Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 290531 AAA
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1030 PM MST THU APR 28 2016

...UPDATED AVIATION DISCUSSION...

.SYNOPSIS...
ANOTHER AREA OF LOW PRESSURE WILL CONTINUE TO MOVE ACROSS THE AREA
THIS EVENING WITH BREEZY CONDITIONS AND A SLIGHT CHANCE OF SHOWERS
AND THUNDERSTORMS...MOST SIGNIFICANT OVER THE HIGHER TERRAIN NORTH
AND EAST OF PHOENIX. MORE SEASONABLY WARM WEATHER WILL RETURN FOR
SATURDAY BEFORE YET ANOTHER WEATHER DISTURBANCE IMPACTS THE REGION
SATURDAY NIGHT INTO SUNDAY. HIGH PRESSURE WILL RETURN BY THE MIDDLE
OF NEXT WEEK...SUPPORTING WARMING TEMPERATURES AND CLEARING SKIES.

&&

.DISCUSSION...

TODAY TURNED OUT TO BE A RATHER COOL...AND BREEZY DAY ACROSS OUR
CWA...WITH HIGH TEMPERATURES ENDING UP WELL BELOW NORMAL FOR THIS
TIME OF YEAR...WITH PHOENIX SKY HARBOR ONLY SEEING A HIGH OF 76...13
DEGREES BELOW THE NORMAL FOR THIS DATE. ALTHOUGH THE UPPER LOW THAT
IS NOW AFFECTING OUR REGION DID BRING US THESE EXPECTED COOL
TEMPS...RAINFALL COVERAGE HAS BEEN A BIT LESS THAN FORECAST...WITH
JUST A FEW SPOTS NEAR THE NORTHERN EDGE OF OUR CWA SEEING MEASURABLE
RAINFALL...AND JUST A FEW HUNDREDTHS OF AN INCH AT THAT. GIVEN THE
FACT THAT THE LATEST RADAR IMAGERY AT THIS HOUR IS NOW SHOWING
SHOWING ACTIVITY NOW WELL OFF TO OUR NORTH AND EAST...AND THE LATEST
HRRR HIGH-RES MODEL RUN IS KEEPING RAINFALL WELL OUTSIDE OF OUR
CWA...HAVE REDUCED POPS THROUGH THE REST OF THE NIGHT INTO THE
SINGLE DIGITS ACROSS OUR LOWER ELEVATIONS. TOMORROW STILL APPEARS
THAT IT WILL BE A DRY DAY ACROSS MOST OF OUR CWA UNDER NORTHWESTERLY
FLOW ALOFT...EXCEPT FOR A SLIGHT CHANCE FOR A SHOWER OVER THE HIGH
ELEVATIONS OF SOUTHERN GILA COUNTY. OUTSIDE OF THESE ADJUSTMENTS AND
SOME MINOR ADJUSTMENTS TO THE HOURLY TEMP/DEWPOINT/WIND
GRIDS...INHERITED FORECASTS ARE LOOKING GOOD...AND NO FURTHER
UPDATES ARE PLANNED.

&&

.PREVIOUS DISCUSSION...
UNSETTLED WEATHER PATTERN CHARACTERIZED BY A LONG SERIES OF
TRANSITORY UPPER LEVEL LOW PRESSURE SYSTEMS CONTINUES...AS YET
ANOTHER UPPER LOW IS IN THE PROCESS OF SHIFTING EAST ACROSS THE
DESERT SOUTHWEST THIS AFTERNOON...BRINGING BREEZY AND COOLER
CONDITIONS ALONG WITH ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS. EARLY THIS AFTERNOON THE MAIN LOW CENTER WAS MOVING
ACROSS NORTH CENTRAL ARIZONA...WHILE A VORT SPOKE ROTATING AROUND
THE LOW WAS WORKING ACROSS THE LOWER DESERTS. AS ADVERTISED
PREVIOUSLY MOISTURE HAS BEEN LIMITED WITH THIS SYSTEM...AND SINCE
THE UPPER JET HAS MOVED SOUTH TO NEAR THE MEXICAN BORDER...THE
DYNAMICS HAVE WEAKENED AND THERMODYNAMICS ARE PLAYING A BIGGER ROLE
IN HELPING GENERATE INSTABILITY SHOWERS. RADAR AT 2 PM SHOWED MOST
OF THE CONVECTION ACROSS THE NORTHERN HALF OF THE STATE WITH MAINLY
ISOLATED SHOWERS OVER THE LOWER DESERTS...MOST NUMEROUS OVER HIGHER
ELEVATIONS NORTH AND EAST OF PHOENIX. BREEZY TO WINDY CONDITIONS
WERE ALSO PRESENT OVER THE LOWER DESERTS...WITH THE STRONGEST WINDS
PERSISTING OVER IMPERIAL COUNTY. EARLIER IN THE MORNING THE WINDS IN
THE IMPERIAL VALLEY EXCEEDED ADVISORY CRITERIA AND A WIND ADVISORY
WAS ISSUED. SINCE NOON THE WINDS GRADUALLY TAPERED OFF AND WERE
BELOW CRITERIA BUT THEY WERE STILL OCCASIONALLY GUSTING OVER 30 MPH
AT EL CENTRO AND IMPERIAL. OTHERWISE...AFTERNOON TEMPS WERE RUNNING
5-10 DEGREES COOLER THAN 24 HOURS AGO AND MOST READINGS WERE IN THE
LOW TO MID 70S. WE WILL CERTAINLY TOP OUT 10 DEGREES OR MORE BELOW
SEASONAL NORMALS OVER MUCH OF THE LOWER DESERT TODAY.

