Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 050459
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
959 PM MST SAT JUL 4 2015

.SYNOPSIS...SOUTHEAST ARIZONA WILL EXPERIENCE AN UPSWING IN SHOWERS
AND THUNDERSTORMS SUNDAY. SLOWER MOVING STORMS WILL ELEVATE HEAVY
RAINFALL CONCERNS. DAYTIME TEMPERATURES WILL REMAIN CLOSE TO
SEASONAL NORMALS.

&&

.DISCUSSION...THE UPPER PATTERN THIS EVENING IS DEFINED UP AN UPPER
RIDGE OF HIGH PRESSURE ELONGATED OVER NEW MEXICO AND CHIHUAHUA
MEXICO AND A TROUGH OF LOW PRESSURE OFF THE COAST OF CALIFORNIA.
THIS UPPER LOW CONTINUES TO SLOWLY NUDGE EAST...SHIFTING THE AXIS OF
THE UPPER RIDGE FROM A NORTH-SOUTH ORIENTATION TO MORE OF A POSITIVE
NE-SW TILT. AS THIS OCCURS...AN AREA OF DIFLUENCE ALOFT OVER FAR SW
NEW MEXICO AND COCHISE COUNTY IN FAR SE ARIZONA HAS HELPED
CONVECTIVE ACTIVITY THIS EVENING. OTHERWISE...THE ENTIRE FORECAST
AREA HAS BEEN RATHER QUIET. THIS MAY BE DUE TO THE COMBINATION OF A
WEAK SUBSIDENCE BEHIND AN MCV THAT TRACKED NORTH THRU THE AREA THIS
MORNING AND THE LACK OF SIGNIFICANT SURFACE HEATING DUE TO THE
EXTENSIVE CLOUD COVER. IN ANY EVENT...WITH THE SOUTHERLY
FLOW...THE REMNANTS OF A THUNDERSTORM COMPLEX THAT HAS
DEVELOPED IN NORTHEAST SONORA LATE THIS EVENING WILL LIKELY MAKE ITS
WAY INTO THE EASTERN PORTIONS OF THE CWA OVERNIGHT TONIGHT. I
UPDATED THE POPS TO REFLECT THIS SCENARIO.

&&

.PREV DISCUSSION...WATER VAPOR IMAGERY AND 04/12Z UPPER-AIR PLOTS
SHOW A RIDGE IN THE GENERAL VICINITY OF THE GREAT BASIN...WITH A LOW
PRESSURE SYSTEM WELL OFFSHORE OF THE SOUTHERN CALIFORNIA COAST.

IR SATELLITE IMAGERY SHOWS EXTENSIVE CLOUDINESS COVERING MUCH OF THE
DESERT SOUTHWEST AND EXTENDING NW INTO THE GREAT BASIN. THE CLOUDS
ARE MOSTLY LEFT OVER DEBRIS CLOUDINESS FROM THE OVERNIGHT
THUNDERSTORM COMPLEX THAT DEVELOPED SOUTH OF THE BORDER AND PUSHED
INTO COCHISE COUNTY. IN ADDITION...THE LATEST VISIBLE SATELLITE
IMAGERY SHOWS AN MCV SEEMINGLY SOMEWHERE BETWEEN TUCSON AND NOGALES
AND CONTINUING TO MOVE TO THE NORTH NORTHWEST. NORMALLY WHEN THESE
FEATURES DEVELOP OVER THE REGION THE CONVECTION TENDS TO DEVELOP ON
THE PERIPHERY OF THE SYSTEM AND THAT IS THE CASE CURRENTLY WITH
RADAR MOSAIC SHOWING MOST OF THE SHOWERS AND STORMS SOUTHWEST OF
TUCSON THROUGH PARTS OF THE METRO AND INTO THE CATALINA`S. THESE
STORMS ALSO CONTINUE TO THE NORTHEAST OVER PARTS OF GRAHAM AND
GREENLEE COUNTIES AS WELL. ONLY ISOLATED ACTIVITY SEEN OVER COCHISE
AND SANTA CRUZ COUNTIES.

