844 FOUS11 KWBC 092056 QPFHSD PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 355 PM EST THU FEB 09 2012 VALID 00Z FRI FEB 10 2012 - 00Z MON FEB 13 2012 DAY 1... ...NORTHERN CASCADES/NORTHERN ROCKIES... THE HIGH AMPLITUDE MID-UPPER RIDGE CENTERED OVER WRN NOAM DRIFTS EAST... WITH A MID-UPPER TROUGH DRIFTING TOWARDS THE COAST. A WEAK SFC LOW MOVES SLOWLY NORTH OFF THE COAST. PACIFIC MOISTURE ADVECTS NORTH ACROSS WESTERN OR/WA OVERNIGHT AND FRI WITH OCCASIONAL 300 MB DIVERGENCE MAXIMA COMING INTO THE CASCADES. THE MODELS CLUSTER IN THE RANGE OF 0.15-0.4 INCHES LIQUID EQUIVALENT...LEADING TO A LOW RISK OF FOUR INCHES OF SNOW. FURTHER INLAND...A BAND OF CONFLUENT FLOW WITH A BACKDOOR COLD FRONT DEVELOPS AS HIGH PRESSURE MOVES EAST ON TO THE PLAINS AND RETURN SOUTHEAST FLOW DEVELOPS. 700 BM CONVERGENCE DEVELOPS FRI AFTERNOON ALONG WITH WEAK 300 MB DIVERGENCE IN THE RIGHT ENTRANCE REGION OF THE UPPER JET. THIS IS EXPECTED TO RESULT IN LIGHT SNOWS DEVELOPING WITH ACCUMS OF 4 INCHES OR MORE ACROSS PORTIONS OF THE NORTHERN ROCKIES. PROBABILITIES WERE EQUALLY WEIGHTED AMONG THE INDIVIDUAL MODELS/SREF MEAN QPF/THERMAL PROFILES. THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT. DAY 2... ...EASTERN NEW ENGLAND/CENTRAL APPALACHIANS... MODELS SHOW THE DEVELOPMENT OF SFC LOW OFF THE MID ATLANTIC COAST AND MOVING NORTHEAST OFF THE NEW ENGLAND COAST SAT...REACHING THE CANADIAN MARITIMES BY SUN MORNING. THE DEVELOPMENT IS COMPLEX WITH MOST OPERATIONAL MODELS SHOWING A DUAL LOW STRUCTURE AND DIFFERENCES BETWEEN MORE DEVELOPMENT/CLOSER TO THE COAST WITH THE NORTHWEST-MOST LOW AND WHETHER THE STRONGER DEVELOPMENT OCCURS WITH THE SOUTHEAST MOST LOW. THE PHASING OF NORTHERN/SOUTHERN STREAM SHORTWAVES AND MAGNITUDE OF THE TROUGH COMING OFF THE EAST COAST WILL HELP DETERMINE WHICH CLUSTER IS MORE CORRECT. PROBABILITIES FOR 4 AND 8 INCHES ARE SHOWN IN CASE THE 12Z-18Z NAM/12Z GEFS MEAN IDEAS OF THE STRONGER/CLOSER IN LOW ARE MORE CORRECT AND MORE SNOW OCCURS ACROSS SOUTHEAST NY/NEW ENGLAND. PRECIP TYPES REMAIN UNCERTAIN AS INDIVIDUAL SOLUTIONS ALSO SHOW POTENTIAL FOR MIXED PRECIPITATION TYPES IN EASTERN LONG ISLAND TO CAPE COD. THE 12Z ECMWF NUDGE OF THE PRIMARY LOW FURTHER OFFSHORE KEEPS RISKS AS MODERATE FOR NOW. LOW LEVEL CONVERGENCE DEVELOPS WITH A COLD FRONT PASSING THROUGH THE OH VLY/CNTRL APPALACHIANS. POST-FRONTAL PERSISTENT MOISTURE COMBINES WITH UPSLOPE NORTHWEST BNDRY LAYER WINDS AND LOCAL 300 MB DIVERGENCE NEAR THE JET CORE TO PRODUCE SOME LOCALLY HVY SNOWS ON SAT ALONG THE WRN SLOPES OF THE WV MTNS. ...RANGES OF WYOMING/ADJACENT