000
FXUS65 KPSR 080354
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
855 PM MST SUN SEP 7 2008
SOUTH-CENTRAL AND SOUTHWEST ARIZONA...AND SOUTHEAST CALIFORNIA
FORECAST DISCUSSION
.SYNOPSIS...
A GRADUAL MOISTENING OF THE ATMOSPHERE IS EXPECTED OVER THE NEXT
SEVERAL DAYS...AS LOW PRESSURE ALOFT DEVELOPS OFF TO OUR WEST. THIS
WILL RESULT IN AN INCREASING THREAT OF SHOWERS AND THUNDERSTORMS
ACROSS THE REGION...ESPECIALLY OVER SOUTH-CENTRAL ARIZONA. THE PEAK
DAYS OF THUNDERSTORM ACTIVITY ARE LIKELY TO BE WEDNESDAY INTO
THURSDAY. BY NEXT WEEKEND...THE UPPER LOW SHOULD PUSH OFF TO OUR
EAST AND BRING A DRYING TREND TO THE REGION. EXPECT TEMPERATURES TO
BE NEAR OR SLIGHTLY BELOW NORMAL DURING MUCH OF THE WEEK.
&&
.DISCUSSION...
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS...MOSTLY HIGH CLOUD
BASED STORMS...DEVELOPED ACROSS PORTIONS OF ARIZONA ON SUNDAY...
WITH MORE WIDESPREAD STORMS OVER SOUTHEAST AZ AND THE MOGOLLON RIM.
AT 03Z ISOLATED SHOWERS AND THUNDERSTORMS WERE NOTED JUST EAST OF
THE COLORADO RIVER NEAR BLYTHE AND YUMA.
A SURPRISING AMOUNT OF MEXICAN MOISTURE FLOWED INTO AZ SATURDAY
NIGHT. IN FACT 00Z MON ARIZONA SOUNDINGS SHOWED PRECIP WATER HAD
DOUBLED IN PHOENIX TO NEARLY AN INCH...FROM 24 HOURS AGO...WITH A
50 PERCENT INCREASE AT FLAGSTAFF AND 25 PERCENT INCREASE AT TUCSON.
AND...IN CONJUNCTION WITH A WEAK PACIFIC 300/250 MB TROF MOVING
ACROSS AZ...AFTERNOON INSTABILITY STORMS DEVELOPED SUNDAY.
AS A SERIES OF WEAK PACIFIC TROFS CONTINUE MOVE INTO THE WESTERN
STATES...INCLUDING AZ THE NEXT FEW DAYS...ADDITIONAL MEXICAN
MOISTURE IS FORECAST TO FLOW NORTH. WEAK UPPER LEVEL TROFS OR
DISTURBANCES WITH THE ADDITIONAL MOISTURE WILL KEEP THE THREAT OF
SHOWERS AND THUNDERSTORMS ALIVE THE NEXT SEVERAL AFTERNOONS.
WE FEEL THE MODELS ARE HAVING A HARD TIME RESOLVING A SIGNIFICANT
SHORTWAVE FEATURE OVER NORTHERN CALIFORNIA THIS EVENING (BEST SEEN
IN WATER VAPOR IMAGERY). THIS FEATURE MAY HAVE SOME INFLUENCE ON A
LARGER THUNDERSTORM OUTBREAK IN PARTS OF AZ TUE OR WED...ITS STILL
HARD TO TELL. FOR NOW THE CURRENT FORECAST TREND OF INCREASING
THREATS FOR SHOWERS AND THUNDERSTORMS THE NEXT FEW DAYS LOOKS OK.
PERHAPS TOMORROW (MON) WE WILL HAVE SOME RESOLUTION ON WHICH DAY WE
MAY SEE A LARGER THUNDERSTORM OUTBREAK THIS WEEK.
FORECASTS LOOK OK FOR NOW. MINOR UPDATES PLANNED.
EXCERPTS FROM PREVIOUS DISCUSSION...
MODELS IN GOOD AGREEMENT THAT THE AMS WILL CONTINUE TO UNDERGO A
GRADUAL MOISTENING AS UPPER LEVEL TROUGHINESS TAKES SHAPE ALONG THE
WEST COAST THE NEXT FEW DAYS AND INCREASES LOW LEVEL SLY WINDS. AS
SURFACE TO 700 MB MIXING RATIOS INCREASE TO NEAR 10 G/KG NEXT FEW
DAYS...RESULTING INCREASE IN CAPE WILL YIELD MORE AND BETTER
RAIN-PRODUCING TSTMS BY MIDWEEK. PRESENCE OF DEVELOPING UPPER LEVEL
TROUGH TO OUR W...AND THE PROXIMITY OF AN INCREASING UPPER LEVEL
JET...WILL ALSO ADD TO THE DYNAMICAL MIX FOR STORM PRODUCTION.
