Hazardous Seas Warning 2, NWS Medford, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
917 PM PST MON JAN 7 2013

.UPDATE...
AN UPDATE WAS ISSUED A SHORT TIME AGO TO ADJUST PRECIPITATION
PROBABILITIES ACROSS THE AREA FOR TONIGHT THROUGH TUESDAY MORNING.
GENERAL CHANGES WERE TO INCREASE PROBABILITIES ALONG THE COAST
AND OVER NORTHWEST SECTIONS OF THE AREA AND TO DECREASE THEM
ELSEWHERE. SKY COVER WAS ALSO ADJUSTED UPWARD THROUGH TUESDAY.
MINOR RELATED CHANGES WERE MADE TO SNOW LEVELS AND PRECIPITATION
AMOUNTS. PATCHY FOG WAS ADDED FOR THE WEST SIDE THROUGH TUESDAY
MORNING. BTL

&&

.DISCUSSION...
TODAY'S WARM FRONT IS LINGERING ACROSS THE AREA WITH PLENTY OF LOW
CLOUDS AND PATCHY FOG. MODELS ARE UNANIMOUS IN SHOWING ANOTHER
WARM FRONTAL WAVE PUSHING INTO THE COAST AND COASTAL MOUNTAINS AND
FROM SOUTHERN UPSLOPE AREAS OF THE UMPQUA DIVIDE NORTHWARD LATER
TONIGHT THROUGH TUESDAY MORNING. SNOW LEVELS WILL REMAIN HIGH AND
PRECIPITATION AMOUNTS SHOULD BE LESS THAN A TENTH OF AN INCH ALL
AREAS. BTL

&&

.AVIATION...
BASED ON THE 09/00Z TAF CYCLE...

THE STABLE...MOIST AIR MASS CONTINUES TO GENERATE A MIX OF IFR
AND MVFR CEILINGS AND VISIBILITIES ACROSS SOUTHERN OREGON AND
NORTHERN CALIFORNIA. WIDESPREAD MOUNTAIN OBSCURATION WILL CONTINUE
TONIGHT. CONDITIONS WILL BE VERY SLOW TO IMPROVE TO MVFR BEHIND A
WARM FRONT THAT WILL PASS THROUGH THE AREA BY LATE THIS EVENING
BEFORE CEILINGS AND VISIBILITIES LOWER AGAIN TONIGHT TO
IFR...ESPECIALLY IN THE WEST SIDE VALLEYS AND ALONG THE COAST. /FB

&&

.PREV DISCUSSION... /ISSUED 145 PM PST MON JAN 7 2013/

07/12Z NAM/GFS IN.

A BUILDING OFFSHORE RIDGE IS PUSHING A WARM FRONT THROUGH THE
AREA AT THIS TIME. LOTS OF DRIZZLE AND FOG OVER THE MEDFORD CWA.
THE 07/12Z MEDFORD SOUNDING SHOWED A FREEZING LEVEL OF 8700 FEET
WITH SATURATED CONDITIONS FROM THE SURFACE TO 13000 FEET.

SOME SHOWERS WILL PERSIST INTO MONDAY EVENING...BUT LATE MONDAY
NIGHT THROUGH TUESDAY EVENING LOOKS DRY WITH THE AREA BETWEEN
SYSTEMS.

THE OFFSHORE RIDGE WILL BREAK TO THE EAST OF THE AREA
TUESDAY...AND A STRONG UPPER TROUGH WILL MOVE ONSHORE WEDNESDAY.
THE MODELS HAVE CONVERGED ON THE TIMING OF THIS FEATURE SO
CONFIDENCE IN THAT RESPECT IS HIGH.

THIS TROUGH WILL PUSH A STRONG COLD FRONT ONSHORE EARLY
WEDNESDAY. THIS FRONT MAY BRING SIGNIFICANT WINDS TO THE
AREA...AND WIND RELATED WARNINGS/ADVISORIES MAY BE NEEDED...MOST
LIKELY EAST OF THE CASCADES...AND MAYBE BRIEFLY IN THE SHASTA
VALLEY. IT WON'T BE UNUSUALLY WET...BUT THERE WILL BE SOME VERY
COLD AIR BEHIND THE FRONT.