CO-SOUTH CENTRAL MT.... THE FRONTAL ZONE PERSISTS OVER THE CENTRAL AND NORTHERN ROCKIES AS THE HIGH BUILDS SOUTHEAST ACROSS THE PLAINS STATES. THE INITIAL 300 MB JET MAXIMA EXTENDS NORTHWEST TO SOUTHEAST ACROSS WY AND THEN PROPAGATES SOUTHEAST INTO THE PLAINS...WITH AN UPPER LEVEL RIDGE BUILDING EAST ACROSS THE ROCKIES. LIKEWISE...THE INITIAL BANDS OF 700 MB CONVERGENCE EXTENDING NORTHWEST-SOUTHEAST ACROSS THE STATE LINGER FOR SEVERAL HOURS AND THEN WEAKEN WITH TIME. THE HIGH QPF AMOUNTS ARE FOCUSED ON THE RANGES OF NORTHWEST AND SOUTHEAST WY...WHERE THE HIGHER PROBABILITIES ARE SHOWN. THE LIMITED DURATION OF THE EVENT KEEPS PROBABILITIES FROM REACHING A HIGH LEVEL. THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT. DAY 3... ...CENTRAL-SOUTHERN GREAT BASIN/ROCKIES... A MID-UPPER TROUGH AND SFC LOW DRIFT EAST ACROSS THE GREAT BASIN...WITH THE UPPER LEVEL JET MAXIMA CROSSING AZ/NM. UPPER DIVERGENCE MAXIMA WITHIN DIFLUENT FLOW ALOFT CROSS THE RANGES OF UT/CO/NORTHERN AZ-NORTHERN NM. MOISTURE WILL BE LIMITED WITH THIS SYSTEM...WITH AREAL PRECIPITABLE WATER VALUES AVERAGING NEAR A QUARTER INCH. HOWEVER...700 MB CONVERGENCE IN ADVANCE OF THE FRONTAL BOUNDARY ACROSS UT/CO/NORTHERN AZ/NORTHER NM AIDS OROGRAPHICS IN PRODUCING ASCENT. THIS RESULTS IN SNOW THREAT AREAS IN PARTS OF THE WASATCH AND SAN JUAN MTNS. THE GFS SHOWS FASTER INLAND MOVEMENT OF THE TROUGH AND THUS WAS GIVEN LESS WEIGHT. THE 00-12Z ECMWF WAS CONSISTENTLY SLOWER AND CLUSTERS WELL WITH THE TIMING OF THE 09Z SREF MEAN/12Z GEFS MEAN/12Z UKMET...SO THESE SOLUTIONS WERE GIVEN GREATER WEIGHTING. THE NAM HAS THE HIGHEST AMOUNTS DUE TO STRONG SUSTAINED 700 MB CONVERGENCE COMING INTO THE SAN JUANS. ...GREAT LAKES... THE MODELS FCST LOW LEVEL CONFLUENT FLOW WITH A BNDRY LAYER WIND MAXIMA EXTENDING FROM LK SUPERIOR ACROSS NORTHERN LK HURON ND THEN DOWNSTREAM INTO LK ONTARIO/ADJACENT PORTIONS OF NEW YORK. AN ENHANCED BAND OF HIGHER RH FLOWS IN CONJUNCTION WITH THE LOW LEVEL JET...SUPPORTING A PERIOD OF LK EFFECT SNOWS. WITH THE LOW LEVEL RIDGE BUILDING FROM THE UPPER MS VALLEY TOWARDS THE UPPER LAKES ON SUN...THE COVERAGE/INTENSITY WILL WIND DOWN. AS A RESULT...PART OF THE FORECAST UNCERTAINTY WILL BE EVENT DURATION. THE SHORT DURATION OF FAVROABLE DEEP MOISTURE LEAVES PROBABILITIIES AS LOW. THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT. PETERSEN $$ 647 FOUS11 KWBC 090906 QPFHSD PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 405 AM EST THU FEB 09 2012 VALID 12Z THU FEB 09 2012 - 12Z SUN FEB 12 2012 DAY 1... THE PROBABILITY OF SIGNIFICANT ICING AND/OR SNOW IS