Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 062217
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
315 PM MST WED MAY 6 2015

.SYNOPSIS...
DRIER AND BREEZY CONDITIONS WILL PERSIST THROUGH THURSDAY BEFORE A
STRONG EASTERN PACIFIC WEATHER SYSTEM MOVES ACROSS THE SOUTHWEST
STATES ON FRIDAY. THE LOW PRESSURE SYSTEM WILL BRING STRONGER GUSTY
WINDS...COOLER TEMPERATURES...AND INCREASING PRECIPITATION CHANCES
THROUGH SATURDAY. A SLOW WARMING TREND COMMENCES LATE IN THE WEEKEND
INTO EARLY NEXT WEEK AS HIGH PRESSURE GRADUALLY REBUILDS OVER THE
DESERT SOUTHWEST.

&&

.DISCUSSION...
AFTERNOON SATELLITE IMAGERY SHOWS PLENTY OF MID LEVEL CLOUDS OVER
THE NORTHERN TWO THIRDS OF ARIZONA...LOTS OF FLOCCUS AND SOME MODEST
BUILD UPS...BUT SO FAR LIGHTNING HAS ONLY BEEN OBSERVED OVER
NORTHWEST NM. THE WEAK SHORT WAVE CONTINUES TO GRADUALLY EXPAND A
LARGER TROUGH OVER THE DESERT SOUTHWEST...ALLOWING THE NEXT UPPER
LEVEL LOW TO BEGIN TO DROP SOUTH ACROSS THE PACIFIC NORTHWEST.

MODELS ARE IN GOOD AGREEMENT THAT THE LOW WILL CLOSE OFF BY THURSDAY
AFTERNOON...THE 549-552DM CENTER TO POSITION JUST NORTH OF THE LOS
ANGELES AREA. THE LOW WILL THEN TRACK EAST AND BEGIN TO WEAKEN...THE
555-558DM CENTER GENERALLY OVER SOUTHERN NV/NW ARIZONA BY FRIDAY
AFTERNOON.

CURRENTLY THE SURFACE GRADIENT HAS ALREADY BECOME ENHANCED/TIGHTENED
FROM THE APPROACHING LOW...AND THIS WILL STRENGTHEN THE WINDS FOR
LOCALLY BREEZY CONDITIONS THIS EVENING. STRONGER GUSTY WINDS ARE
EXPECTED THURSDAY AFTERNOON AND EVENING...MAINLY ACROSS SOUTHEAST
CALIFORNIA NEAR KIPL WHERE GUSTS IN EXCESS OF 35 MPH WILL BE
POSSIBLE FOR SEVERAL HOURS. BLOWING DUST IS POSSIBLE...BUT NOT
WIDESPREAD AREAL COVERAGE...JUST MORE ISOLATED TO DUST PRONE AREAS.

AS THE LOW BEGINS TO SHIFT EAST FRIDAY AFTERNOON...THE UPPER LEVEL
JET/250MB 80-100KT ENERGY BEGINS TO NOSE ACROSS SOUTHERN CALIFORNIA
INTO ARIZONA...AND SOME MODEST AMOUNTS OF MOISTURE ARE IMPORTED INTO
THE REGION. HOWEVER...RIGHT NOW IT APPEARS THAT THE BEST MOISTURE
AND DYNAMICS ASSOCIATED WITH THE SYSTEM WILL REMAIN NORTH OF OUR
FORECAST AREA. SO...ONLY SLIGHT CHANCES OF SHOWERS/THUNDERSTORMS ARE
FORECAST FOR ANY AREA OF OUR CWA FRIDAY INTO SATURDAY. IF THE LOW
SAGS A BIT FARTHER SOUTH AND HAS A BETTER FETCH OF MOISTURE THAT
ACCOMPANIES THE 850-700MB WINDS...POSSIBLY PRECIPITATION CHANCES
WILL IMPROVE. THE VARIOUS RUNS OF THE GFS SEEM TO INTRODUCE MORE
MOISTURE...AND CARRY HIGHER POP/QPF AMOUNTS...BUT RUN TO RUN
CONTINUITY IS LACKING. UNSEASONABLY COOL AIR WILL MOVE IN WITH THE
STORM SYSTEM WITH 850MB TEMPERATURES DROPPING TO AROUND 12C ON
FRIDAY...AND THIS WILL KNOCK DOWN OUR TEMPERATURES AS LOW AS 15
DEGREES BELOW NORMAL FRIDAY AND SATURDAY...WITH HIGHS TOPPING OUT IN
THE MID-UPPER 70S BOTH DAYS.

