Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 191602
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
900 AM MST TUE AUG 19 2014

.SYNOPSIS...ABUNDANT MOISTURE COMBINED WITH AN APPROACHING UPPER LOW
WILL GENERATE NUMEROUS SHOWERS AND THUNDERSTORMS TODAY EAST OF THE
TOHONO O`ODHAM NATION WITH THE POTENTIAL FOR VERY HEAVY RAINFALL.  A
SLIGHTLY DRIER ATMOSPHERE AND LESS FORCING WILL ALLOW FOR A MORE
TYPICAL AMOUNT OF CONVECTION THE REMAINDER OF THE WEEK WITH A VERY
MODEST DRYING TREND INTO THIS WEEKEND.  BELOW NORMAL DAYTIME
TEMPERATURES WILL PREVAIL THROUGH THURSDAY FOLLOWED BY A GRADUAL
WARMING TREND LATER THIS WEEK.

&&

.DISCUSSION...AN UPPER LOW CURRENTLY OFF THE CENTRAL COAST OF
CALIFORNIA IS DROPPING SOUTHEAST WITH A LOBE OF ENERGY APPROACHING
YUMA THIS MORNING.  THE MORNING SOUNDING WAS RATHER WET WITH A PW
NEAR 1.7 AND UNSTABLE WITH AN LI OF -5...BASICALLY PRIMED.  THE LOBE
OF ENERGY NEAR YUMA IS FOCUSING THE LIFT ACROSS CENTRAL AND NORTHERN
AZ AT THIS TIME AND THAT IS WHERE ABUNDANT CONVECTION IS ALREADY IN
PLACE.  WE ARE AT THE TAIL END OF THIS ENERGY...ENOUGH THAT
CONVECTION HAS ALREADY DEVELOPED OVER THE CATALINAS AND RINCONS BUT
WILL NEED TO WAIT A FEW MORE HOURS FOR THE LOW TO MOVE CLOSER AND
HEATING TO KICK IN FOR SIGNIFICANT DEVELOPMENT TODAY.  STORM MOTION
TODAY WILL BE TO THE NORTHEAST.

WHILE STRONG WINDS ARE ALWAYS A THREAT WITH THUNDERSTORMS THE
PRIMARY CONCERN TODAY IS HEAVY RAIN AND THE POTENTIAL FOR
RUNOFF/FLOODING PROBLEMS.  SOUTHEAST ARIZONA HAS BEEN PRIMED THE
LAST WEEK WITH AREAS OF HEAVY RAIN SO SOME AREAS WILL RESPOND
QUICKLY TO ADDITIONAL HEAVY RAIN.  CASE IN POINT...HEAVY RAIN LAST
NIGHT OVER THE RINCONS AND SOUTHEAST CATALINAS RESULTED IN HIGH
FLOWS IN THE WASHES WITH 3 ROADS AROUND THE METRO AREA CURRENTLY
CLOSED DUE TO HIGH WATER.  AS A RESULT OF THESE CONCERNS A FLASH
FLOOD WATCH WAS ISSUED ON THE NIGHT SHIFT AND THAT LOOKS GOOD AT
THIS POINT.  AS THE DAY PROGRESSES AND CONVECTION DEVELOPS...REFER
TO THE LATEST STATEMENTS AND WARNINGS TO KEEP UP WITH WHERE FLOODING
IS A THREAT.

AS THE UPPER LOW CONTINUES TO APPROACH THE REGION IT WILL PUSH SOME
DRIER AIR IN OVERNIGHT FROM THE WEST BEHIND THE MAIN AREA OF SHOWERS
AND THUNDERSTORMS WHICH WILL RESULT IN A DECREASE IN THE CONVECTION
ACROSS THE REGION FROM WEST TO EAST.  AS A RESULT OF THE DRIER AIR
MOVING IN ALOFT AND LIMITED FORCING...THERE WILL BE LESS AREAL
COVERAGE OF STORMS ON WEDNESDAY...BUT THANKS TO PLENTY OF NEAR
SURFACE MOISTURE IT SHOULD REMAIN SOMEWHAT ACTIVE.

OPERATIONAL MODELS STILL HAVING ISSUES ON WHEN THE SRN CA UPPER LOW
WILL LIFT THRU THE STATE...ALTHOUGH AT THIS POINT I AM LEANING
TOWARD THE SLOWER SOLUTIONS WHICH WOULD BE THE ECMWF/NAM WHICH
PUSHES THE SYSTEM THROUGH SOMETIME FRIDAY.  THE FASTER GFS IS
SLOWING THE SYSTEM WITH EACH RUN AND THIS MORNINGS 12Z RUN LOOKING
EVEN MORE LIKE THE OTHER TWO.  THIS WOULD MEAN DECENT ACTIVITY AGAIN
THURSDAY INTO EARLY FRI.

ALL THIS CONVECTION AND MOISTURE WILL RESULT IN BELOW NORMAL HIGH
TEMPERATURES TODAY THROUGH THURSDAY...THEN WITH LESS CONVECTION AND
DRIER CONDITIONS TEMPS SHOULD RISE TO MORE NORMAL LEVELS THEREAFTER.
CERNIGLIA

&&

.AVIATION...VALID THRU 20/18Z.
EXPECT SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS DEVELOPING
LATE THIS MORNING OR EARLY AFTERNOON...THEN PERSISTING INTO THE
EVENING HOURS TONIGHT. MVFR VISIBILITIES AND WIND GUSTS OF 45-50 KTS
WILL OCCUR WITH THE STRONGER TSRA. CLOUD DECKS WILL MAINLY BE AT
6-12K FT AGL. OUTSIDE OF THUNDERSTORM OUTFLOWS...SURFACE WIND WILL
GENERALLY BE LESS THAN 10 KTS THRU WEDNESDAY MORNING. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.
&&

.FIRE WEATHER...SCATTERED TO NUMEROUS THUNDERSTORMS WILL OCCUR TODAY
THROUGH WEDNESDAY AS AMPLE MOISTURE REMAINS ACROSS SOUTHEASTERN
ARIZONA.  WITH THE ABUNDANT MOISTURE IN PLACE...LOCALLY HEAVY
RAINFALL IS EXPECTED THIS AFTERNOON AND EVENING WITH THE POTENTIAL
FOR HEAVY RUNOFF/FLOODING PROBLEMS.  ALSO THE STRONGER THUNDERSTORMS
WILL PRODUCE STRONG...GUSTY AND ERRATIC WINDS.  EXPECT SOMEWHAT LESS
COVERAGE OF THUNDERSTORMS DURING THE LATTER PART OF THE WEEK AND
NEXT WEEK.  HOWEVER...MOISTURE WILL BE SUFFICIENT FOR ISOLATED TO
SCATTERED MAINLY AFTERNOON AND EVENING THUNDERSTORMS. OUTSIDE OF THE
THUNDERSTORM OUTFLOWS...20-FOOT WINDS WILL EXHIBIT NORMAL DIURNAL
TRENDS AND WILL BE MOSTLY LESS THAN 15 MPH.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
 FLASH FLOOD WATCH TODAY FROM 12 NOON UNTIL 11 PM FOR MOST OF SE AZ.

&&

$$

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