Forecast-Discussion
000
FXUS65 KPSR 042050
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
150 PM MST SAT SEP 4 2010
.UPDATE...
UPDATED AVIATION AND FIRE WEATHER SECTIONS.
&&
.SYNOPSIS...
STRONG HIGH PRESSURE ALOFT WILL BRING A CONTINUATION OF WELL ABOVE
NORMAL DAYTIME HIGH TEMPERATURES THROUGH SUNDAY. EXPECT TEMPERATURES
TO DRIFT LOWER NEXT WEEK AS THE HIGH PRESSURE SYSTEM MOVES OFF TO
THE EAST...WHILE A COUPLE OF RATHER STRONG LOW PRESSURE SYSTEMS MOVE
THROUGH THE INTERMOUNTAIN WEST. IN FACT...SLIGHTLY BELOW NORMAL
TEMPERATURES WILL PREVAIL ACROSS THE REGION WEDNESDAY THROUGH
FRIDAY. THERE WILL BE A SLIGHT CHANCE OF ISOLATED THUNDERSTORMS
ACROSS THE HIGHER TERRAIN NORTH AND EAST OF PHOENIX TODAY THROUGH
NEXT TUESDAY.
&&
.DISCUSSION...
AZ SOUNDINGS THIS MORNING SHOW A NOTABLE GAINS IN MOISTURE FROM
YESTERDAY MORNING...AT LEAST PART OF WHICH WAS REALIZED DURING THE
DAY YESTERDAY. ACCORDINGLY...THE TEMPERATURE PROFILES IN THE LOWER
LEVELS ARE NOT AS WARM. THUS TEMPS OVER SOUTH-CENTRAL ARIZONA WILL
NOT BE QUITE AS HOT...AS IS FORECAST. ALOFT HOWEVER THERE HAS BEEN
WARMING ABOVE 500 MB AND THIS WILL SERVE TO REDUCE INSTABILITY
DESPITE THE MOISTURE GAIN...THOUGH AN ISOLATED THUNDERSTORM IS STILL
POSSIBLE OVER ZONE 24 AND MORE LIKELY OVER THE WHITE MOUNTAINS AND
PORTIONS OF SOUTHEAST ARIZONA. WITH NO SOUNDING AVAILABLE FROM THE
YUMA AREA ON WEEKENDS...THE TRENDS IN THE MOISTURE PROFILE DO NOT
NECESSARILY APPLY TO FAR WESTERN ARIZONA AND SOUTHEAST CALIFORNIA.
GPS IPW SENSORS SUGGEST THAT THEY DONT BECAUSE PRECIPITABLE WATER
VALUES ARE LOWER DESPITE THE GULF SURGE EVIDENT AT YUMA. RADAR WIND
PROFILE SHOWS THIS AS BEING SHALLOW...AND WEAKENING...AS WOULD BE
EXPECTED FROM AN MCS OUTLFOW TYPE OF SURGE. RUC FORECAST SOUNDING
REFLECTS THIS SURGE AND SHOWS IT BEING QUITE SHALLOW...MAYBE TOO
SHALLOW. NET EFFECT WILL BE SOME SLIGHT COOLING...MAINLY IN THE
SOUTHERN PORTIONS OF THE LOWER COLORADO RIVER VALLEY...BUT NOT
ENOUGH TO CANCEL THE EXCESSIVE HEAT WARNING.
12Z MODELS CONTINUE TO SHOW THE ANTICYCLONE CENTERED OVER SOUTHERN
CALIFORNIA WEAKENING AND SHIFTING EASTWARD SUNDAY AS A TROUGH OVER
WESTERN CANADA AND THE PACIFIC NORTHWEST MOVES INLAND AND DEEPENS.
MORE LATER.
PREVIOUS DISCUSSION...
UPPER LEVEL HIGH PRESSURE THAT BROUGHT EXCESSIVE HEAT TO THE LOWER
DESERT ON FRIDAY WAS CENTERED JUST NORTHWEST OF LOS ANGELES THIS
MORNING...WITH RIDGE AXIS EXTENDING EAST ACROSS CENTRAL ARIZONA.
CENTER OF THE HIGH WILL MIGRATE SLOWLY EAST TODAY AND TONIGHT...THEN
WEAKEN SLOWLY AND MOVES TO SOUTHERN NEW MEXICO BY SUNDAY EVENING. AS
SUCH...WELL ABOVE NORMAL DAYTIME HIGHS WILL PERSIST THROUGH SUNDAY.
FORECAST SOUNDINGS INDICATE BOUNDARY LAYER TEMP WILL BE...ON
AVERAGE...1-3 F LOWER OVER THE LOWER DESERT TODAY COMPARED TO
FRIDAY...AND 1-2 F LOWER SUNDAY COMPARED TO TODAY. EXCESSIVE HEAT
WARNING...DRIVEN BY EXPECTED MAX TEMPS...WILL REMAIN IN EFFECT OVER
FAR SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA TODAY. AS EXPECTED...
