Dust Devil in Arizona, May 11, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
930 AM MST MON MAY 11 2015

.SYNOPSIS... WEAK HIGH PRESSURE WILL BRING NEAR NORMAL TEMPERATURES
WITH PLENTY OF SUNSHINE THROUGH THURSDAY ACROSS THE DESERT
SOUTHWEST. ANOTHER UNSEASONABLY COOL LOW PRESSURE SYSTEM WILL AFFECT
THE REGION LATE THURSDAY THROUGH SATURDAY USHERING IN MUCH COOLER
TEMPERATURES...BREEZY CONDITIONS...AND A CHANCE FOR RAIN.

&&

.DISCUSSION...

VISIBLE SATELLITE IMAGERY SHOWS SOME SCATTERED HIGH CLOUDS MOVING
ACROSS THE REGION FROM WEST TO EAST. SURFACE OBSERVATIONS ARE
INDICATING MUCH WARMER TEMPERATURES FOR MOST STATIONS. INDEED...MOST
LOCATIONS SHOULD HAVE AT OR ABOVE NORMAL TEMPS FOR TODAY...BREAKING
THE EXTENDED COOL DOWN THAT WAS PRESENT FOR SEVERAL DAYS. THIS TREND
WILL BE SHORT LIVED HOWEVER...WITH A WEAK RIDGE IN PLACE FOR MONDAY
AND TUESDAY TO BE FOLLOWED BY A COUPLE OF SYSTEMS. FIRST IS A WEAK
INVERTED TROUGH THAT IS NOW LOCATED OFF THE CA COAST. THIS TROUGH
WILL PASS THROUGH SRN AZ TUESDAY INTO WEDNESDAY AND WILL BEGIN THE
DOWNWARD TREND IN TEMPS AND A SLIGHT CHANCE FOR SHOWERS IN FAR ERN
AZ...BUT NOT IN OUR CWA. THE BIGGER WEATHER MAKER WILL BE A STRONG
LOW PRESSURE SYSTEM DROPPING DOWN THE PACIFIC COAST BEGINNING ON
FRIDAY. AT THIS TIME THERE IS SOME MODEL DIVERGENCE IN THE FINAL
SOLUTION FOR THIS SYSTEM. BEST CONSENSUS IS FOR THE LOW CENTER TO
MOVE ACROSS CENTRAL TO NRN AZ FRIDAY EVENING INTO SATURDAY. THE
ECMWF IS MORE AGGRESSIVE MOVING THE LOW OUT MORE QUICKLY EARLY
SATURDAY WHEREAS THE GFS LINGERS IT OVER NRN AZ FOR AN EXTRA DAY.
BOTTOM LINE FOR OUR CWA...ANOTHER SEASONABLY COOL SYSTEM WILL BE IN
FORCE THIS COMING WEEKEND WITH HIGH TEMPS POSSIBLY REACHING DOWN
INTO THE MID TO UPPER 70S AND AT LEAST A CHANCE FOR SOME SHOWERS.
LOOKING FURTHER OUT...YET ANOTHER SIMILAR LOW PRESSURE SYSTEM IS
PICKED UP ON MODELS AND MAY BRING ANOTHER SURGE OF COOLER TEMPS
EARLY NEXT WEEK.

 &&

.PREVIOUS DISCUSSION... UPPER LEVEL ANALYSIS SHOWS A RIDGE AXIS
ABOUT TO MOVE INTO ARIZONA WITH 500MB HEIGHTS INCREASING TO AROUND
576DM. THIS WILL BRING A GOOD AMOUNT OF WARMING TODAY WITH EXPECTED
AFTERNOON HIGHS IN THE MIDDLE 90S ACROSS THE DESERTS...OR JUST A
COUPLE DEGREES ABOVE NORMAL. TUESDAY INTO WEDNESDAY WILL SEE A
RETURN TO A BROAD TROUGHING PATTERN WITH SOUTHWEST UPPER LEVEL FLOW
OVER THE DESERT SOUTHWEST. THIS WILL HELP TO LOWER HEIGHTS SLIGHTLY
AND KNOCK AFTERNOON HIGHS DOWN A FEW DEGREES...OR RIGHT AROUND
SEASONAL NORMALS. MODEL GUIDANCE NOW SHOWS A WEAK SHORTWAVE TROUGH
QUICKLY COMING OFF THE PACIFIC THROUGH SOUTHERN BAJA INTO SOUTHEAST
ARIZONA TUESDAY EVENING. INDICATIONS ARE THAT THERE WILL BE
SUFFICIENT MID LEVEL MOISTURE...BUT LOW LEVEL MOISTURE WILL LIKELY
BE CONFINED TO NEW MEXICO. AS THE WAVE SWINGS THROUGH...SHOULD BE
ABLE TO MANAGE A FEW SHOWERS OVER THE HIGH TERRAIN OF EASTERN
ARIZONA...BUT GENERALLY EAST OF OUR CWA.

