AGL/ WILL PERSIST THROUGH THE
EVENING...DECREASING OVERNIGHT. AN EASTERLY WIND WILL IMPORT HIGHER
MOISTURE TO LOCATIONS EAST OF TUCSON FRIDAY. THIS WILL RESULT IN
SCATTERED LOW-LEVEL CLOUDS /7-11K FT AGL/ AND SCATTERED TO BROKEN
MID-LEVEL CLOUDS /12-16K FT AGL/ WITH SCATTERED AFTERNOON AND
EVENING SHRA/TSRA. SURFACE WIND GENERALLY LESS THAN 10 KTS...EXCEPT
GUSTY IN VCNTY OF SHRA/TSRA. AVIATION DISCUSSION NOT UPDATED FOR TAF
AMENDMENTS.

&&

.FIRE WEATHER...THERE WILL BE A CHANCE OF SHOWERS AND THUNDERSTORMS
ACROSS THE THE EASTERN HALF OF THE FORECAST AREA FRIDAY. WINDS WILL
GENERALLY BE OUT OF THE EAST FRIDAY...WITH EXCEPT ERRATIC OUTFLOWS
ASSOCIATED WITH THUNDERSTORMS.

FRIDAY EVENING WILL SEE A SHIFT IN THE WINDS TO AN EAST/SOUTHEAST
DIRECTION WITH A BACKDOOR FRONTAL PASSAGE. EXPECT WIND SPEEDS TO BE
ELEVATED INTO SUNDAY...GENERALLY BETWEEN 10 AND 20 MPH...WITH SOME
LOCALLY HIGHER SPEEDS POSSIBLE. PRECIPITATION CHANCES WILL LOWER
OVER THE UPCOMING WEEKEND INTO THE SLIGHT CHANCE CATEGORY.

TROPICAL MOISTURE WILL THEN BE ON THE INCREASE NEXT WEEK...WITH
TROPICAL STORM ODILE INFLUENCE REACHING THE FORECAST AREA. EXPECT
AN INCREASE IN SHOWER AND THUNDERSTORM ACTIVITY AND AREAL COVERAGE
BY THE MIDDLE OF NEXT WEEK.

&&

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

&&

$$

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

PREV DISCUSSION...FRANCIS







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