THE 17Z RUN OF THE HRRR WANTS TO SHOW ONLY ISOLATED ACTIVITY AS WE
HEAD INTO THIS EVENING...AND THIS WOULD GIVE CREDANCE TO THE NOTION
THAT THE MCV TENDS TO SUPPRESS ACTIVITY NEAR THE SYSTEM AS IT MOVES
NORTHWARD THROUGH THE STATE. HOWEVER...EARLIER RUNS OF THE HRRR
(EVEN THE 16Z RUN) WERE SHOWING MORE SCATTERED ACTIVITY INTO THE
EVENING HOURS. THAT SAID...GIVEN THAT TODAY IS THE FOURTH...WITH
PLENTY OF EVENING FESTIVITIES SCHEDULED...THINK THE BEST COURSE OF
ACTION WOULD BE TO KEEP THE SCATTERED ACTIVITY IN THE FORECAST FOR
TONIGHT. THEN...IF SATELLITE AND RADAR TRENDS SUGGEST THE 17Z RUN OF
THE HRRR WITH ONLY ISOLATED ACTIVITY IS CORRECT...THE EVENING SHIFT
CAN UPDATE THE FORECAST TO REFLECT A LOWER THREAT OF THUNDERSTORMS
IMPACTING EVENING HOLIDAY CELEBRATIONS.

MODELS SUGGEST SUNDAY WITH BE AN ACTIVE DAY WITH THE MCV HAVING
MOVED WELL TO THE NORTH BY THAT TIME. IF WE SEE MORE SUN
TOMORROW...THEN WE SHOULD DEFINITELY HAVE AN ACTIVE DAY.

BY MONDAY...AS THE LOW PRESSURE SYSTEM OVER THE PACIFIC IS PROGGED
TO MAKE ITS WAY TOWARD THE WEST COAST AND EVENTUALLY INTO THE GREAT
BASIN...WE SHOULD SEE MORE OF A SOUTHWESTERLY COMPONENT TO OUR
WINDS...WHICH WILL PUSH MOISTURE EASTWARD...THUS LIMITING
THUNDERSTORM ACTIVITY MOSTLY TO AREAS BETWEEN TUCSON AND THE NEW
MEXICO BORDER FOR MUCH OF THE WORK WEEK.

&&

.AVIATION...VALID THRU 06/06Z.
ALTHOUGH STORM COVERAGE IS DOWN ACROSS SOUTHEAST ARIZONA AGAIN THIS
EVENING...THERE IS A CHANCE OF WEAK -SHRA/-TSRA OVERNIGHT TONIGHT IN
COCHISE AND GRAHAM COUNTY. OTHERWISE...SCATTERED TO NUMEROUS -TSRA/
-SHRA WILL OCCUR SUNDAY AFTERNOON AND EVENING. BRIEF WIND GUSTS OF
40-45 KTS MAY ACCOMPANY THE STRONGER TSRA. OTHERWISE...CLOUD DECKS
WILL MAINLY BE AT OR ABOVE 8K FT AGL AND SURFACE WIND WILL GENERALLY
BE LESS THAN 10 KTS. AVIATION DISCUSSION NOT UPDATED FOR TAF
AMENDMENTS.

&&

.FIRE WEATHER...SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS WILL
OCCUR THIS WEEKEND. THE MAIN IMPACT WILL BE THE COMBINATION OF BRIEF
STRONG AND GUSTY WINDS AND HEAVY RAINFALL. SOMEWHAT REDUCED COVERAGE
OF SHOWERS AND THUNDERSTORMS WILL BEGIN MONDAY. THEREAFTER...
ADEQUATE MOISTURE WILL MAINTAIN ISOLATED TO SCATTERED
SHOWERS AND THUNDERSTORMS TUESDAY INTO NEXT SATURDAY. GENERALLY
LIGHT TERRAIN DRIVEN WINDS WILL PREVAIL OUTSIDE OF THUNDERSTORM
INFLUENCES.

&&

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

&&

$$

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