209
FXUS65 KPSR 141144
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
444 AM MST SAT DEC 14 2019
UPDATE
UPDATED AVIATION AND FIRE WEATHER DISCUSSION.
SYNOPSIS
HIGH PRESSURE WILL RESULT IN NEAR TO SLIGHTLY ABOVE NORMAL
TEMPERATURES FOR THE BEGINNING OF THE WEEKEND. SKIES WILL REMAIN
MOSTLY SUNNY WITH OCCASIONAL INCREASES IN HIGH CLOUDS. A MOSTLY
DRY WEATHER SYSTEM WILL ARRIVE SUNDAY BRINGING COOLER TEMPERATURES
ACROSS THE AREA WITH CHILLY MORNING LOW TEMPERATURES MONDAY AND
TUESDAY. TEMPERATURES WILL REBOUND VERY SLOWLY THROUGH THE FIRST
HALF OF NEXT WEEK AS ANOTHER DRY WEATHER SYSTEM PASSES THROUGH THE
AREA.
DISCUSSION
EARLY THIS MORNING, A RATHER FLAT UPPER LEVEL HIGH PRESSURE RIDGE
WAS IN PLACE ACROSS ARIZONA AND FAR SOUTHEAST CALIFORNIA. 500MB
HEIGHTS OVER THE SOUTHERN DESERTS WERE IN THE 582-585DM BALLPARK,
SUFFICIENT TO KEEP HIGH TEMPERATURES RUNNING NEAR OR SLIGHTLY ABOVE
SEASONAL NORMALS. 2 AM IR IMAGERY SHOWED JUST A BIT OF LARGELY THIN
HIGH CLOUDS STREAMING THROUGH THE FLOW WITH SKIES GENERALLY MOSTLY
CLEAR. WE CAN EXPECT ANOTHER DAY TODAY SIMILAR TO THE PAST FEW DAYS,
WITH HIGHS IN THE WARMER LOWER DESERTS STAYING ABOVE NORMAL AND IN
THE UPPER 60S TO LOW 70S FOR THE MOST PART AS THE FLAT UPPER RIDGE
STAYS OVERHEAD.
VERY LITTLE HAS CHANGED WITH RESPECT TO THE FORECAST FOR SUNDAY INTO
EARLY NEXT WEEK. A FAST MOVING, PROGRESSIVE UPPER TROF IS STILL
EXPECTED TO RACE ACROSS ARIZONA, DROPPING SOUTHEAST WITH MOST OF THE
ENERGY/MOISTURE MOVING THROUGH NORTHERN ARIZONA/FOUR CORNERS AREA
AND SIGNIFICANTLY LIMITING ANY CHANCE OF PRECIPITATION ACROSS OUR
AREA. POP TRENDS CONTINUE TO FALL OFF AND WE SHOULD ONLY SEE JUST A
FEW LIGHT RAIN OR HIGHER ELEVATION SNOW SHOWERS MOVE THROUGH
SOUTHERN GILA COUNTY SUNDAY INTO SUNDAY EVENING. MOST OF THE POPS
ARE NOW LESS THAN 15 PERCENT, AND THIS IS SUPPORTED BY MOS, NBM AND
NAEFS FORECAST POPS. THE MAIN IMPACT OF THE PASSING SYSTEM WILL BE
TO USHER IN A COOLING TREND; HIGHS FALL TO AROUND NORMAL SUNDAY WITH
PHOENIX TO LOWER TO A SEASONAL NORMAL 65 DEGREES, AND THEN TEMPS
FALL OFF ANOTHER FEW DEGREES AND TO BELOW NORMAL LEVELS ON MONDAY.
PHOENIX SHOULD SEE A HIGH IN THE LOW 60S MONDAY WITH SKY HARBOR ONE
OF THE WARMER READINGS AT 63 DEGREES. COOLEST MORNING LOW OF THE
NEXT WEEK LIKELY TO BE TUESDAY MORNING, WITH LOWS DROPPING TO NEAR
FREEZING OVER SOME OF THE HIGHER TERRAIN ZONES TO THE EAST OF
PHOENIX.