LESS THAN 10 PERCENT. DAY 2... ...NORTHERN CASCADES/NORTHERN AND CENTRAL ROCKIES... A SHRTWV LIFTING OUT OF THE BASE OF THE LONGWV TROF OVER THE ERN PAC WILL BEGIN TO UNDERCUT THE STRONG RIDGE CENTERED OVER WRN NOAM...MOVING INTO THE PAC NW FRI MORNING AND BRINGING A CHANCE FOR SNOW ACROSS THE HIER PEAKS OF THE NRN CASCADES. ENERGY/PAC MOISTURE SPILLING DOWNSTREAM ACROSS THE RIDGE WILL OVERRUN A BACKDOOR COLD FRONT DRIVEN W UP AGAINST THE NRN ROCKIES BY A WELL-DEFINED SHRTWV DROPPING THRU THE BACKSIDE OF THE DEEP TROF CENTERED OVER ERN CAN. THIS IS EXPECTED TO PRODUCE SNOWS WITH ACCUMS OF 4-INCHES OR MORE ACROSS PORTIONS OF THE ROCKIES PARTICULARLY FROM THE LEWIS RANGE OF NWRN MONT TO THE LARAMIE MTNS OF SERN WY. ...CENTRAL APPALACHIANS... SELY FLOW AHEAD OF SRN STREAM SHRTWV MOVING OUT OF THE SRN PLAINS AND THRU THE LWR MS VLY WILL MOVE SOME MODESTLY DEEPER MOISTURE UP INTO THE OH VLY/CNTRL APPALACHIANS AHEAD OF AN ARCTIC COLD FRONT DROPPING SEWD INTO THE REGION AS THE AFOREMENTIONED SHRTWV DROPPING OUT OF CANADA BEGINS TO MOVE THRU THE BASE OF THE NRN STREAM TROF. ALONG WITH FAVORABLE UPR JET DYNAMICS AND OROGRAPHIC LIFT THIS COULD PRODUCE SOME LOCALLY HVY SNOWS ON SAT ALONG THE WRN SLOPES OF THE CNTRL WV MTNS. FOR NOW THIS APPEARS THIS APPEARS TO BE THE BEST CHANCE FOR ANY HVY SNOWS OVER THE ERN CONUS THRU THE SHORT-TERM. AS THE SRN STREAM SHRTWV MOVES THRU THE SOUTHEAST...MODELS SHOW THE DEVELOPMENT OF SFC LOW DEEPENING ALONG THE COAST NEAR THE NC/VA BORDER SAT MORNING. THIS LOW IS THEN FORECAST TO TRACK TO THE NE REACHING THE CANADIAN MARITIMES BY SUN MORNING. MODELS HAVE BEEN TRENDING INTO BETTER AGREEMENT AND SHOW THE PROGRESSIVE NRN STREAM TROF PUSHING THE LOW FAR ENOUGH OFFSHORE ALONG A TRACK THAT WOULD ONLY AFFORD MINOR ACCUMS FOR LONG ISL AND THE NEW ENG COAST SAT INTO EARLY SUN. THIS WILL BARE WATCHING HOWEVER...SHOULD THE MODELS TREND SLOWER WITH THE NRN STREAM. THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT. DAY 3... ...CENTRAL GREAT BASIN TO THE CENTRAL ROCKIES... A SECOND SHRTWV WILL MOVE INTO THE WEST...UNDERCUTTING THE RIDGE...THIS ONE FURTHER TO THE S DIGGING ACROSS CA INTO THE CENTRAL GREAT BASIN/SOUTHWEST. MOISTURE WILL BE LIMITED WITH THIS SYSTEM...HOWEVER MID/UPR LVL DYNAMICS ALONG WITH OROGRAPHICS COULD BE SUFFICIENT ENOUGH TO PRODUCE SOME SCT HEAVIER AMTS SOME OF THE MTNS OF NWRN NV...AS WELL AS PARTS OF THE WASATCH AND SAN JUAN MTNS. THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT. PEREIRA $$ 890 FOUS11 KWBC 081958 QPFHSD PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 258 PM EST WED