Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 031140
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
440 AM MST SUN MAY 3 2015

.SYNOPSIS...A PACIFIC LOW PRESSURE SYSTEM WILL BRING A CHANCE OF
SHOWERS AND THUNDERSTORMS ALONG WITH A COOLING TREND THROUGH
TUESDAY. THE BEST CHANCE FOR WIDESPREAD RAINFALL WILL OCCUR MONDAY.
DRY CONDITIONS WITH AFTERNOON BREEZINESS AND HIGH TEMPERATURES A FEW
DEGREES BELOW NORMAL WILL THEN PREVAIL DURING THE LATTER PART OF
THIS WEEK.

&&

.DISCUSSION...IR SATELLITE IMAGERY AND SURFACE OBSERVATIONS
INDICATED SCATTERED TO BROKEN MID-LEVEL CLOUDS ACROSS NRN COCHISE/
GREENLEE/GRAHAM/SERN PINAL COUNTIES EARLY THIS MORNING. CLEAR SKIES
PREVAILED FROM TUCSON SWD/WWD ACROSS SANTA CRUZ/WRN PIMA COUNTIES.
DEWPOINTS AT LOWER ELEVATIONS VALID 03/11Z RANGED FROM THE UPPER 30S-
LOWER 40S. AWIPS BLENDED TOTAL PRECIP WATER PRODUCT VALID 09Z
YIELDED VALUES FROM 0.70-0.85 INCH ACROSS SE AZ. THE UPPER LEVEL
PATTERN EARLY THIS MORNING WAS CHARACTERIZED BY A STRONG BAND OF
WESTERLIES FROM THE PACIFIC NW INTO THE NRN CONUS PLAINS.
MEANWHILE...A TROUGH WITHIN A WEAKER SRN BRANCH OF WESTERLIES WAS
LOCATED WEST OF THE SRN CALIFORNIA/NRN BAJA CALIFORNIA COASTS NEAR
20N-30N AND 120W-130W.

VARIOUS 03/00Z NWP MODELS SUGGEST THAT ANY MEASURABLE RAINFALL FROM
SHOWERS/THUNDERSTORMS TODAY WILL BE LIMITED TO LOCALES EAST OF
TUCSON. THUS...THE OFFICIAL FORECAST WAS ADJUSTED FOR THIS SCENARIO.
THERE IS A SLIGHT CHANCE OF SHOWERS THIS MORNING ACROSS THE WHITE
MOUNTAINS FOLLOWED BY GENERALLY A SLIGHT CHANCE OF SHOWERS/TSTMS
THIS AFTERNOON ACROSS COCHISE/GREENLEE/GRAHAM COUNTIES. PRECIP-FREE
CONDITIONS SHOULD OCCUR TODAY FROM TUCSON WWD ACROSS THE CENTRAL
DESERTS.

THE UPPER TROUGH AND OCCASIONAL CLOSED UPPER LOW IS THEN PROGGED TO
APPROACH THE SRN CALIFORNIA COAST TONIGHT. A WEAK CLOSED UPPER LOW
IS THEN DEPICTED VIA THE 03/00Z NAM/GFS/ECMWF/CMC TO BE CENTERED
OVER THE LOWER COLORADO RIVER VALLEY MON AFTERNOON. INCREASED
MOISTURE WITH PWATS PERHAPS APPROACHING ONE INCH...A SLIGHTLY
UNSTABLE ENVIRONMENT WITH GFS CAPES OF 200-400 J/KG...AND A NEGATIVE
TILTED UPPER SYSTEM...SUGGEST TOWARD INCREASED COVERAGE OF SHOWERS/
TSTMS TONIGHT-MON.

THUS...A SLIGHT CHANCE OF SHOWERS/TSTMS EXISTS ACROSS THIS ENTIRE
FORECAST AREA BY LATE TONIGHT INTO MON MORNING. CHANCE-CATEGORY POPS
THEN OCCURS MON AFTERNOON/NIGHT FROM TUCSON NEWD INTO THE WHITE
MOUNTAINS. A SLIGHT CHANCE OF SHOWERS/TSTMS CONTINUES ELSEWHERE MON
AFTERNOON/NIGHT. PRECIP CHANCES WILL DECREASE FROM SW-NE TUE AS THE
MID-LEVEL TROUGH AXIS MOVES WELL EWD INTO NEW MEXICO...AND A
SHORTWAVE RIDGE APPROACHES FROM THE WEST. HAVE CONTINUED WITH A
CHANCE OF SHOWERS/TSTMS TUE AFTERNOON/EVENING NE OF TUCSON WITH DRY
CONDITIONS ELSEWHERE. A FEW LINGERING SHOWERS MAY OCCUR LATE TUE
NIGHT/EARLY WED MORNING ACROSS THE WHITE MOUNTAINS. OTHERWISE...
DRY CONDITIONS WILL PREVAIL AS THE UPPER RIDGE AXIS MOVES EWD ACROSS
THE AREA.

