FXUS66 KEKA 101122
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
322 AM PST THU DEC 10 2009

.SYNOPSIS...THE COLD AIRMASS WILL CONTINUE TO MODIFY AS A STORM
SYSTEM MOVES CLOSER TO CALIFORNIA. RAIN IS EXPECTED TO SPREAD
ONSHORE ON FRIDAY WITH OFF AND ON SHOWERS THROUGH THE WEEKEND.
SNOW IS POSSIBLE IN THE INTERIOR VALLEYS AT THE ONSET OF THE
PRECIPITATION AS COLD AIR WILL INITIALLY BE TRAPPED. WARM AIR
WILL OVERTAKE THE REGION LATE FRIDAY AS SOUTHERLY WINDS INCREASE.

&&

.DISCUSSION...WEAK RIDGING TODAY WILL BE SHUNTED OFF TO THE EAST
TONIGHT AS DEVELOPING LOW PRESSURE NEAR 40N 135W PUSHES A WARM
FRONT TOWARD NRN CA. HIGH CLOUDS HAVE INCREASED AHEAD OF THIS
FRONT NOT ALLOWING TEMPS TO BOTTOM OUT LIKE WE HAVE SEEN OVER THE
PAST SEVERAL NIGHTS. DESPITE THIS...WE WILL HANG ON TO THE HARD
FREEZE WARNING FOR CAZ001 (AS TEMPS ARE CURRENTLY NEAR 29F) BUT DROP
IT FOR CAZ002 WHERE THE CLOUDS WILL BE THICKEST. 

THE TIMING OF RAIN APPROACHING THE COAST WILL BE TRICKY TODAY DUE
TO THE VERY DRY AIRMASS CURRENTLY IN PLACE. MODELS PAINT QPF OVER
MENDOCINO COUNTY BY THIS AFTERNOON...BUT WE WILL DELAY THE ONSET
BY ABOUT 6 HRS TO ALLOW THE AIRMASS TO MOISTEN. AS PRECIP
BEGINS...IT MAY FALL IN THE FORM OF SNOW ACROSS INTERIOR VALLEYS DUE
TO THE RESIDUAL COLD AIR BEING TRAPPED. ENOUGH MIXING IS EXPECTED
BY FRI NIGHT TO ALLOW ALL AREAS TO REALIZE THE WARMER AIR
ALOFT...TURING THE PRECIP TO ALL RAIN AOB 3500 FT. THIS FIRST LOW
WEAKENS TONIGHT BUT SHOWERS WILL STILL PERSIST DUE TO WAA
PROCESSES. THE MAIN IMPACT OF THIS LOW IS TO OPEN UP THE DOOR FOR A
MORE MOIST ZONAL FLOW. 

A SECONDARY LOW WILL FORM IN A SIMILAR LOCATION (NEAR 40N 130W)
FRI NIGHT AND HEAD STRAIGHT FOR NRN CA ON SAT. BY THIS TIME...THE
JET STREAM IS FOCUSED ON CENTRAL CA ENHANCING LIFT AND BRINGING IN
PLENTY OF MOISTURE. HIGHEST RAIN AMOUNTS APPEAR TO BE CONCENTRATED
OVER THE SIERRA IN CENTRAL CA...BUT UP TO AN INCH IS NOT OUT OF
THE QUESTION FOR NW CA.

THIS LOW PRESSURE SYSTEM MOVES OVER NRN CA SAT NIGHT EXITING TO
THE EAST ON SUN. THE STEADIER RAINS SHOULD COME TO AN END EARLY
SUN...BUT WITH RESIDUAL MOISTURE HANGING AROUND...WE CANNOT RULE
OUT SHOWERS FOR MUCH OF THE DAY AS WE WILL BE UNDER AN UNSTABLE NW
FLOW ALOFT. A SHORTWAVE RIDGE MOVES OVER THE AREA ON MON...AND THIS IS
WHEN THE LONGER RANGE MODELS DIVERGE IN THEIR SOLUTIONS. THE GFS
ENSEMBLE BUILDS A RIDGE IN THE SE PACIFIC DEFLECTING THE STORM
TRACK NORTH OF OUR AREA. ALL THE OPERATIONAL MODELS HAVE THIS
RIDGE...BUT ITS PLACEMENT IS FARTHER SOUTH AND ITS NOT AS STRONG.
THIS ALLOWS THE STORM TRACK TO FOCUS A PARADE OF STORMS ON NRN CA.
TO ACCOUNT FOR THIS UNCERTAINTY...WE HAVE TRENDED POPS FROM ABOVE
CLIMO IN THE NORTH TO BELOW IN THE SOUTH. WITH THE MODELS
STRUGGLING AS MIGHTILY AS THEY HAVE AS OF LATE...I WOULD NOT PUT
MUCH FAITH IN THE FCST BEYOND THE WEEKEND AT THIS TIME. JCA

&&

.AVIATION...DRY/COLD/STABLE AIR MASS OVER THE REGION WILL CONTINUE
TO RESULT IN VFR CONDITIONS. MVFR CEILINGS ALONG WITH A CHANCE OF
LIGHT RAIN/SNOW WILL RETURN TONIGHT THROUGH FRIDAY MORNING AS LOW 
PRESSURE APPROACHES THE REGION. DJB

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
HARD FREEZE WARNING UNTIL 9 AM PST THIS MORNING CAZ001.

SCA FOR WINDS FROM MIDNIGHT TONIGHT TO 4 PM PST SATURDAY PZZ475.

&&

$$

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