Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 041609
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
910 AM MST MON MAY 4 2015

.SYNOPSIS...THERE IS A CHANCE OF SHOWERS AND THUNDERSTORMS MAINLY
NORTH OF TUCSON INTO TONIGHT. A CHANCE OF SHOWERS AND THUNDERSTORMS
EXISTS TUESDAY...ESPECIALLY NORTHEAST OF TUCSON. DRY CONDITIONS WILL
THEN PREVAIL WEDNESDAY INTO THE UPCOMING WEEKEND. EXPECT BREEZY TO
PERHAPS WINDY CONDITIONS TO OCCUR THURSDAY AND FRIDAY. DAYTIME
TEMPERATURES WILL BE BELOW NORMAL THIS WEEK.

&&

.DISCUSSION...THE UPPER PATTERN THIS MORNING IS DEFINED BY AN UPPER
LOW POSITIONED ALONG THE SOUTHERN CALIFORNIA COASTLINE...ANOTHER LOW
IN THE GULF OF ALASKA AND A BROAD RIDGE OF HIGH PRESSURE SPREAD OUT
OVER THE EASTERN STATES. THE MAIN FORECAST ISSUE FOR TODAY WILL BE
HANDLING THE LOCATION AND TIMING OF SHOWERS/THUNDERSTORMS ACROSS THE
FORECAST AREA AS THE UPPER LOW MOVES THRU ARIZONA OVER THE NEXT 24-
36 HOURS.

THE KEMX RADAR AND VISIBLE SATELLITE IMAGERY THIS MORNING INDICATED
ISOLATED TO WIDELY SCATTERED SHOWERS AND THUNDERSTORMS EXTENDING
ACROSS EASTERN PIMA AND SOUTHEAST PINAL COUNTIES MOVING NORTH AT 20
MPH. MOST OF THESE STORMS HAVE WEAKENED OVER THE PAST HOUR...BUT
THEY WERE RESPONSIBLE FOR LOCALIZED RAINFALL BETWEEN A TENTH TO A
QUARTER INCH OF RAIN AROUND THE TUCSON METRO WITH EVEN SOME SMALL
HAIL OBSERVED IN ORACLE. THE 12Z KTWC UPPER AIR SOUNDING INDICATED A
MODERATELY UNSTABLE AND MOIST ATMOSPHERE...ESPECIALLY IN THE LOWER
LEVELS WITH A PRECIPITABLE WATER VALUE OF 0.89 INCHES. THE STRONGER
STORM MOVEMENT THIS MORNING WAS HELPFUL IN KEEPING THE OVERALL
RAINFALL AMOUNTS RATHER LIGHT.

THE LATEST WATER VAPOR IMAGERY INDICATED THAT THE UPPER LOW OVER
SOUTHERN CALIFORNIA IS BEGINING TO BECOME NEGATIVELY TILTED AS IT
CONTINUES TO LIFT NORTHEAST TOWARD WEST-CENTRAL ARIZONA. MODELS ARE
ALL IN GOOD AGREEMENT THAT THE BEST DEFORMATION/DIFLUENCE ALOFT
WILL OCCUR ACROSS THE NORTHERN HALF OF ARIZONA THIS AFTERNOON...WITH
THE SOUTHERN PERIPHERY OF THIS FIELD EXTENDING ACROSS NORTH AND
NORTHWEST PORTIONS OF OUR FORECAST AREA /NORTH OF TUCSON/. THE
COMBINATION OF THIS LARGE SCALE FORCING...THE FACT THAT THE DEEPER
MOISTURE /PRECIPITABLE WATER VALUES UP TO 1.00 INCH/ CONTINUES TO
MOVE NORTH INTO CENTRAL ARIZONA...AND THE SLOWING STORM MOTION WILL
MAKE THE NORTHERN PORTIONS OF OUR FORECAST AREA THE PRIME LOCATION
FOR SHOWERS AND THUNDERSTORMS. THESE STORMS WILL BE CAPABLE OF
PRODUCING LOCALIZED HEAVY RAINFALL...BRIEF THUNDERSTORM OUTFLOW
GUSTS THAT MAY LEAD TO LOCALIZED BLOWING DUST AND SMALL TO MEDIUM
SIZED HAIL.

