Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 302221
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
321 PM MST THU JUL 30 2015

.SYNOPSIS...STORM COVERAGE WILL BE LESS TODAY...OTHERWISE WE WILL
CONTINUE TO HAVE ENOUGH MOISTURE FOR A CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MUCH OF SOUTHEAST ARIZONA INTO NEXT WEEK.

&&

.DISCUSSION...WATER VAPOR IMAGERY...30/12Z UPPER-AIR PLOTS AND
RECENT MODEL DATA SHOW A RIDGE CENTERED OVER THE SOUTHERN
PLAINS...WITH THE PESKY UPPER LOW STILL OFF THE WEST COAST OF THE
BAJA PENINSULA. THIS SYSTEM WILL BECOME ABSORBED BY THE MAIN PACIFIC
LOW WHICH IS WELL TO THE WEST OF THE SOUTHERN CALIFORNIA/NORTHERN
BAJA COASTS. A WEAK IMPULSE IS CURRENTLY LIFTING TO THE NORTH
NORTHEAST ACROSS THE FOUR CORNERS REGION. AS A RESULT...VISIBLE AND
IR SATELLITE IMAGERY SHOWS EXTENSIVE CLOUDINESS ASSOCIATED WITH THIS
FEATURE THAT EXTEND FROM SOUTHERN CALIFORNIA...ACROSS NORTHERN
ARIZONA AND INTO MUCH OF WESTERN NEW MEXICO. CLOSER TO HOME...
VISIBLE IMAGERY SHOWS CUMULUS DEVELOPMENT OVER MAINLY MOUNTAIN TOPS.
A FEW SHOWERS AND STORMS STRUGGLING TO DEVELOP WITH ONLY ISOLATED
MOUNTAIN STORMS AT THIS TIME. THAT SAID...I LOWERED THE POP FORECAST
CONSIDERABLY TO ACCOUNT FOR DRIER AND MORE STABLE AIRMASS.

THIS MORNINGS SOUNDING WAS MUCH DRIER COMPARED TO YESTERDAY
MORNING...WITH THE PW DOWN TO 1.25 INCHES COMPARED TO WEDNESDAY
MORNINGS 1.62 INCHES. VARIOUS SOURCES OF PW SUGGEST THAT CURRENT
READINGS RANGE FROM AROUND 1.1 - 1.3 INCHES AND MAY DROP EVEN LOWER
BEFORE ALL IS SAID AND DONE. DEWPOINT TEMPERATURES CURRENTLY RANGE
FROM THE MID 50S TO THE LOWER 60S...WHICH IS ABOUT 3 TO 5 DEGS
COOLER/DRIER THAN THIS TIME YESTERDAY.

EVEN THOUGH WE ARE DRIER THAN THE PAST 12 TO 24 HOURS...MODELS SHOW
PW`S INCREASING FRIDAY INTO THE 1.5 - 1.7 INCH RANGE AS A WEAK
DISTURBANCE MOVES UP FROM THE SOUTHEAST LATE IN THE DAY AND
POTENTIALLY ENHANCES ACTIVITY. BY SATURDAY A WEAK IMPULSE TO OUR
WEST MOVES TO THE NORTH ACROSS WESTERN ARIZONA WITH PW`S AROUND 1.4 -
1.6 INCHES. SO...I MAINTAIN A LOW GRADE MONSOON FORECAST WITH LOW
END SCATTERED ACTIVITY FOR MUCH OF THE FORECAST AREA FRIDAY AND
MOSTLY CENTRAL AND EASTERN AREAS FOR SATURDAY.

BY SUNDAY THE MODELS SHOW HIGH PRESSURE CENTERED EITHER JUST TO OUR
EAST OR SOUTH (GFS HAS IT OVER NEW MEXICO AND ECMWF EXTENDING FROM
EASTERN PACIFIC ACROSS CENTRAL BAJA AND NORTHERN SONORA). BOTH
MODELS SHOW A DRYING TREND WITH PW`S FROM THE GFS DOWN TO ABOUT 1.2
INCHES. SO...I HAVE THE BEST THREAT FOR SHOWERS AND THUNDERSTORMS
BETWEEN TUCSON AND THE NEW MEXICO BORDER.

FROM MONDAY THROUGH THURSDAY THE HIGH WILL MEANDER ACROSS THE DESERT
SOUTHWEST IN SOME FORM OR FASHION. ECMWF HAS BEEN THE DRIER MODEL
BETWEEN THE GFS AND ECMWF. FOR NOW I CONTINUE WITH A FORECAST ON
MONDAY THAT IS SIMILAR TO MONDAY...BUT THEN EACH DAY THEREAFTER
SHOULD BE A STANDARD LOW GRADE MONSOON FORECAST...WITH THE BEST
THREAT BETWEEN NOGALES AND DOUGLAS AS WELL AS THE MOUNTAIN TOPS.

FOR TUCSON...HIGH TEMPS WILL BE SLIGHTLY ABOVE NORMAL FRIDAY AND
SATURDAY AND 4 TO 6 DEGS ABOVE NORMAL SUNDAY THROUGH THURSDAY...
ALTHOUGH THE WARMEST DAY SHOULD BE TUESDAY.

&&

.AVIATION...VALID THRU 31/23Z.
FEW-SCT CLOUDS AT 7-10K FT AGL AND SCT CLOUDS ABOVE 20K FT AGL THRU
31/04Z...THEN DECREASING CLOUDS...WITH A FEW CLOUDS AT 8-12K FT AGL
BY 31/09Z. SCT-BKN CLOUDS AT 6-9K FT AGL AND BKN CLOUDS AT 10-14K FT
AGL AFT 31/19Z. ISOLD -SHRA/-TSRA OVER THE HIGHER TERRAIN THRU
31/03Z...WITH SCT SHRA/TSRA DEVELOPING AFT 31/20Z. BRIEF WIND GUSTS
TO NEAR 35 KTS POSSIBLE IN AND AROUND THE STRONGER TSRA. OUTSIDE OF
STORM INFLUENCES...SFC WINDS WILL GENERALLY BE LESS THAN 12 KTS WITH
A FEW HIGHER GUSTS IN THE AFTERNOON/EARLY EVENING HOURS. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...ISOLATED SHOWERS AND THUNDERSTORMS WILL OCCUR MAINLY
ACROSS THE HIGHER TERRAIN THROUGH THIS EVENING BEFORE DIMINISHING.
DRYING IS THEN EXPECTED ACROSS THE WESTERN HALF OF THE FORECAST AREA
INTO EARLY NEXT WEEK...WITH ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS CONTINUING OVER EASTERN AREAS. STRONG OUTFLOW WINDS
WILL BE POSSIBLE NEAR THUNDERSTORMS. OTHERWISE...20-FT WINDS WILL
GENERALLY BE TERRAIN DRIVEN AND LESS THAN 15 MPH...WITH SOME
AFTERNOON AND EARLY EVENING BREEZINESS DUE TO THE STRONG DAYTIME
HEATING.

&&

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

&&

$$

PUBLIC...MOLLERE
AVIATION/FIRE WEATHER...ZELL

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