EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 143 AM EST SUN JAN 28 2018 VALID 12Z WED JAN 31 2018 - 12Z SUN FEB 04 2018 ...A WINTRY WEATHER THREAT FOR THE NWRN US/ROCKIES AND INTO THE ERN US... ...GUIDANCE/PREDICTABILITY ASSESSMENT... THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM A COMPOSITE OF THE 18 UTC GEFS MEAN...12 UTC ECMWF ENSEMBLE MEAN...AND WPC CONTINUITY. THIS SEEMS PRUDENT CONSIDERING THE ABOVE NORMAL LOCAL FORECAST SPREAD WITH THE MAIN WEATHER/THREAT FOCUSING FEATURES DESPITE REASONABLY SIMILAR GFS/GEFS MEAN AND ECMWF/ECMWF ENSEMBLE MEAN LARGER SCALE FLOW EVOLUTIONS. THE 00 UTC GFS/ECMWF HAVE TRENDED THE LAST FEW NIGHTS TOWARD THE ENSEMBLE MEAN COMPOSITE...AT LEAST TEMPORARILY BOLSTERING FORECASTER CONFIDENCE. ...WEATHER HIGHLIGHTS/THREATS... A POTENT LEAD SHORTWAVE TROUGH ENERGY/HEIGHT FALLS PUNCHES PROGRESSIVELY OUT FROM THE NWRN US TO THE N-CENTRAL US BY MIDWEEK. WEAKER UPSTREAM IMPULSES WILL SUPPORT ADDITIONAL PERIODS OF MODEST PRECIPIATION INCLUDING HEAVIER TERRAIN ENHANCED SNOWS ACROSS THE NWRN US AND ESPECIALLY THE NRN ROCKIES WITH ADDED NRN STREAM IMPULSES OF UNCERTAIN TIMINGS. DOWNSTREAM...A MAIN FRONT REACHES THE GREAT LAKES WED/THU...DRAGGING A TRAILING COLD FRONT THROUGH THE PLAINS AND INTO THE LOWER MS/OH VALLEY. THE SFC LOW CENTER WILL TRACK THROUGH SRN CANADA WITH MOST OF THE PRECIPITATION TO START...BUT INCREASED GULF MOISTURE WILL SUPPORT AN EXPANDED PRECIPITATION AREA ALONG/AHEAD OF THE COLD FRONT WED/THU ACROSS THE E-CENTRAL STATES/SOUTHEAST. MODELS HAVE THEN BEEN SHOWING VARYING DEGREES OF SFC WAVE DEVELOPMENT OUT OF THE LOWER MS VALLEY NORTHEASTWARD THROUGH THE MID-ATLANTIC ON FRIDAY THEN INTO THE ATLANTIC SATURDAY OFF THE NEW ENG COAST. AS SUCH DEVELOPMENT IS SENSITIVE TO SMALLER SCALE FEATURES WITH LONG LEAD TIMES...ENSEMBLE TRENDS WILL REMAIN MORE USEFUL FOR THE NEXT FEW DAYS THAN ANY GIVEN DETERMINISTIC RUN. ENOUGH COLD AIR SHOULD BE IN PLACE TO THE NORTH OF THE FRONT TO SUPPORT A WIDESPREAD SWATH OF POTENTIALLY HEAVY SNOW PARALLEL TO ANY SFC LOW TRACK OR AT LEAST PARALLEL TO THE UPPER TROUGH AXIS PROPAGATION. SCHICHTEL