FOR THE REST OF THE AFTERNOON AND THROUGH THE EVENING...AS THE LOW
AND ASSOCIATED VORT LOBE PUSH EAST...AND AS THE MAIN LOW CENTER
MOVES INTO THE FOUR CORNERS AREA...A CLEARING AND DRYING TREND FROM
THE WEST WILL DEVELOP AS MORE SUBSIDENT AIR WORKS IN FROM THE WEST.
THERE WILL BE A LINGERING SLIGHT CHANCE OF SHOWERS THROUGH THE
EVENING FROM PHOENIX NORTH AND EAST WITH THE BEST CHANCES ACROSS
HIGHER TERRAIN OF SOUTHERN GILA COUNTY. AFTER MIDNIGHT TONIGHT POPS
SHOULD BE JUST SINGLE DIGITS FROM THE GREATER PHOENIX AREA WESTWARD
UNDER PARTLY CLOUDY SKIES. THE DRY SUBSIDENT NORTHWEST FLOW BEHIND
THE EXITING LOW WILL CONTINUE FRIDAY...GIVING CLEARING SKIES FROM
THE WEST ALONG WITH WARMING TEMPERATURES. HIGHS IN THE CENTRAL
DESERTS WILL RISE INTO THE LOWER 80S...BUT REMAIN BELOW NORMAL WHILE
THE WESTERN DESERTS CLIMB CLOSER TO NORMAL AND INTO THE MID TO UPPER
80S. THERE WILL BE A LINGERING SLIGHT CHANCE OF SHOWERS AND MAYBE AN
AFTERNOON THUNDERSTORM ACROSS SOUTHERN GILA COUNTY HOWEVER AS A BIT
OF WRAP AROUND MOISTURE WORKS THROUGH THE AREA AND COOLER AIR ALOFT
PERSISTS CREATING SLIGHT INSTABILITY.

AND YET ANOTHER PACIFIC LOW WILL FOLLOW HOT ON THE HEELS OF TODAYS
SYSTEM...MOVING ACROSS THE DESERT SOUTHWEST IN A SIMILAR FASHION
THIS WEEKEND. THE LOW WILL BEHAVE MUCH LIKE TODAYS LOW...WITH MOST
OF THE MOISTURE AND PRECIPITATION CONFINED TO THE NORTHERN HALF OF
THE STATE KEEPING THE MOST SIGNIFICANT PRECIP IN OUR AREA CONFINED
TO THE NORTHERN DESERTS AND HIGHER TERRAIN NORTH AND EAST OF
PHOENIX. IT WILL BE BREEZY ONCE AGAIN BUT MOST LIKELY THE WINDS WILL
STAY BELOW WIND ADVISORY THRESHOLDS. AFTER A MODEST WARMUP SATURDAY
THAT WILL NOT EVEN REACH SEASONAL NORMALS...COOLING WILL FOLLOW ONCE
AGAIN ON SUNDAY ALTHOUGH BEST PERFORMING GRIDDED GUIDANCE DOES NOT COOL
THE DESERTS DOWN AS LOW AS TODAYS READINGS...MOST DESERTS WILL STAY
IN THE LOW TO MID 80S. ENSEMBLE GUIDANCE AS WELL AS OPERATIONAL RUNS
FROM THE GFS AND ECMWF ARE PRETTY CONSISTENT WITH THE HANDLING OF
THIS NEXT LOW OVER THE WEEKEND AND CONFIDENCE IN THE PRECIP...WIND
AND TEMPERATURE FORECASTS IS RELATIVELY HIGH.

UPPER LOW SHIFTS OFF TO THE NORTHEAST MONDAY AS HIGH PRESSURE ALOFT
BUILDS IN ALONG THE SRN CA COAST AND DRIER SUBSIDENT NORTHWEST FLOW
ALOFT OVERSPREAD THE LOWER DESERTS. EXPECT HIGHS MONDAY TO RISE INTO
THE MID 80S TO LOW 90S UNDER SUNNY SKIES. SOME RESIDUAL MOISTURE
WILL REMAIN OVER THE HIGHER TERRAIN EAST OF PHOENIX AND AN ISOLATED
INSTABILITY SHOWER OR THUNDERSTORM IS POSSIBLE MAINLY ACROSS AREAS
EAST OF GLOBE.

