Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 260818
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
116 AM MST SUN APR 26 2015

.UPDATE...TO AVIATION DISCUSSION...

&&

.SYNOPSIS...
A STRONG COLD FRONT WILL MOVE THROUGH THE REGION EARLY TONIGHT
BRINGING GUSTY WINDS AND GOOD CHANCES FOR RAIN. CHANCES FOR
SHOWERS AND THUNDERSTORMS WILL INCREASE THIS EVENING AND INTO
TONIGHT...BUT MAINLY ACROSS PORTIONS OF SOUTHWEST AND SOUTH CENTRAL
ARIZONA. LINGERING SHOWERS ARE EXPECTED SUNDAY OVER EASTERN
ARIZONA...WITH CLEARING OVER SOUTHEAST CALIFORNIA AND SOUTHWEST
ARIZONA. DRIER AND MUCH WARMER WEATHER IS EXPECTED NEXT WEEK.

&&

.DISCUSSION...

...POTENT UPPER TROUGH AND FRONTAL PASSAGE ACROSS THE REGION TONIGHT
WITH STRONG GUSTY WINDS AND THUNDERSTORM CHANCES...

VIGOROUS MID SPRING PACIFIC STORM SYSTEM CONTINUED TO MOVE EASTWARD
ACROSS THE DESERT SOUTHWEST EARLY THIS EVENING...BRINGING SCATTERED
TO NUMEROUS SHOWERS AS WELL AS EMBEDDED THUNDERSTORMS TO THE STATE.
00Z PLOT DATA SHOWED THE LARGEST H5 HEIGHT FALLS ACROSS NWRN ARIZONA
AND FAR SRN NEVADA...WITH 70M FALLS NEAR LAS VEGAS. COLDEST
AIR...NEAR THE CENTER OF THE LOW...WAS WELL TO OUR NORTH AND
NORTHWEST...WITH READINGS DOWN TO MINUS 22C AT 500MB OVER FAR SRN
NEVADA/FAR NWRN AZ. CORRESPONDINGLY THE MOST SIGNIFICANT CONVECTION
HAS STAYED TO OUR NORTH...ALTHOUGH AT 8 PM A CLUSTER OF SOMEWHAT
WEAK STORMS WERE SEEN MOVING THROUGH PORTIONS OF LA PAZ
COUNTY...APPROACHING NORTHWEST MARICOPA COUNTY. IR IMAGERY AT 8 PM
SHOWED GENERALLY CLOUDY SKIES OVER MOST OF ARIZONA WITH PARTIAL
CLEARING TAKING PLACE WEST OF THE LOWER COLORADO RIVER VALLEY.

GUIDANCE REMAINS CONSISTENT IN CALLING FOR THE STORM TO DIVE
SOUTHEASTWARD ACROSS ARIZONA TONIGHT...BRINGING SOME OF THE BEST
FORCING TO CENTRAL AZ BY 12Z SUNDAY. A LARGE BULLSEYE OF MID LEVEL Q
CONVERGENCE AND STRONG PVA FOCUS INTO MARICOPA COUNTY AFTER MIDNIGHT
TONIGHT AND THERE APPEARS TO BE SUFFICIENT MOISTURE TO ALLOW FOR
NUMEROUS SHOWERS FORMING OVER THE CENTRAL DESERTS STARTING LATER
THIS EVENING AND PERSISTING WELL PAST MIDNIGHT. DESPITE SOMEWHAT
LIMITED CAPE VALUES...THERE IS ENOUGH FORCING AND A STRONG ENOUGH
UPPER WIND FIELD TO ALLOW ISOLATED STORMS TO FORM TONIGHT...AND ANY
STORM THAT FORMS HAS THE POTENTIAL TO PRODUCE GUSTY WINDS IN EXCESS
OF 40 MPH AS WELL AS SMALLER HAIL AND BRIEF MODERATE TO HEAVY RAIN.
BY SUNRISE SUNDAY...CLEARING WILL TAKING PLACE WEST OF MARICOPA
COUNTY AS STRONGER SUBSIDENCE BEHIND THE PASSING TROF MOVES INTO THE
AREA. STRONG AND GUSTY WEST WINDS CONTINUED OVER PORTIONS OF
IMPERIAL AND EASTERN RIVERSIDE COUNTY EARLY THIS EVENING...WITH
OCCASIONAL GUSTS REACHING TO NEAR OR SLIGHTLY ABOVE WIND ADVISORY
LEVELS. EXPECT THE WINDS TO GRADUALLY TAPER OFF AND FOR THE MOST
PART SHOULD DROP BELOW CRITERIA BY THE TIME THE ADVISORY ENDS AT 9
PM. FORECASTS HAVE BEEN ADJUSTED FOR CURRENT SKY...POP AND WEATHER
TRENDS AND APPEARS TO BE IN GOOD SHAPE FOR NOW.

