EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 220 AM EST THU FEB 01 2018 VALID 12Z SUN FEB 04 2018 - 12Z THU FEB 08 2018 ...PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT... MEDIUM RANGE FLOW ALOFT SHOULD CONTINUE TO FEATURE RIDGING OFF THE WEST COAST AND BROAD CYCLONIC FLOW/TROUGHING DOWNSTREAM OVER MUCH OF THE REST OF THE LOWER 48. THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM THE 18 UTC GEFS AND 12 UTC NAEFS/ECMWF ENSEMBLE MEANS AND WPC CONTINUITY. THE MEANS BLENDED WELL WITH DETERMINISTIC MODEL GUIDANCE SUN/MON...BUT OFFERED A MUCH MORE RUN TO RUN CONSISTENT MESSAGE BY NEXT TUE-THU. ...WEATHER HIGHLIGHTS/THREATS... A LONG SERIES OF PROGRESSIVE IMPULSES DIGGING SEWD TO THE LEE OF AN ERN PACIFIC MID-UPPER LEVEL MEAN RIDGE POSITION WILL SUPPORT PERIODS OF MODEST PAC NW PRECIPITATION OVER THE NEXT WEEK. FURTHER EXPECT TERRAIN ENHANCED SNOWS ACROSS THE NWRN US AND ESPECIALLY THE NRN ROCKIES WITH ADDITIONAL NRN STREAM IMPULSE PASSAGES...ALONG WITH POST-FRONTAL UPSLOPE SNOWS. DOWNSTREAM...A SUPERBOWL SUNDAY CLIPPER SYSTEM SUPPORTED BY NRN STREAM SHORTWAVE ENERGIES WILL SPREAD SNOWS FROM THE MIDWEST/GREAT LAKES TO THE NORTHEAST. UNDERNEATH...RAINS WILL MEANWHILE INCREASE OVER THE GULF COAST/TN VALLEY/SERN US INTO SUNDAY WITH RETURN FLOW AS PER SRN STREAM IMPULSE AND INDUCED SURFACE WAVE PASSAGE. WIDESPREAD MODERATE TO HEAVIER PCPN WILL EXPAND RAPIDLY NEWD ACROSS THE ERN US INTO MONDAY WITH LOW DEVELOPMENT. LATEST GUIDANCE OFFERS AN INTERIOR ERN US TO NERN STATES WINTER WEATHER THREAT AS MOISTURE WRAPS OVER THE WAVY FRONT ON THE ERN PERIPHERY OF AN EXPANDING CENTRAL TO ERN US ARCTIC AIRMASS. FORECAST SPREAD INCREASES IN THIS FLOW REGIME FROM THE S-CENTRAL TO ERN US MID-LATER NEXT WEEK WITH GUIDANCE OFFERING A WIDE VARIETY OF FRONTAL LOW DEVELOPMENTS OF LESS THAN AVERAGE PREDICTABILITY. HOWEVER...THE 00 UTC ECMWF HAS JOINED RECENT TRENDS FROM THE GFS TO DEVELOP A MUCH DEEPER EAST-CENTRAL TO ERN US LOW WED/THU COMPARED TO MOST EARLIER GUIDANCE. THIS WOULD CLEARLY ENHANCE SYSTEM POTENTIAL/THREAT AS DEEPER MOISTURE REBOUNDS IN THE WAKE OF THE LEAD SYSTEM ON THE LEADING FRONTAL EDGE OF THE NEXT COLD HIGH SURGE. SCHICHTEL