EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 310 AM EDT THU APR 12 2018 VALID 12Z SUN APR 15 2018 - 12Z THU APR 19 2018 ...GREAT LAKES TO INTERIOR NORTHEAST SPRING SNOW/ICE THREAT SUN-TUE AS STRONG CONVECTION/HEAVY RAINS SWEEP UNDERNEATH OVER A WARMED ERN U.S... ...GUIDANCE/PREDICTABILITY ASSESSMENT... LATEST MODELS AND ENSEMBLES HAVE CONVERGED UPON A BETTER CLUSTERED MEDIUM RANGE FLOW EVOLUTION OVER THE LOWER 48 STATES...BOLSTERING OVERALL FORECAST CONFIDENCE IN AN ACTIVE PATTERN. HOWEVER...THERE REMAINS UNCERTAINTY WITH THE SPECIFICS OF FEATURES THAT ACT TO FOCUS LOCAL SENSIBLE WEATHER/THREATS. ACCORDINGLY...THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM A COMPOSITE BLEND OF THE LATEST GFS/ECMWF...GEFS/NAEFS/ECMWF ENSEMBLE MEANS...THE NATIONAL BLEND OF MODELS...AND WPC CONTINUITY. THIS BLEND OF REASONABLY COMPATABLE GUIDANCE MANAGES TO MAINTAIN WELL ORGANIZED SYSTEMS WHILE TENDING TO MITIGATE THE LESS PREDICTABLE SMALLER SCALE FEATURES. ...WEATHER/THREAT HIGHLIGHTS... A PRONOUCED PERIOD WITH SNOW/ICE WILL OCCUR ACROSS THE COOLED GREAT LAKES AND SPREAD INTO THE COLD AIR DAMMED INTERIOR NORTHEAST SUN INTO TUE AS THE SUPPORTING UPPER LEVEL LOW AND WELL ORGANIZED SURFACE LOW/FRONTAL SYSTEM TRACK THROUGH/UNDERNEATH AT MODEST SPEED. FARTHER SOUTH...DEEP SOUTHERLY FLOW IN ADVANCE OF A TRAILING WAVY COLD FRONT WILL FEED COPIOUS AMOUNTS OF MOISTURE FROM THE GULF OF MEXICO AND WRN ATLANTIC. WITH STRONG DYNAMIC LIFT AND INSTABILITY...CONVECTION IS EXPECTED TO FLOURISH AND MAY OFFER A SEVERE WEATHER THREAT AS MONITORED BY THE STORM PREDICTION CENTER. A WIDESPREAD SWATH OF HEAVY CONVECTIVE RAINS OFFER TRAINING POTENTIAL...BUT THE FRONT SWEEPS THROUGH TO LIMIT EVEN HEAVIER TOTALS. THE WEST COAST WILL HAVE ANOTHER INCOMING SYSTEM BEGIN TO PUSH THROUGH BY THE END OF THE WEEKEND AND INTO EARLY NEXT WEEK. THE MID-UPPER LEVEL TROUGH WILL SWING OVER THE WEST COAST TO THE INTERMOUNTAIN WEST/ROCKIES MON/TUE AND THEN EJECT EASTWARD OVER THE CENTRAL AND ERN U.S...PRODUCING MODEST PRECIPITATION. BY NEXT WED/THU...YET ANOTHER AMPLIFIED SYSTEM WILL REACH THE WEST COAST. PRECIPITATION WILL AGAIN BEGIN TO INCREASE ACROSS THE PACIFIC NORTHWEST AND N-CENTRAL CALIFORNIA AS THE MID-UPPER LEVEL TROUGH/HEIGHT FALLS APPROACH. RAINFALL ALONG WITH HIGHER ELEVATION SNOW IS THEN EXPECTED TO SPREAD INLAND INTO THE INTERMOUNTAIN WEST BY AROUND NEXT THU. WPC MEDIUM RANGE 500MB PROGS...SURFACE/FRONTS PROGS...SENSIBLE WEATHER GRIDS...QPF GUIDANCE...AND WINTER WEATHER OUTLOOK SNOW/SLEET PROBABILITY FORECASTS CAN BE FOUND AT... http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 SCHICHTEL