Special Weather Statement, NWS Phoenix, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
327 PM MST SUN SEP 13 2015

.SYNOPSIS...
SEVERAL PACIFIC WEATHER DISTURBANCES WILL MOVE THROUGH THE REGION
THE FIRST HALF OF THIS WEEK KEEPING STORM CHANCES GOING...MAINLY EAST
OF THE LOWER COLORADO RIVER VALLEY. BEST CHANCES LOOK TO BE TONIGHT
INTO MONDAY NIGHT. BY THURSDAY...DRIER AND STABLE AIR TAKES OVER.
TEMPERATURES WILL DROP SEVERAL DEGREES BELOW NORMAL BEFORE WARMING A
FEW DEGREES DURING THE LATTER HALF OF THE WEEK.

&&

.DISCUSSION...
REST OF TODAY/TONIGHT...
THE SHORT WAVE IS BEGINNING TO TRANSITION INTO NORTHERN ARIZONA. THE
CLOUDINESS WITH IT HAS THINNED DOWN QUITE A BIT AS WELL. CONVECTION
HAS BEGUN OVER HIGHER TERRAIN AREAS INCLUDING OUR FORECAST ZONE
24...SOUTHERN GILA AND FAR NORTHEAST MARICOPA COUNTIES. AFTERNOON
TEMPERATURES ARE RUNNING SEVERAL DEGREES WARMER OVER MUCH OF
SOUTHWEST ARIZONA AND SOUTHEAST CALIFORNIA COMPARED TO 24 HOURS AGO.
CONVERSELY...THE CENTRAL DESERTS HAVE BEEN RUNNING COOLER DUE TO THE
EARLIER CLOUD COVER. DEW POINTS HAVE DROPPED INTO THE 50S AT MOST
LOWER DESERT LOCATIONS DUE TO DAYTIME MIXING. TEMP/DEW POINT SPREADS
WILL BE SUFFICIENT FOR EVAPORATIVELY ENHANCED DOWNDRAFTS AND IN TURN
OUTFLOW BOUNDARIES WHICH COULD INITIATE NEW STORMS. HI-RES MODELS
INCLUDING HRRR AND AND U OF A WRF/S ARE DEPICTING THAT SCENARIO TO
VARYING DEGREES SUCH THAT STORMS FROM ZONE 24 AND AREAS OUTSIDE OF
OUR CWA SPAWN DEVELOPMENT OVER THE SOUTH-CENTRAL DESERTS THIS
EVENING. MADE AN EARLIER ADJUSTMENT TO DECREASE THE AFTERNOON POPS
OVER THE PHOENIX AREA BUT INCREASE THE EVENING POPS. A CAVEAT IS THAT
MODEST LOWER LEVEL MOISTURE TENDS TO INHIBIT WIDESPREAD STORM
DEVELOPMENT. AS MENTIONED IN PREVIOUS DISCUSSION...THERE IS SOME
DYNAMICAL ASSISTANCE TODAY WITH AN UPPER LEVEL SHORT WAVE COINCIDING
WITH THE LEFT EXIT REGION OF A JET STREAK...MAINLY BENEFITING
NORTHERN ARIZONA.

MONDAY THROUGH WEDNESDAY...
THE UPPER TROUGH/LOW CENTERED NEAR THE S.F. BAY AREA WILL WEAKEN AND
GET KICKED EASTWARD BY A LARGER UPSTREAM TROUGH MONDAY. IT WILL COME
THROUGH OUR AREA LATER IN THE DAY AS A SHORT WAVE/VORT MAX WITH A
DIVQ BULLSEYE. WHILE THE MODELS SHOW MOIST ADVECTION TAKING PLACE
OVERNIGHT...THEY ARE CONSERVATIVE WITH THE CAPE WHICH IS DUE AT LEAST
IN PART TO WARMING ALOFT. THE MODELS ARE ALSO SHOWING THAT THE VORT
MAXW WILL LAG BEHIND THE BETTER MOISTURE BY THE TIME IT MOVES IN.
THUS POPS ARE SOMEWHAT CONSERVATIVE GIVEN THE SYNOPTIC PATTERN.
STORMS THAT DO FORM WILL HAVE SOME VERTICAL WIND SHEAR TO OPERATE IN
WHICH AIDS LONGEVITY. TUESDAY IS SOMETHING OF A REPEAT OF MONDAY IN
THAT THE UPPER TROUGH MOVES INLAND AND WEAKENS BUT IT WEAKENS EVEN
FASTER AND HAS LESS OF A LEFTOVER SHORT WAVE. THUS POPS ARE LOWER FOR
TUESDAY THAN MONDAY. ON WEDNESDAY...YET ANOTHER UPPER TROUGH MOVES
INLAND WHICH HELPS ADVECT SOME MOISTURE FROM THE EAST PACIFIC.
HOWEVER...IT IS HAVING TO OVERCOME DRY AIR. THE END RESULT IS THAT
THERE ARE ONLY SLIGHT CHANCE POPS OVER PORTIONS OF SOUTH-CENTRAL
ARIZONA. WITH TROUGHING PUSHING THE RIDGE TO THE EAST...TEMPERATURES
TREND DOWN SEVERAL DEGREES BELOW NORMAL.

