000 FOUS11 KWBC 262027 QPFHSD PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 327 PM EST THU NOV 26 2009 VALID 00Z FRI NOV 27 2009 - 00Z MON NOV 30 2009 DAYS 1-3... APPALACHIANS... AMPLIFIED UPR LOW/VORT CENTER WILL PASS OVER THE GTLKS/NRN OH VLY TONIGHT AND FRIDAY WITH STRONG NW FLOW DEVELOPING BEHIND THE SYSTEM. FAVORED TERRAIN OF THE PA/WV APPALACHIANS WILL EXPERIENCE UPSLOPE/SOMEWHAT MOIST FLOW DURING THROUGH FRIDAY. MODEL SOUNDINGS FROM SW PA SHOW SNOW LVL DIPPING TO 2KFT BY MIDNIGHT TONIGHT AND REMAINING AT THAT LEVEL THROUGH TOMORROW. THIS MEANS 2-3 INCHES OF SNOWFALL IS POSSIBLE AOA THIS LEVEL...BUT MELTING WILL BE A LIMITING FACTOR ESPECIALLY AFTER SUNRISE FRIDAY. INTERIOR NORTHEAST TO NRN NEW ENG... COASTAL LOW CURRENTLY IN CAPE HATTERAS MARITIMES WILL DEVELOP QUICKLY OVERNIGHT AND BEGIN TO WRAP SIGNIFICANT MSTR WELL INLAND AS IT APPROACHES NEW ENGLAND ON FRIDAY...CONTINUING THROUGH SATURDAY. THE RELATIVELY WARM START TO THE SYSTEM WILL LIMIT SNOW TO THE HIGHER ELEVATIONS FRIDAY NIGHT...BUT THE EXACT SNOW LVL IS STILL UNCERTAIN GIVEN UPSTREAM PHASING ISSUES WITH THE ERN CONUS TROF. 12Z GUIDANCE SETTLING ON AN ECMWF TRACK AS THE GFS WRAPS UP THE LOW AND SWINGS IT TOO FAR WEST THROUGH ME OWING TO ITS STRONG PHASING. THAT SOLUTION WOULD HAMPER CAA AND SNOW AMTS. NAM IS VERY ROUST WITH CAA AND INDICATES VERY HIGH TOTALS FOR AREAS AOA 2KFT. HPC DOES PREFER A STRONG LOW SOLUTION SHOWN IN THE GFS...ONLY WITH THE MORE ELY TRACK. HPC INDICATES 8-10 INCHES IN THE HIGH ELEVATIONS OF THE WHITE MTNS EXTENDING THROUGH NH/WRN ME...QUICKLY TAPERING OFF WITH ELEVATION. NORTHWEST/SIERRA NEVADA... POS TILT/ELONGATED UPR TROF WILL CONTINUE TO SLIDE OUT OF THE NE PAC INTO WA/OR OVERNIGHT WHILE STEADILY EVOLVING INTO A SPLIT STREAM INVOLVING A NRN BAJA CLOSED LOW. A FRONTAL SFC WAVE WILL SLIDE THROUGH THE PAC NW TONIGHT AND FOCUS PRECIP IN THE NRN ROCKIES WHERE HT FALLS AND A BRIEF SHOT OF ENHANCED PAC MSTR WILL ACCOUNT FOR A FEW INCHES OF HIGH ELEVATION SNOW. THE TROF/SFC BOUNDARY WILL SLIDE EWD ACRS THE WRN CONUS THROUGH THE WEEKEND CARRYING PRECIP ALONG AND EAST OF THE AXIS. MODELS INDICATE MODEST MSTR AT BEST WITH THIS SYSTEM...AND IT DOES NOT CARRY PARTICULARLY COLD AIR...SO ONLY THE FAVORED HIGH ELEVATION TERRAIN WILL SEE SNOW. CO... A SLIGHT RISK OF 4 INCH AMOUNTS WAS INDICATED FROM SE WY TO NRN NM AS THE CUTOFF LOW OVER THE SOUTHWEST U.S. BEGINS TO MOVE EASTWARD. 12Z MODELS AGREE ON THE DEVELOPMENT OF BROAD SCALE UPSLOPE FLOW FOCUSED IN SRN/CNTRL CO BY SUNDAY MORNING SUGGESTING THAT GENERALLY LIGHT TO LOCALLY MODERATE SNOWFALL IS POSSIBLE IN THIS REGION. SNOWFALL EXCEEDING 4 INCHES IS POSSIBLE GIVEN THE UNCERTAINTY SHOWN BY SEVERAL DAYS OF MODEL RUNS WITH REGARDS TO THE FORWARD SPEED OF THE SYSTEM. THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT. SOWKO $$