Weather Service Report


383 
FXUS65 KPSR 202101
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
200 PM MST MON APR 20 2015

.SYNOPSIS... MOSTLY CLEAR SKIES AND ABOVE NORMAL TEMPERATURES ARE 
EXPECTED THROUHG TUESDAY WHILE BIG CHANGES ARE POSSIBLE WEDNESDAY 
INTO FRIDAY. AN APPROACHING STORM SYSTEM IS FORECAST TO BRING COOLER 
TEMPERATURES DURING THIS TIME AND A CHANCE OF SHOWERS AND 
THUNDERSTORMS MAINLY FOR THURSDAY. HIGH PRESSURE AND WARMER 
TEMPERATURES WILL EVENTUALLY SETTLE BACK INTO THE REGION FOR THE 
COMING WEEKEND. 

&&

.DISCUSSION...A FLAT UPPER LEVEL HIGH PRESSURE RIDGE WAS IN PLACE 
OVER ARIZONA EARLY THIS AFTERNOON...AND 12Z PLOT AND RAOB DATA 
INDICATED THE PRESENCE OF DRY WEST FLOW ALOFT. 2 PM IR IMAGERY 
SHOWED SUNNY SKIES ACROSS THE AREA WITH JUST A FEW CUMULUS 
DEVELOPING OVER THE HIGHER TERRAIN EAST OF PHOENIX...MAINLY OVER 
AREAS EAST OF GLOBE. H5 HEIGHTS HAVE STARTED TO FALL OFF SLIGHTLY 
BUT THE BOUNDARY LAYER IS STILL WARM AND HIGH TEMPS TODAY WILL BE 
SIMILAR TO YESTERDAY WITH SOME OF THE WARMER DESERTS REACHING INTO 
THE LOWER RANGE OF THE 90S.

BEGINNING THIS EVENING AND CONTINUING THROUGH TOMORROW A SPLIT IN 
THE FLOW WILL DEVELOP INLAND OVER THE WESTERN CONUS WITH AN UPPER 
LEVEL RIDGE FORMING OVER THE PAC NORTHWEST...WITH A SOUTHERN BRANCH 
TROF FORMING OVER NRN BAJA AND THE FAR SWRN STATES. AN UPPER LEVEL 
WEAK CLOSED LOW WILL FORM TUESDAY ALONG THE FAR SERN CA 
COAST...GIVING A DRY SOUTHWEST FLOW ALOFT TO FAR SERN CA AND 
ARIZONA. THERE MAY BE A FEW HIGH CLOUDS IN THE UPPER FLOW BUT 
OVERALL SKIES SHOULD BE SUNNY TUESDAY...AND WITH HEIGHTS ALOFT 
CONTINUING TO TAPER OFF HIGH TEMPS MAY FALL A DEGREE OR TWO AS WELL. 
STILL...HIGHS WILL BE WELL ABOVE NORMAL WITH A FEW OF THE WARMEST 
DESERTS REACHING TO AROUND 90 DEGREES.

PROGS ARE IN GOOD AGREEMENT THAT A DEEPER UPPER TROF WILL DEVELOP 
JUST OFF THE SRN CA/NRN BAJA COAST ON WEDNESDAY WITH A CLOSED UPPER 
LOW SETTING UP NEAR 120 W 30 N...OFF THE FAR SERN CA COAST. 
AGAIN...LITTLE CHANGE IN THE SENSIBLE WEATHER IS EXPECTED ACROSS THE 
AREA AS DRY SOUTHWEST FLOW ALOFT PERSISTS. THERE MAY BE JUST ENOUGH 
MID LEVEL MOISTURE...INSTABILITY AND LIFT OVER THE HIGHER TERRAIN OF 
JOSHUA TREE NP TO SUPPORT A SLIGHT CHANCE FOR AFTERNOON SHOWERS OR 
THUNDERSTORMS. WE SHOULD SEE HIGH TEMPS CONTINUE TO DROP OFF A BIT 
AND MOST DESERTS WILL TOP OUT IN THE MID TO UPPER 80S UNDER MOSTLY 
SUNNY SKIES.

