Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 030330
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
830 PM MST MON MAY 2 2016

.SYNOPSIS...
TEMPERATURES WILL QUICKLY WARM TUESDAY AND PEAK WEDNESDAY UNDER HIGH
PRESSURE. SOME LOWER DESERTS WILL APPROACH TRIPLE DIGITS. THE HEAT
WILL NOT LAST LONG AS ANOTHER STORM SYSTEM ROLLS IN FROM THE
PACIFIC. WINDS WILL INCREASE WEDNESDAY AND BE STRONGEST THURSDAY
LEADING TO AREAS OF BLOWING DUST. FRIDAY INTO THE WEEKEND WILL
FEATURE BELOW NORMAL TEMPERATURES...VARIOUS CLOUD COVER...AND MODEST
CHANCES FOR RAIN.

&&

.DISCUSSION...
WEAK UPPER LOW LINGERED OVER FAR NORTHWEST ARIZONA EARLY THIS
EVENING...AND IT WAS EASILY SEEN IN THE 00Z PLOT DATA WHICH DEPICTED
MODEST CYCLONIC SHEAR TO THE SOUTH OF THE LOW AND ACROSS THE
SOUTHERN DESERTS. DESPITE THE CYCLONIC NATURE OF THE FLOW...MOISTURE
OVER THE SOUTHERN DESERTS WAS LIMITED...CONFINED TO A THIN LAYER
NEAR 700MB...AND THE STABILITY ACROSS SOUTHERN ARIZONA WAS MUCH
GREATER THAN OVER NORTHERN ARIZONA. 00Z FLG SOUNDING SHOWED MODEST
CAPE AND NEGATIVE LIFTED INDICES...WHILE THE TUS RAOB WAS QUITE
STABLE WITH LI VALUES CLOSER TO PLUS 4. AS SUCH...CONVECTION THIS
AFTERNOON AND EARLY EVENING WAS CONFINED TO THE HIGHER TERRAIN OF
NORTHERN ARIZONA...WELL TO THE NORTH OF PHOENIX...AND THE SOUTHERN
DESERTS MERELY SAW A BIT OF HIGH BASED CUMULUS CLOUDS. AS OF 8 PM
MOST OF THOSE CLOUDS HAD DISSIPATED FOLLOWING SUNSET AND LACK OF
HEATING. FOR THE REST OF TONIGHT...AS THIS UPPER LOW CONTINUES TO
WEAKEN AND SHIFT NORTH...WE WILL SEE GENERALLY CLEAR SKIES ACROSS
THE SOUTHERN DESERTS ALONG WITH LIGHT AND MOSTLY DIURNAL WINDS.
FORECASTS LOOK TO BE IN GOOD SHAPE AND NO UPDATES ARE NEEDED AT THIS
TIME.

.PREVIOUS DISCUSSION...
CONVECTION HAS FLARED UP THIS AFTERNOON IN THE AREAS PREVIOUSLY
EXPECTED...JUST NORTH OF OUR FORECAST AREA. THIS WAS IN RESPONSE TO
THE UPPER LEVEL LOW NOW ENTERING NW ARIZONA. THIS SYSTEM IS WELL
HANDLED BY THE VARIOUS MODELING SYSTEMS AND WILL MOVE EAST TONIGHT
AND SHEAR OUT OVER NEW MEXICO TOMORROW AS THE HIGH AMPLITUDE
ANTICYCLONE CURRENTLY OVER WESTERN MONTANA ELONGATES AND ENCOMPASSES
THE ENTIRE WEST.

WARM UP CONTINUES TUESDAY AND INTO WEDNESDAY WHEN WE WILL SEE PEAK
TEMPERATURES. CURRENT FORECAST CONTINUES WITH 99 FOR PHOENIX THOUGH
GIVEN OUR TYPICAL FORECAST ERROR OF 2 DEGREES ON DAY 3 THERE IS
CERTAINLY A NON-ZERO CHANCE OF HITTING 100. THIS WOULD BE A BIT LATER
THAN THE 1981-2010 AVERAGE OF MAY 2. YUMA WILL ALSO BE CLOSE AT
FORECAST OF 98.

