FXUS66 KHNX 271715
AFDHNX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JOAQUIN VALLEY - HANFORD CA
915 AM PST FRI NOV 27 2009
.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL MOVE INTO AND ACROSS THE REGION TODAY
THROUGH SATURDAY BRINGING A THREAT OF RAIN AND SNOW ALONG WITH MUCH
COOLER TEMPERATURES. HIGH PRESSURE WILL REBUILD BEGINNING SUNDAY
WITH DRY AND WARMING WEATHER MONDAY THROUGH WEDNESDAY.
&&
.DISCUSSION...
THE UPPER-LEVEL TROUGH IS MOVING INTO NORTHERN CALIFORNIA THIS
MORNING. RADAR INDICATES THAT THE FRONTAL RAIN BAND EXTENDS NORTHEAST
FROM THE SAN FRANCISCO BAY AREA ACROSS THE SACRAMENTO VALLEY. THE
PRECIPITATION BAND IS ON TRACK TO REACH THE NORTHERN FRINGES OF THE
HANFORD WARNING/FORECAST AREA THIS AFTERNOON...THEN SPREAD SOUTH TO
THE TEHACHAPI MOUNTAINS THROUGH THE EVENING HOURS.
THE 12Z NAM-12 CONTINUES TO FORECAST A 500-MB -26 C COLD POOL TO
DROP DOWN THE WEST SIDE OF THE SAN JOAQUIN VALLEY OVERNIGHT. WILL
KEEP THE SLIGHT CHANCE OF THUNDERSTORMS FOR THE CENTRAL AND SOUTHERN
SAN JOAQUIN VALLEY THIS EVENING. RFC QPF GUIDANCE FOR FRESNO IS LESS
THAN A TENTH OF AN INCH...AND THE NEW 12Z MODEL GUIDANCE IS EVEN
DRIER. SUSPECT RAINFALL AMOUNTS ON THE VALLEY FLOOR WILL BE MAINLY A
FEW HUNDREDTHS OF AN INCH...WITH HIGHER AMOUNTS IN THUNDERSTORMS OR
HEAVY SHOWERS.
NO CHANGES PLANNED TO THE CURRENT FORECAST.
&&
.AVIATION...
LOCAL MVFR CEILINGS WILL OCCUR IN MERCED COUNTY TODAY...OTHERWISE
VFR CONDITIONS WILL PREVAIL ACROSS THE CENTRAL CALIFORNIA INTERIOR
UNTIL 00Z SATURDAY. AFTER 00Z SATURDAY...AREAS OF MVFR CEILINGS AND
VISIBILITIES WILL OCCUR ACROSS SIERRA NEVADA AND KERN COUNTY
MOUNTAINS WITH LOCAL MVFR CONDITIONS IN SHOWERS IN THE SAN JOAQUIN
VALLEY AS PRECIPITATION SPREADS SOUTHWARD. VFR CONDITIONS WILL
PREVAIL ELSEWHERE ACROSS THE CENTRAL CALIFORNIA INTERIOR BETWEEN 00Z
SATURDAY AND 18Z SUNDAY.
&&
.AIR QUALITY ISSUES...
ON FRIDAY NOVEMBER 27 2009...FIREPLACE/WOOD STOVE BURNING IS
PROHIBITED IN KERN AND TULARE COUNTIES. FURTHER INFORMATION IS
AVAILABLE AT VALLEYAIR.ORG
&&
.PREV DISCUSSION... /ISSUED 750 AM PST FRI NOV 27 2009/
SYNOPSIS...
A LOW PRESSURE SYSTEM WILL MOVE INTO AND ACROSS THE REGION TODAY
THROUGH SATURDAY BRINGING A THREAT OF RAIN AND SNOW ALONG WITH MUCH
COOLER TEMPERATURES. HIGH PRESSURE WILL REBUILD BEGINNING SUNDAY
WITH DRY AND WARMING WEATHER MONDAY THROUGH WEDNESDAY.
DISCUSSION....DISCUSSION...HIGH CLOUD SHIELD IS NOW SPREADING
OVER THE FORECAST AREA AHEAD OF THE INCOMING PACIFIC SYSTEM.
UPSTREAM RADAR SHOWS THE LEADING EDGE OF PRECIPITATION HAS JUST
REACHED THE UKIAH AREA AND IT SHOULDN'T AFFECT THE CENTRAL
CALIFORNIA INTERIOR UNTIL LATER THIS AFTERNOON AND THIS WILL BE
LIMITED TO MERCED COUNTY. I HAVE DELAYED THE ONSET OVER THE REST
OF THE AREA TO THIS EVENING AND OVERNIGHT AS THE FRONTAL SYSTEM
AND PARENT CLOSED LOW MAKE A STEADY MARCH TO THE SOUTHEAST.