FOLLOWING A VERY FAST MOVING SHORT WAVE ON TUESDAY (WHICH WILL HAVE
NO EFFECT ON HIGH TEMPERATURES DUE TO ITS VERY TRANSITORY NATURE),
ANOTHER RATHER PROGRESSIVE UPPER TROF PUSHES EAST AND ACROSS THE
AREA WEDNESDAY INTO THURSDAY. AS WITH THE WEEKEND SYSTEM, LATEST
TRENDS CONTINUE TO SHOW A DRIER SYSTEM FOR US WITH VERY LITTLE
CHANCES FOR PRECIPITATION. MOST PRECIP WITH THE MID WEEK SYSTEM WILL
STAY NORTH AND OVER THE HIGHER TERRAIN OF NORTHERN ARIZONA. NAEFS
POPS SHOW SOME SINGLE DIGIT NUMBER FOR THE SOUTHERN DESERTS, AND
GEFS PLUMES FOR PHOENIX ARE BASICALLY FLAT-LINED AT ZERO FOR THE
NEXT 7 DAYS. GEFS QPF ENSEMBLE MEMBERS ALSO SHOW VIRTUALLY NO QPF
ANYWHERE IN OUR AREA FROM ANY MEMBER WITH THIS SYSTEM. ABOUT THE
ONLY THING THAT THE MID WEEK SYSTEM WILL DO IS USHER IN SOME
INCREASE IN CLOUD COVER, AND KEEP TEMPERATURES HOVERING NEAR OR
SLIGHTLY BELOW SEASONAL NORMAL THROUGH THURSDAY. AFTER THAT,
STRONGER RIDGING ALOFT RETURNS FOR FRIDAY INTO SATURDAY ALLOWING FOR
A WARMING TREND THAT WILL PUSH HIGHS ABOVE NORMAL. ON FRIDAY THE
FORECAST HIGH FOR PHOENIX IS 68 DEGREES, 3 DEGREES ABOVE NORMAL.
AVIATION
UPDATED AT 1145Z.
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
NO MAJOR AVIATION WEATHER CONCERNS THROUGH AT LEAST SATURDAY
EVENING. THE WINDS WILL REMAIN FAIRLY LIGHT, MOSTLY AT OR BELOW 8
KTS, WITH DIRECTIONS FOLLOWING TYPICAL DIURNAL TENDENCIES. THE
WINDS WILL BECOME WESTERLY BETWEEN 20Z-22Z ALTHOUGH THERE MAY
BE A SHORT PERIOD OF SOUTHERLY WINDS DURING THAT TIME UNTIL THE
WINDS BECOME PREDOMINANTLY WESTERLY. WIND DIRECTIONS WILL SHIFT
EASTERLY AGAIN THIS EVENING BUT WILL MAINTAIN A SLIGHT SOUTHERLY
DIRECTIONAL COMPONENT. CEILINGS SHOULD NOT BE A MAJOR PROBLEM
REMAINING AOA 8K FEET.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
THE PRIMARY AVIATION CONCERN WILL BE THE STRENGTHENING OF THE
WESTERLY WINDS LATE THIS AFTERNOON. GUSTS UPWARDS OF 25 KTS ARE
VERY LIKELY, PARTICULARLY AT KIPL, ALTHOUGH STRONG GUSTS AT KBLH
ARE ALSO POSSIBLE.
FIRE WEATHER
MONDAY THROUGH FRIDAY:
A WEATHER SYSTEM WILL PASS THROUGH THE AREA EARLY NEXT WEEK. THE
PRIMARY CHANGE WILL BE COOLER TEMPERATURES, PARTICULARLY DURING
THE OVERNIGHT AND EARLY MORNING HOURS. THIS SYSTEM WILL BE FAIRLY
DRY WITH HARDLY ANY RAIN CHANCES. MIN RH VALUES WILL BE THE LOWEST
TUESDAY AFTERNOON, 15-25%, WITH MOST DAYS IN THE 20-35% RANGE. MAX
RH VALUES WILL ALSO BE THE LOWEST ON TUESDAY IN THE 40-50% RANGE
WITH SLIGHTLY HIGHER VALUES ON ALL OTHER DAYS. WINDS WILL REMAIN
FAIRLY LIGHT OUTSIDE OF AN OCCASIONAL BREEZE OR TWO, WITH
DIRECTIONS MOSTLY FOLLOWING DIURNAL TENDENCIES. EXPECT NIGHTTIME
INVERSION LAYERS TO DEVELOP EACH NIGHT AND SLOWLY LIFT BY LATE
MORNING.
SPOTTER INFORMATION STATEMENT
SPOTTERS SHOULD FOLLOW STANDARD REPORTING PROCEDURES.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...WIND ADVISORY FROM 1 PM THIS AFTERNOON TO 10 AM PST SUNDAY FOR
CAZ562.
DISCUSSION...CB
AVIATION...DEEMS
FIRE WEATHER...DEEMS
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