Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 031625
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
925 AM MST TUE MAR 3 2015

.SYNOPSIS...
LOW PRESSURE...THAT WILL BE MOVING SLOWLY SOUTHWARD ACROSS THE
REGION...WILL KEEP THE WEATHER RATHER UNSETTLED AND COOL THROUGH
WEDNESDAY. A SLIGHT CHANCE OF SHOWERS...AND EVEN A FEW THUNDERSTORMS
CAN BE EXPECTED OVER SOUTH CENTRAL ARIZONA THROUGH TUESDAY EVENING.
A RETURN TO ABOVE NORMAL TEMPERATURES IS LIKELY BY THURSDAY...INTO
THE WEEKEND AS HIGH PRESSURE SYSTEM BUILDS OVER THE DESERT
SOUTHWEST.

&&

.DISCUSSION...
INTERESTING WEATHER THIS MORNING AS PATCHY DENSE FOG DEVELOPED
ACROSS PORTIONS OF THE GREATER PHOENIX METROPOLITAN AREA...AND MUCH
OF NORTHWEST PINAL COUNTY. A TROF OF LOW PRESSURE CONTINUED TO SAG
SOUTHEAST ACROSS THE DESERT SOUTHWEST WITH THE TROF AXIS RUNNING
NE-SW ACROSS FAR SERN CA/SRN NEVADA. ORIENTATION OF THE TROF PLACED
A WEAK SWLY FLOW ACROSS THE LOWER DESERTS WHICH CONTINUED TO ADVECT
IN MODEST AMOUNTS OF MOISTURE. OVERALL MOISTURE VALUES ARE LESS THAN
24 HOURS AGO...WITH PWAT VALUES RUNNING AROUND ONE HALF INCH...BUT
THE BOUNDARY LAYER REMAINS QUITE MOIST. SURFACE DEWPOINTS ACROSS THE
CENTRAL DESERTS WERE RUNNING IN THE MID TO UPPER 40S AT 9 AM. SOME
UNEXPECTED CLEARING EARLY THIS MORNING ALLOWED SURFACE TEMPS TO FALL
OFF AND REACH THE CROSSOVER TEMPERATURE AND AS SUCH PATCHY DENSE FOG
DEVELOPED IN THE GREATER PHOENIX AREA...DROPPING VIS AT SKY HARBOR
TO 1/4 MILE. OTHER AREAS...NEAR SOUTH MOUNTAIN...ALONG INTERSTATE 8
AND THE SALT RIVER BED...AND ESPECIALLY SOUTHEAST OF THE VALLEY IN
CASA GRANDE...SAW LOCALLY DENSE FOG WITH VIS VALUES DOWN AT OR BELOW
1/4 MILE. WE ISSUED A DENSE FOG ADVISORY FOR ZONE 28 EFFECTIVE UNTIL
10 AM.

FOR THE REST OF TODAY...THE FOG WILL GRADUALLY ERODE UNDER THE
INFLUENCE OF INCREASING SUN/MIXING...AND WE WILL SEE PARTLY CLOUDY
SKIES THROUGH THE AFTERNOON. AS THE TROF AXIS SLOWLY MOVES IN FROM
THE WEST TODAY AND THIS EVENING THERE WILL BE SUFFICIENT INSTABILITY
TO ALLOW FOR A SLIGHT CHANCE OF SHOWERS OR AFTERNOON THUNDERSTORMS.
DYNAMICS ARE RATHER WEAK...AS THE WIND FIELDS ASSOCIATED WITH THE
PASSING TROF ARE NOT VERY IMPRESSIVE...SO ANY STORM THAT DEVELOPS
WILL BE ON THE WEAK SIDE AS WELL. FORECASTS HAVE BEEN TWEAKED FOR
CURRENT SKY AND WEATHER TRENDS AND ARE IN GOOD SHAPE FOR NOW.

.PREVIOUS DISCUSSION...
TODAY THROUGH WEDNESDAY...
AFTER A RATHER WET AND COOL MONDAY...WITH SOME OF THE MOST FAVORED
AREAS ACROSS NORTHERN MARICOPA COUNTY SEEING UP TO AN INCH OF
RAIN...TODAY LOOKS LIKE IT WILL BE A QUIETER ONE...AS THE UPPER TROF
THAT BROUGHT US ALL THE RAIN AND CLOUDS HAS NOW MOVED OFF WELL TO
OUR EAST...INTO THE CENTRAL PLAINS.

