Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 030422
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
921 PM MST THU JUL 2 2015

.SYNOPSIS...EXPECT A STEADY INCREASE IN THE NUMBER OF STORMS INTO
THIS WEEKEND. SLOWER MOVING STORMS WILL START TO INCREASE HEAVY
RAINFALL CONCERNS WITH WET MICROBURSTS POSSIBLE. DAYTIME
TEMPERATURES WILL REMAIN CLOSE TO SEASONAL NORMALS INTO THIS HOLIDAY
WEEKEND.

&&

.DISCUSSION...THE WATER VAPOR IMAGERY THIS EVENING INDICATED AN
ELONGATED UPPER HIGH EXTENDING FROM NORTHERN NEVADA INTO SOUTHERN
NEW MEXICO...WITH ITS CENTER OVER NORTHEAST ARIZONA. STORMS THIS
EVENING HAVE BEEN CONFINED TO THE EAST OF TUCSON...AND APPEAR TO
HAVE FIRED GENERALLY ALONG THE MOISTURE DISCONTINUITY/BOUNDARY
ALOFT. MODELS ALL SHOW A SLIGHT SHIFTING THE HIGH AXIS WESTWARD
OVERNIGHT...WITH THE 00Z GFS AND NAM BOTH DEPICTING AN AREA OF
HIGHER OMEGA AT 300 MB TO THE NE OF TUCSON...GENERALLY E PINAL AND
GRAHAM COUNTIES. BELIEVE THAT THIS WILL BE THE FAVORED AREA FOR WEAK
CONVECTION OVERNIGHT.

STORMS ARE STILL ACTIVE LATE THIS EVENING ACROSS SOUTHERN GRAHAM AND
EASTERN COCHISE. THE LATEST RUN OF THE HRRR INDICATED THAT THIS
CONVECTION WILL WEAKEN BUT BECOME MORE GENERALIZED LIGHT TO MODERATE
RAIN EXTENDING INTO NORTHEAST PIMA AND EASTERN PINAL INTO THE EARLY
MORNING HOURS. THIS FITS THE CURRENT TRENDS AND LARGER SCALE
PICTURE...SO MODIFIED INHERITED POPS TO REFLECT THIS SCENARIO.

&&

.PREV DISCUSSION...THE ATMOSPHERE IS TEMPORARILY BECOMING MORE
STABLE WITH A MUCH WEAKER FLOW AS THE RIDGE AXIS REORIENTS FROM A
POSITION NORTH OF OUR AREA TO ONE THAT IS MORE TYPICALLY AMPLIFIED
EAST OF OUR AREA. AS THIS HAPPENS THE BRISK EASTERLY FLOW IS TURNING
INTO AN INCREASING AND DEEPENING SOUTHERLY FLOW.

FRIDAY WILL START TO INCREASE A BIT AS THE NEW FLOW REGIME SETS
UP...THEN INCREASING THUNDERSTORMS FOR THE WEEKEND INTO EARLY NEXT
WEEK. THESE WILL BE MORE TYPICAL SUMMER THUNDERSTORMS WITH HEAVY
RAIN AND ISOLATED WET MICROBURST CONCERNS...NOT THE STRONG
MESOCYCLONES OF TUESDAY.

SATURDAY WILL BE BUSY SOUTH OF TUCSON WITH POSSIBLE OUTFLOWS FROM
THE SOUTH IMPACTING METRO TUCSON IN THE EARLY EVENING HOURS. BY
SUNDAY AND SUNDAY NIGHT THE LONG SOUTHERLY ENHANCED FETCH WILL BE IN
PLACE WITH MARKEDLY INCREASED THUNDERSTORM COVERAGE.

AT THAT POINT THE LARGE SCALE PATTERN SUGGESTS A SIGNIFICANT
WEAKNESS UNDERCUTTING THE RIDGE TO OUR WEST WHILE HIGH PRESSURE
WEAKENS TO OUR EAST. THE PROBLEM IS OUR MEAN FLOW MAY BECOME MORE
SOUTHWESTERLY THAN SOUTHERLY WITH THIS...PUSHING THE BETTER CHANCE
OF THUNDERSTORMS MAINLY EAST OF OUR AREA. THERE WILL BE A TIGHT
GRADIENT OF STORM ACTIVITY...DIMINISHING FROM EAST TO WEST WITH A
MINOR DIFFERENCE IN POSITION OF LARGER SCALE FEATURES MAKING A BIG
DIFFERENCE IN THE CONVECTION FORECAST FOR SOUTHEAST ARIZONA. BEST
GUESS IS THAT AFTER MONDAY...WESTERN AREAS WILL SEE LESS COVERAGE
WHILE SOUTHEASTERN AND EASTERN AREAS REMAIN BUSIER.

&&

.AVIATION...VALID THRU 04/06Z. THUNDERSTORMS IN SOUTHERN GRAHAM AND
EASTERN COCHISE COUNTIES WILL WEAKEN AND BECOME MORE GENERALIZED
LIGHT TO MODERATE SHOWERS AROUND MIDNIGHT. THE BEST CHANCE OF
SHOWERS WILL BE TO THE NORTHEAST OF TUCSON IN EASTERN PINAL AND
GRAHAM COUNTIES. SLOW CLEARING BY DAYBREAK FRIDAY...BEFORE ANOTHER
CHANCE OF THUNDERSTORMS FRIDAY AFTERNOON. BRIEF WIND GUSTS OF 30-45
KTS AND MVFR CONDITIONS POSSIBLE NEAR THE STRONGEST STORMS TONIGHT
AND FRIDAY AFTERNOON/EVENING. OTHERWISE EXPECT NORMAL DIURNAL WIND
TRENDS. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...ADEQUATE MOISTURE AND A FAVORABLE FLOW PATTERN WILL
CONTINUE TO PROVIDE AN INCREASING CHANCE OF MAINLY AFTERNOON AND
EVENING SHOWERS AND THUNDERSTORMS INTO THE UPCOMING HOLIDAY WEEKEND
WITH HIGH TEMPERATURES WITHIN A FEW DEGREES OF NORMAL.

&&

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

&&

$$

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