Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 051037
AFDPSR

AREA FORECAST DISCUSSION...CORRECTION
NATIONAL WEATHER SERVICE PHOENIX AZ
340 AM MST TUE MAY 5 2015

&&

.SYNOPSIS... LOW PRESSURE OVER THE WESTERN UNITED STATES IS EXPECTED
TO KEEP TEMPERATURES BELOW NORMAL THROUGH THE REMAINDER OF THIS
WEEK. SCATTERED SHOWERS THIS MORNING WILL GIVE WAY TO PARTLY CLOUDY
SKIES LATE THIS AFTERNOON AS A WEATHER DISTURBANCE THAT BROUGHT
WIDESPREAD MEASURABLE RAINFALL ON MONDAY TO SOUTH CENTRAL AND SW
ARIZONA MOVES OFF TO THE EAST. ANOTHER DISTURBANCE THAT WILL BE
MOVING INTO THE REGION LATER THIS WEEK WILL BRING EVEN COOLER
TEMPERATURES...GUSTY WINDS...AND EVEN A SLIGHT CHANCE FOR A SHOWER
BEFORE A SLOW WARMING TREND COMMENCES FROM THE LATER PART OF THIS
WEEKEND INTO EARLY NEXT WEEK AS HIGH PRESSURE GRADUALLY REBUILDS
OVER THE DESERT SOUTHWEST.

&&

.DISCUSSION...
TODAY AND TONIGHT... A DRYING TREND IS EXPECTED TO CONTINUE AS THE
UPPER LOW CENTER THAT BROUGHT SO MUCH THUNDERSTORM ACTIVITY TO SOUTH-
CENTRAL AND SW AZ ON MONDAY...WHICH IS NOW CENTERED OVER NE
AZ...BEGINS TO MOVE OFF TO THE EAST. A WEAK SHORTWAVE THAT IS NOW
ROTATING AROUND THE PARENT LOW CENTER IS PRODUCING SCATTERED LIGHT
SHOWERS OVER SOUTH-CENTRAL ARIZONA AT THE PRESENT TIME.
HOWEVER...THE COMBINATION OF A WELL WORKED-OVER AIRMASS AND WARMING
ALOFT HAS NOW PRETTY MUCH ENDED ANY THUNDERSTORM ACTIVITY. THE
LATEST GFS AND NAM MODELS ARE INDICATING THAT SHOWER ACTIVITY WILL
PRETTY MUCH END BY MIDDAY OVER THE LOWER DESERTS OF SOUTH-CENTRAL
AZ...WITH LIGHT SHOWER ACTIVITY PERHAPS LINGERING INTO THE EARLY
EVENING HOURS OVER THE HIGHER TERRAIN NORTH AND EAST OF PHOENIX.
TEMPERATURES THIS AFTERNOON WILL LIKELY BE A COUPLE OF DEGREES
WARMER THEN WHAT WE SAW YESTERDAY DUE TO MORE SUNSHINE AND A
SLIGHTLY WARMER AIRMASS...WITH LOWER DESERT HIGHS RISING INTO THE 85-
90 DEGREE RANGE.

WEDNESDAY... DRY CONDITIONS AND A BIT MORE WARMING (OVER SOUTH-
CENTRAL AZ) IS EXPECTED ON WEDNESDAY AS WEAK RIDGING PASSES OVER THE
REGION AHEAD OF THE NEXT UPPER LOW CENTER APPROACHING FROM THE WEST.
HOWEVER...HIGH TEMPERATURES ARE STILL EXPECTED TO REMAIN SLIGHTLY
BELOW NORMAL VALUES. SOME INCREASE IN AFTERNOON WESTERLY WINDS CAN
BE EXPECTED OVER SE CA AS WINDS ALOFT INCREASE AHEAD OF THE NEXT
SYSTEM.

THURSDAY THROUGH SATURDAY... ALTHOUGH LATEST MODEL SUITES ARE
CONSISTENT WITH EARLY RUNS ON THE BASIC IDEA THAT ANOTHER UPPER LOW
CENTER WILL AFFECT OUR REGION DURING THIS PERIOD...SOME DIFFERENCES
BETWEEN THE MODEL SUITES HAVE EMERGED ON THE TRACK OF THIS SYSTEM.
WHILE THE EURO AND GEM MODELS CONTINUE TO TAKE THIS LOW CENTER TO
OUR NORTH...ALONG THE AZ/UT BORDER...THE GFS NOW MOVES THE UPPER LOW
CENTER RIGHT ACROSS OUR CWA. IF THE GFS WERE TO VERIFY...EVEN COOLER
TEMPERATURES WOULD RESULT...WITH MANY LOWER DESERT LOCATIONS SEEING
HIGH ONLY IN THE 70S ON FRIDAY AND SATURDAY...ALONG WITH A CHANCE
FOR SHOWERS AS WELL. ALTHOUGH ALL THREE MODELS STILL INCREASE SFC
WINDS ACROSS THE REGION DURING THIS PERIOD...THEY ALL NOW KEEP
MINIMUM RH/S ELEVATED A BIT...MOSTLY IN THE UPPER TEENS AND
20S...WHICH WOULD KEEP FIRE DANGER LEVELS FROM RISING AS MUCH AS HAD
BEEN EARLIER EXPECTED. I HAVE DECIDED THE RAISE POPS AND COOL
TEMPERATURES A BIT TO REFLECT THIS POSSIBLE GFS SOLN.

SUNDAY THROUGH TUESDAY..ALL THREE GLOBAL MODELS CONTINUE TO SHOW
HIGH PRESSURE SLOWLY REBUILDING OVER THE REGION AS THE
AFOREMENTIONED UPPER LOW MOVES OFF TO THE EAST...WITH DRY CONTINUES
AND A GRADUAL WARMING TREND FORECAST THROUGH THIS PERIOD.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
ISOLATED TO SCATTERED SHOWERS...POSSIBLY A STRAY
THUNDERSTORM...ANTICIPATED TO DEVELOP AFT 07Z AS AN EMBEDDED
DISTURBANCE WITHIN THE UPPER TROUGH TRACKS THROUGH SOUTHERN ARIZONA
TONIGHT. HELD OFF ON USING MENTIONING SHWRS IN PREVAILING WEATHER OR
EVEN IN TEMPO GROUPS DUE TO UNCERTAINTIES ASSOCIATED WITH DECLINING
HUMIDITY AND WEAKENING OF THE WEATHER DISTURBANCE.
INSTEAD...UTILIZED VCSH. THE SYSTEM SHIFTS EASTWARD DURING THE DAY
TUESDAY FOR A DOWNTREND IN PRECIP POTENTIAL ALONG WITH DECREASING
CLOUDS. ANTICIPATE LIGHT SURFACE WINDS TONIGHT TRENDING TOWARD SOUTH
AND SOUTHWEST DURING THE DAY TUESDAY.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS OVER YUMA AND LA PAZ
COUNTY ANTICIPATED TO HANG ON THROUGH 09Z BEFORE DIMINISHING.
ANTICIPATE VFR CONDITIONS EXCEPT IN VERY LOCALIZED AREAS WITH
HEAVIEST SHOWERS. SURFACE WINDS WILL FAVOR EAST AND NORTHEAST
DIRECTIONS OVERNIGHT BEFORE TRENDING TO SOUTHERLY DURING THE DAY AND
BECOMING GUSTY IN THE AFTERNOON.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
GUSTY WINDS WITH A COOLING 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...AJ
FIRE WEATHER...CB



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