AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MEDFORD OR 853 PM PST MON FEB 13 2012

.PREV DISCUSSION... /ISSUED 313 PM PST MON FEB 13 2012/ SHORT TERM...A FEW LIGHT SHOWERS AND FLURRIES ARE LINGERING THIS AFTERNOON...MAINLY ALONG NORTHWEST FACING SLOPES SUCH AS THE UMPQUA DIVIDE...SISKIYOU MOUNTAINS AND SOUTHERN AND EASTERN MODOC COUNTY. THIS ACTIVITY WILL TAPER OFF DURING THE EVENING WHILE A HIGH PRESSURE RIDGE THAT IS PRESENTLY OFFSHORE BUILDS INTO OUR AREA. THIS WILL STABILIZE THE AIR MASS AND SHOULD LEAD TO PATCHES OF LATE NIGHT AND MORNING VALLEY FOG. WITH A PROGRESSIVE PATTERN...ANOTHER COLD BUT WEAKER UPPER LEVEL TROUGH WILL FOLLOW WITH PRECIPITATION LIKELY IN COOS AND MUCH OF DOUGLAS COUNTY BEFORE THE END OF TUESDAY AFTERNOON. THE 18Z NAM HAS TRENDED CLOSER TOWARD THE 12Z GFS AND ECMWF SOLUTIONS BUT IT IS STILL FARTHEST INLAND WITH THE FORECAST TRACK OF THE TROUGH...AND THUS THE DRIEST. THE GFS/ECMWF SOLUTION HAS BETTER RUN TO RUN CONSISTENCY AND IS FAVORED. THE SNOW LEVEL ON TUESDAY LOOKS TO BE AROUND 3000 FEET IN THE AFTERNOON THEN FALL TO 1500 FEET BY THE END OF THE NIGHT. THE MAJORITY OF ANY LIGHT PRECIPITATION SHOULD FALL TUESDAY EVENING WITH ELEVATIONS ABOVE 2000 FEET LIKELY TO RECEIVE AN INCH OF A SNOW...ESPECIALLY ONCE AGAIN AT NORTHWEST FACING SLOPES. BY SUNRISE ON WEDNESDAY MORNING...THE CENTER OF THE TROUGH IS EXPECTED TO REACH THE VICINITY OF RENO WITH A STRONGER AND BROADER RIDGE BUILDING NORTHEASTWARD TO THE OREGON COAST. THIS RIDGE WILL PERSIST FROM WEDNESDAY INTO AT LEAST EARLY THURSDAY MORNING WITH PATCHES OF VALLEY FOG EACH MORNING. THE GFS IS SLIGHTLY STRONGER AND FASTER THAN THE ECMWF WITH A COLD FRONT INDICATED TO BE FOCUSED ON VANCOUVER ISLAND AND WASHINGTON ON THURSDAY. THE SOUTHERN EDGE OF THE FRONT MAY BE STRONG AND MOIST ENOUGH TO BRING LIGHT PRECIPITATION TO OUR AREA THURSDAY AFTERNOON AND/OR NIGHT. THE HIGHEST PROBABILITY IS FOR COOS AND DOUGLAS COUNTIES NORTHWARD. SNOW LEVELS WOULD BE MUCH HIGHER THAN WITH THE PREVIOUS FEW SYSTEMS...AROUND 5500 FEET. LONG TERM...FRIDAY THROUGH MONDAY. THE PROGRESSIVE UPPER LEVEL PATTERN IS SET TO CONTINUE INTO THE WEEKEND. ANOTHER SHORT WAVE ENERGY IS EXPECTED TO CROSS 140W. THE TROUGH WILL HELP BRING A LOW PRESSURE TROUGH AND ANOTHER COLD FRONT TO OUR FORECAST AREA SATURDAY. BOTH THE ECMWF AND THE GFS ARE CONSISTENT WITH THE TIMING THROUGH SATURDAY ALTHOUGH THE GFS SHOWS A SLIGHTLY DEEPER LOW PRESSURE. THE ECMWF ON THE OTHER HAND TAKES THE LOW PRESSURE EAST IN A STRONGER WESTERLY FLOW AND KEEPS OUR FORECAST AREA IN SHOWERS ON SUNDAY. THE GFS SOLUTION HOWEVER KEEPS THE CLOSED LOW INTACT AND DROPS THE LOW INTO SOUTHERN OREGON THEN ON TO RENO. THE GFS SOLUTION WOULD LEAD TO A GREATER CHANCE OF LOW LEVEL NIGHTTIME SNOW. HAVE GONE WITH HIGH POPS FOR SATURDAY THROUGH SUNDAY AND KEPT SNOW LEVEL AROUND 2000 FEET FOR SOUTHWEST OREGON. BOTH MODELS THEN BUILD A LONG WAVE RIDGE INTO 130-140W WITH NORTHWEST FLOW INTO OUR FORECAST AREA. THIS WILL LEAD TO UPSLOPE OVERRUNNING RAIN/SNOW SHOWERS FOR MONDAY. AVIATION...AREAS OF MVFR CEILINGS AND MOUNTAIN OBSCURATIONS ARE PERSISTING ACROSS SOUTHERN OREGON AND NORTHERN CALIFORNIA THIS AFTERNOON. WEAK HIGH PRESSURE WILL ARRIVE TONIGHT WITH A STABILIZING AIR MASS. THIS ALONG WITH LINGERING GROUND MOISTURE WILL LEAD TO AREAS OF VALLEY LOW CLOUDS AND FOG WITH AREAS OF IFR CONDITIONS EXPECTED TO DEVELOP LATE IN THE EVENING INTO TUESDAY MORNING. CONDITIONS ARE EXPECTED TO IMPROVE DURING THE LATE MORNING.

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