THEREFORE...HAVE INCREASED POPS BY WEDNESDAY INTO THE CHANCE
CATEGORY OVER MOST OF THE SOUTH-CENTRAL AZ DESERTS...WITH MOSTLY
SLIGHT CHANCES UNTIL THEN. WITH THE ADDED MOISTURE AND GRADUAL
LOWERING OF THICKNESSES...ALSO CALLING FOR SOMEWHAT COOLER
AFTERNOONS.
AFTER MIDWEEK...LOTS DEPEND ON HOW QUICKLY THE WEST COAST UPPER LOW
MOVES EWD. THE EURO HAS MORE ENERGY IN THE NRN BRANCH SYSTEM AND
KEEPS THE SRN BRANCH TROUGH VERY WEAK...WHILE THE GFS CLOSED LOW
OPENS UP AS PUSHES IT EWD THRU AZ BY SATURDAY. EURO WOULD ARGUE FOR
LESS WX FRIDAY AND SATURDAY...WITH THE GFS CALLING FOR CONTINUED
THREAT OF STORMS. WILL GO MIDDLE OF THE ROAD FOR NOW AND KEEP SLIGHT
CHANCES GOING THU AND FRI OVER SCNTRL DESERTS EWD...THEN JUST ZONE
24 ON SATURDAY. TEMPS SHOULD BEGIN SLOWLY WARMING BACK UP NEXT
WEEKEND AS HEIGHTS BEGIN TO RISE AGAIN AND AMS DRIES OUT.
&&
.AVIATION...
SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KBLH...KNYL...AND KIPL
AIRFIELDS. ISOLATED SHOWERS AND THUNDERSTORMS WILL CONTINUE NEAR
THE ABOVE AIRFIELDS THROUGH 06Z MON. GUSTY AND VARIABLE WINDS 15 TO
25 KNOTS ARE POSSIBLE...ALONG WITH SCT TO BKN CLOUDS AOA 15 THSD
MSL. AFTER 06Z MON...EXPECT SCT CLOUDS BASED NEAR 15 THSD MSL AND
LIGHT WINDS THROUGH 18Z. AFTER 18Z MON...AND THROUGH 04Z TUE...
ISOLATED AFTERNOON AND EARLY EVENING SHOWERS AND THUNDERSTORMS...
ALONG WITH GUSTY AND VARIABLE SURFACE WINDS BETWEEN 15 AND 25 KNOTS
ARE FORECAST.
SOUTH CENTRAL AZ...INCLUDING KPHX AND KIWA AIRFIELDS. SCT TO BKN
CLOUDS AOA 14 THSD MSL ...WITH ISOLATED SPRINKLES OR LIGHT SHOWERS
POSSIBLE THROUGH 08Z MON. AFTER 08Z...SCT TO BKN CLOUDS AOA 14 THSD
MSL WITH LIGHT EAST WIND UNDER 10 KNOTS. BETWEEN 20Z MON AND 04Z
TUE...SCT CLOUDS BASED NEAR 10 THSD MSL WITH LIGHT WIND. ALSO...
ISOLATED MOUNTAIN THUNDERSTORMS WITH TOPS TO 35 THSD ARE POSSIBLE 60
TO 80 MILES NORTH THROUGH SOUTHEAST OF KPHX.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
TUESDAY THROUGH FRIDAY...AN AREA OF LOW PRESSURE WILL DEVELOP OFF
THE COAST OF SOUTHERN CALIFORNIA...BRINGING A SLIGHT CHANCE OF
SHOWERS AND THUNDERSTORMS TUESDAY FOR THE ENTIRE FORECAST
AREA...WITH A BETTER CHANCE IN THE HIGHER TERRAIN OF CENTRAL
ARIZONA. SLIGHT CHANCES OF THUNDERSTORMS WILL CONTINUE WEDNESDAY AND
THURSDAY IN THE HIGHER TERRAIN AREAS OF SOUTHERN GILA COUNTY.
TEMPERATURES WILL REMAIN NEAR SEASONAL NORMALS...WHILE AFTERNOON
HUMIDITY VALUES WILL RANGE FROM THE MID-TEENS IN SOUTHEAST
CALIFORNIA TO THE MID-TWENTIES IN SOUTH-CENTRAL ARIZONA.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...VASQUEZ/ESTLE
AVIATION...VASQUEZ
FIRE WEATHER...ROGERS