MEDIUM RANGE MODELS ARE ALL IN GOOD AGREEMENT ON THE TIMING OF THIS
UPPER LOW EJECTING OUT OF ARIZONA BY TUESDAY AFTERNOON. ADDITIONAL
STORM DEVELOPMENT WILL POSSIBLE ON THE SOUTHERN PERIPHERY OF THIS
FEATURE LATE TONIGHT AND EARLY TUESDAY AS IT EJECTS...BUT THE
INTENSITY WILL SIGNIFICANTLY WANE THROUGH THE DAY.

THE UPPER LOW CURRENTLY IN THE GULF OF ALASKA WILL THEN FILL INTO
THE MEAN TROUGH ACROSS THE WESTERN STATES THE SECOND HALF OF THE
WORK WEEK. RIGHT NOW...BOTH THE GFS AND ECMWF ARE INDICATING THAT
THIS SYSTEM WILL DIVE SOUTH ALONG THE WEST COAST...WITH THE BEST
CHANCE FOR PRECIPITATION LIMITED TO THE GREAT BASIN. THIS PATH WOULD
LEAVE SOUTHEAST ARIZONA HIGH AND DRY...WITH BREEZY TO LOCALLY WINDY
CONDITIONS AND LIMITED CRITICAL FIRE WEATHER CONDITIONS THE SECOND
HALF OF THE WORK WEEK.

&&

.PREV DISCUSSION...UPPER LEVEL TROUGH WAS OVER THE SWRN CONUS EARLY
THIS MORNING...WITH WEAK LOW PRESSURE ALOFT CENTERED NEAR THE SRN
CALIFORNIA COAST. THE UPPER TROUGH WILL MOVE EWD INTO THE SRN
ROCKIES TUE. 04/00Z NAM/GFS/ECMWF/CMC WERE IN EXCELLENT AGREEMENT
WITH DEPICTING THE BULK OF PRECIP ASSOCIATED WITH THIS SYSTEM TO
OCCUR NORTH OF THIS FORECAST AREA.

HOWEVER...THERE WILL BE SUFFICIENT MOISTURE IN COMBINATION WITH A
MODERATELY UNSTABLE ENVIRONMENT TO PRODUCE SCATTERED TO PERHAPS
NUMEROUS SHOWERS AND THUNDERSTORMS LATER TODAY AND INTO TONIGHT. THE
OFFICIAL FORECAST CONTINUES WITH AT LEAST A SLIGHT CHANCE OF SHOWERS/
TSTMS ACROSS SE ARIZONA THRU TONIGHT. A GOOD CHANCE OF SHOWERS/TSTMS
EXISTS THIS AFTERNOON AND EVENING ACROSS THE WHITE MOUNTAINS...AND
CHANCE-CATEGORY POPS REMAIN FOR THE TUCSON METRO AREA. BRIEF WIND
GUSTS THIS AFTERNOON ASSOCIATED WITH STRONGER THUNDERSTORMS MAY LEAD
TO LOCALIZED BLOWING DUST REDUCING VISIBILITIES.

PRECIP CHANCES WILL DECREASE FROM SW-NE TUE AS THE MID-LEVEL TROUGH
AXIS MOVES WELL EWD INTO NEW MEXICO. THERE IS A CHANCE OF SHOWERS/
TSTMS TUE MORNING ACROSS THE WHITE MOUNTAINS...AND A SLIGHT CHANCE
OF SHOWERS/TSTMS SOUTHWARD AND SOUTHWESTWARD TO THE INTERNATIONAL
BORDER. A CHANCE OF SHOWERS/TSTMS TUE AFTERNOON/EVENING WILL BE
CONFINED MAINLY ACROSS THE WHITE MOUNTAINS. DRY CONDITIONS WILL THEN
PREVAIL AREA-WIDE LATE TUE NIGHT INTO SUN.

