Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 061224
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
524 AM MST FRI MAY 6 2016

.UPDATE...UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS.

&&

.SYNOPSIS...
A LARGE PACIFIC LOW PRESSURE SYSTEM WILL MOVE ACROSS THE DESERT
SOUTHWEST OVER THE NEXT FEW DAYS. THIS SYSTEM WILL BRING A GOOD
CHANCE FOR SHOWERS...PLUS POTENTIAL FOR THUNDERSTORMS...ALONG WITH
MUCH COOLER CONDITIONS. BEST CHANCES FOR RAIN WILL BE TODAY INTO
SATURDAY. THE LOW PRESSURE SYSTEM WILL BEGIN TO MOVE EAST
SUNDAY...FOLLOWED BY DRY AND MUCH WARMER WEATHER NEXT WEEK.

&&

.DISCUSSION...
TODAY THROUGH SUNDAY...
THE LOW PRESSURE SYSTEM WHICH BROUGHT THE WINDS AND THE BEGINNING OF
A COOLING TREND IS CENTERED JUST OF SANTA BARBARA EARLY THIS MORNING.
WATER VAPOR IMAGERY SHOWS MULTIPLE VORT LOBES WITHIN THE SYSTEM. AT
THE SURFACE... ONE OF WHICH IS MOVING ASHORE INTO FAR SOUTHERN
CALIFORNIA. A SURFACE LOW REMAINS CENTERED OVER THE MOHAVE DESERT.
MODELS CONTINUE TO DEPICT THE UPPER LOW/UPPER TROUGH TRACKING
EASTWARD TODAY AND SATURDAY THEN BEGIN EXITING SUNDAY. IN THE
PROCESS...THERE WILL BE A SERIES OF VORT LOBES MOVING THROUGH FOR
SOME DYNAMICAL ASCENT AT TIMES PLUS COLDER AIR ALOFT FOR SOME
DESTABILIZATION. THERE MAY ALSO BE SOME ADDED DYNAMICAL ASCENT TODAY
ASSOCIATED WITH THE LEFT EXIT REGION OF THE JET. AS THE SYSTEM TRACKS
EAST WITH TIME THE JET AXIS MOVES FURTHER AWAY.

ONE OF THE AFOREMENTIONED VORT LOBES IS MOVING ASHORE INTO FAR
SOUTHERN CALIFORNIA. THIS FEATURE IS NOT INITIALIZED WELL BY THE
LATEST MODELS. BUT IR IMAGERY SHOWS COLD CLOUD TOPS AND THERE IS EVEN
SOME ISOLATED LIGHTNING BEING DETECTED WITHIN THE ASSOCIATED
CLOUDINESS. THIS FEATURE WILL AFFECT MAINLY WESTERN PORTIONS OF THE
FORECAST AREA TODAY BUT THERE WILL ALSO BE SOME STEEPENING LAPSE
RATES EVERYWHERE AND THUS AN UPRAMPING OF POPS TODAY. HI-RES MODELS
ARE A MIXED BAG AS TO THE ONSET OF SHOWERS OVER SOUTH-CENTRAL ARIZONA
TODAY. SOME OF THEM INDICATE A BAND OF SHOWERS DEVELOPING THIS
MORNING...POSSIBLY DUE TO THE SURFACE TROUGH AND ASSOCIATED LOWER
LEVEL CONVERGENCE. THERE IS ALSO SOME UPPER LEVEL
DIFFLUENCE/DIVERGENCE THERE AS WELL. THE MAIN THEME OF THE MODELS IN
TERMS OF PRECIP POTENTIAL IS THAT CHANCES INCREASE FROM WEST TO EAST
AS THE DAY WEARS ON AND PEAKS EAST OF THE LOWER COLORADO RIVER VALLEY
TONIGHT AS A VORT LOBE MOVES THROUGH. POPS TREND DOWN DOWN SATURDAY
BEHIND THE EXITING LOBE BUT DONT GO AWAY ENTIRELY DUE TO LINGERING
MOISTURE AND ANOTHER VORT LOBE...THOUGH THAT ONE TRACKS MOSTLY SOUTH.
YET ANOTHER ONE COMES THROUGH SUNDAY BUT ON THE BACK SIDE OF THE LOW
AS THE SYSTEM IS SHIFTING NORTHEASTWARD. PEAK PRECIPITABLE WATER
VALUES ARE NEAR 1 INCH AT THE COAST BUT WITH RAIN SHADOWING WE WILL
SEE LESS AND THUS NOT LOOKING FOR A BIG PRECIP EVENT...BUT CONSIDERING
WE ARE GETTING INTO THE VERY DRIEST TIME OF YEAR...IT WILL BE
NOTABLE. THERE WILL ALSO BE A THREAT OF THUNDERSTORMS. WHILE CAPE IS
LOOKING MODEST...JUST ENOUGH TO UPGRADE MENTION TO CHANCE IN SOME
AREAS...SLIGHT CHANCE ELSEWHERE.

