Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 031611
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
911 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...AFTERNOON BREEZINESS AND HIGH TEMPERATURES A FEW
DEGREES BELOW NORMAL WILL THEN PREVAIL DURING THE LATTER PART OF
THE WEEK.

&&

.DISCUSSION...CURRENT FORECAST ON TRACK WITH CHANCES FOR
THUNDERSTORMS INCREASING INTO MONDAY THEN DRYING OUT AGAIN AFTER
TUESDAY. TEMPERATURE TRENDS ALSO LOOK GOOD.

MORNING OBSERVATIONAL DATA SHOWING MORE SURFACE MOISTURE TODAY
VERSUS SATURDAY BUT MID AND UPPER LEVEL MOISTURE A BIT LESS.
SOUNDING IS UNSTABLE ENOUGH TO SUPPORT THUNDERSTORMS ALTHOUGH
EXPECT COVERAGE TO BE LIMITED AND MAINLY CONFINED TO AREAS NORTH
OF TUCSON. STILL...WITH ANY STORM THAT DOES DEVELOP THERE IS THE
POTENTIAL FOR GUSTY WINDS WHICH COULD KICK UP BLOWING DUST. HAVE
MADE SLIGHT ADJUSTMENTS TO THE AFTERNOON FORECAST TO INCREASE
RAIN CHANCES IN PORTIONS OF PINAL AND GRAHAM COUNTIES.

EARLY MODEL RETURNS SHOWING THIS TREND OF FAVORING NORTHERN AREAS
WITH RAIN CONTINUING THE NEXT COUPLE OF DAYS AS THE SYSTEM OFF THE
PACIFIC COAST DRAWS NEARER.

&&

.AVIATION...VALID THRU 05/18Z
EXPECT ISOLATED TO SCATTERED HIGH BASED -TSRA/-SHRA NE OF A KCGZ-
KFHU THIS AFTERNOON WITH NORTHERN AREAS ESPECIALLY FAVORED.
CHANCES WILL REMAIN BEST IN THESE AREAS INTO MONDAY WITH A GENERAL
INCREASE IN OVERALL COVERAGE. BRIEF WIND GUSTS MAINLY OF 35-45 KTS
AND BLDU MAY OCCUR WITH -TSRA...ESPECIALLY DURING THE AFTERNOON
HOURS. SURFACE WIND THIS AFTERNOON WILL BE SWLY/WLY AT 12-18 KTS
WITH GUSTS OF 20-25 KTS...DIMINISHING AFTER DARK. 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.

&&

.PREV 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.

&&

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

&&

$$

DROZD

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