Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 161017
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
317 AM MST WED APR 16 2014

.SYNOPSIS...
DRY WESTERLY FLOW ALOFT WILL PERSIST THROUGH MUCH OF THE WORK WEEK
WITH HIGH TEMPERATURES WARMING INTO THE 90S OVER THE WARMER DESERTS.
A WEAK UPPER LEVEL LOW APPROACHING FROM THE EAST PACIFIC WILL SPREAD
INCREASING MOISTURE AND CLOUDS INTO THE AREA FRIDAY INTO THE
EARLY WEEKEND...LEADING TO A SLIGHT CHANCE OF SHOWERS ACROSS SOUTH
CENTRAL ARIZONA AND THE POSSIBILITY FOR SLIGHTLY COOLER DAYTIME
TEMPERATURES. THE COOL DOWN WILL BE SHORT LIVED...AS HIGH PRESSURE
QUICKLY RETURNS THROUGH THE LATE WEEKEND.

&&

.DISCUSSION...
MORNING WATER VAPOR IMAGERY INDICATES MOSTLY CLEAR SKIES ACROSS MUCH
OF ARIZONA AND SOUTHERN CALIFORNIA. SUBTROPICAL JET AND ASSOCIATED
HIGH CLOUD BANDS CONTINUE TO GRADUALLY SINK SOUTHWARD ACROSS NORTHERN
MEXICO AS SHORTWAVE ENERGY DROPS INTO THE GREAT BASIN. DRY NORTHWEST
FLOW WILL CONTINUE FOR THE FORECAST ZONES TODAY...WITH RIDGING
BUILDING TO OUR WEST AND THE SHORTWAVE IMPULSE BRUSHING BY THE FOUR
CORNERS. NEIGHBORING RAOBS SHOWED ADDITIONAL WARMING THROUGH THE
LOWER ATMO LAYERS WHICH SUPPORTED LOW TO MID 90 DEGREE READINGS
TUESDAY. FORECASTED 850MB TEMPS EXPECTED IN THE 20C/21C RANGE BY
THIS AFTERNOON...ADDING A FEW DEGREES ON TO OBSERVED HIGH VALUES
FROM TUESDAY.

THURSDAY THROUGH SATURDAY...
STORM SYSTEM OFF THE PACIFIC WILL MOVE INTO THE AREA...WHILE
TROUGHING ALSO EXPANDS INTO THE WESTERN CONUS. WARM DAYTIME
TEMPERATURES IN THE 90S WILL LINGER INTO THURSDAY AS FLOW BECOMES
SOUTH TO SOUTHWESTERLY AND ADDITIONAL WAA OCCURS UNDER VERY BRIEF
SHORTWAVE RIDGING. THE SYSTEM WILL MOVE ONSHORE THURSDAY NIGHT AND
SLOWLY MOVE THROUGH THE REGION FRIDAY INTO SATURDAY. THE SYSTEM WAS
NEVER PRESENTED AS OVERLY WET OR STRONG/WELL-ORGANIZED...BUT FORECAST
SOUNDINGS AND PWAT PLOTS HAVE INCREASED OVER THE PAST FEW RUNS. THE
16/00 AND 16/06Z NAM MOISTURE FIELDS ARE SOME OF THE MOST
AGGRESSIVE...AND ALSO THE BEST INITIALIZED FROM LAST
EVENING...ATTEMPTING TO DRAW 1 INCH PWAT VALUES FROM OFF THE PACIFIC
AND INTO ARIZONA BY FRIDAY MIDDAY. GFS/SREF/EC SOLNS ARE MORE
CONSERVATIVE...BUT STILL DRAW NEAR THREE QUARTER INCH VALUES INTO THE
AREA FRIDAY. THE BULK OF ANY INCREASE MOISTURE ON ALL THE FORECAST
SOUNDINGS LIE AT 700MB AND ABOVE...WITH INVERTED V TRACES DOWN TO THE
SURFACE.

ONLY MINOR ADJUSTMENTS WERE MADE TO THE POP GRIDS...WHICH ALREADY HAD
SLIGHT CHANCES FOR THE FOOTHILLS/HIGHER TERRAIN NORTH AND EAST OF
PHOENIX. SLIGHT CHANCES WERE ADDED TO THE FOOTHILL TERRAIN OF LA PAZ
COUNTY AND NORTHERN MARICOPA FOR FRIDAY GIVEN THE MODEL CONSENSUS AND
SLIGHT BOOST IN MOISTURE FIELDS. WHILE SIGNIFICANT RAINFALL IS NOT
EXPECTED BY ANY MEANS...LIGHT SPRINKLES AND VIRGA ARE MORE LIKELY
FROM NORTHERN LA PAZ/MARICOPA COUNTY EASTWARD. HIGH BASED SHOWERS AND
DRY SUB-CLOUD LAYERS COULD ENHANCE WIND GUSTS AND ANY OUTFLOWS FROM
SHOWERS/STORMS FOR FRIDAY AND SATURDAY.