ATTENTION THEN TURNS TO ANOTHER SIGNIFICANT UPPER LOW COMING OUT OF
THE NORTHERN PACIFIC ON TUESDAY AND WEDNESDAY...QUICKLY DIVING
SOUTHWARD OFF THE WEST COAST ON THURSDAY. MODEL GUIDANCE OVERALL IS
STILL IN GOOD AGREEMENT WITH THE STRENGTH AND THE TRACK OF THE UPPER
LOW AS THE LOW CENTER APPROACHES THE CALIFORNIA COAST THURSDAY NIGHT.
FOR OUR REGION...WE WILL SEE LOWERING HEIGHTS ON THURSDAY AND
SLIGHTLY COOLER TEMPERATURES...BUT WE SHOULD STAY DRY THROUGH THE
DAYTIME HOURS. AVAILABLE MOISTURE WITH THIS SYSTEM IS STILL IN
QUESTION AND MODEL GUIDANCE CONTINUES TO FLUCTUATE A BIT...BUT IT
DOES LOOK LIKE THE BULK OF THE MOISTURE WILL GET DRAWN INTO OUR AREA
LATE THURSDAY NIGHT INTO FRIDAY. RAIN CHANCES BEGIN THURSDAY NIGHT
WITH HIGHEST POPS IN FAVORED UPSLOPE AREAS NORTH AND EAST OF PHOENIX.
AT THIS POINT...STORM DYNAMICS DON/T LOOK TO BE OVERLY
IMPRESSIVE...BUT WE SHOULD SEE A SIGNIFICANT JET MAX OVER THE
NORTHERN BAJA INTO SOUTHEAST ARIZONA DURING THE DAY FRIDAY ALLOWING
FOR BROAD VERTICAL ASCENT OVER MUCH OF ARIZONA.

BEST CHANCES FOR MEASURABLE RAINFALL LOOKS TO BE DURING THE DAYTIME
HOURS FRIDAY...BUT STILL A BIT HESITANT TO GO HIGHER THAN CHANCE POPS
DUE TO BEING FOUR DAYS OUT AND QUESTIONS WITH MOISTURE AVAILABILITY.
ALSO STILL TOO EARLY TO SPECULATE ON QPF AMOUNTS...BUT WITH FORECAST
PRECIPITABLE WATER VALUES APPROACHING THE 99TH PERCENTILE OF
CLIMATOLOGY...CAN/T RULE OUT THE POSSIBILITY OF HAVING SOME HEAVIER
LOCALIZED RAINFALL AMOUNTS. BY FRIDAY NIGHT INTO SATURDAY...SOME
MODEL DIFFERENCES COME INTO PLAY WITH THE EUROPEAN EJECTING THE LOW
MORE QUICKLY THAN THE GFS...BUT THERE WILL LIKELY STILL BE LINGERING
CHANCES FOR RAIN INTO SATURDAY FROM PHOENIX INTO THE HIGHER TERRAIN
AREAS TO THE NORTH AND EAST. AS WITH THIS PAST FRIDAY AND
SATURDAY...WE WILL AGAIN SEE A COUPLE DAYS OF SIGNIFICANTLY COOLER
TEMPERATURES AS HIGHS FOR THIS COMING FRIDAY AND SATURDAY WILL LIKELY
NOT MANAGE TO TOP 80 DEGREES.

AFTER THE UPPER LOW EXITS EASTWARD LATER SATURDAY...BROAD SCALE
TROUGHING SHOULD REMAIN AS ANOTHER WEAKER SHORTWAVE TROUGH IS
FORECAST TO DROP DOWN ALONG THE WEST COAST. THIS WILL LIKELY KEEP
TEMPERATURES SEVERAL DEGREES BELOW NORMAL INTO EARLY NEXT WEEK.

&&

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

NO SIGNIFICANT AVIATION IMPACTS THROUGH TUESDAY MORNING WITH ONLY
PERIODIC CIRRUS OVER THE REGION. CENTRAL ARIZONA AERODROMES MAY HOLD
A SOUTHERLY SFC WIND FOR SEVERAL HOURS THIS AFTERNOON BEFORE BRIEFLY
VEERING TO THE TYPICAL WESTERLY DIRECTION...THOUGH SPEEDS SHOULD
REMAIN BELOW 12KT. A FEW STRONGER WESTERLY GUSTS MAY BE POSSIBLE AT
KIPL THIS EVENING...THOUGH CONFIDENCE IS TOO LOW TO INCLUDE IN THIS
TAF PACKAGE.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
WEDNESDAY THROUGH SUNDAY...
FAIRLY SEASONABLE DRY WEATHER WILL PREVAIL WEDNESDAY AND THURSDAY
BEFORE MORE HUMID WEATHER AND ANOTHER UNSEASONABLY COOL STORM SYSTEM
AFFECTS THE DISTRICT FRIDAY THROUGH THE WEEKEND. BREEZY WINDS WILL
PRECEDE THIS SYSTEM THURSDAY...AND COULD COMBINE WITH LOWER HUMIDITY
VALUES TO APPROACH CRITICAL FIRE WEATHER CONDITIONS. OTHERWISE AS
THE SYSTEM PUSHES THROUGH THE REGION OVER THE WEEKEND...TEMPERATURES
WILL DROP AND UNSEASONABLY HIGH HUMIDITY VALUES WILL PERSIST.
CHANCES FOR WETTING RAIN...ESPECIALLY ACROSS THE HIGHER TERRAIN OF
CENTRAL ARIZONA...WILL ALSO INCREASE FRIDAY AND SATURDAY.

&&

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

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DISCUSSION...WATERS/KUHLMAN
AVIATION...MO
FIRE WEATHER...MO/INIGUEZ