Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 040950 AAA
AFDPSR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PHOENIX AZ
250 AM MST MON MAY 4 2015

.UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS.

&&

.SYNOPSIS...A SERIES OF PACIFIC WEATHER DISTURBANCES IS FORECAST TO
MOVE ACROSS THE REGION THIS WEEK...KEEPING TEMPERATURES BELOW NORMAL
THROUGH THE ENTIRE PERIOD. THE FIRST IN THIS SERIES OF DISTURBANCES
IS EXPECTED TO PRODUCE SCATTERED TO NUMEROUS SHOWERS AND
THUNDERSTORMS ACROSS SOUTH CENTRAL ARIZONA TODAY AND TUESDAY. A
SECOND...COLDER DISTURBANCE IS THEN EXPECTED TO BRING EVEN COOLER
TEMPERATURES...AND GUSTY WINDS FOR THE END OF THIS WEEK.

&&

.DISCUSSION...
MONDAY THROUGH TUESDAY...
FOR THE SHORT-TERM...LATEST FORECASTS CONTINUE TO BE ON TRACK ON THE
DETAILS OF A RATHER STRONG...AND MOIST (FOR MAY) UPPER LOW THAT IS
NOW PRODUCING SCATTERED SHOWERS AND THUNDERSTORMS ACROSS SOUTH-
CENTRAL ARIZONA. THE COMBINATION OF RATHER HIGH PWATS (AROUND 0.90
INCH) AND DECENT INSTABILITY (LI`S IN THE -2 TO -4 RANGE)...ALONG
WITH GOOD DIFFLUENCE ALOFT IS WHAT IS TRIGGERING THIS ACTIVITY. THE
LATEST FORECASTS SOUNDINGS SUGGEST THAT THIS ACTIVITY WILL CONTINUE
INTO THE MID-MORNING HOURS BEFORE TAKING A BIT OF A BREAK LATER THIS
MORNING/EARLY THIS AFTERNOON AS SLIGHTLY DRIER AIR MOVES IN FROM THE
SOUTH. A SECOND ROUND OF CONVECTIVE ACTIVITY IS LIKELY LATER THIS
AFTERNOON INTO THIS EVENING AS THE MAIN UPPER LOW CENTER PASSES
OVER THE REGION. THE MAIN IMPACTS FROM THE STRONGER STORMS WILL BE
TO PRODUCE GUSTY WINDS AND BRIEF HEAVY RAINS...UP TO AROUND 1/2 INCH
AS THEY PASS OVER A SPECIFIC LOCATION. A GRADUAL CLEARING/DRYING
TREND IS THEN EXPECTED FROM LATE TONIGHT INTO TUESDAY AS THE UPPER
LOW LIFTS OUT TO THE NORTHEAST. THIS COMBINATION OF COOLER AIR ALOFT
AND CONSIDERABLE CLOUDINESS/SHOWERS WILL KEEP LOWER DESERT HIGHS IN
THE 80S TODAY AND TUESDAY...ABOUT 3-6 DEGREES BELOW NORMAL FOR THIS
TIME OF YEAR.

WEDNESDAY...WEAK RIDGING AHEAD OF THE NEXT MAJOR TROF TO PRODUCE DRY
CONDITIONS...MOSTLY CLEAR SKIES...AND SLIGHTLY WARMER TEMPERATURES.

THURSDAY THROUGH SATURDAY...GLOBAL MODELS CONTINUE TO MOVE ANOTHER
COOL TROF TO OUR NORTH...ACROSS THE GREAT BASIN...WITH VERY GOOD
INTERMODEL AND RUN-TO-RUN AGREEMENT ON THE DETAILS OF THIS SYSTEM.
THE MAIN IMPACTS FROM THIS SECOND SYSTEM WILL TO BRING EVEN COOLER
TEMPS INTO THE REGION...UP TO 10 DEGREES BELOW NORMAL ON
FRIDAY...AS THE UPPER LOW PASSES CLOSEST TO OUR CWA...AND STRONG
WESTERLY WINDS...WITH GUSTS UP TO 30 MPH. THE COMBINATION OF THESE
STRONG WINDS AND A RATHER DRY AIRMASS WILL LIKELY RAISE FIRE DANGER
LEVELS ACROSS THE REGION...ESPECIALLY ACROSS SW AZ...THE LOWER
COLORADO RIVER VALLEY...AND SE CA.

