Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 011142 CCA
AFDPSR

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE PHOENIX AZ
442 AM MST TUE SEP 1 2015

.UPDATE...UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS...

&&

.SYNOPSIS...
A SIGNIFICANT REDUCTION IN SHOWER AND THUNDERSTORM ACTIVITY IS
EXPECTED ACROSS THE REGION TODAY AS SOMEWHAT DRIER AIR WORKS ITS WAY
IN FROM THE WEST. AN INCREASE IN THUNDERSTORM ACTIVITY IS THEN
EXPECTED ON WEDNESDAY AND THURSDAY AS LOW PRESSURE OFF THE CALIFORNIA
COAST PULLS TROPICAL MOISTURE NORTHWARD INTO THE REGION. A RETURN OF
DRIER AIR INTO THE REGION WILL THEN ONCE AGAIN REDUCE CHANCES FOR
SHOWERS AND THUNDERSTORMS FROM FRIDAY ONWARD INTO THE UPCOMING
WEEKEND.

&&

.DISCUSSION...
.TODAY AND TONIGHT...
AFTER A VERY ACTIVE MONDAY AFTERNOON/EVENING..A SIGNIFICANT
REDUCTION IN CONVECTIVE ACTIVITY APPEARS TO BE IN THE CARDS ACROSS
SOUTH-CENTRAL ARIZONA TODAY AND TONIGHT. THE LATEST GFS MODEL RUN IS
NOW SHOWING A REDUCTION IN PWAT VALUES OVER THE REGION TODAY...AS THE
UPPER TROF THAT IS NOW OFF THE CA COAST REPOSITIONS ITSELF A BIT
CLOSER TO THE COAST. ALSO...THE GFS 200MB STREAMLINE FORECAST IS
SHOWING THE FLOW ALOFT WILL BE BECOMING ANTICYCLONIC AND CONFLUENT
BY THIS AFTERNOON/EVENING. THESE FACTORS...ALONG WITH THE FACT THAT
THE ATMOSPHERE WAS WELL WORKED- OVER BY YESTERDAY/S STORMS IS
EXPECTED TO GREATLY LIMIT THE AMOUNT OF CONVECTIVE ACTIVITY
TODAY/TONIGHT...WITH POPS WELL DOWN IN THE SLIGHT CHANCE RANGE (AT
MOST) ACROSS THE LOWER DESERTS...WITH SOMEWHAT HIGHER POPS OVER THE
HIGHER TERRAIN EAST OF PHOENIX.

.WEDNESDAY AND THURSDAY...
THESE TWO DAYS (ESPECIALLY THURSDAY) ARE EXPECTED TO BE MORE ACTIVE
WEATHERWISE ACROSS SOUTH-CENTRAL AZ...AS MID-LEVEL MOISTURE FROM THE
REMAINS OF TROPICAL CYCLONE 14E ARE SWEPT NORTHWARD INTO THE REGION
BY THE UPPER LOW TO OUR WEST. ALTHOUGH THE CENTER OF THIS TROPICAL
SYSTEM IS NOT EXPECTED TO GET EVEN REMOTELY CLOSE TO OUR REGION (THE
NHC HAS IT DISSIPATING OFF THE SOUTHERN BAJA COAST BY SAT
NIGHT)...THERE IS GOOD MODEL CONSENSUS ON THE TRACK OF THIS TROPICAL
SYSTEM (WITH A TIGHT GROUPING OF THE GFS ENSEMBLE MEMBERS)...WITH THE
GFS PULLING A SIGNIFICANT MOISTURE PLUME NORTHWARD INTO OUR
REGION...WITH PWATS EXCEEDING 1.80 INCH OVER SOUTH-CENTRAL ARIZONA BY
THURSDAY AFTERNOON. THE COMBINATION OF THIS MOISTURE ALONG WITH GOOD
VERTICAL WIND SHEAR (50KTS AT 300MB)...WITH LIKELY RESULT IN A
INCREASE IN CONVECTIVE ACTIVITY ON WEDNESDAY...AND WIDESPREAD
ACTIVITY ON THURSDAY. STORMS THAT DEVELOP WILL ONCE AGAIN BE CAPABLE
OF PRODUCING VERY STRONG WINDS AND LOCALLY HEAVY RAINS (ESPECIALLY ON
THURSDAY). THE COMBINATION OF INCREASED CLOUDINESS/RAINFALL AND
SOMEWHAT COOLER AIR ALOFT IS EXPECTED TO BRING HIGH TEMPS DOWN...WITH
MANY LOWER DESERT LOCATIONS ACROSS SOUTH-CENTRAL ARIZONA LIKELY
SEEING HIGHS ONLY IN THE 90S ON THURSDAY.