ALTHOUGH THIS SYSTEM IS NOT LIKELY TO BE A MAJOR PRECIPITATION
PRODUCER, THE TIMING OVER THE HOLIDAY WEEKEND IS CERTAINLY A
CONCERN. BASED ON THE LATEST MODEL DATA, THE AIR ASSOCIATED WITH
THIS LOW IS COLD ENOUGH TO DRIVE SNOW LEVELS DOWN TO PASS LEVEL IN
THE KERN COUNTY MOUNTAINS AND THE TREMENDOUSLY TRAVELED ROUTES OF
I-5 OVER THE GRAPEVINE AND HIGHWAY 58 OVER TEHACHAPI PASS WILL
MOST LIKELY BE AFFECTED BY A LIGHT SNOWFALL. ANY SNOW ON THESE
ROUTES WILL CERTAINLY CAUSE MAJOR TRAVEL PROBLEMS AND A WINTER
WEATHER ADVISORY HAS BEEN ISSUED FOR THIS EVENING THROUGH MID
SATURDAY MORNING. IT LOOKS LIKE THE COLDEST AIR AND GREATEST
WINTER WEATHER THREAT WILL ARRIVE AFTER MIDNIGHT TONIGHT...PEAKING
BEFORE SUNRISE ON SATURDAY MORNING. AGAIN SNOWFALL MAY NOT EXCEED
AND INCH OR SO ON THE SUMMITS BUT IT IS VERY SIGNIFICANT. AS FOR
THE RAINFALL PROSPECTS, THE RAIN WILL ACCOMPANY THE FRONT AND AS
THE COLD POOL FROM THE LOW MOVES DOWN THE WEST SIDE OF THE SAN
JOAQUIN VALLEY IN THE EVENING, AN ISOLATED THUNDERSTORM CANNOT BE
RULED OUT AS 500 MB TEMPERATURES ARE PROGGED TO FALL TO AS LOW AS
-28C.
PART TWO OF THIS STORM SYSTEM WILL BE THE CONTINUED THREAT OF A
MONO WIND EVENT IN THE SIERRA. LATEST DATA SHOWS LITTLE CHANGE
OVER THE PAST 24 HOURS AND INDICATES A NORTHEAST PERPENDICULAR
FLOW TO THE SIERRA WITH 500 MB WINDS AS STRONG AS 70 KNOTS...A 110
KNOT NORTHEAST TO SOUTHWEST ORIENTED JET STREAM, AND SURFACE HIGH
PRESSURE BUILDING INTO THE GREAT BASIN. WILL KEEP THINGS AS A
WATCH AT THIS TIME AND LET THE DAY SHIFT MAKE THE DECISION TO WARN
OR NOT.
WITH THE UPPER LOW NOW PROJECTED TO MAKE A SLOW DOWN AS IT SINKS
TOWARDS THE MEXICAN BORDER ON SATURDAY AND SATURDAY EVENING, I
HAVE INTRODUCED POPS TO THE KERN COUNTY DESERTS AND EXTENDED THE
POPS FOR THE KERN MOUNTAINS. ALL IN ALL ACTIVE WEATHER FOR A CHANGE.
FOR THE UPCOMING WEEK, STRONG RIDGING IS STILL PROJECTED FOR
MONDAY AND TUESDAY HOWEVER THE HIGHLY AMPLIFIED RIDGE PATTERN
PREVIOUSLY SUGGESTED BY GFS AND ECMWF MODELS LASTING INTO THURSDAY
IS NO LONGER IN THE CARDS. NOW THE MODEL SOLUTIONS ARE FAR LESS
AMPLIFIED AND BRING ANOTHER THREAT OF RAIN AND SNOW EITHER LATE
WEDNESDAY OR THURSDAY. STILL MUCH DISAGREEMENT IN THE STRENGTH AND
TRACK OF ANY INCOMING SYSTEM THUS THE GRIDS WILL REMAIN DRY FOR NOW.
AVIATION...
LOCAL MVFR CEILINGS WILL OCCUR IN MERCED COUNTY TODAY...OTHERWISE
VFR CONDITIONS WILL PREVAIL ACROSS THE CENTRAL CALIFORNIA INTERIOR
UNTIL 00Z SATURDAY. AFTER 00Z SATURDAY...AREAS OF MVFR CEILINGS AND
VISIBILITIES WILL OCCUR AS PRECIPITATION SPREADS SOUTHWARD INTO THE
KERN COUNTY MOUNTAINS. VFR CONDITIONS WILL PREVAIL ELSEWHERE ACROSS
THE CENTRAL CALIFORNIA INTERIOR BETWEEN 00Z SATURDAY AND 12Z SUNDAY.
AIR QUALITY ISSUES...
ON FRIDAY NOVEMBER 27 2009...FIREPLACE/WOOD STOVE BURNING IS
PROHIBITED IN KERN AND TULARE COUNTIES. FURTHER INFORMATION IS
AVAILABLE AT VALLEYAIR.ORG
&&
.HNX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM SATURDAY EVENING THROUGH SUNDAY MORNING FOR
THE FOOTHILLS AND HIGHER ELEVATIONS OF THE SOUTHERN SIERRA NEVADA
FROM YOSEMITE NATIONAL PARK TO KINGS CANYON /CAZ093-096/.
WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 10 AM PST
SATURDAY FOR THE KERN COUNTY MOUNTAINS /CAZ095/.
&&
$$
PUBLIC...SANGER
AVN/FW...BEAN
PREVIOUS DISCUSSION...PUBLIC...DUDLEY
AVN/FW...DURFEE
WEATHER.GOV/HANFORD
