FXUS65 KPSR 251710
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1010 AM MST WED NOV 25 2009
.SYNOPSIS...
HIGH PRESSURE ALOFT WILL KEEP CONDITIONS DRY AND WARM THROUGH FRIDAY.
A LOW PRESSURE SYSTEM WILL BRING COOLER AND BREEZY CONDITIONS TO THE
AREA THIS WEEKEND...WITH BELOW NORMAL TEMPERATURES LIKELY BY SUNDAY.
&&
.DISCUSSION...AN UPPER LEVEL RIDGE IS CURRENTLY ANCHORED OVER THE
WESTERN CONUS. SATELLITE SHOWS CLEAR SKIES OVER ENTIRE FORECAST
AREA. THE RIDGE WILL REMAIN IN PLACE THROUGH FRIDAY...LEADING TO
THREE MORE DAYS OF ABOVE NORMAL TEMPERATURES.
CURRENT FORECAST PACKAGE LOOKED GOOD. ONLY CHANGE MADE WAS SOME
MINOR ADJUSTMENTS TO AFTERNOON MAX TEMPERATURES.
&&
.PREV DISCUSSION...
ISSUED AT 729 AM MST WED NOV 25 2009
RIDGE OF HIGH PRESSURE OVER THE WESTERN STATES WILL CONTINUE WELL
ABOVE NORMAL TEMPERATURES THROUGH FRIDAY...UNDER CLEAR SKIES.
TEMPERATURES ACROSS THE LOWER DESERTS THANKSGIVING DAY ARE EXPECTED
TO TOP OUT IN THE UPPER 70S TO NEAR 80...BEFORE A COUPLE DEG OF
COOLING FRIDAY.
MODELS IN GOOD AGREEMENT THAT A STRONG PACIFIC LOW PRESSURE SYSTEM
WILL MOVE THROUGH THE REGION THIS WEEKEND...WITH THE LATEST
GFS/ECMWF INDICATING THE BEST CHANCE FOR MOUNTAIN SNOW AND LOWER
ELEVATION RAIN SATURDAY NIGHT INTO SUNDAY. EVEN STILL...MOISTURE IS
LIMITED WITH THIS SYSTEM GIVEN THE INLAND TRAJECTORY...AND THE MAIN
IMPACT WILL BE SIGNIFICANTLY COOLER WEATHER. MODELS ARE INDICATING
A STRONG JET ON THE BACKSIDE OF THE TROUGH WILL AID IN BRINGING MUCH
COLDER AIR FROM THE NORTHERN STATES ALL THE WAY SOUTHWARD INTO
ARIZONA. BETWEEN TODAY AND SUNDAY...BOTH THE GFS AND ECMWF ARE
INDICATING 700MB TEMPS WILL DROP FROM AROUND 3.5C TO -6C...WITH
HIGHS AROUND 60 SUNDAY ACROSS THE WARMEST DESERTS. WINDS WILL ALSO
INCREASE RATHER DRAMATICALLY OVER THE WEEKEND...PARTICULARLY ALONG
THE CO RIVER VALLEY WESTWARD. THE ELEVATED WIND SPEEDS OVERNIGHT
SATURDAY INTO SUNDAY SHOULD KEEP TEMPS OVER THE WESTERN DESERTS
RATHER MILD SUNDAY MORNING...IN THE MID 40S TO NEAR 50. LESS WIND IS
EXPECTED OVER THE CENTRAL ARIZONA ZONES...WITH OVERNIGHT LOWS
DROPPING SEVERAL DEG...INTO THE LOW 40S /AND EVEN THIS MIGHT BE TOO
WARM/. BY MONDAY MORNING...LESS WIND AND CLEAR SKIES WILL LEAD TO
MAXIMUM RADIATIONAL COOLING...WITH OVERNIGHT LOWS DIPPING INTO THE
UPPER 30S ACROSS THE COOLER DESERT LOCALES.