.FRIDAY THROUGH TUESDAY...
ALTHOUGH THERE WILL BE REDUCTION IN AVAILABLE MOISTURE OVER THE
REGION AS SOUTHWESTERLY FLOW ALOFT SWEEPS THE MOISTURE FROM THE
REMAINS OF TROPICAL CYCLONE 14E OFF TO THE NORTH AND EAST...MORE
SOUTHERLY FLOW BELOW 700MB IS EXPECTED TO CONTINUE TO IMPORT AT LEAST
SOME MOISTURE INTO SOUTH-CENTRAL AZ...WITH PWATS REMAINING IN THE
1.00-1.50 INCH RANGE) DURING THE ENTIRE PERIOD. THIS LEFT-OVER
MOISTURE...COMBINED WITH FAIR-TO-GOOD VERTICAL WIND SHEAR IS EXPECTED
TO ALLOW AT LEAST SOME SHOWER/THUNDERSTORM ACTIVITY TO DEVELOP EACH
DAY. ON THE OTHER HAND...MUCH DRIER AIR OVER SE CA/SW AZ IS EXPECTED
TO KEEP THOSE REGIONS PRETTY MUCH THUNDERSTORM-FREE DURING THIS
PERIOD.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
GIVEN THE WIDESPREAD CONVECTION MONDAY EVENING...THE ATMOSPHERE IS
LIKELY TOO CONTAMINATED TO SUPPORT ADDITIONAL STORMS TODAY. COULD SEE
SOME DISTANT STORMS WELL EAST AND SOUTH OF PHOENIX BUT AT THIS POINT
NEARLY ALL NUMERICAL GUIDANCE SUGGESTS THE PHOENIX AREA TERMINALS
WILL BE IN THE CLEAR THIS AFTERNOON. GOING WITH THE IDEA OF SOME
AFTERNOON CU ALONG WITH TYPICAL DIURNAL WINDS,

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
FEW/SCT HIGH CLOUDS SHOULD BE THE RULE ACROSS SOUTHWEST AZ/SOUTHEAST
CA THIS AFTERNOON. NO WEATHER-RELATED AVIATION IMPACTS EXPECTED.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
MOISTURE WILL INCREASE ACROSS THE AREA BY THE MIDDLE OF THE WEEK
RESULTING IN ELEVATED STORM CHANCES FROM PHOENIX EASTWARD ON
THURSDAY. MOISTURE VALUES WILL WANE A BIT INTO THE WEEKEND ALTHOUGH
DAILY STORM CHANCES WILL REMAIN PRESENT THROUGH EARLY NEXT WEEK. MINIMUM
RH VALUES WILL FALL BELOW 15 PERCENT THURSDAY ACROSS SOUTHEAST
CALIFORNIA WITH VALUES ABOVE 15 PERCENT EXPECTED EAST OF THE LOWER
COLORADO RIVER. FOR FRIDAY INTO THE WEEKEND...LATEST GUIDANCE MORE
INSISTENT UPON A RETURN TO DEEPER MOISTURE...HIGHER HUMIDITY AND
BETTER RAIN CHANCES...PARTICULARLY ACROSS SOUTH CENTRAL ARIZONA.

&&

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

&&

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

$$

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

DISCUSSION...PERCHA
AVIATION...LEINS
FIRE WEATHER...LEINS



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