FEB 08 2012 VALID 00Z THU FEB 09 2012 - 00Z SUN FEB 12 2012 DAY 1... THE PROBABILITY OF SIGNIFICANT ICING AND/OR HEAVY SNOW IS LESS THAN 10 PERCENT. DAYS 2/3... ...WASHINGTON CASCADES/NORTHERN ROCKIES... WARM ADVECTION PRECIPITATION WILL BE THE KEY INGREDIENT FOR SNOWFALL ACCUMULATIONS IN THE NORTHERN WASHINGTON CASCADES AND NORTHERN ROCKIES OF IDAHO...WESTERN MONTANA AND NORTHWEST WYOMING. PACIFIC TROUGH AND ATTENDANT SURFACE LOW MOVING NORTHWARD INSIDE OF 130 W...SPREADS A BROAD WARM FRONT...WITH ISENTROPIC LIFT GENERATING AREAS OF SNOWFALL ABOVE 4500-5000FT MSL ACROSS WASHINGTON. DOWNSTREAM...VERY LITTLE COLD AIR TO WORK WITH WEST OF THE DIVIDE...WITH SNOWFALL GENERALLY AT/ABOVE 6000FT MSL IN IDAHO...NORTHERN NEVADA AND WESTERN MONTANA. ACROSS THE NORTHWEST...GIVEN THE PRIMARY SURFACE TRACK STAYS OFFSHORE ALONG THE PAC NW COAST AND INTO BC...LIMITED MOISTURE STREAMS DOWNWIND...CURBING TOTAL SNOWFALL ACCUMULATIONS...TO A MAXIMA OF 2-4 INCHES FOR EACH 24 HOUR PERIOD. SMALL AREAS OF 4+ INCH AMOUNTS CLOSELY FOLLOWED THE NAM/SREF AND ECMWF THERMAL SOLUTIONS WITH THE ENSEMBLES IDENTIFYING THE MT BAKER AREA ABOVE 5500FT MSL FOR 4-8 INCHES. EAST OF THE DIVIDE...A MUCH COLDER LOW-LEVEL AIRMASS WITH ORIGINS IN CANADA WILL BE IN PLACE AS MID-LEVEL WARM ADVECTION ADVANCES EASTWARD AND LIGHT SNOWFALLS DEVELOP IN TOP-DOWN FASHION...TO VALLEY FLOORS. MUCH OF THE COLD ADVECTION BEGINS TO MOVE SEWD INTO NW MONTANA THURSDAY EVENING...SPREADING INTO CENTRAL/EASTERN MONTANA AND NORTHERN WYOMING ON FRIDAY AND COLORADO ON SATURDAY. MUCH OF THE EAST SIDE SNOWFALL OCCURRING IN EAST CENTRAL/SOUTHERN MONTANA...CENTRAL WYOMING AND EASTERN COLORADO WILL BE GENERATED BY MECHANICAL LIFT/TURBULENT MIXING FROM A RATHER BROAD UPSLOPE FLOW COMPONENT AND AXIS OF H85-H7 FRONTOGENESIS. ...GREAT LAKES AND CENTRAL APPALACHIANS... VERY COLD UPPER-LEVEL VORTEX AND EMBEDDED SHORTWAVE ENERGY ANCHORS OVER HUDSON BAY AND EASTERN CANADA ON DAY 2/3 AND SLOWLY SLIPS SOUTHWARD INTO THE NORTHEAST AND EASTERN GREAT LAKES. SHORTWAVE ENERGY ROTATING THROUGH THE BASE OF THE TROUGH...SPREADS ACROSS THE UPPER GREAT LAKES AND ALONG THE ST LAWRENCE VALLEY INTO NORTHERN NEW ENGLAND...WITH LAKE-EFFECT SNOW SHOWERS ACROSS PORTIONS OF MICHIGAN...WESTERN NEW YORK AND DOWNWIND OF LAKE ERIE. BY FRIDAY NIGHT AND SATURDAY...BROAD UPSLOPE NORTHWEST FLOW WILL BE GENERATING SNOWFALLS ACROSS THE APPALACHIANS OF WESTERN PENNSYLVANIA...EASTERN OHIO...FAR WESTERN MARYLAND AND PORTIONS OF EASTERN WEST VIRGINIA/SOUTHWESTERN VIRGINIA. THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT. VOJTESAK $$