FXUS66 KHNX 242235
AFDHNX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JOAQUIN VALLEY - HANFORD CA
235 PM PST THU DEC 24 2009

.SYNOPSIS...
HIGH PRESSURE PREVAILS THROUGH THE REST OF THIS WEEK...COLD AIR IS 
IN PLACE WITH AREAS OF FREEZING TEMPERATURES EXPECTED TONIGHT IN THE 
SAN JOAQUIN VALLEY. A SERIES OF LOW PRESSURE SYSTEMS COULD BRING 
UNSETTLED CONDITIONS SUNDAY THROUGH THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...
INITIAL REPORTS INDICATE THAT THIS MORNING/S FREEZE WAS PRIMARILY A 
WEST SIDE EVENT...WITH THE COLDEST LOWS /25 DEGREES/ AT N.A.S. 
LEMOORE AND THE HANFORD MUNICIPAL AIRPORT.

20Z /NOON PST/ READINGS SHOW THAT BOTH TEMPERATURES AND DEWPOINTS 
ARE RUNNING SLIGHTLY ABOVE PERSISTENCE. WITH CLEAR SKIES AND LIGHT 
WINDS TONIGHT...TEMPERATURES SHOULD COOL TO SATURATION...RESULTING 
IN PATCHY FOG DEVELOPMENT AFTER MIDNIGHT. DUE TO THE ANTICIPATED HIGH
VOLUME OF HOLIDAY TRAFFIC OVERNIGHT AND CHRISTMAS MORNING...HAVE 
ISSUED A SPECIAL WEATHER STATEMENT /SFOSPSHNX OR WWUS86 KHNX/ FOR 
THE MORNING FOG THREAT.

THE 18Z NAM-12 AND GFS RUNS CONTINUE TO FORECAST AN AMPLIFYING UPPER-
LEVEL RIDGE ALONG THE CALIFORNIA COAST TONIGHT...MOVING ONSHORE 
FRIDAY BEFORE BEING UNDERCUT BY THE NEXT TROUGH SATURDAY. BEYOND 
THIS POINT...THERE IS LESS CONSISTENCY AMONG THE 18Z RUNS...OR WITH 
THE EARLIER RUNS...AS A LOW CLOSES OFF WEST OF THE PACIFIC NORTHWEST 
AND DROPS SOUTH OFF THE CALIFORNIA COAST. THE 18Z RUNS HAVE 
DIFFERENCES IN BOTH THE TIMING AND THE TRAJECTORY OF THIS LOW AS IT 
DROPS SOUTH...ALTHOUGH THE GFS AND ECMWF ARE IN BETTER AGREEMENT WITH
THE LOW MOVING INTO NORTHERN BAJA CALIFORNIA BY 18Z MONDAY.

DESPITE THESES DIFFERENCES...THERE IS CONSENSUS FOR A SOUTHERLY 
MIGRATION OF THE LOW PARALLELING THE COAST SUNDAY. THIS WILL SET 
THE STAGE FOR THE NEXT PRECIPITATION EVENT...WITH THE NAM-12 
BRINGING PRECIPITATION INTO THE HANFORD WARNING/FORECAST AREA AFTER 
08Z SUNDAY /MIDNIGHT PST/. THE MODELS HAVE TRENDED DRIER WITH THIS 
SYSTEM...AND THE NAM-12 SHOWS CONSIDERABLE RAIN-SHADOWING OVER THE 
CENTRAL AND SOUTHERN SAN JOAQUIN VALLEY...AS WELL AS WRAP-AROUND 
PRECIPITATION OVER THE TEHACHAPI MOUNTAINS SUNDAY NIGHT. DUE TO THE 
UNCERTAINTIES AMONG THE MODELS...WILL NOT MAKE ANY CHANGES TO QPF 
THIS AFTERNOON.

ANOTHER UPPER-LEVEL RIDGE IS FORECAST TO BUILD ALONG THE COAST 
TUESDAY BEHIND THE TROUGH. A SHORT-WAVE DROPS ALONG THE LEADING EDGE 
OF THE RIDGE INTO THE GREAT BASIN TUESDAY NIGHT...WITH THE ECMWF 
STRONGEST WITH THE WAVE. THIS WILL BRING ANOTHER CHANCE OR 
PRECIPITATION TO /AT LEAST/ THE SOUTHERN SIERRA NEVADA TUESDAY NIGHT 
INTO WEDNESDAY.

THE ECMWF IS MORE AGGRESSIVE THAN THE GFS BRINGING THE RIDGE ONSHORE 
WEDNESDAY NIGHT AND THURSDAY. HAVE REDUCED THE POPS FOR THE CENTRAL 
AND SOUTHERN SAN JOAQUIN VALLEY TO BELOW 15 PERCENT FOR A DRY 
FORECAST...BUT WITH ENOUGH UNCERTAINTY DUE TO THE DISPARATE MODEL 
SOLUTIONS.

&&

.AVIATION...
IN THE SAN JOAQUIN VALLEY...PATCHY FOG DEVELOPING TONIGHT IN LOW 
LYING AREAS...RESULTING IN AREAS OF MVFR AND LOCAL IFR 
VISIBILITIES IN FREEZING FOG 09Z-18Z. OTHERWISE REMAINDER OF THE 
CENTRAL CA INTERIOR...VFR THROUGH 00Z SATURDAY.

&&

.AIR QUALITY ISSUES...
NONE.

&&

.HNX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

PUBLIC...SANGER
AVN/FW...MV
SYNOPSIS...WP

WEATHER.GOV/HANFORD