Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 191542
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
840 AM MST SUN APR 19 2015

.SYNOPSIS... MOSTLY CLEAR SKIES AND ABOVE NORMAL TEMPERATURES ARE
EXPECTED TODAY THROUGH TUESDAY. LOOK FOR HIGHS IN THE LOWER DESERTS
TO BE NEAR 90 EACH DAY. BIG CHANGES ARE THEN POSSIBLE WEDNESDAY INTO
FRIDAY...AS AN APPROACHING STORM SYSTEM BRINGS COOLER TEMPERATURES
AND CHANCE OF SHOWERS INTO THE REGION.

&&

.DISCUSSION... DRY WESTERLY FLOW ALOFT WAS IN PLACE ACROSS ARIZONA
AND FAR SERN CA THIS MORNING...AS SEEN IN THE MORNING PLOT AND RAOB
DATA. IR IMAGERY AT 8 AM SHOWED SUNNY SKIES ACROSS THE AREA. SURFACE
DEWPOINTS OVER THE LOWER DESERTS REMAINED ON THE DRY SIDE AND MOSTLY
RANGED FROM THE MID 20S TO MID 30S. 500MB PLOTS SHOWED LITTLE CHANGE
IN H5 HEIGHTS...HOWEVER THE BOUNDARY LAYER CONTINUED TO WARM AND
TEMPS AT 8 AM OVER THE LOWER DESERTS WERE RUNNING 2-8 DEGREES WARMER
THAN 24 HOURS AGO. UNDER SUNNY SKIES...WE CAN EXPECT MOST OF THE
WARMER LOWER DESERTS TO CLIMB INTO THE LOWER 90S THIS AFTERNOON.
CURRENT FORECASTS ARE IN FINE SHAPE AND NO UPDATES ARE NEEDED.

.PREVIOUS DISCUSSION...SATELLITE THIS MORNING SHOWS MOSTLY CLEAR
SKIES OVER THE ENTIRE FORECAST AREA. MODEL SOUNDINGS SHOW A VERY DRY
PROFILE OVER  THE REGION WITH PWAT AROUND ONE THIRD OF AN INCH.
SURFACE OBSERVATIONS ALSO SHOW BOUNDARY LAYER MOISTURE HAS
DECREASED...WITH DEW POINTS ACROSS MOST OF THE REGION LESS THAN 20
DEGREES...AND RH RANGING FROM 10 TO 20 PERCENT.

5H HEIGHTS HAVE RISEN 5 TO 6 DM ACROSS THE REGION IN THE LAST 24
HOURS...AS HIGH PRESSURE BUILDS BACK INTO THE REGION IN THE WAKE OF
THE EXITING TROF. THIS WILL RESULT IN WARMER TEMPERATURES TODAY THAN
ON SATURDAY...WITH READINGS IN THE LOW 90S EXPECTED ACROSS MUCH OF
THE LOWER DESERTS. WARM AND DRY CONDITIONS WILL THEN PERSIST ANOTHER
COUPLE OF DAYS...WITH HIGHS CONTINUING TO CLIMB A FEW DEGREES ABOVE
NORMAL THROUGH TUESDAY.

MODELS THE LAST FEW DAYS HAVE BEEN ADVERTISING BIG CHANGES FOR THE
END OF THE WEEK...WITH COOLER TEMPERATURES AND THE POSSIBILITY OF
RAIN IN THE REGION. THIS WILL DEVELOP AS FLOW BECOMES SPLIT...
RESULTING IN ENERGY FROM PACIFIC SHORT WAVES PROPAGATING OVER AND
UNDER THE WEST COAST RIDGE. BY TUESDAY...BOTH THE GFS AND ECMWF
DEVELOP CLOSED LOWS OFF THE SAN DIEGO COAST. THIS WILL HELP TO
TRANSPORT SOME MOISTURE INTO SE CA AND EVENTUALLY INTO SOUTH-CENTRAL
ARIZONA. BIG QUESTION IS IF THIS WILL RESULT IN ANY SIGNIFICANT
PRECIPITATION AND IF SO WHERE THAT WILL OCCUR. LATEST MODEL RUNS
INDICATE BEST TIME FOR RAINFALL WILL BE THURSDAY AFTERNOON INTO
FRIDAY AND THAT UPSLOPE REGIONS WILL HAVE THE GREATEST LIKELIHOOD OF
RECEIVING APPRECIABLE ACCUMULATIONS. THE GFS INDICATES A HALF AN
INCH IS POSSIBLE IN NE MARICOPA AND SOUTHERN GILA COUNTIES. THE
ECMWF THOUGH IS FORECASTING ONLY AROUND A QUARTER TO A THIRD OF AN
INCH.

APRIL IS A NORMALLY DRY MONTH...BUT AS NOTED CONFIDENCE IS
INCREASING IN THE DEVELOPMENT OF A RAIN PRODUCING EVENT. ALTHOUGH
THIS MAY NOT RESULT IN WIDESPREAD PRECIPITATION...WITH RUN TO RUN
MODEL CONSISTENCY AND MOS GUIDANCE CONTINUING TO SHOW SOME HIGH
POPS...DECIDED TO RAMP UP THE POPS IN THE THURSDAY THROUGH FRIDAY
TIME PERIOD A BIT. TEMPERATURES NOW ARE NOT/T LOOKING QUITE AS COOL
DURING THE EVENT AS THEY HAD EARLIER...BUT WILL STILL BE ABOUT TEN
DEGREES COLDER THAN READINGS EXPECTED TODAY THROUGH TUESDAY.

&&

.AVIATION... SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND
KSDL...SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND
KBLH...

DRY WESTERLY FLOW ALOFT WILL CONTINUE TO PRODUCE MOSTLY CLEAR SKIES
AND LIGHT WINDS AOB 10 KNOTS THROUGH MONDAY MORNING.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...HIGH PRESSURE OVER THE REGION WILL KEEP
TEMPERATURES ABOVE NORMAL AND WINDS ON THE LIGHT SIDE THROUGH
WEDNESDAY. A PACIFIC LOW CENTER MOVING INLAND INTO THE REGION WILL
THEN BRING COOLER TEMPERATURES...AFTERNOON BREEZINESS...AN INCREASE
IN THE CLOUD COVER...AND EVEN A SLIGHT CHANCE FOR SHOWERS ON
THURSDAY. HIGH PRESSURE BUILDING BACK INTO THE DESERT SOUTHWEST WILL
THEN BRING BACK WARMER AND DRIER CONDITIONS BACK TO THE REGION ON
FRIDAY AND SATURDAY. MINIMUM HUMIDITIES IN THE 5 TO 15 PERCENT RANGE
ON TUESDAY WILL RISE INTO THE 20 TO 30 PERCENT RANGE BY
THURSDAY...THEN DROP BACK DOWN INTO AFTER SOME WESTERLY BREEZES LATE
THIS AFTERNOON/EARLY EVENING...STRONG HIGH PRESSURE AT THE SFC AND
ALOFT ALONG WITH A VERY DRY AIRMASS TO KEEP SKIES MAINLY CLEAR AND
WINDS ON THE LIGHT SIDE...MOSTLY AOB 8 KTS THROUGH THE REMAINDER OF
THE TAF PERIOD...MAINLY FOLLOWING TYPICAL DIURNAL TRENDS.THE 15 TO
25 PERCENT RANGE BY SATURDAY...WITH FAIR TO GOOD OVERNIGHT
RECOVERIES.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.
CA...NONE.

&&

$$

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

DISCUSSION...CB
PREVIOUS DISCUSSION...MCLANE
AVIATION...KUHLMAN
FIRE WEATHER...PERCHA



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