WINDS WILL PICK-UP WEDNESDAY AHEAD OF THE NEXT SYSTEM. CONFIDENCE ON
THE OVERALL EVOLUTION OF THE INCOMING CUT-OFF LOW IS FAIRLY HIGH AS
IT HAS BEEN FORECAST FOR MANY DAYS AT THIS POINT. SOUTH/SOUTHWEST
WINDS ON WEDNESDAY WILL LIKELY CAUSE SOME ISSUES INCLUDING BLOWING
DUST. WINDS WILL BE STRONGER ON THURSDAY AND THIS IS THE DAY WE MAY
EVENTUALLY NEED A WI.Y AND BD.Y. GEFS-BASED EXTREME FORECAST INDEX IS
HIGHLIGHTING THE PRE-FRONTAL WINDS THURSDAY TO BE IN THE 95TH
PERCENTILE WHICH HISTORICALLY CORRESPONDS TO ENOUGH WIND TO CAUSE
IMPACTS.

THE OTHER CONCERN AS THIS SYSTEM COMES IN IS WITH THE FIRE WEATHER
DANGER. IT DOES LOOK LIKE WE WILL HIT WIND AND HUMIDITY TRIGGERS FOR
A RF.W BUT FUELS ARE QUESTIONABLE AT THIS POINT GIVEN CURRENT
GREENNESS AND RECENT RAINS. WILL HOLD OFF ON ANY FW.A FOR OUR AREA
BUT IT IS HIGHLIGHTED IN THE FIRE WEATHER FORECAST.

EVENTUALLY THE SPECTER OF RAIN WILL COME WITH THE SYSTEM BUT NOT
UNTIL FRIDAY WHEN BETTER ISENTROPIC LIFT/MOISTURE FLUX/DYNAMICAL
COOLING/PVA ARRIVE. GEFS-BASED CALIBRATED POPS ARE SHOWING A BROAD
20-30 PERCENT CHANCE FOR SOME RAIN FRIDAY INTO SATURDAY THUS
INCREASED POPS A BIT. OVERALL DOESN/T APPEAR TO BE A WASHOUT EVENT BY
ANY MEANS. TEMPERATURES WILL ALSO COOL SIGNIFICANTLY...ON THE ORDER
OF 20 DEGREES FROM WEDNESDAY TO FRIDAY. HOW THE WEEKEND PLAYS OUT IS
STILL UP IN THE AIR AS MODELS NOTORIOUSLY HAVE A DIFFICULT TIME
RESOLVING THE MIGRATION OF CLOSED LOWS IN THE SOUTHWEST. OVERALL IT
WILL BE COOLER AND GENERALLY CLOUDY...RAIN CHANCES WILL LIKELY CHANGE
AS SPECIFICS ON INDIVIDUAL VORT LOBES COME INTO FOCUS IN THE DAYS
AHEAD.

&&

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

AS HIGH PRESSURE ALOFT SLOWLY BUILDS INTO THE AREA FROM THE WEST
TONIGHT...WE SHOULD SEE LIGHT AND MOSTLY DIURNAL WINDS UNDER
GENERALLY CLEAR SKIES. WE MAY SEE A FEW HIGH BASED CUMULUS FORM
AGAIN IN THE AFTERNOON ON TUESDAY BUT NOTHING OF CONSEQUENCE FOR
AVIATION. AGAIN...WINDS WILL BE LIGHT VARIABLE OR LIGHT DIURNAL NEXT
24 HOURS...ESPECIALLY OVER THE CENTRAL DESERTS AND IN THE GREATER
PHOENIX AREA. MOST WINDS WILL BE AOA 10KT AT THE TAF SITES THROUGH
TUESDAY AFTERNOON AT LEAST. NO AVIATION IMPACTS EXPECTED AT ANY
TERMINAL FOR AT LEAST THE NEXT 24 HOURS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
WEDNESDAY THROUGH SUNDAY...
WINDS WILL INCREASE WEDNESDAY AND ONCE AGAIN THURSDAY AS A STORM
SYSTEM MOVES INTO THE SOUTHWEST. THERE WILL LIKELY BE A SEVERAL HOUR
WINDOW THURSDAY AFTERNOON WHERE WINDS AND HUMIDITY VALUES HIT
CRITICAL THRESHOLDS ACROSS PORTIONS OF MARICOPA...PINAL...AND GILA
COUNTIES. QUESTIONS REMAIN ON FUEL LEVELS DUE TO RECENT RAINS AND
CURRENT GREEN LEVELS. MUCH COOLER TEMPERATURES...LESS WIND...AND
HIGHER HUMIDITY LEVELS ARE EXPECTED FRIDAY THROUGH THE WEEKEND ALONG
WITH THE POSSIBILITY OF WETTING RAINS.

&&

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION IS NOT EXPECTED.

&&

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

$$

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

DISCUSSION...CB
PREVIOUS DISCUSSION...INIGUEZ
AVIATION...CB
FIRE WEATHER...INIGUEZ



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