check out HPC's final extended discussion today EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 136 PM EST FRI JAN 28 2011 VALID 12Z MON JAN 31 2011 - 12Z FRI FEB 04 2011 ...MAJOR WINTER STORM SETTING UP NEXT WEEK FROM THE ROCKIES TO THE NORTHEAST... MEDIUM RANGE GUIDANCE IS AGREEABLE WITH THE LARGE SCALE SCENARIO OF AN ELONGATED MEAN TROF EXTENDING FROM NERN CANADA SWWD INTO THE SWRN CONUS... LIKELY WITH SOME SEPARATION BETWEEN SRN CANADA/NRN TIER CONUS FLOW AND WRN/SRN CONUS FLOW. THIS TROF WILL BE SUPPORTED BY A MEAN RIDGE THAT SHOULD PERSIST OVER THE ERN PAC/WRN CANADA ALBEIT WITH SOME CHANGE IN SHAPE OVER TIME. WHILE A GOOD CONSENSUS EXISTS WITH THE LARGE SCALE MEAN EVOLUTION... THERE IS LOWER THAN AVERAGE CONFIDENCE IN DETAILS DUE TO THE SPLIT FLOW NATURE OF THE NOAM PATTERN AND ADDITIONAL UNCERTAINTIES PRESENTED BY ERN PAC ENERGY THAT MAY TRY TO PASS THRU THE MEAN RIDGE BY MID-LATE WEEK. THE MOST PROMINENT SFC SYSTEM FOR WHICH SHRTWV UNCERTAINTIES COME INTO PLAY IS FCST TO TRACK NEWD FROM THE SRN PLAINS TUE ONWARD. TO VARYING DEGREES THE 00Z GFS AND ECMWF HAVE MADE MEANINGFUL NWWD ADJUSTMENTS FROM FAIRLY SUPPRESSED TRACKS IN MULTIPLE PREVIOUS RUNS. THE ECMWF TREND IS MORE EXTREME AS ITS PREVIOUS TWO RUNS WERE ON THE SERN SIDE OF THE ENVELOPE AND THE NEW 00Z RUN IS NOW ON THE NWRN SIDE OF GUIDANCE. THE CANADIAN IS A FAST EXTREME TO BRING SWRN CONUS ENERGY INTO THE PLAINS AND IS ALSO IN THE NWRN PART OF THE SPREAD... WHILE THE UKMET TRACK IS NOT QUITE AS FAR NWWD AS ITS PREVIOUS RUN. OVERALL PREFER A GEFS MEAN/12Z ECMWF ENSEMBLE MEAN SOLN THAT FALLS IN THE MIDDLE OF LATEST AND RECENT GUIDANCE GIVEN THE SENSITIVITY OF SHRTWV DETAILS AND SIGNIFICANT RUN TO RUN CONTINUITY CHANGES. BEHIND THIS SYSTEM... BY WED NIGHT-FRI THERE IS CONSIDERABLE SPREAD REGARDING ENERGY THAT MAY TRY TO PASS THRU THE ERN PAC MEAN RIDGE. THE 00Z ECMWF AND SLOWER 00Z GFS BOTH SEEM A LITTLE STRONG SO THE ENSEMBLE MEAN BLEND USED FOR THE PLAINS/ERN CONUS SYSTEM PROVIDES A MORE TOLERABLE SOLN AT THIS TIME. THE GEFS MEAN IS A LITTLE EXTREME WITH ITS SLOWER TIMING/WWD ELONGATION OF THE TROF SETTLING OVER THE SWRN CONUS SO INCLUSION OF THE ECMWF MEAN TONES DOWN THIS ASPECT OF THE FCST. WHILE DAYS 5-7 WED-FRI FOLLOW A BLEND OF THE GEFS/12Z ECMWF MEANS... MISSING DATA DUE TO EARLIER COMMS ISSUES PRECLUDED USE OF THE ECMWF MEAN FOR DAYS 3-4. THUS THE EARLIER PART OF THE FCST STARTED WITH A BLEND OF GFS/ECMWF/GEFS MEAN SOLNS TO ARRIVE AT AN ACCEPTABLE COMPROMISE. UPDATED MORNING PRELIMS USE A MULTIMODEL BLEND OF 00Z GFS/ECMWF/CMC/UKMET/GFS ENS MEAN. THE RESULT IS NEARLY IDENTICAL TO THE EARLIER USED SOLUTION. 12Z MODEL GUIDANCE FOLLOWS CONTINUITY AND A COMPOSITE OF THE RUNS WOULD CONTINUE TO YIELD THE BLENDED SOLUTION OF HPC. NO CHANGES FOR AFTERNOON FINALS. AS SHORTWAVE ENERGY MOVES INTO THE FOUR CORNERS REGION EARLY TUESDAY AND ARCTIC HIGH PRESSURE PLUNGES DEEP INTO THE PLAINS WITH GREATER THAN 20 DEGREE NEGATIVE TEMPERATURE ANOMALIES. THIS WILL BRING STRONG UPSLOPE FLOW INTO THE CO ROCKIES FRONT RANGE WITH MDT/HVY SNOWFALL TO THE SRN ROCKIES SPREADING EWD INTO THE CENTRAL PLAINS. MID LEVEL ENERGY SHEARS OUT EWD AND A MDT SFC LOW DEVELOPS OVER ERN TX BY TUESDAY. THIS LOW MOVES NEWD INTO KY/TN WED AND REFORMS OFF THE MID ATLC CAPES AND RAPIDLY MOVES NEWD OFF NOVA SCOTIA BY THURSDAY. MDT TO HVY RAINFALL POTENTIAL SOUTH OF THE LOW PRESSURE TRACK WITH SNOW ACROSS THE CENTRAL PLAINS AND MAINLY NORTH OF THE OH RIVER AND MASON DIXON LINE INTO NEW ENG. HEAVY SNOW THREAT INDICATED BY OPERATIONAL MODELS QPF OUTPUT/ANALOGS AND FAVORABLE MID AND UPPER LEVEL JET STRUCTURE WITH ICING THREAT ALONG THE CHANGE OVER AND THEN THE DAMMED IN AREA IN THE MID ATLC PIEDMONT. PACIFIC RECON FLIGHTS REQUESTED INTO THE CRITICAL UNCERTAINTY AREA AHEAD OF THIS SYSTEM IN THE NE PACIFIC. IF A FLIGHT IS AVAILABLE THIS DATA COULD GET INTO THE MODEL SYSTEMS BY THE RUNS OF SUNDAY 00Z/12Z 30 JAN. RAUSCH/ROSENSTEIN Ñ |