Special Weather Statement, NWS Tucson, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
250 PM MST TUE OCT 6 2015

.SYNOPSIS...A STRONG UPPER LEVEL LOW PRESSURE SYSTEM WILL CONTINUE
TO MOVE SLOWLY SOUTHEAST ACROSS THE STATE THROUGH WEDNESDAY. THIS
WILL RESULT IN ISOLATED TO SCATTERED STRONG THUNDERSTORMS THROUGH
THIS EVENING ACROSS ALL OF SOUTHERN ARIZONA AND THEN MAINLY FROM
TUCSON EASTWARD ON WEDNESDAY. IN ADDITION...EXPECT COOLER DAYTIME
TEMPERATURES THROUGH WEDNESDAY...AND THEN A WARMING TREND INTO THE
WEEKEND. A FEW SHOWERS OR STORMS WILL STILL BE POSSIBLE ALONG THE
NEW MEXICO AND INTERNATIONAL BORDERS INTO THE UPCOMING WEEKEND.

&&

.DISCUSSION...A STRONG UPPER LOW PRESSURE SYSTEM WAS CENTERED ALONG
THE COLORADO NEAR BLYTHE CALIFORNIA. THIS SYSTEM HAS SHOWN VERY
LITTLE MOVEMENT OVER THE LAST 12 HOURS. THE POSITION OF THIS UPPER
LOW HAS PUT MUCH OF THE STATE IN AN ASCENT REGION...WITH COLDER AIR
ALOFT NOSING IN WITH THE UPPER LOW...RESULTING IN STEEP LAPSE RATES.
IN ADDITION...TWO VORT LOBES WERE NOTED ROTATING NORTH/NORTHEAST
ACROSS THE STATE OUT AHEAD OF THE UPPER LOW WHICH HELPED ENHANCE
CONVECTIVE DEVELOPMENT ACROSS THE FORECAST AREA TODAY. ALL OF THESE
FACTORS...A CLASSIC TEXTBOOK CASE...LED TO AN EARLY START TO THE
SHOWER/THUNDERSTORM DEVELOPMENT TODAY...WITH ISOLATED TO SCATTERED
STRONG TO SEVERE THUNDERSTORMS EXPECTED TO CONTINUE THROUGH THE
EVENING HOURS TONIGHT BEFORE SLOWLY DIMINISHING. WITH ALL OF THE
ABOVE INGREDIENTS REMAINING IN PLACE...WE WILL BE ABLE TO HAVE
REPEATED STORM DEVELOPMENT OVER THE SAME AREAS INTO THE EVENING
HOURS TONIGHT. THE MOST FAVORED AREA FOR THUNDERSTORM DEVELOPMENT
THROUGH THIS EVENING WILL BE ACROSS THE NORTHERN HALF/NORTHEAST
PORTION OF THE FORECAST AREA.

THE UPPER LOW WILL MOVE SLOWLY SOUTHEAST ACROSS THE FORECAST AREA
THROUGH LATE WEDNESDAY BEFORE SLIDING SOUTH INTO NORTHERN MEXICO.
THIS WILL LEAD TO A CONTINUED CHANCE OF SHOWER/STORM DEVELOPMENT ON
WEDNESDAY...MAINLY FROM TUCSON EASTWARD TO THE NEW MEXICO BORDER.
COOLER DAYTIMES TEMPERATURES WILL PERSIST THROUGH WEDNESDAY AS THE
UPPER LOW TRACKS NEARLY OVERHEAD.

AN UPPER RIDGE WILL THEN BEGIN TO BUILD IN ALONG THE WEST COAST AND
INTO THE GREAT BASIN NORTH OF THE AREA LATE IN THE WEEK AND THROUGH
THE UPCOMING WEEKEND. AS THIS HAPPENS...THE UPPER LOW LOSES ITS MID
LATITUDE SUPPORT AND RETROGRADES WESTWARD ACROSS NORTHERN MEXICO.
THE POSITION OF THE LOW WILL BE CLOSE ENOUGH FOR THE MENTION OF
SLIGHT CHANCE POPS ALONG THE INTERNATIONAL BORDER THROUGH THIS TIME
FRAME...ESPECIALLY WITH SOME LINGERING MOISTURE AND WARMER DAYTIME
TEMPERATURES.

BY EARLY NEXT WEEK...THE UPPER LOW HAS SHIFTED WESTWARD TO WEST OF
THE BAJA PENINSULA. WITH A BROAD RIDGE OVER THE SOUTHWESTERN UNITED
STATES...AND THE UPPER LOW CUT-OFF UNDERNEATH THIS RIDGE...THE FLOW
ACROSS ARIZONA WILL CONTINUE TO BE SOUTHERLY. LIMITED MOISTURE...
ALONG WITH TEMPERATURES WARMING BACK INTO THE 90S WILL RESULT IN A
CONTINUED SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS.

&&

.AVIATION...VALID THRU 08/00Z.
SCT TO NMRS TSRA WILL MOVE RAPIDLY NE THRU 07/02Z. SOME TSRA WILL
HAVE GUSTS TO 45 KTS AND HAIL...ESPECIALLY NORTH OF INTERSTATE 10 OR
N OF A KAVQ-KTUS-KLSB. AFT 07Z/02Z EXPECT ISOLD TO SCT SHRA/TSRA
AREAWIDE. OTHERWISE EXPECT CLOUD BASES OF SCT-BKN040-060 WITH MT
OBSCURATIONS IN TSRA.  SFC WINDS SW 10-20KTS TIL 07/02Z OUTSIDE OF
TSRA OTHERWISE SFC WINDS LESS THAN 12 KTS. AVIATION DISCUSSION NOT
UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...AN AREA OF LOW PRESSURE WILL BE HANGING AROUND THE
SW US MUCH OF THE COMING WEEK. THE BEST CHANCE FOR SHOWERS AND
THUNDERSTORMS IN SE AZ WILL CONTINUE THROUGH WEDNESDAY BUT COOLER
TEMPERATURES AND UNSETTLED WEATHER WILL PERSIST THROUGH THE WEEKEND.
AS THE LOW MOVES SOUTHWARD...A STRONG EAST WIND WILL DEVELOP OVER SE
ARIZONA FRIDAY. OTHERWISE...20 FOOT WINDS WILL BE FAIRLY LIGHT
OUTSIDE OF THUNDERSTORMS.

&&

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

&&

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