THURSDAY THROUGH SUNDAY...
ALTHOUGH STRONG UPPER LEVEL SOUTHWEST WINDS WILL CONTINUE...DUE TO
ADDITIONAL PACIFIC SHORTWAVES FLOWING WELL NORTH OF THE AREA...
MODELS INSIST THAT A STABLE AND WARM AIRMASS WILL PRECLUDE ANY SHWR
ACTIVITY. AFTN TEMPS THESE DAYS SHOULD BE NEAR NORMAL.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
MODERATE CONFIDENCE EXISTS REGARDING TS APPROACHING PHOENIX
TERMINALS LATE AFTERNOON/EARLY EVENING SUNDAY. WHILE CONFIDENCE IS
LOWER IN TS DIRECTLY HITTING ANY GIVEN AIRFIELD...IMPACTS FROM
SHIFTING STRONGER OUTFLOW WINDS WILL BE MORE LIKELY.
HOWEVER...TIMING WIND DIRECTIONS AND SPEEDS WILL BECOME PROBLEMATIC
DUE TO A GREATER LIKELIHOOD OF SEVERAL OUTFLOWS INTERSECTING ACROSS
THE PHOENIX METRO. MODELS SUGGEST TS MOVING INTO THE PHOENIX AREA
AROUND 00Z...THOUGH HAVE DELAYED ARRIVAL OF VCTS IN TAF PACKAGE BY
AN HOUR OR TWO. OTHERWISE...CIGS SHOULD GENERALLY REMAIN AOA 10K FT
THROUGH MONDAY MORNING.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND
KBLH...
MODERATE CONFIDENCE THAT AVIATION IMPACTS SHOULD BE LIMITED TO WINDS
ACROSS SOUTHEAST CALIFORNIA THROUGH TUESDAY MORNING AS TS ACTIVITY
SHOULD REMAIN OVER EAST CNTRL ARIZONA...AND WEST OVER THE MOUNTAINS
OF FAR SW CALIFORNIA AND THE BAJA SPINE. A BRIEF PERIOD OF GUSTY
WEST WINDS AFTER SUNSET WILL BE POSSIBLE AT KIPL...WITH A GENERAL
PREVAILING SOUTH SFC WIND AT KBLH. MUCH STRONGER WINDS WILL BE
POSSIBLE AFTER THIS VALID TAF PERIOD MONDAY LATE AFTERNOON/EVENING.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
WEDNESDAY THROUGH SUNDAY...
MOISTURE WILL STEADILY DECLINE BEGINNING WEDNESDAY WITH LITTLE TO NO
CHANCE OF WETTING RAINFALL THROUGH THE WEEKEND. WITH TEMPERATURES
NOT STRAYING TOO FAR FROM AVERAGE FOR MID SEPTEMBER...AFTERNOON
MINIMUM HUMIDITY VALUES WILL FALL INTO A 15 TO 30 PERCENT RANGE.
OVERNIGHT RECOVERY WILL GENERALLY BE GOOD. WINDS WILL TEND TO BE
SOMEWHAT GUSTY FROM THE WEST DURING THE AFTERNOON
HOURS...PARTICULARLY WEDNESDAY...WITH A TENDENCY FOR A LIGHT
DRAINAGE COMPONENT OVERNIGHT.

&&

.SPOTTER INFORMATION STATEMENT...
SPOTTERS ARE ENCOURAGED TO REPORT ACCORDING TO STANDARD PROCEDURES.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&

VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX

DISCUSSION...AJ/VASQUEZ
AVIATION...MO
FIRE WEATHER...MO

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PHOENIX AZ
421 PM MST SUN SEP 13 2015

AZZ024-140000-
SOUTHERN GILA/TONTO NF FOOTHILLS AZ-
421 PM MST SUN SEP 13 2015

...SPECIAL WEATHER STATEMENT...

AT 420 PM MST...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM
NEAR GLOBE...MOVING NORTHEAST AT 15 MPH.

BRIEF HEAVY RAIN...SMALL HAIL...AND GUSTY WINDS IN EXCESS OF 35 MPH
WILL BE POSSIBLE WITH THIS STORM.

LOCATIONS IMPACTED INCLUDE...
GLOBE...MIAMI...CLAYPOOL...CUTTER...CENTRAL HEIGHTS-MIDLAND CITY AND
INSPIRATION.

LAT...LON 3325 11074 3334 11093 3350 11084 3341 11060
TIME...MOT...LOC 2320Z 216DEG 12KT 3338 11077

MEYERS