HOWEVER...THE WEATHER TODAY AND TONIGHT STILL LOOKS LIKE IT WILL BE
RATHER UNSETTLED...WITH ISOLATED-TO-SCATTERED SHOWERS TO CONTINUE
OVER SOUTH-CENTRAL ARIZONA...ESPECIALLY OVER THE HIGHER TERRAIN
NORTH AND EAST OF PHOENIX. THIS CONTINUATION OF SHOWER CHANCES IS
DUE TO A COMBINATION OF MOIST SOUTHWESTERLY FLOW ALOFT THAT IS BEING
GENERATED BY ANOTHER UPPER LOW CENTER THAT IS NOW POSITIONED OFF THE
SOUTHERN CA COAST THIS MORNING...AND A COUPLE OF WEAK SHORTWAVES
THAT WILL BE DROPPING SOUTHWARD ACROSS AZ AS THE STRONG LONG-WAVE
UPPER TROF THEY ARE EMBEDDED IN MOVES SOUTHEASTWARD ACROSS THE
CENTRAL ROCKIES INTO THE CENTRAL PLAINS. ALTHOUGH MOISTURE LEVELS
THROUGH THE COLUMN LOOK TO BE RATHER LIMITED...WITH PWATS IN THE
0.50-0.60 INCH RANGE...THERE APPEARS THAT THERE WILL BE ENOUGH
DYNAMICS/INSTABILITY TO TRIGGER LIGHT SHOWERS...AND EVEN ONE OR TWO
THUNDERSTORMS TODAY AND TONIGHT AS THE SHORTWAVES PASS ACROSS THE
REGION...WITH PERHAPS A TENTH OF AN INCH OR SO OF RAIN FALLING FROM
THE HEAVIER SHOWERS...AND EVEN A DUSTING OF SNOW OVER OUR HIGHEST
PEAKS. TEMPERATURES ARE EXPECTED TO REMAIN BELOW NORMAL TODAY...WITH
850MB TEMPERATURES AROUND 5C KEEPING LOWER DESERT HIGHS DOWN IN THE
60S AND LOW 70S...IN SPITE OF CONSIDERABLE SUNSHINE. THE CHANCES FOR
PRECIP WILL PRETTY MUCH END BY MIDDAY ON WEDNESDAY AS THE UPPER LOW
THAT IS NOW OFF THE SOUTHERN CA COAST MOVES OFF WELL TO OUR SOUTH
AND EAST...CUTTING OFF THE MOISTURE FEED FROM THE PACIFIC...AND
RIDGING BEGINS TO BUILD IN FROM THE WEST BEHIND THE MAIN LONG-WAVE
TROF.

THURSDAY...

A DRYING AND SUBSIDENT NORTHERLY FLOW ALOFT WILL SET
UP ACROSS THE AREA AS HIGH PRESSURE ALOFT STARTS TO BUILD ALONG THE
CA COAST. THIS WILL LEAD TO SUNNY SKIES...AND CONTINUED WARMING
WITH HIGH TEMPS REACHING INTO THE LOW TO MID 70S...AND TOWARDS
SEASONAL NORMALS.

FRIDAY INTO EARLY NEXT WEEK...
A WARMING TREND IS EXPECTED TO CONTINUE THROUGH THIS PERIOD UNDER
MAINLY CLEAR SKIES AS HIGH PRESSURE STRENGTHENS OVER THE
REGION...WITH A GOOD CHANCE FOR HIGHS NEAR 80 ACROSS THE LOWER
DESERTS BY THE WEEKEND...AND EVEN INTO THE MID 80S BY NEXT TUESDAY.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...
LOCALIZED AND PATCHY FOG DEVELOPMENT WILL CONTINUE TO FAVOR AREAS OF
THE SOUTHEAST PHX METRO AND NW PINAL COUNTY THROUGH THE MORNING...AT
TIMES GENERATING LOCALLY DENSE VSBYS INTO IFR VALUES. ANOTHER ROUND
OF MID TO HIGH LEVEL CLOUDS WILL APPROACH FROM THE SOUTHWEST...WHICH
SHOULD HELP MITIGATE FURTHER FOG DEVELOPMENT THIS MORNING. CANNOT
RULE OUT ISOLATED SHOWER DEVELOP LATER INTO THE DAY/AFTERNOON WITH
THE UPPER TROUGH AXIS STILL OVERHEAD AND ABUNDANT LOW-LEVEL MOISTURE
STILL PREVALENT. HOWEVER...WILL NOT INCLUDE MENTION IN THE TAFS THIS
TIME UNTIL COVERAGE PICKS UP ON AREA RADARS. SFC WINDS WILL REMAIN
LIGHT THROUGH WEDNESDAY MORNING...AND TYPICAL OVERNIGHT SHIFT TO AN
EASTERLY DIRECTION MAY BE VERY DELAYED OR NON-EXISTENT LATE TONIGHT.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
NO AVIATION CONCERNS THROUGH WEDNESDAY MORNING WITH JUST OCCASIONAL
HIGH CLOUDS AND A FEW AFTERNOON CU TO DEAL WITH. SFC WINDS WILL
GENERALLY FAVOR A NORTHWEST DIRECTION...HOWEVER THE WEAK PRESSURE
GRADIENT MAY ALLOW EXTENDED PERIODS OF VARIABLE DIRECTION WITH
SPEEDS AOB 6 KT.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
STRONG HIGH PRESSURE WILL PROVIDE SEASONABLY WARM AND DRY CONDITIONS
TO THE DISTRICT DURING THE END OF OF THIS WEEK INTO EARLY NEXT WEEK.
WITH TEMPERATURES SLIGHTLY ABOVE NORMAL...AFTERNOON HUMIDITY LEVELS
WILL REGULARLY FALL INTO A 15 TO 25 PERCENT RANGE WITH GOOD
OVERNIGHT RECOVERY. WINDS WILL FAVOR A NORTH TO NORTHEAST TRAJECTORY
THROUGH THE PERIOD...WITH SOME OCCASIONAL GUSTINESS OVER RIDGE TOPS
BUT ALL IN ALL VERY TYPICAL SPEEDS. OVERALL...FIRE DANGER WILL BE
LIMITED DURING THIS TIME FRAME.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...PERCHA/CB
AVIATION...NOLTE/MO
FIRE WEATHER...MO











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