.PREVIOUS DISCUSSION...
TODAY THUS FAR HAS BEEN FAIRLY QUIET ACROSS THE AREA EXCEPT FOR SOME
LIGHT SHOWERS PASSING THROUGH RIVERSIDE AND LA PAZ COUNTIES WITH
SOME RECENT DEVELOPMENT JUST TO OUR NORTH IN YAVAPAI COUNTY. THESE
SHOWERS WERE IN RESPONSE TO A WEAKENING SHORTWAVE TROUGH MOVING INTO
CENTRAL ARIZONA OUT AHEAD OF THE MAIN TROUGH THAT WILL AFFECT THE
AREA LATER TODAY AND TONIGHT. CURRENT WATER VAPOR AND UPPER HEIGHT
ANALYSIS SHOWS A RATHER IMPRESSIVE UPPER TROUGH APPROACHING FROM THE
NORTHWEST WITH THE MAIN SHORTWAVE TROUGH JUST WEST OF LAS VEGAS.
DIFLUENT FLOW ALOFT OVER SOUTHERN NEVADA AND UTAH ALONG WITH STRONG
500MB HEIGHT FALLS CENTERED OVER THE SIERRAS ARE HELPING TO SPARK
OFF SCATTERED SHOWERS AND THUNDERSTORMS. WINDS AHEAD OF AN ADVANCING
COLD FRONT HAVE BECOME GUSTY ACROSS SOUTHEAST CALIFORNIA WITH SOME
GUSTS TO AROUND 35 KNOTS. AS THE FRONT MOVES THROUGH THIS
EVENING...CAN EXPECT SOME WIND GUSTS UP TO 40-45 KNOTS IN SOME
LOCALIZED SPOTS ALONG WITH THE POTENTIAL FOR SOME BLOWING DUST.

THE MAIN SHORTWAVE TROUGH AND COLD FRONT WILL QUICKLY DIVE
SOUTHEASTWARD THROUGH THE REST OF TODAY...REACHING SOUTH-CENTRAL
ARIZONA AROUND 06Z THIS EVENING. STILL EXPECTING SCATTERED TO
WIDESPREAD SHOWERS AND THUNDERSTORMS TO DEVELOP AHEAD OF THESE
FEATURES DURING THE EVENING TIME FRAME WITH BEST CHANCES STRETCHING
FROM NORTHERN LA PAZ COUNTY THROUGH MUCH OF MARICOPA COUNTY...INTO
SOUTHERN GILA COUNTY. CONDITIONS REMAIN RATHER MOIST BETWEEN 8-10K
FEET...BUT FURTHER MOISTENING IN THE MID LEVELS WILL OCCUR AS THE
TROUGH AND COLDER AIR MOVES IN FROM THE NORTHWEST. THE MOIST
CONDITIONS...WEAK UPSLOPE LOW LEVEL FLOW...AND STRONG FORECAST MODEL
OMEGA FOR THIS EVENING ACROSS SOUTH-CENTRAL ARIZONA...WILL ALL COME
INTO PLAY TO AID IN SHOWER AND THUNDERSTORM DEVELOPMENT. STRONGER
SHOWERS OR THUNDERSTORMS WILL HAVE THE POTENTIAL TO BRING SOME GUSTY
WINDS DOWN TO THE SURFACE...SO SOME STRONGER SUB-SEVERE GUSTS ARE
POSSIBLE.

BY SUNDAY MORNING...THE MAIN SHORTWAVE TROUGH WILL BE MOVING INTO
WESTERN NEW MEXICO WITH SUBSIDENCE ALOFT WORKING INTO OUR WESTERN
ZONES. CHANCES FOR LINGERING SHOWERS WILL BE POSSIBLE THROUGH SUNDAY
MORNING FROM AROUND PHOENIX EASTWARD WITH BEST CHANCES OVER THE
HIGHER TERRAIN OF EAST-CENTRAL ARIZONA. BY MID TO LATE SUNDAY
AFTERNOON...THE DRIER AIR BEHIND THE TROUGH WILL HAVE MIXED OUT THE
LOW LEVELS ENOUGH TO BASICALLY KEEP ANY REMAINING SHOWER CHANCES
OVER HIGHER TERRAIN AREAS. OUR WESTERN ZONES SHOULD CLEAR OUT FAIRLY
QUICKLY ON SUNDAY WITH HIGHS REBOUNDING BACK INTO THE LOW TO MID
80S. ELSEWHERE...TEMPERATURES SHOULD ONLY PEAK OUT IN THE UPPER 70S
ACROSS THE SOUTH-CENTRAL ARIZONA DESERTS.

