Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 240255
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
755 PM MST SAT MAY 23 2015

.SYNOPSIS...
A SERIES OF LOW PRESSURE SYSTEMS MOVING THROUGH ARIZONA WILL KEEP
TEMPERATURES BELOW NORMAL THROUGH THE REMAINDER OF THE MEMORIAL DAY
WEEKEND. ISOLATED SHOWER ACTIVITY IS POSSIBLE OVER PARTS OF SOUTH-
CENTRAL ARIZONA...THOUGH MEASURABLE PRECIPITATION WILL GENERALLY
REMAIN EAST OF PHOENIX. A GRADUAL WARMING AND DRYING TREND IS
EXPECTED NEXT WEEK...WITH TEMPERATURES RETURNING TO THE UPPER 90S
AND EVEN ABOVE THE 100 DEGREE MARK BY NEXT WEEKEND.

&&

.DISCUSSION...
THE LARGE SCALE WRN CONUS NEGATIVE HEIGHT ANOMALY REMAINS STUCK IN
PLACE THIS EVENING...WITH ONE SHORTWAVE LIFTING NORTH THROUGH WRN
COLORADO WHILE A SECONDARY PV ANOMALY DESCENDS SOUTHEAST ALONG THE
CALIFORNIA COAST. GIVEN THIS CONFIGURATION....THE FORECAST AREA WILL
REMAIN IN A SUBSIDENCE REGIME THROUGH THE NIGHT WITH DIURNAL CU
ALREADY LARGELY DISSIPATING...AND HAVE CLEANED UP SKY COVER GRIDS AS
A RESULT. MOST OTHER SALIENT WEATHER PARAMETERS ONLY NEEDED
SLIGHT ADJUSTMENTS TO ACCOUNT FOR SHORT TERM TRENDS.

THE AFOREMENTIONED COMPACT PV ANOMALY HEADING TOWARDS ARIZONA ON
SUNDAY STILL LOOKS TO CARRY A FAIR AMOUNT OF DYNAMICAL
ENERGY...HOWEVER MOST RECENT MODEL OUTPUT STILL SUGGESTS VERY
LIMITED MOISTURE PROFILES (5-6 G/KG BOUNDARY LAYER MIXING RATIOS).
OTHER THAN ALONG THE RIM WHERE SCT SHOWERS WILL DEVELOP...SOME HIGH
RESOLUTION MODELS WANT TO SHOW ADDITIONAL ISOLD SHOWERS THROUGH
PARTS OF CENTRAL AND SOUTHEAST ARIZONA IN ASSOCIATION WITH THE SMALL
COLD CORE. FEEL SOME VIRGA AND A EXTREMELY ISOLATED SHOWER COULD BE
POSSIBLE WITH THE DRY SUBCLOUD LAYER...BUT NOT ENOUGH EVIDENCE
EXISTS TO MAKE SUBSTANTIAL INCREASES TO POPS IN THIS EVENINGS
UPDATE.

&&

.PREVIOUS DISCUSSION...
/223 PM MST SAT MAY 23 2015/
TONIGHT THROUGH MONDAY... A UNSEASONABLY STRONG...AND COOL PACIFIC
UPPER LOW CENTER THAT BROUGHT WELL-BELOW NORMAL TEMPERATURES TO THE
DESERT SOUTHWEST OVER THE LAST FEW DAYS IS NOW CENTERED OVER EAST-
CENTRAL UTAH THIS AFTERNOON...AND IS FORECAST TO MOVE INTO CO/WY
TONIGHT AND ON SUNDAY. IN THE WAKE OF THIS LOW CENTER...COOL...BUT
RELATIVELY DRY NORTHWESTERLY FLOW CONTINUES OVER OUR CWA. THE COOL
AIR OVER THE REGION...WITH 850MB TEMPS IN THE 14-16C RANGE...WILL BE
KEEPING MOST LOWER DESERT HIGHS WELL DOWN IN THE 80S THIS AFTERNOON.
AFTER ANOTHER COOL NIGHT TONIGHT...WITH MOST LOWER DESERT LOCATIONS
SEEING LOWS ONCE AGAIN FALLING INTO THE 55-65 DEGREE RANGE...A NEW
SHORTWAVE...THAT IS NOW MOVING INTO NORTHERN CA...IS EXPECTED TO
ROTATE SOUTHWARD AND EASTWARD AROUND THE MAIN LOW CENTER ACROSS
SOUTHERN AZ ON SUNDAY. ALTHOUGH THIS NEXT SYSTEM IS QUITE DRY...WITH
PWATS ONLY RISING INTO THE 0.40-0.50 INCH RANGE...GOOD DIFLUENCE
AHEAD OF THE SHORTWAVE AND DECENT MID-LEVEL COOLING (500MB TEMPS
FALLING TO AS LOW AS -18C)...ALONG WITH GOOD UPSLOPE FLOW...SHOULD
BE ENOUGH TO TRIGGER A FEW SHOWERS AND THUNDERSTORM OVER THE HIGHER
TERRAIN OF SOUTH-CENTRAL ON SUNDAY AFTERNOON...AS THE UPPER LOW
PASSES OVER OUR REGION. ALONG WITH THE SHOWER CHANCES...THIS
SHORTWAVE WILL ALSO KEEP OUR TEMPERATURES WELL BELOW NORMAL AGAIN ON
SUNDAY. GIVEN THAT FACT THAT THE AIRMASS ASSOCIATED WITH THIS NEW
SHORTWAVE WILL BE ALMOST AS COOL AS THE ONE WE ARE SEEING
TODAY...HIGH ON SUNDAY WILL LIKELY BE HARD-PRESSED TO GET OUT OF THE
MID-80S ACROSS THE LOWER DESERTS...JUST A COUPLE OF DEGREES WARMER
THEN WHAT WE ARE FORECASTING FOR TODAY.

