000
FXUS66 KMFR 280459
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
859 PM PST MON DEC 27 2010
.DISCUSSION...GFS AND ECMWF VERY SIMILAR WITH EVENTS OF THE NEXT 2
DAYS WITH WARM OVERRUNNING THROUGH THE DAY TUESDAY FOLLOWED BY A
RAPIDLY MOVING COLD FRONT CROSSING THE REGION TUESDAY EVENING AND
OVERNIGHT. CONSIDERABLE PRECIPITATION IS EXPECTED WITH THE COLD
FRONT THAT SHOULD IMPACT WESTERN SISKIYOU COUNTY INCLUDING THE
MOUNT SHASTA AREA WITH SNOW LEVELS PERHAPS LOWERING TO 3000 FEET
OR BELOW TUESDAY EVENING DUE TO THE EFFECT OF HEAVY AND CONTINUOUS
PRECIPITATION. THIS WOULD IMPACT I5 SO WILL NEED TO CONSIDER A
WINTER STORM FOR THAT AREA. THE OTHER AREA OF IMMEDIATE CONCERN
IS THE CASCADES WHERE 1-2 FEET OF SNOW IS EXPECTED DURING THE 24
TO 36 HOUR PERIOD BEGINNING TUESDAY. THERE MAY BE A 6 HOUR PERIOD
TUESDAY EVENING WHERE 6-12 INCHES OF SNOW IS POSSIBLE RESULTING IN
HAZARDOUS DRIVING CONDITIONS OVER THE CASCADE PASSES. MAY NEED TO
UPGRADE THE WINTER WEATHER ADVISORY TO A WINTER STORM THERE.
SUFFICIENT SNOW IS EXPECTED TUESDAY NIGHT ACROSS THE EAST-SIDE
ZONES THAT ADVISORIES ARE PROBABLY WARRANTED. THEN THERE IS THE
ISSUE OF LOW SNOW LEVELS WEST OF THE CASCADES WEDNESDAY. SNOW
LEVELS WILL LIKELY FALL TO 1000-1500 IN THE SHOWERS BEHIND THE
COLD FRONT BUT PRECIPITATION WILL BE SPOTTY DUE TO ITS SHOWERY
NATURE AND THE FACT THAT OROGRAPHICALLY FAVORED AREAS WILL BE THE
FOOTHILLS RATHER THAN THE VALLEYS. AN ADVISORY IS CERTAINLY
WARRANTED WEST OF THE CASCADES WEDNESDAY...BUT I HAVE MY DOUBTS
ABOVE A WINTER STORM WARNING.
PRECIPITATION WILL BEGIN TO DIMINISH WEDNESDAY NIGHT AS THE TROUGH
MOVES EAST OF THE REGION. ON THURSDAY A COLD NORTHWEST FLOW WILL
PREVAIL OVER THE REGION...BUT WITH LITTLE MOISTURE AROUND.
LONG TERM...FRIDAY THROUGH MONDAY. FRIDAY STARTS OFF WITH A COOL TO
COLD AIR MASS DEPENDING ON WHICH MODEL YOU CHOOSE. THE GFS AND ECMWF
AGREE ON THE GENERAL IDEA OF AN UPPER RIDGE OFF THE PACIFIC
NORTHWEST COAST WITH NORTHERLY TO NORTHWESTERLY FLOW OVER THE
REGION. HOWEVER...THE ECMWF HAS A MUCH SHARPER RIDGE THAT USHERS IN
COLD AIR FROM NORTH AND EAST WHILE THE GFS IS MORE BROAD WITH THE
RIDGE AND THUS NOT AS COLD. LITTLE IF ANY PRECIPITATION SHOULD FALL
FRIDAY WITH MORNING LOW TEMPERATURES REACHING SINGLE DIGITS ON THE
EAST SIDE AND THE 20S ON THE WEST SIDE. HIGHS SHOULD TOP OUT IN THE
20S ON THE EAST SIDE AND LOW 40S ON THE WEST. PATCHY FREEZING FOG IS
EXPECTED ON THE WEST SIDE WITH LIGHT WINDS AND INCREASED SURFACE
MOISTURE.
MODELS CONTINUE TO DIVERGE FRIDAY EVENING INTO SATURDAY WITH THE GFS
DROPPING A SHORTWAVE AND SOME PRECIPITATION OVER THE REGION BUT THE
ECMWF MAINTAINING A CLOSED LOW OFFSHORE AND DRY WEATHER INLAND. THE
FORECAST FAVORS THE GFS BECAUSE CONTINUED NORTHWEST FLOW SEEMS MORE
PLAUSIBLE AND THE GFS HAS KEYED IN ON UPCOMING NORTHWEST FLOW AHEAD
OF THE ECMWF. ADDITIONALLY...THE GFS RECENT RUNS HAVE SHOWED A
GRADUAL TREND TOWARD ITS CURRENT SOLUTION. SNOW LEVELS FOR THE
PRECIPITATION FRIDAY EVENING TO SATURDAY MORNING WILL BE
LOW...AROUND 2000 FEET FOR MOST PLACES.
DRY AND COOL WEATHER IS EXPECTED SATURDAY EVENING THROUGH MONDAY IN
CONTINUED NORTHERLY AND NORTHWESTERLY FLOW ALOFT. IT WILL BE
INTERESTING TO SEE WHICH SOLUTIONS MODELS TREND TOWARD...THE CUTOFF
LOW SOLUTION FROM ECMWF OR NORTHWEST FLOW SOLUTION FROM GFS.
THE ONLY GRIDS UPDATED THIS EVENING WERE THE QPF/SNOWFALL GRIDS
FOR TUESDAY EVENING. QUITE A BIT MORE PRECIPITATION IS EXPECTED
THAN PREVIOUSLY FORECAST. WILL DELAY THE WARNING/ADVISORY
DECISIONS UNTIL THE NEW GFS AND ECMWF ARE IN.
&&
.AVIATION...WIDESPREAD MVFR CIGS/VSBYS -RA/-SN GRADUALLY
SPREADING INLAND TONIGHT. EXPECT LOCAL IFR CIGS/VSBYS TO DEVELOP
MAINLY ALONG THE COAST.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...HIGH WIND WARNING UNTIL 4 AM PST TUESDAY FOR ORZ021-022.
WINTER STORM WATCH FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY
AFTERNOON ABOVE 1500 FEET FOR ORZ023>026.
WINTER WEATHER ADVISORY FROM 4 AM TUESDAY TO 4 AM PST WEDNESDAY
FOR ORZ027-028.
CA...NONE.
PACIFIC COASTAL WATERS...GALE WARNING UNTIL 7 AM PST TUESDAY FOR PZZ350-356-370-
376.
HAZARDOUS SEAS WARNING UNTIL 4 PM PST TUESDAY FOR
PZZ350-356-370-376.
$$
DG/MW