THE UPPER LOW WILL STILL AFFECT ARIZONA INTO EARLY SATURDAY WITH A
TRAILING VORTICITY LOBE FORECAST TO SWING THROUGH SOUTH-CENTRAL AND
EASTERN ARIZONA BETWEEN 12-18Z. THIS WILL LIKELY SPARK OFF
ADDITIONAL SHOWERS AND POTENTIALLY SOME THUNDERSTORMS UNDER STEEP
MID LEVEL LAPSE RATES. AFTER 18Z SATURDAY...SUBSIDENCE ALOFT WILL
QUICKLY TAKE OVER FROM WEST TO EAST WITH SKIES CLEARING AND ONLY A
SLIGHT CHANCE OF SOME LINGERING SHOWERS OVER OUR EASTERN HIGH
TERRAIN AREAS.

SUNDAY INTO EARLY NEXT WEEK WILL TRANSITION BACK INTO MORE NORMAL
CONDITIONS WITH WEAK RIDGING ALOFT TAKING OVER AND TEMPERATURES
WARMING BACK TOWARD NORMAL STARTING NEXT MONDAY. WILL BE WATCHING
ANOTHER POTENTIAL STORM SYSTEM FOR THE MIDDLE OF NEXT WEEK DROPPING
OUT OF THE NORTHERN PACIFIC...BUT AT THIS TIME BOTH THE GFS AND
EUROPEAN KEEP IT WELL TO OUR NORTH.

&&

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

AS AN AREA OF LOW PRESSURE MOVES EAST ACROSS CENTRAL ARIZONA THIS
WILL LEAD TO LOCALLY BREEZY TO WINDY CONDITIONS OVER THE NEXT 24
HOURS FOR ALL TAF LOCATIONS LISTED ABOVE.

FOR CENTRAL ARIZONA SITES...EXPECTING A PREDOMINANT SOUTHERLY
COMPONENT THROUGH MID AFTERNOON 06 MAY BEFORE SWINGING WESTERLY JUST
BEFORE 00Z 07 MAY. WINDS WILL LIKELY REMAIN FROM THE WEST OVERNIGHT
AND INTO THURSDAY MORNING. WIND SPEEDS ELEVATED WITH GUSTS AROUND 20-
25 KTS WILL LINGER THROUGH 06Z 07 MAY.

FOR SOUTHEAST CALIFORNIA...WINDS WILL HOLD A WESTERLY AND SOUTHERLY
DIRECTION AT IPL AND BLH RESPECTIVELY AND SEE BREEZY TO WINDY GUSTS
20-25 KTS THROUGH LATE EVENING TONIGHT.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
AN AREA OF LOW PRESSURE WILL CONTINUE TO MOVE EAST...LEAVING MUCH
COOLER TEMPERATURES AND HIGHER HUMIDITY LEVELS ACROSS THE FORECAST
AREA...WITH ISOLATED SHOWERS AND THUNDERSTORMS LINGERING OVER THE
HIGHER TERRAIN OF SOUTH-CENTRAL ARIZONA SATURDAY AFTERNOON/EVENING.
THE TREND CHANGES SUNDAY THROUGH TUESDAY...HIGH PRESSURE ALOFT WILL
BUILD BACK INTO THE AREA FROM THE WEST...RESULTING IN A DRYING AND
WARMING TREND ALONG WITH LESS WIND. MINIMUM RH VALUES WILL LOWER
INTO THE TEENS SUNDAY...THEN FALL BELOW 15 PERCENT EARLY NEXT WEEK
WITH THE DRIER DESERTS SEEING SOME AREAS WITH SINGLE DIGIT
HUMIDITIES. HIGH TEMPERATURES OVER THE DESERTS MONDAY AND TUESDAY
WILL RISE MOSTLY INTO THE LOWER 90S.

&&

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

$$

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

DISCUSSION...MEYERS/KUHLMAN
AVIATION...CDEWEY
FIRE WEATHER...MEYERS/CB



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