MONDAY WILL LIKELY BE OUR LAST DAY OF SIGNIFICANTLY BELOW NORMAL
TEMPERATURES...AS ANOTHER...WEAKER SHORTWAVE BRUSHES BY TO OUR NORTH
AND EAST. THIS NEXT SHORTWAVE COULD ONCE AGAIN PRODUCE A SHOWER OR
TWO OVER THE HIGHER TERRAIN NORTH AND EAST OF PHOENIX ON MONDAY
AFTERNOON...BUT THE VAST MAJORITY OF MEASURABLE RAINFALL IS EXPECTED
TO REMAIN WELL TO OUR NORTH...OVER THE RIM COUNTY AND WHITE
MOUNTAINS. HIGHS ON MONDAY ARE EXPECTED TO RISE INTO THE LOW 90S AT
MOST LOWER DESERT LOCATIONS.

TUESDAY THROUGH SATURDAY... A GRADUAL WARMING TREND IS EXPECTED
THROUGH THIS PERIOD AS THE FLOW ALOFT BECOMES MORE ZONAL AS THE MAIN
LONG-WAVE TROF SHIFTS OFF TO OUR NORTH AND EAST. LOWER DESERT HIGHS
ARE EXPECTED TO RISE INTO THE UPPER 90S BY FRIDAY...AND INTO THE
100S NEXT SATURDAY...AS RIDGING BECOMES ESTABLISHED OVER THE REGION
BEHIND THE LAST WEAK UPPER TROF THAT WILL BE MOVING EASTWARD ACROSS
THE GREAT BASIN ON THURSDAY AND FRIDAY.

&&

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

VERY LITTLE TO NO AVIATION IMPACTS THROUGH SUNDAY EVENING. MOST
DIURNAL CU HAS DISSIPATED...AND ONLY OCCASIONAL SCT MID/HIGH CLOUDS
WILL PASS BY TERMINALS SUNDAY. SFC WINDS AT PHOENIX AERODROMES WILL
BE SEASONABLY LIGHT WITH VERY TYPICAL WIND SHIFT TIMING. GUSTY W/SW
WINDS OVER SOUTHEAST CALIFORNIA SHOULD GENERALLY WEAKEN DURING THE
OVERNIGHT HOURS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...
DRIER AND WARMER CONDITIONS WILL DEVELOP INTO THE REGION OVER THE
COMING WEEK AND RESULT IN OUR WARMEST TEMPERATURES SO FAR THIS YEAR
BY NEXT WEEKEND. THE WEATHER PATTERN WILL STILL REMAIN SOMEWHAT
ACTIVE OVERHEAD...AS A FEW WEAK DISTURBANCES BRUSH PAST OR THROUGH
THE AREA. HOWEVER...THESE WILL BE ON THE DRY SIDE. TEMPERATURES WILL
GRADUALLY WARM CLOSER TOWARD SEASONAL NORMALS. AS A RESULT...
AFTERNOON RELATIVE HUMIDITY VALUES WILL FALL BACK INTO THE TEENS
FOLLOWING FAIR TO GOOD OVERNIGHT RECOVERY. HOWEVER...WINDS WILL
GENERALLY REMAIN LIGHT FOLLOWING TYPICAL DAILY PATTERNS LEADING TO
MINIMAL FIRE WEATHER CONCERNS.

&&

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

&&

$$

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

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



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