FOR THE COMING WORK WEEK...A LARGE RIDGE IS FORECAST TO TAKE OVER
WITH DRY CONDITIONS AND WARMING TEMPERATURES. HIGHS BY MONDAY SHOULD
REACH NEAR NORMALS AND ONCE THE UPPER LEVEL RIDGE FINALLY TAKES
OVER...TEMPERATURES WILL HEAT UP EVEN MORE WITH FORECAST HIGHS IN
THE MIDDLE TO UPPER 90S FOR WEDNESDAY AND THURSDAY ACROSS THE
DESERTS. THOUGH THERE ARE SOME MODEL DIFFERENCES BEYOND NEXT
THURSDAY...THE GENERAL CONSENSUS IS THAT LARGE SCALE TROUGHING WILL
PUSH THE RIDGE OUT THE REGION ALLOWING FOR SOME MODERATION IN
TEMPERATURES...BUT CONTINUING WITH THE DRY CONDITIONS.

&&

AVIATION...

SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
MAIN FRONTAL FEATURE AND PREDOMINANT SHOWER ACTIVITY HAS CLEARED
MOSTLY EAST OF THE PHX METRO. WINDS IN THE WAKE OF THE FRONTAL
PASSAGE WILL BE MUCH CALMER IN TERMS OF SPEEDS AND ON THE MORE
VARIABLE SIDE IN TERMS OF HEADINGS. THERE MAY BE SOME SUBTLE DRIFT
TO EAST HEADING TOWARDS SUNRISE...AS RAIN COOLED AIR FLOWS INTO THE
METRO FROM THE HIGHER TERRAIN TO THE EAST...HOWEVER SPEEDS SHOULD
STILL REMAIN ON THE LIGHT SIDE AND UNDER 6KTS EVEN IF EAST HEADINGS
ARE REALIZED. MID-LEVEL CIGS AOA 8-10KFT WILL PERSIST INTO THE
EVENING WITH SOME POCKETS OF FEW-SCT PATCHES AROUND 5KFT. ANOTHER
ROUND OF STRONG WEST WINDS PROGGED LATER TOWARDS MIDDAY...WITH GUSTS
IN THE 20KT RANGE POSSIBLE AGAIN.


SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND
KBLH...
MAIN WEATHER ISSUE IN THE TAFS WILL BE GUSTY WEST WINDS
TONIGHT...AND WE MAY SEE OCCASIONAL GUSTS OVER 30KT THROUGH 05Z OR
SO BEFORE THEY START TO TAPER OFF. FOR THE MOST PART EXPECT VIS
VALUES AOA 6SM FOR THE REST OF TONIGHT AS WINDS SLOWLY TAPER OFF.
MAY SEE A FEW CIGS AROUND 8-10K FEET AT KBLH THROUGH MIDNIGHT WITH A
SHOWER POSSIBLE...BUT THEN CLEARING WILL OCCUR AS THE MAIN TROF
EXITS TO THE EAST. LLWS IS POSSIBLE AT KBLH AFTER MIDNIGHT AS
SURFACE WINDS TAPER OFF BELOW 12KT...BUT 35KT NORTHWEST WINDS SET UP
JUST ABOVE THE SURFACE. HAVE MENTIONED THIS IN THE KBLH TAF. EXPECT
A RETURN TO GUSTY NORTHWEST/NORTH WINDS DOWN THE RIVER SUNDAY WITH
OCCASIONAL GUSTS ABOVE 25KT POSSIBLE. BREEZY WEST WINDS WILL ALSO
OCCUR AT KIPL SUNDAY...UNDER MOSTLY SUNNY SKIES.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
IN THE WAKE OF THE DEPARTING TROUGH...NEXT WEEK WILL SEE THE ARRIVAL
OF A STRONG UPPER RIDGE OVER THE SOUTHWESTERN CONUS FROM MONDAY
THROUGH MOST OF THE WEEK. TEMPERATURES WILL WARM SUBSTANTIALLY AND
APPROACH THE TRIPLE DIGIT MARK FOR THE LATTER PART OF THE WEEK.
AFTERNOON HUMIDITIES WILL DROP INTO THE LOWER TEENS AND UPPER SINGLE
DIGITS WITH FAIR OVERNIGHT RECOVERIES EXPECTED. WINDS WILL BE GNLY
LIGHT AND SHOULD FOLLOW TYPICAL DIURNAL PATTERNS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...CB
PREVIOUS DISCUSSION...KUHLMAN
AVIATION...NOLTE/CB
FIRE WEATHER...NOLTE/LEINS


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