FXUS66 KMFR 261158
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
358 AM PST SAT DEC 26 2009

.DISCUSSION...A 500MB RIDGE AXIS IS SITUATED ALONG THE CASCADES
SOUTHWARD INTO NORTHERN CALIFORNIA EARLY THIS MORNING. SATELLITE
IMAGERY SHOWING LOW CLOUDS AND FOG ENTRENCHED OVER THE WESTERN
VALLEYS AND EVEN SOME LOW CLOUDS/FOG GETTING INTO NORTHERN KLAMATH
COUNTY NEAR CRESCENT. TEMPERATURES WILL COOL ALOFT TODAY AND THIS
SHOULD HELP WEAKEN THE STRONG INVERSION THAT HAS BEEN IN PLACE
OVER THE LAST FEW DAYS. EVEN SO, FOG WILL BE STUBBORN TO BREAK
OVER THE DEEPER WEST SIDE VALLEYS AND HIGH TEMPERATURES THERE WILL
ONLY BE IN THE MID TO PERHAPS UPPER 30S.

THIS IS A BIT OF A CONCERN FOR TONIGHT INTO SUNDAY MORNING AS A 
SPLIT FLOW DEVELOPING OVER THE EASTERN PACIFIC OCEAN ALLOWS A WEAK 
DISTURBANCE TO COME EASTWARD WITH SOME LIGHT PRECIPITATION. WHILE 
TEMPERATURES IN THE WESTERN VALLEYS WILL BE CLOSE TO FREEZING LATER 
TONIGHT INTO SUNDAY MORNING, THIS IS NOT THE SAME SITUATION AS THE 
PAST FREEZING RAIN EVENT WHERE LOW LEVEL ARCTIC AIR HAD PREVIOUSLY 
SETTLED IN OVER THE AREA. THE AIR MASS IN PLACE AHEAD OF THIS SYSTEM 
IS WARMER AND WITH INCOMING CLOUD COVER AND LIGHT SOUTHERLY FLOW, 
ODDS ARE THAT TEMPERATURES WILL STAY JUST ABOVE FREEZING AS THE 
PRECIPITATION MOVES IN OVERNIGHT INTO SUNDAY MORNING. EVEN SO, IT 
BEARS WATCHING, SO STAY TUNED FOR ANY UPDATES THAT MAY BE ISSUED 
LATER TODAY. THE BEST RAIN CHANCES WITH THIS SYSTEM WILL BE ALONG
THE COAST, IN THE COAST RANGE AND IN SISKIYOU COUNTY. IN THE
FAVORED UPSLOPE AREAS OF SOUTHERN SISKIYOU COUNTY, THERE WILL
ALSO BE A PERIOD OF SNOW LATER TONIGHT INTO SUNDAY MORNING WITH
SNOW LEVELS RUNNING BETWEEN 3500 AND 4000 FEET. THIS WILL BRING A
COUPLE OF INCHES NEAR THE MOUNT SHASTA/MCCLOUD AREA. BY LATER
SUNDAY AFTERNOON AND EVENING, THE STEADIEST PRECIPITATION WILL
PUSH NORTH OF THE CWA. MOST AREAS, WITH THE EXCEPTION OF A FEW
LIGHT SHOWERS OVER THE WEST SIDE AND ALONG THE COAST, SHOULD BE
DRY SUNDAY NIGHT INTO MONDAY. SHORTWAVE RIDGING SHOULD BE OVER THE
AREA MONDAY NIGHT INTO TUESDAY AS THE NEXT SYSTEM MOVES TOWARD THE
COAST.

NO CHANGES TO THE LONG TERM MADE EARLY THIS MORNING. PREVIOUS
DISCUSSION FOLLOWS. ECMWF AND GFS ARE BOTH IN GOOD AGREEMENT WITH
THE SYSTEM THAT MOVES THROUGH THE REGION TUESDAY NIGHT...WITH
ALMOST IDENTICAL JET PROGNOSIS. BOTH REMAIN IN GOOD AGREEMENT WITH
WEAK RIDGE BUILDING BEHIND THIS SYSTEM ON THURSDAY. THE JET
SOLUTION BEGINS TO VARY A BIT WITH THE EC DIGGING THE JET DOWN A
BIT FARTHER SOUTH...DEEPENING THE UPPER TROUGH MORE THAN THE NEAR
ZONAL GFS SOLUTION. HOWEVER...THE TIMING OF FRIDAYS SYSTEM IS
STILL VERY CLOSE WITH BOTH MODELS AND THIS HAS GIVEN ME GREATER
CONFIDENCE TO WALK UP THE POPS SUBSTANTIALLY ON ALL THE SYSTEMS
THAT ARE MOVING THROUGH THE EXTENDED PERIODS.

&&

.AVIATION...WIDESPREAD VLIFR CIGS AND VISIBILITY WILL IMPACT THE
WEST SIDE VALLEYS THIS MORNING INCLUDING RBG AND MFR. SOME
IMPROVEMENT WILL OCCUR THIS AFTERNOON BUT A FEW AREAS WILL LIKELY
HOLD ONTO IFR CONDITIONS ALL DAY. ON THE COAST, OTH WILL BE VFR
TODAY WITH LOCAL MVFR CIGS POSSIBLE LATER TONIGHT AS RAIN MOVES
IN. ELSEWHERE, WITH THE EXCEPTION OF LOW CLOUDS AND FOG IN
NORTHERN KLAMATH COUNTY EARLY THIS MORNING, VFR CONDITIONS ARE
EXPECTED OVER THE EAST SIDE THROUGH TODAY WITH PERHAPS LOCAL MVFR
CIGS LATER TONIGHT INTO SUNDAY MORNING.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR ORZ023-
     ORZ024-ORZ025-ORZ026-ORZ029-ORZ030-ORZ031.
     HIGH SURF ADVISORY FROM 9 AM THIS MORNING TO 4 PM PST SUNDAY FOR 
     ORZ021-ORZ022.
     DENSE FOG ADVISORY UNTIL 10 AM PST THIS MORNING FOR ORZ023-
     ORZ024-ORZ026.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS FROM 4 PM 
     THIS AFTERNOON TO 4 PM PST SUNDAY FOR PZZ370-PZZ376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 4 AM PST TUESDAY 
     FOR PZZ350-PZZ356-PZZ370-PZZ376.

$$

SPILDE