Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 281611
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
911 AM MST TUE JUL 28 2015

.SYNOPSIS...EXPECT AN INCREASE IN THUNDERSTORMS TODAY AND ESPECIALLY
WEDNESDAY AS DEEPER MOISTURE RETURNS. WE WILL THEN CONTINUE TO HAVE
A CHANCE OF MAINLY AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS
INTO THE COMING WEEKEND.

&&

.DISCUSSION...WATER VAPOR IMAGERY AND 28/12Z UPPER-AIR PLOTS SHOW A
RIDGE CENTERED OVER THE SOUTHERN PLAINS WITH A LOW PRESSURE SYSTEM
OFF THE WEST COAST OF THE SOUTHERN BAJA PENINSULA. BETWEEN THESE TWO
SYSTEMS SOUTH TO SOUTHEASTERLY FLOW WILL USHER IN ADDITIONAL
MOISTURE BEGINNING TODAY BUT CONTINUING THROUGH WEDNESDAY.
PRECIPITABLE WATER VALUES FROM VARIOUS SOURCES INDICATE THAT
READINGS WILL RANGE FROM 1.5 - 1.7 DURING THE NEXT COUPLE OF DAYS OR
SO. THE LATEST CIRA LPW IMAGE SHOWS VALUES WELL OVER 2 INCHES OVER
CENTRAL PORTIONS OF THE GULF OF CALIFORNIA. MODELS SHOW THIS
MOISTURE BEING TRANSPORTED TO THE NORTH NORTHWEST OVER EXTREME
SOUTHWESTERN ARIZONA DURING THE NEXT 24 HOURS OR SO. MEANWHILE PW`S
ARE ADVERTISED TO REMAIN AROUND THE 1.5 - 1.7 INCH RANGE FARTHER
EAST OVER MY CENTRAL ZONES AND A BIT LOWER IN THE 1.3 - 1.5 INCH
RANGE FOR EXTREME EASTERN ZONES...WHICH IS STILL SIGNIFICANT.

IR AND VISIBLE SATELLITE IMAGERY SHOWS MID LEVEL CLOUDINESS MAINLY
OVER NORTHERN FRINGES OF THE FORECAST AREA...AS WELL AS ALONG THE
NEW MEXICO BORDER.

BASED ON LATEST RUNS OF THE WRF/NAM AND GFS AS WELL AS HRRR...IT
LOOKS LIKE THE INHERITED POP FORECAST FOR TODAY SEEMS REASONABLE...
WITH A FOCUS ALONG THE INTERNATIONAL BORDER AND THE CENTRAL AND
WESTERN SECTIONS OF PIMA COUNTY...WHICH INCLUDES THE TOHONO O`ODHAM
NATION.

FOR DETAILS REGARDING THE FORECAST BEYOND TODAY...PLEASE REFER TO
THE PREVIOUS DISCUSSION BELOW.

&&

.AVIATION...VALID THRU 29/18Z.
SCT TO BKN CLOUDS 8-12K FT AGL...MAINLY WEST AND NORTH OF THE TUCSON
AREA AND ALONG THE NEW MEXICO BORDER. MORE WIDESPREAD SHRA/TSRA
EXPECTED TODAY FARTHER NORTH AND WEST INCLUDING KTUS. BRIEF MVFR
CONDITIONS AND VRB WIND GUSTS TO 40 KTS POSSIBLE IN AND AROUND THE
STRONGER TSRA. OUTSIDE OF STORM INFLUENCE...SFC WINDS WILL BE LESS
THAN 12 KTS WITH SOME HIGHER GUSTS FROM FROM THE WEST AND NORTHWEST
DURING THE AFTERNOON ESPECIALLY NEAR KSAD. AVIATION DISCUSSION NOT
UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...MOISTURE IS ON THE INCREASE UNDER THE INFLUENCE OF
DEEPER SOUTHERLY FLOW. THE RESULT WILL BE AN INCREASE IN SHOWERS AND
THUNDERSTORMS THIS WEEK. TODAY THROUGH FRIDAY...MORE WIDESPREAD
CONVECTIVE ACTIVITY WILL OCCUR OVER ALL SOUTHEASTERN ARIZONA ZONES.
STRONG OUTFLOWS NEAR STORMS COULD PRODUCE WIND GUSTS TO 45 MPH.
OTHERWISE...20-FT WINDS WILL GENERALLY BE TERRAIN DRIVEN AND LESS
THAN 15 MPH WITH SOME AFTERNOON GUSTINESS FROM THE WEST OR NORTHWEST
DUE TO DAYTIME HEATING. WINDS WILL DEVELOP MORE OF AN EASTERLY
COMPONENT BEGINNING THURSDAY.

&&

.PREV DISCUSSION...WEDNESDAY IS COMING TOGETHER WITH THE BEST
MOISTURE AND DYNAMICS FOR SOUTHEAST ARIZONA. AN IMPULSE IN THE
DEEPENING SOUTHERLY FLOW SHOULD HELP FOCUS STORM COVERAGE...AND AS
THE LOW NEAR CENTRAL BAJA LIFTS NORTHWARD...WE SHOULD SEE STRONGER
FLOW AND DECENT SHEAR FOR MUCH OF SOUTHEAST ARIZONA WEDNESDAY
AFTERNOON. ISOLATED SEVERE AND FLASH FLOOD POTENTIAL. ORGANIZED
CONVECTIVE OUTFLOWS POSSIBLE WITH GOOD SOUTHERLY OR SOUTHEASTERLY
ORIENTATION TO PUSH A LOT OF DUST AHEAD OF STORMS INTO FAVORED
LOCATIONS IN PINAL AND NORTHERN PIMA COUNTIES.

THURSDAY WILL STILL HAVE PLENTY OF MOISTURE WITH SOLID THUNDERSTORM
POTENTIAL ON PAPER...BUT WE`LL HAVE TO SEE HOW THE ATMOSPHERE IS
LOOKING IF WEDNESDAY AND WEDNESDAY EVENING GO OFF BIG. BY FRIDAY WE
MAY STRUGGLE A BIT BEHIND THE MID LEVEL IMPULSE LIFTING
NORTHEASTWARD AND SOME SLIGHT MID LEVEL WARMING AS THE HIGH DECIDES
TO SPREAD IN FROM THE EAST.

FOR THE WEEKEND WE SHOULD STILL HAVE SOLID MOISTURE IN THE SOUTHEAST
PART OF THE STATE...BUT WE COULD SEE DIMINISHING THUNDERSTORM
COVERAGE IN WESTERN AREAS DEPENDING ON THE PLACEMENT OF THE HIGH
CENTER. IT SHOULD STILL BE AT LEAST IN A POSITION FOR THUNDERSTORM
COVERAGE NEAR TO JUST UNDER CLIMO FOR EARLY AUGUST WITH THE HIGH A
LITTLE WEAKER THAN WHAT WE WOULD LIKE TO SEE.

&&

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

&&

$$

CURRENT DISCUSSION...MOLLERE
PREVIOUS DISCUSSION...MEYER/RASMUSSEN

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