AFTER THE TROUGH MOVES ONSHORE...SHORT WAVES PLUNGING DOWN THE
BACKSIDE OF THE TROUGH WILL CAUSE IT TO DIG JUST INLAND FROM THE
COAST. THIS WILL INDUCE COLD NORTHERLY WINDS ALOFT COMING OUT OF
BRITISH COLUMBIA...AND TEMPERATURES WILL CONTINUE TO COOL THURSDAY
INTO FRIDAY. THE MODEL SOLUTIONS SHOW 850 MB TEMPERATURES PEAKING
AT +5 TO +8C TUESDAY EVENING...THEN PLUNGING TO -6 TO -8C FRIDAY
MORNING. SNOW LEVELS WILL LOWER TO AROUND 1000 FEET WEDNESDAY
NIGHT INTO THURSDAY. SINCE THE SHORT WAVES WILL KEEP THE POST-
FRONTAL SHOWERS GOING INTO FRIDAY...THIS MAY BE A SIGNIFICANT LOW
LEVEL SNOW EVENT FOR THE WESTERN VALLEYS.

EXTENDED DISCUSSION...FRIDAY THROUGH MONDAY. THE LARGE SCALE TROUGH
DRAPED ACROSS THE WESTERN CONUS WILL BE SLOW TO PROGRESS EAST...AND
THEREFORE WILL INFLUENCE THE PATTERN OVER SOUTHERN OREGON AND
NORTHERN CALIFORNIA THROUGH THE MAJORITY OF THE EXTENDED PERIOD.
THE MAIN FEATURES OF CONCERN WILL BE SMALL SCALE AND HARD TO
FORECAST SHORTWAVES DROPPING ALONG THE WESTERN SIDE OF THE
TROUGH...EACH OF WHICH COULD UP PRECIPITATION CHANCES. THE
UNCERTAINTY OF THESE SMALL FEATURES IS TOO HIGH TO PIN DOWN ANY
SPECIFICS OF TIMING OR STRENGTH. HOWEVER THERE IS SOME CONFIDENCE
THAT A LARGER WAVE WILL ENTER THE AREA AND BRING ANOTHER ROUND OF
PRECIPITATION DURING THE WEEKEND.

SHOWERS ON THE BACK SIDE OF THE TROUGH WILL CONTINUE THROUGH
FRIDAY...AND SNOW LEVELS WILL GRADUALLY RISE FROM AROUND 1300 FEET
TO NEAR 2000 FEET BY THE END OF THE DAY. SHOWERS WILL BE TAPERING
OFF
DURING THE SAME TIME AS SHORT WAVE RIDGING BUILDS INTO THE REGION
FROM THE NORTH...SO THEREFORE DO NOT EXPECT MUCH ACCUMULATION OF
PRECIPITATION. FROM FRIDAY MORNING THROUGH FRIDAY NIGHT...MOST
LOCATIONS THAT DO RECEIVE SNOW SHOULD SEE LESS THAN AN INCH. WEST
SIDE VALLEY FLOORS AND THE EAST SIDE WILL LIKELY ONLY SEE A DUSTING
OF SNOW...WHILE HIGHER ELEVATIONS ALONG THE SOUTHERN COASTAL RANGE
AND IN THE CASCADES COULD SEE AN INCH OR TWO OF ADDITIONAL SNOW.

ONCE THE SHORTWAVE RIDGE WEAKENS...THE STRONGEST SHORT WAVE IS
EXPECTED TO DROP SOUTH INTO THE REGION FROM THE CANADIAN MARITIME
SATURDAY. SNOW LEVELS WILL REMAIN AROUND 2000 FEET FOR MOST OF THE
AREA...SO DO NOT EXPECT VALLEY SNOW AT THIS TIME...AND OVERALL
PRECIPITATION AMOUNTS SHOULD BE LIGHT. BY EARLY NEXT WEEK...THE
LARGE SCALE TROUGH SHOULD PUSH FAR ENOUGH EAST TO ALLOW A HIGH
AMPLITUDE RIDGE OVER THE EASTERN PACIFIC TO BUILD EAST. WITH THE
PACIFIC NORTHWEST UNDER NORTHERLY FLOW ON THE PERIPHERY OF THIS
RIDGE...EXPECT DRY CONDITIONS AND COOL TEMPERATURES TO PREVAIL FOR
THE REMAINDER OF THE TERM. 15

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.

CA...NONE.

PACIFIC COASTAL WATERS...HAZARDOUS SEAS WATCH FROM LATE TUESDAY
NIGHT THROUGH WEDNESDAY
     AFTERNOON FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 4 AM PST
WEDNESDAY
     FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR WINDS FROM 7 AM TUESDAY TO 10 AM PST
     WEDNESDAY FOR PZZ350-370.

BTL/CMC/FJB