MODEL GUIDANCE IS STILL HAVING PROBLEMS WITH TIMING AND MOISTURE 
AVAILABILITY FOR THE SYSTEM EXPECTED TO ARRIVE IN ARIZONA DURING THE 
LAST PORTION OF WORK WEEK...SOMETIME THURSDAY INTO FRIDAY. RUN TO 
RUN AND DAY TO DAY THE PRIME TIME FOR PRECIP SHIFTS...LATER... 
EARLIER AND BACK AGAIN. LATEST GFS IS NOW ABOUT 12 HOURS FASTER THAN 
THE ECMWF AND IS ALSO WETTER. GFS SUGGESTS PRIME TIME FOR PRECIP IS 
THURSDAY INTO THURSDAY EVENING...WITH THE BEST THREAT OVER SERN AZ. 
ECMWF IS QUITE DRY THURSDAY INTO THURSDAY EVENING AND SUGGESTS AFTER 
MIDNIGHT THURSDAY INTO FRIDAY MORNING. WITH A CLOSED LOW SOLUTION 
TEND TO FAVOR THE SLOWER EMCWF BUT DUE TO INCONSISTENCY AND LACK OF 
CONFIDENCE...OPTED TO MAKE NO MAJOR CHANGES AND MAINLY BLENDED OUR 
FORECAST WITH SURROUNDING OFFICES. WILL KEEP A CHANCE OF SHOWERS 
GOING ACROSS SOUTH CENTRAL AZ THURSDAY INTO THURSDAY NIGHT... 
BECOMING A SLIGHT CHANCE FRIDAY. SLIGHT CHANCES FOR AFTERNOON 
THUNDERSTORMS SEEM A GOOD BET AS GUIDANCE CALLS FOR MODEST CAPE AND 
LIFTED INDICES DOWN TO MINUS 2 OR SO. 

CONFIDENCE IN THE TEMPERATURE FORECAST FOR THURSDAY AND EVEN FRIDAY 
IS STILL ON THE LOW SIDE AS A LOT DEPENDS ON THE CLOUD COVER AND 
POTENTIAL FOR RAIN. EITHER WAY...THURSDAY LOOKS LIKE IT WILL BE THE 
COOLEST DAY WITH HIGHS 5-10 DEGREES BELOW NORMAL WITH SOME RECOVERY 
IN TEMPERATURES ON FRIDAY AS THE TROUGH EXITS TO EAST AND SOME WEAK 
UPPER LEVEL RIDGING TAKES OVER. THE COMING WEEKEND SHOULD SEE A 
RETURN TO MORE TYPICAL LATE APRIL WEATHER WITH DRY CONDITIONS AND 
TEMPERATURES BACK NEAR 90 DEGREES OVER THE LOWER DESERTS.

&&

.AVIATION... SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND 
KSDL...SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND 
KBLH...
 
STRONG HIGH PRESSURE AT THE SFC AND DRY WESTERLY FLOW ALOFT TO KEEP 
SKIES MAINLY CLEAR THROUGH THE TAF PERIOD...EXCEPT FOR A FEW HIGH 
CLOUDS...AND WINDS ON THE LIGHT SIDE...EXCEPT FOR 8-12 KT WESTERLY 
BREEZES AT THE PHX AREA TERMINALS...AND SOUTHERLY TO SOUTHWESTERLY 
BREEZES AT KBLH AND KIPL DURING THE AFTERNOON AND EARLY EVENING 
HOURS ON TUESDAY.
 
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
 
&&

.FIRE WEATHER... 
THURSDAY THROUGH MONDAY...
A RATHER STRONG (FOR APRIL) PACIFIC STORM SYSTEM IS STILL EXPECTED 
TO BRING MUCH COOLER TEMPERATURES AND SCATTERED SHOWERS...AND AN 
ISOLATED THUNDERSTORM TO THE REGION ON THURSDAY AND THURSDAY 
NIGHT...WITH MANY LOWER DESERT LOCATIONS SEEING HIGHS RISING ONLY IN 
THE 70S ON THURSDAY AFTERNOON. SHOWERS TO LINGER INTO FRIDAY ACROSS 
SOUTH-CENTRAL ARIZONA WITH CLEARING SKIES AND SOMEWHAT WARMER 
TEMPERATURES ACROSS SOUTHWEST ARIZONA AND SOUTHEAST CA...AS THE 
STORM SYSTEM MOVES OFF TO THE EAST. DRY CONDITIONS TO RETURN FROM 
SATURDAY INTO NEXT MONDAY...WITH A SLOW WARMING TREND...AS HIGH 
PRESSURE GRADUALLY REBUILDS BACK INLAND OVER THE REGION. MINIMUM 
HUMIDITIES IN THE 15 TO 25 PERCENT RANGE ON THURSDAY TO SLOWLY DROP 
BACK DOWN INTO THE 8 TO 18 PERCENT RANGE BY MONDAY...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/KUHLMAN
AVIATION...PERCHA
FIRE WEATHER...PERCHA

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