SUNDAY AND MONDAY...A WARMING TREND IS LIKELY DURING THIS PERIOD AS
RIDGING ALOFT ATTEMPTS TO BUILD NORTHWARD INTO THE DESERT SW...WITH
HIGHS LIKELY TO RISE TO NEAR NORMAL BY MONDAY.

&&

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

SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE TO MOVE NORTH
ACROSS THE GREATER PHOENIX AREA THROUGH AT LEAST 12Z...AFFECTING ALL
OF THE TAF SITES. EXPECTING CIGS TO LOWER TO AROUND 4-6KFT...AND
THIS WILL VARY BASED ON INTENSITY OF PASSING SHOWERS...THROUGH
APPROX 15Z AND THEN IMPROVE FOR A BIT INTO THE EARLY AFTERNOON
HOURS. EXPECTING ANOTHER ROUND OF ISOLATED/SCATTERED LATE-DAY -SHRA
AFTER 22Z AIDED BY HEAT OF THE DAY...BUT AT THIS POINT WILL ONLY
MENTION VCTS AS CONFIDENCE IN AREAL COVERAGE IS LOW. WINDS WILL BE
TRICKY DUE TO THE NATURE OF SCATTERED SHOWERS/STORMS...WITH
DIRECTIONS RAPIDLY CHANGING FROM TIME TO TIME AS OUTFLOW MOVE
THROUGH THE AREA. EXPECT WINDS TO FAVOR AN EASTERLY COMPONENT MOST
OF THE TIME THROUGH LATE MORNING...THEN RETURNING TO THE SOUTHWEST
DURING THE AFTERNOON HOURS.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
NOT EXPECTING ANY SHOWERS TO IMPACT EITHER KIPL OR KBLH. MOST LIKELY
IMPACT FROM THE APPROACHING TROUGH WILL BE IN THE FORM OF BLOWOFF
CIRRUS AND BREEZY AFTERNOON WINDS. OTHERWISE...WEATHER IMPACTS SHOULD
BE CONFINED TO AREAS EAST OF THE CO RIVER.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
WEDNESDAY THROUGH SUNDAY...
DRY WEATHER...AND SLIGHTLY WARMER TEMPERATURES TO RETURN WEDNESDAY
AS WEAK HIGH PRESSURE PASSES OVER THE REGION. GUSTY WINDS WITH A
COOOLING TREND TO PREVAIL ACROSS THE REGION FROM THURSDAY ONWARD
INTO SATURDAY AS ANOTHER PACIFIC STORM SYSTEM MOVES ACROSS THE GREAT
BASIN. FRIDAY WILL LIKELY BE THE COOLEST DAY WITH HIGH TEMPERATURES
ACROSS THE LOWER DESERTS FALLING INTO THE LOW TO MIDDLE 80S. FIRE
DANGER LEVELS WILL LIKELY BE ELEVATED DURING THIS PERIOD AS
AFTERNOON HUMIDITIES FALL INTO THE TEENS. A WARMING TREND WILL TAKE
PLACE THIS WEEKEND...AND THERE WILL BE LESS WIND AS THE
AFOREMENTIONED PACIFIC STORM SYSTEM BEGINS TO MOVE OFF TO THE EAST
AND HIGHER PRESSURE ALOFT BUILDS INTO THE AREA FROM THE WEST.

&&

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

$$

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

DISCUSSION...PERCHA
AVIATION...LEINS/CB
FIRE WEATHER...PERCHA/CB


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