TUESDAY/WEDNESDAY...UPPER RIDGING IS EXPECTED TO BUILD AGAIN OVER
THE WESTERN CONUS...WITH MOST OF THE SOUTHWEST UNITED STATES UNDER
DRY NORTHERLY FLOW ALOFT...WITH TEMPERATURES RETURNING TO NEAR
NORMAL FOR THIS TIME OF YEAR.
&&
.AVIATION...
SOUTHEAST CA...SOUTHWEST AND SOUTH CENTRAL AZ...INCLUDING KIPL...
KBLH...KPHX...AND KIWA.
HIGH PRESSURE ALOFT WILL AGAIN LEAD TO MOSTLY CLEAR OR CLEAR SKIES
FOR THE NEXT 24 HOURS...THE ONLY CLOUDINESS BEING HIGH THIN CIRRUS.
OTHERWISE WINDS WILL BE GENERALLY ON THE LIGHT SIDE...AND FAVOR THE
NORTH THROUGH EAST. WINDS WILL BE MOSTLY FROM THE NORTH DOWN THE
LOWER CO RIVER VALLEY THROUGH THURSDAY MORNING...WITH SOME GUSTS TO
20KT OR SO FROM 18Z WED THROUGH 01Z THU. OCCASIONAL BREEZES FROM THE
NORTHEAST ARE LIKELY ACROSS PORTIONS OF SOUTH-CENTRAL ARIZONA...WITH
A FEW GUSTS TO 18KT POSSIBLE MAINLY DURING THE MORNING HOURS TODAY.
VFR CONDITIONS EXPECTED ALL AIRFIELDS NEXT 24 HOURS.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
FRIDAY THROUGH TUESDAY...
HIGH PRESSURE ALOFT WILL BEGIN TO WEAKEN FRIDAY AS AN UPPER LEVEL
LOW PRESSURE SYSTEM BEGINS TO TAKE SHAPE OVER THE WESTERN UNITED
STATES. HIGH TEMPERATURES WILL REMAIN WELL ABOVE SEASONAL NORMALS
WITH THE WARMEST DESERTS REACHING TO NEAR 80 DEGREES. WINDS WILL BE
ON THE LIGHT SIDE...AND MINIMUM RH VALUES WILL BE BELOW 15 PERCENT
OVER MUCH OF THE LOWER DESERTS. OVER THE WEEKEND A VIGOROUS AND
RATHER COLD LOW PRESSURE SYSTEM WILL DEVELOP OVER ARIZONA...LEADING
TO SUBSTANTIAL COOL DOWN ALONG WITH INCREASING WIND. AS THE LOW
DROPS SOUTH INTO ARIZONA SATURDAY NIGHT INTO SUNDAY...WINDY
CONDITIONS WILL DEVELOP OVER SOUTHEAST CALIFORNIA AND SOUTHWEST
ARIZONA...WITH PEAK GUSTS BETWEEN 25KT AND 35KT FROM THE NORTH
EXPECTED. THIS WILL BE A RATHER DRY SYSTEM FOR OUR AREA...WITH JUST
A SLIGHT CHANCE FOR SHOWERS EXPECTED OVER THE HIGHER TERRAIN EAST OF
PHOENIX...MAINLY DURING THE DAY SUNDAY.
OTHERWISE MUCH COOLER AND DRIER AIR WILL BE USHERED INTO THE STATE
WITH THIS SYSTEM. HIGH TEMPERATURES SUNDAY WILL LOWER INTO LOWER 60S
OVER MOST OF THE DESERTS...AND THIS WILL BE 10 DEGREES OR SO BELOW
SEASONAL NORMALS. BY MONDAY MINIMUM RH VALUES WILL DROP BELOW 15
PERCENT OVER MOST OF THE DESERTS...BEHIND THE EXITING LOW. LESS WIND
ALONG WITH A WARMING TREND IS EXPECTED EARLY NEXT WEEK AS HIGHER
PRESSURE RETURNS ...ALTHOUGH THE AIRMASS WILL REMAIN QUITE DRY.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...MCLANE/WANEK
AVIATION...CB
FIRE WEATHER...CB
