Hazardous Seas Warning 45, NWS Medford, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
850 AM PDT SUN OCT 30 2011

.DISCUSSION...THE 12Z NAM IS IN AND THE 12Z GFS HAS JUST BEGUN TO
ARRIVE. THE FOCUS OF THE FORECAST REMAINS ON TWO SYSTEMS. THE
FIRST IS A WEAK COLD FRONT THAT WILL REACH THE SOUTHERN OREGON
COAST NORTH OF CAPE BLANCO LATE THIS MORNING THEN WEAKEN FURTHER
AS IT MOVES INLAND TONIGHT INTO EARLY MONDAY MORNING. THE SECOND
SYSTEM WILL BE MORE NOTABLE...BOTH IN TERMS OF THE AMOUNT OF
PRECIPITATION AND ALSO DUE TO LOWER SNOW LEVELS. IT WILL REACH THE
COAST LATE WEDNESDAY AND MOVE INLAND WEDNESDAY NIGHT...AND BE
FOLLOWED BY WIDESPREAD SHOWERS IN A COLD AIR MASS THURSDAY INTO
THURSDAY NIGHT. ANOTHER FRONTAL SYSTEM MAY ARRIVE NEXT WEEKEND.

&&

.AVIATION...LIFR CIGS/VIS WILL CONTINUE IN THE KLAMATH BASIN AND LOCALLY
IN THE UMPQUA BASIN THIS MORNING. VIS WILL CONTINUE TO IMPROVE
THROUGH 18Z AT THE COAST AS A WEAK COLD FRONT APPROACHES BUT
CEILINGS WILL RETURN TO MVFR. PATCHY FOG WILL ALSO GRADUALLY
DISSIPATE IN WESTERN JACKSON AND JOSEPHINE COUNTIES...OTHERWISE
VFR CONDITIONS CONTINUE THROUGH THE AFTERNOON. MVFR CONDITIONS
WILL SPREAD INLAND TO THE UMPQUA BASIN THIS AFTERNOON AND ACROSS
SOUTHWEST OREGON TONIGHT.

&&

.PREV DISCUSSION... /ISSUED 315 AM PDT SUN OCT 30 2011/

DISCUSSION...CURRENT SATELLITE IMAGE SHOWS MID LEVEL CLOUDS MOVING
TOWARDS THE OREGON COAST. SURFACE OBSERVATIONS INDICATE PATCH FOG
HAS FORMED AROUND THE KLAMATH BASIN AND NORTH BEND. TEMPERATURE AND
DEWPOINT VALUES ARE CLOSE IN THE UMPQUA BASIN AND WE COULD SEE
PATCHY FOG THERE IN THE NEXT FEW HOURS. A WEAK COLD FRONT REACHES
THE COAST LATE THIS MORNING...THEN SLOWLY MOVING INLAND THIS
AFTERNOON THROUGH TONIGHT. THE FRONT IS EXPECTED TO WEAKEN AS IT
MOVES INLAND AND HAVE KEPT QPF AMOUNTS LIGHT TODAY THROUGH TONIGHT.

THE FRONT WILL HAVE MOVED INTO NORTHERN CAL MONDAY MORNING WITH
UPSLOPE FLOW BEHIND IT. THEREFORE WE CAN EXPECT SPRINKLES OR PATCHY
DRIZZLE TO DEVELOP ON WEST FACING SLOPES OF THE CASCADES AND NORTH
FACING SLOPES OF THE SISKIYOUS. AN UPPER TROUGH MOVES INTO THE AREA
MONDAY AFTERNOON PUSHING THE FRONT SOUTHEAST OF THE CWA. THE GFS
SHOWS SOME QPF OVER SOUTHEAST MODOC COUNTY MONDAY AFTERNOON WHILE
THE NAM IS DRY...SUSPECT THE BEST DYNAMICS WILL BE EAST AND
THEREFORE HAVE KEPT THAT AREA DRY.

COOL AND DRY AIRMASS MOVES INTO THE REGION MONDAY NIGHT THROUGH
TUESDAY WITH HIGH PRESSURE BUILDING EAST OF THE CASCADES. THIS WILL
BRING ANOTHER ROUND OF COLD TEMPERATURES EAST OF THE CASCADES.
MEANWHILE WESTSIDE VALLEYS WILL HAVE TEMPERATURES NEAR FREEZING. AT
THE SAME TIME A THERMAL TROUGH DEVELOPS AND STRENGTHENS IN NORTHERN
CAL RESULTING IN GALE FORCE WINDS OVER THE SOUTHERN OUTER MARINE
WATERS AND GUSTY WINDS OVER THE HIGHER TERRAIN IN WESTERN SISKIYOU
COUNTY AND COAST RANGE.

BIG CHANGES (AT LEAST RELATIVE TO WHAT WE HAVE EXPERIENCED RECENTLY)
ARE AHEAD STARTING WEDNESDAY AFTERNOON. THE MODELS ARE IN GOOD
AGREEMENT IN BRINGING A STRONG COLD FRONT TO WESTERN OREGON
WEDNESDAY AFTERNOON. THEY HAVE BEEN TRENDING FASTER WITH THE ONSET
OF THE COLD FRONT. SO THE MORNING WILL START OUT DRY...THEN
PRECIPITATION REACHES THE COAST MID TO LATE AFTERNOON...THEN MOVING
INLAND WEDNESDAY NIGHT. THIS FRONT COULD BRING OUR FIRST SIGNIFICANT
PRECIPITATION EVENT TO THE COAST RANGE AND CASCADES IN ALMOST A
MONTH. A COOL AIR MASS FOLLOWS RESULTING IN SNOW LEVELS LOWERING
AROUND 4000 TO 4500 FEET IN OREGON AND 5000 TO 5500 FEET IN NORTHERN
CAL. THEREFORE IT'S A GOOD BET THE CASCADES AND NORTHERN LAKE AND
KLAMATH COUNTY WILL SEE RAIN CHANGING OVER TO WET SNOW WITH SOME
ACCUMULATION POSSIBLE BY DAYBREAK THURSDAY.

DEEP UPPER TROUGH REMAINS OVER THE AREA THURSDAY AND FRIDAY WITH
RAIN AND SNOW SHOWERS EXPECTED TO PERSIST. SNOW LEVELS THURSDAY WILL
BE AROUND 4000 FEET...3500 FEET THURSDAY NIGHT AND 4000 FEET
FRIDAY.  MP

&&

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

CA...NONE.
PZ...HAZARDOUS SEAS WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY
     MORNING FOR PZZ356.
     HAZARDOUS SEAS WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY
     EVENING FOR PZZ370-376.
     GALE WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY MORNING FOR
     PZZ376.

DW