ATMOSPHERE DID MOISTEN UP ACROSS SOUTH-CENTRAL AZ COMMENCING FRIDAY
AFTERNOON...AND SOME MOIST ADVECTION WILL OCCUR ACROSS WESTERN AZ
AND EXTREME SOUTHEAST CALIFORNIA TODAY. STILL...SFC DEW POINTS WILL
BE BELOW CLIMO...AND THAT...COMBINED WITH EXPECTED MID-LEVEL
WARMING...RESULTS IN DESERT SOUNDINGS PRETTY MUCH DEVOID OF CAPE.
CANNOT RULE OUT AN ISOLATED STORM OVER THE HIGHER TERRAIN EAST OF
PHOENIX TODAY THROUGH LABOR DAY...BUT THATS ABOUT IT. RATHER STRONG
TROUGH OF LOW PRESSURE MOVES EAST ACROSS THE INTERMOUNTAIN WEST...
MAINLY TO OUR NORTH...LATE SUNDAY INTO LABOR DAY...WHILE UPPER HIGH
MOVES WELL OFF TO OUR SOUTHEAST. AS RIDGE LOSES ITS GRIP ON THE
SOUTHWEST UNITED STATES...A COOLING TREND WILL COMMENCE...WITH LABOR
DAY HIGH TEMPS 4-6 DEGREES LOWER THAN WHAT OCCURS SUNDAY (EVEN
SO...MAX TEMPS LABOR DAY WILL BE A FEW DEGREES ABOVE CLIMO).
IN EXTENDED...ECMWF AND GFS AGREE THAT SOUTHWESTERLY FLOW WILL
PREVAIL OVER THE SOUTHWEST UNITED STATES...WITH A RATHER STRONG
TROUGH OF LOW PRESSURE FORECAST TO DEVELOP ALONG OR NEAR THE PACIFIC
COAST...THEN MOVE SLOWLY EAST ACROSS THE INTERMOUNTAIN WEST LATER IN
THE WEEK. FORECAST TEMPS SHOULD BE NEAR NORMAL TUESDAY...BUT LOWER
TO SLIGHTLY BELOW NORMAL THE REST OF THE WORK WEEK. IN ADVANCE OF
THE STRONG TROUGH...A WEAK WEATHER DISTURBANCE IS FORECAST TO BE
EJECTED EAST ACROSS SOUTHERN AZ/SONORA MEXICO ON TUESDAY...AND THIS
SYSTEM MAY TAP INTO ENOUGH MOISTURE TO INCREASE THE CHANCE FOR A
THUNDERSTORM MAINLY OVER THE HIGHER TERRAIN EAST OF PHOENIX.
&&
.AVIATION...
SOUTH-CENTRAL ARIZONA...INCLUDING KPHX AND KIWA...
WINDS FROM THE SOUTHEAST ARE EXPECTED TO BECOME LIGHT AND VARIABLE
FAVORING FROM THE NORTHWEST LATE THIS AFTERNOON AND EARLY THIS
EVENING...THEN FROM THE EAST LATE THIS EVENING THROUGH SUNDAY
MORNING. A FEW CLOUDS NEAR 12 THOUSAND FEET ARE EXPECTED...THEN
BECOMING CLEAR BY LATE THIS EVENING THROUGH SUNDAY. ISOLATED
THUNDERSTORMS THIS AFTERNOON AND EARLY THIS EVENING ARE EXPECTED TO
STAY OVER THE HIGHER TERRAIN WELL NORTHEAST AND EAST OF THE GREATER
PHOENIX AREA.
SOUTHEAST CALIFORNIA...SOUTHWEST AND INCLUDING KIPL...KBLH...CLEAR
SKIES AND LIGHT DIURNAL WINDS ARE EXPECTED THROUGH SUNDAY...MOSTLY
FROM THE SOUTH AT KBLH.
DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...
LOW PRESSURE ALOFT FROM THE NORTH PACIFIC IS EXPECTED TO DEVELOP
NEAR THE WEST COAST WITH COOLER WEATHER DURING THE MIDDLE OF THE
WEEK. THIS SYSTEM WILL ALSO RESULT IN BREEZY WINDS FROM THE SOUTHWEST
IN THE AFTERNOONS WITH GUSTS BETWEEN 20 AND 30 MPH TUESDAY AND
WEDNESDAY. THE AIR WILL BE DRY WITH MINIMUM AFTERNOON RELATIVE
HUMIDITY BELOW 15 PERCENT.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...EXCESSIVE HEAT WARNING FROM 10 AM TO 8 PM MST TODAY
AZZ020-021-025-026.
CA...EXCESSIVE HEAT WARNING FROM 10 AM TO 8 PM PDT TODAY
CAZ031>033.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...AJ/DG
AVIATION...ELLIS
FIRE WEATHER...ELLIS
NWS PSR Office Area Forecast Discussion
