Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Sun Feb 17 2019 Valid 12Z Wed Feb 20 2019 - 12Z Sun Feb 24 2019 ...Multi-day Heavy Rain Threat for Lower Mississippi/Tennessee Valleys to the Southern/Central Appalachians and Snow/Ice for the Mid-Mississippi/Ohio Valleys and Northern/Central Mid-Atlantic to Southern New England... ...Cold weather persists in the western to central U.S., with unsettled weather focusing into the Southwest... ...Overview... Persistent western U.S. mid-upper level troughing will be reinforced during the medium range period by shots of renewed energy. This feature plus an unyielding Bahamas upper ridge creates a favorable pattern for a multi-day heavy rain threat this week from the lower MS/TN Valleys to the Srn/Central Appalachians and a snow/ice threat from the Mid-MS/OH Valleys to especially for the n-central Mid-Atlantic to srn New England Wed-Thu. ...Guidance/Predictability Assessment and Preferences... Guidance seems to agree well with ejection of a lead mid/upper-level trough from the Plains to Northeast Wed-Thu and an upstream pattern this week of potent upper troughs/height falls progressing overtop a northeast Pacific ridge that then dig sharply southward to reinforce a western U.S. mean trough. This pattern offers above normal predictability into Friday, but confidence decreases next weekend as guidance is more mixed with main upper trough ejection from the Southwest and downstream phasing and surface cyclogenesis potential over the east-central U.S. Ensemble means offer more consistent guidance. Accordingly, the WPC medium range suite was derived from a multi-model blend of the reasonably well clustered 18 UTC GFS/GEFS mean and 12 UTC ECMWF/ECMWF ensemble mean, but substantially reduced weighting on deterministic models next weekend amid gradually growing forecast spread/uncertainty with pattern transiiton. ...Weather Highlights/Hazards... An prolonged excessive rainfall threat from the lower MS/TN Valleys to the Srn/Central Appalachians will be a main story this week. Deep layered and highly anomalously moist southwest flow channeled from the Southern Plains to the East will act to sustain a Southeast ridge and fuel multi-day threats of heavy rain/training. On the northern edge, a cold surface high and cold air damming in the Mid-Atlantic region is expected, leading to frozen precipitation. Potentially heavy snow and ice is a possibility from the Middle Mississippi Valley to Ohio Valley and especially the northern Mid-Atlantic into southern New England Wed-Thu. With anomalously low heights in the western U.S., much below average temperatures will prevail for the western and central U.S. A main low is progged to dig from the Pacific Northwest to California Wed/Thu to the Southwest by Fri along with enhanced precipitation including higher elevation heavy snow. The main system is expected to eject northeastward across the central and east-central U.S. next weekend. Schichtel WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation and winter weather outlook probabilities are found at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4