RAINFALL AMOUNTS BY LATE TUE NIGHT ARE CONTINUED TO BE PROJECTED AS
FAIRLY LIGHT...WITH AMOUNTS GENERALLY RANGING FROM A FEW HUNDREDTHS
OF AN INCH TO ONE THIRD OF AN INCH IN THE VALLEYS...AND FROM A TENTH
OF AN INCH TO ONE HALF OF AN INCH OR SO 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.

FLOW ALOFT WILL BECOME INCREASINGLY SWLY WED AS THE NEXT UPPER
TROUGH DEEPENS WEST OF THE AREA. SOME BREEZINESS SHOULD RETURN WED
AFTERNOON FOLLOWED BY BREEZY TO PERHAPS WINDY CONDITIONS THUR-FRI AS
LOW PRESSURE ALOFT STRENGTHENS OVER NRN/CENTRAL CALIFORNIA AND THE
GREAT BASIN. LESS WIND IS FORECAST TO OCCUR SAT AS THE UPPER LOW
FILLS NORTH OF THE AREA...AND A SHORTWAVE RIDGE APPROACHES FROM THE
WEST SUN.

HIGH TEMPS TODAY WILL GENERALLY BE ABOUT 5-10 DEGS F OR SO COOLER
VERSUS TEMPS ACHIEVED SUN AFTERNOON. BELOW NORMAL DAYTIME TEMPS WILL
PREVAIL TUE-SAT FOLLOWED BY TEMPS TRENDING CLOSER-TO-NORMAL SUN.

&&

.AVIATION...VALID THRU 05/18Z.
A LOW PRESSURE SYSTEM NEAR THE SOUTHERN CALIFORNIA COAST WILL MOVE
NORTHEAST INTO NORTHERN ARIZONA BY EARLY TUESDAY MORNING. ADEQUATE
MOISTURE WILL LEAD TO SCATTERED -TSRA/-SHRA MAINLY NORTH OF KTUS
INTO EARLY TUESDAY MORNING. BRIEF WIND GUSTS MAINLY OF 35-45 KTS MAY
OCCUR WITH TSRA...ESPECIALLY THIS AFTERNOON AND EARLY THIS EVENING.
OTHERWISE...CLOUD DECKS INTO EARLY TUESDAY MORNING WILL GENERALLY
RANGE FROM 5-10K FT AGL. SURFACE WIND THIS 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...THERE IS A CHANCE OF SHOWERS AND THUNDERSTORMS
MAINLY FROM TUCSON NORTHEASTWARD INTO THE WHITE MOUNTAINS THROUGH
TONIGHT. RAINFALL AMOUNTS WILL BE FAIRLY LIGHT...GENERALLY RANGING
FROM A FEW HUNDREDTHS OF AN INCH TO AROUND ONE HALF OF AN INCH. THE
POTENTIAL FOR BRIEF...STRONG GUSTY AND ERRATIC WINDS ASSOCIATED WITH
THUNDERSTORMS EXISTS MAINLY THIS AFTERNOON AND EVENING. A CHANCE OF
SHOWERS AND THUNDERSTORMS CONTINUES MOSTLY ACROSS THE WHITE
MOUNTAINS TUESDAY AND TUESDAY EVENING.

THEREAFTER...DRY CONDITIONS WILL PREVAIL WEDNESDAY THROUGH THE
UPCOMING WEEKEND. BREEZY TO LOCALLY WINDY CONDITIONS MAY RETURN AS
EARLY AS WEDNESDAY...BUT WILL BE MORE LIKELY TO OCCUR THURSDAY AND
FRIDAY. THE COMBINATION OF GUSTY SOUTHWEST TO WEST WINDS AND LOW
RELATIVE HUMIDITIES MAY PRODUCE CRITICAL FIRE WEATHER CONDITIONS
THURSDAY AND FRIDAY DURING THE AFTERNOON HOURS. THE BEST CHANCE FOR
THESE CRITICAL FIRE WEATHER CONDITIONS TO OCCUR WILL BE AT
ELEVATIONS BELOW 5000 FEET FROM TUCSON SOUTHWARD AND SOUTHEASTWARD
TO THE INTERNATIONAL BORDER.

&&

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

&&

$$

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