CLOUDS WILL INCREASE FROM THE WEST BEGINNING LATE THURSDAY...WITH
MOSTLY CLOUDY TO OVERCAST SKIES EXPECTED FRIDAY. DAYTIME TEMPERATURES
FRIDAY WILL SEE SEVERAL DEGREES OF COOLING...BUT ONLY BACK TOWARDS
MID APRIL NORMALS...MID TO UPPER 80S AND A FEW ISOLATED 90 DEGREE
POCKETS. CLOUDS WILL CLEAR OUT TO THE EAST SATURDAY...ALONG WITH THE
MAIN BODY OF TROUGH. FRIDAY`S COOL DOWN WILL BE SHORT LIVED AS UPPER
80S/LOW 90S RETURN UNDER HIGH PRESSURE ALOFT FOR THE WEEKEND.

NEXT WEEK...
MEDIUM RANGE OPERATIONAL AND ENSEMBLE MODEL FORECASTS ARE IN DECENT
AGREEMENT FOR THE EARLY PART OF NEXT WEEK`S FORECAST COMPARED TO
THEIR PERFORMANCE JUST 24 HOURS AGO. HIGH PRESSURE FROM OVER THE
WEEKEND WILL TRANSITION EASTWARD BEGINNING MONDAY...AS A LARGE AND
POTENT PACIFIC STORM MOVES INTO THE WEST COAST. IN GENERAL...LOWER
STORM HEIGHTS AND THE POTENTIAL FOR THE UPPER JET AS FAR SOUTH AS
ARIZONA COULD BRING SIGNIFICANT COOLING BY THE EARLY TO MIDDLE PART
OF NEXT WEEK (POTENTIALLY INTO THE LOW TO MID 80S ATTM). THE BULK OF
THE BEST WAVE ENERGY LOOKS REMAINS TO OUR NORTH...SO ONLY BLENDED A
FEW PERCENT OF CLIMO POPS INTO THE EXTENDED GRIDS FOR NOW.

&&

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

NO AVIATION IMPACTS THROUGH WEDNESDAY AFTERNOON WITH MOSTLY CLEAR
SKIES THROUGH THE PERIOD. THE PRESSURE GRADIENT WILL STAY VERY WEAK
THROUGH WEDNESDAY MORNING YIELDING FREQUENT LIGHT AND VARIABLE WIND
HEADINGS. ONLY A SLIGHT INCREASE IN THE GRADIENT WEDNESDAY AFTERNOON
WILL ALLOW WEST WINDS TO INCREASE ABOVE 10KT AT SOME AERODROMES.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
FRIDAY THROUGH TUESDAY...
A WEAK WEATHER DISTURBANCE WILL BRING A MODEST INCREASE IN
MOISTURE...CLOUDINESS...AND AFTERNOON BREEZINESS TO THE DISTRICT
FRIDAY AND SATURDAY...WITH A SLIGHT CHANCE FOR SHOWERS AND
THUNDERSTORMS WITH THIS IMPULSE...PARTICULARLY ACROSS THE HIGHER
TERRAIN NORTH AND EAST OF PHOENIX. EVEN WITH SOMEWHAT MORE MOIST
CONDITIONS...AFTERNOON HUMIDITY LEVELS WILL STILL FALL INTO THE
TEENS...AND ANY THUNDERSTORM GENERATED GUSTY WINDS MAY POSE AN
ENHANCED FIRE WEATHER RISK GIVEN THE ANTECEDENT DRY FUEL CONDITIONS.
HIGH PRESSURE BUILDING OVER THE DESERT SOUTHWEST FROM THE WEST WILL
THEN BRING DRY CONDITIONS BACK OVER THE REGION...ALONG WITH WARMER
TEMPERATURES FOR SUNDAY AND MONDAY. THE FORECAST FOR NEXT TUESDAY IS
MUCH MORE UNCERTAIN...WITH SOME COMPUTER MODELS KEEPING HIGH
PRESSURE IN PLACE...WITH DRY CONDITIONS AND ABOVE NORMAL
TEMPERATURES CONTINUING...WHILE OTHERS ARE BRINGING A VIGOROUS LOW
PRESSURE CENTER INLAND OVER THE REGION...WHICH WOULD BRING MUCH
COOLER TEMPERATURES...GUSTY WINDS...AND A CHANCE FOR SHOWERS TO THE
DISTRICT.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...NOLTE
AVIATION....MO
FIRE WEATHER...PERCHA




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