STORM TOTAL RAINFALL AMOUNTS AT THIS TIME ARE FORECAST TO GENERALLY
RANGE FROM ONE TENTH TO ONE THIRD OF AN INCH ACROSS THE VALLEYS...AND
ONE HALF OF AN INCH TO THREE QUARTERS OF AN INCH ACROSS THE
MOUNTAINS. THE HEAVIEST AMOUNTS SHOULD OCCUR FROM THE CATALINA/
RINCON MOUNTAINS NEAR TUCSON...THE PINALENO/GALIURO MOUNTAINS OF
GRAHAM COUNTY...AND THE WHITE MOUNTAINS.

A LOW PRESSURE SYSTEM ALOFT OVER THE PACIFIC NW WED WILL DEEPEN OVER
NRN/CENTRAL CALIFORNIA THUR. THIS UPPER LOW WILL CONTINUE TO DEEPEN
OVER THE GREAT BASIN FRI...THEN WEAKEN OVER THE NRN/CENTRAL ROCKIES
SAT. ALTHOUGH DRY CONDITIONS WILL PREVAIL WED-SAT...THE MAIN IMPACT
WILL LIKELY BE GUSTY WINDS DURING THE AFTERNOON/EARLY EVENING
HOURS...PARTICULARLY THUR-FRI.

A COOLING TREND WILL OCCUR INTO MON FOLLOWED BY NO SIGNIFICANT
CHANGE IN DAYTIME TEMPS TUE. EXPECT ABOUT 3-5 DEGS F OF WARMING
WED...THEN A FEW DEGS OF DAILY COOLING IS ON TAP THUR-FRI.
DAYTIME TEMPS NEXT SAT SHOULD AVERAGE A FEW DEGS BELOW NORMAL.

&&

.AVIATION...VALID THRU 05/00Z.
EXPECT ISOLATED TO SCATTERED -TSRA/-SHRA EAST OF KTUS TODAY WITH
DRY CONDITIONS ELSEWHERE. A LOW PRESSURE SYSTEM WILL APPROACH THE
SOUTHERN CALIFORNIA COAST TONIGHT. THIS SYSTEM WILL THEN MOVE SLOWLY
EASTWARD ACROSS SOUTHERN CALIFORNIA MONDAY. INCREASING MOISTURE WILL
BRING ISOLATED TO SCATTERED -TSRA/-SHRA TONIGHT THROUGH MONDAY.
BRIEF WIND GUSTS MAINLY OF 35-45 KTS MAY OCCUR WITH TSRA...
ESPECIALLY DURING THE AFTERNOON HOURS. OTHERWISE...CLOUD BASES
THROUGH MONDAY AFTERNOON WILL GENERALLY RANGE FROM 8-15K FT AGL.
SURFACE WIND THIS AFTERNOON AND MONDAY AFTERNOON WILL BE SWLY/WLY AT
12-18 KTS WITH GUSTS OF 20-25 KTS. SURFACE WIND WILL BE LESS THAN 10
KTS AT OTHER TIMES. AVIATION DISCUSSION NOT UPDATED FOR TAF
AMENDMENTS.

&&

.FIRE WEATHER...A LOW PRESSURE SYSTEM APPROACHING FROM THE WEST WILL
BRING A CHANCE OF SHOWERS AND THUNDERSTORMS THROUGH TUESDAY. THE
BEST CHANCE FOR WIDESPREAD RAINFALL COVERAGE WILL OCCUR MONDAY.
EXPECT BRIEF STRONG...GUSTY AND ERRATIC WINDS WITH THUNDERSTORMS. A
COOLING TREND WILL ALSO OCCUR THROUGH TUESDAY. DRY CONDITIONS WILL
THEN PREVAIL WEDNESDAY THROUGH SATURDAY. BREEZY TO LOCALLY WINDY
CONDITIONS SHOULD OCCUR DURING THE LATTER PART OF THE WEEK. THE
COMBINATION OF GUSTY SOUTHWEST TO WEST WINDS AND LOWER AFTERNOON
HUMIDITIES MAY PRODUCE LOCALIZED CRITICAL FIRE WEATHER CONDITIONS
THURSDAY AND FRIDAY.

&&

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

&&

$$

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

FRANCIS



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