TUESDAY THROUGH LATE NEXT WEEK...
DETERMINISTIC AND ENSEMBLE MODEL AGREEMENT IS FAIRLY GOOD FOR THE
MEDIUM TO EXTENDED RANGE PERIOD WITH HIGH AMPLITUDE RIDGING
OVERTAKING MUCH OF THE INTERMOUNTAIN WEST/ROCKIES EARLY TUESDAY AND
LINGERING THROUGH THURSDAY. INCREASING THICKNESSES AND RECOVERING
ATMO THERMAL PROFILE WILL ALLOW FOR NEAR TO ABOVE AVERAGE
TEMPERATURES WITH MANY LOWER DESERT SITES RETURNING TO THE 90S BY
TUESDAY. 500MB HEIGHTS HEAD INTO THE LOW 580 DAM RANGE EASILY PEAKING
SURFACE TEMPERATURES INTO THE MID-90S BY THE MIDDLE PORTION OF THE
WEEK. SOME OF THE WARMEST DESERT LOCALES...SUCH AS TACNA AND EL
CENTRO...COULD FLIRT WITH THE TRIPLE-DIGIT READINGS...BUT THE CLIMATE
STATIONS OF PHOENIX AND YUMA STILL ARE IN THE CLEAR WITH THE LATEST
GUIDANCE. LATE WEDNESDAY INTO THURSDAY THE UPPER RIDGE WILL CLEAR
EAST OF THE AREA AS A PACIFIC TROUGH APPROACHES THE WEST COAST. MORE
OCEANIC TRACK AND SOUTHERLY REACHES OF THIS TROUGH COULD SPELL
INCREASING HUMIDITIES INTO THE REGION ALONG WITH A COOLING TREND FOR
TEMPERATURES FOR THE WEEKEND AFTER NEXT.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...

AS THE UPPER LOW THAT BROUGHT THE GUSTY WESTERLY WINDS AND SOME
CLOUDINESS TO THE PHX AREA TERMINALS TODAY STARTS TO MOVE OFF TO THE
NORTH AND EAST...SFC PRESSURE GRADIENTS WILL BEGIN TO
RELAX...ALLOWING WINDS TO REVERT TO A MORE TYPICAL EASTERLY
DIRECTION LATE TONIGHT AND EARLY FRIDAY. WESTERLY WINDS ARE THEN
EXPECTED TO REDEVELOP DURING THE LATE MORNING HOURS ON FRIDAY...THEN
INCREASE INTO THE 12-15 KT RANGE...WITH GUSTS AS HIGH AS 22 KTS ON
FRIDAY AFTERNOON/EARLY EVENING...BEFORE DIMINISHING LATER FRIDAY
EVENING. DRY CONDITIONS TO PREVAIL THROUGH THE TAF PERIOD...WITH FEW-
SCT MID-HIGH CLOUD LAYERS PERSISTING THROUGH FRIDAY.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

WESTERLY WINDS TO PREVAIL THROUGH THE TAF PERIOD...WITH SPEEDS
DIMINISHING LATER TONIGHT AND EARLY FRIDAY BEFORE INCREASING A BIT
ON FRIDAY AFTERNOON. SKIES TO REMAIN MAINLY CLEAR THROUGH THE TAF
PERIOD AT BOTH TAF SITES.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...
AS A DRIER LOW PRESSURE SYSTEM MOVES THROUGH SUNDAY AND EARLY MONDAY
EXPECT SIGNIFICANTLY LOWER THAN NORMAL HIGH TEMPERATURES ON SUNDAY
...IN THE LOW 80S...TO INCREASE TO SLIGHTLY BELOW NORMAL ON TUESDAY
AND THEN TO TO NEAR NORMAL ON WEDNESDAY WHEN HIGH PRESSURE AND DRIER
AIR BUILDS IN. IN ADDITION...THERE WILL BE NO CHANCE OF WETTING RAIN
WITH SUNDAY`S SYSTEM. MINIMUM RELATIVE HUMIDITIES ON SUNDAY WILL BE
DRY IN THE UPPER TEENS TO MID 20 PERCENT RANGE AND WILL BECOME VERY
DRY BY TUESDAY AND WEDNESDAY IN THE MID SINGLE DIGITS TO LOWER
TEENS. OVERNIGHT RECOVERIES ARE EXPECTED TO BE GOOD TO EXCELLENT ON
SUNDAY NIGHT...FAIR TO GOOD ON MONDAY NIGHT AND FAIR BY TUESDAY
NIGHT. WINDS WILL BE BE LIGHT EXCEPT FOR SOME BREEZY CONDITIONS
SUNDAY AFTERNOON IN THE TONTO FOOTHILLS AND SOUTHERN GILA COUNTY AS
WELL AS ON WEDNESDAY AFTERNOON IN SW AZ...THE LOWER COLORADO RIVER
VALLEY AND SE CA.

&&

.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...PERCHA/CB/NOLTE
AVIATION...PERCHA
FIRE WEATHER...SAWTELLE



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