AS FOR TEMPS...CONTINUED COLD AIR ADVECTION WILL MAKE FOR MUCH COOLER
CONDITIONS TODAY OVER SOUTH-CENTRAL ARIZONA...AS MUCH AS 20
DEGREES. THERE WILL BE LESS COOLING FURTHER WEST BECAUSE OF ALREADY
HAVING COOLED INTO THE 80S YESTERDAY. THUS...HIGHS ON THE LOW DESERTS
WILL BE IN THE 70S FRIDAY AND SATURDAY THEN WARMING AT LEAST A FEW
DEGREES ON SUNDAY.

MONDAY THROUGH THURSDAY...
PACIFIC RIDGING SLOWLY BUILDS INTO THE WESTERN STATES DURING THE NEXT
WORKWEEK FOR A WARMING TREND. EXPECT DESERTS TO FLIRT WITH 100 AGAIN
BY THURSDAY.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL... FLOW WILL
VEER THROUGHOUT THE DAY AHEAD OF A LOW PRESSURE SYSTEM. HOWEVER...A
PERIOD OF 10-15 KT CROSS-WINDS IS LIKELY THIS MORNING AT KPHX.
BREEZY SOUTHWESTERLY WINDS ARE ALSO ANTICIPATED THIS
AFTERNOON...THOUGH THEY WILL BE WEAKER THAN THOSE OBSERVED THURSDAY
WITH GUSTS GENERALLY AROUND 25 KT. SCATTERED SHOWERS ARE EXPECTED TO
MOVE INTO THE PHOENIX AREA THIS EVENING...BEFORE DISSIPATING BEFORE
MIDNIGHT. OTHERWISE...CLOUD BASES WILL GENERALLY HOVER BETWEEN 5K
AND 8K FT...PERHAPS BECOMING BKN TOWARDS SATURDAY MORNING.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
BREEZY SOUTH AND SOUTHWESTERLY FLOW WILL PERSIST AHEAD OF A PACIFIC
LOW PRESSURE SYSTEM. SCATTERED SHOWERS ARE ALSO EXPECTED TO DEVELOP
LATER THIS MORNING AND EARLY THIS AFTERNOON AT KIPL/KBLH. A BRIEF
THUNDERSTORM IS ALSO POSSIBLE...THOUGH THE POTENTIAL FOR HAZARDS
SUCH AS GUSTY WINDS AND BLOWING DUST IS LOW. IMPROVING CONDITIONS
ARE LIKELY BY 02Z SATURDAY AS THE ACTIVITY SHIFTS TO THE EAST.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SUNDAY THROUGH THURSDAY... THE SLOW-MOVING WEATHER SYSTEM WILL
WEAKEN AND MOVE NORTHEASTWARD OUT OF THE REGION SUNDAY.
NEVERTHELESS...A FEW SHOWERS WILL BE POSSIBLE SUNDAY...MAINLY NORTH
AND EAST OF PHOENIX. THEREAFTER...A WARMING AND DRYING TREND WILL
TAKE PLACE AS HIGH PRESSURE RETURNS TO THE DESERT SOUTHWEST. ABOVE
NORMAL TEMPERATURES ARE LIKELY BY TUESDAY OR WEDNESDAY...PERHAPS
REACHING THE 100 DEGREE MARK AGAIN IN THE LOWER DESERTS.
DESPITE THE LOW RHS...FIRE DANGER WILL GENERALLY REMAIN LOW THROUGH
THE WEEK WITH LIGHT WINDS AND RELATIVELY MOIST FUELS.

&&

.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...AJ
AVIATION...HIRSCH
FIRE WEATHER...HIRSCH


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