Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 413 AM EDT Wed Mar 21 2018 Valid 12Z Wed Mar 21 2018 - 12Z Fri Mar 23 2018 ...Spring equinox arrives as yet another nor'easter is expected to impact the Mid-Atlantic northward into coastal New England... ...Unsettled weather will move across the western U.S. with the flash flooding likely for coastal central to southern California... A hyperactive weather pattern continues across the U.S. as we are facing yet another significant nor'easter, the fourth one since early this month, expected to impact the Eastern Seaboard during the next couple of days. This particular nor'easter will be more prolonged than previous ones as a larger upper-level cyclone currently over the Ohio Valley will push eastward while interacting and intensifying a developing surface cyclone just off the Mid-Atlantic coast. The surface cyclone is expected to deepen rapidly during the day today off the Delmarva Peninsula as energy is taken from the cold upper low to intensify the surface cyclone over the relatively warm Atlantic waters. Rain will initially be the primary precipitation near the coast but as the day progresses, the rain/snow line is forecast to progress eastward toward the coast when cold air from the upper-level low arrives. As the cyclone is expected to intensify rapidly just off the coast, bursts of heavy wet snow could form on the back side the low across the northern Mid-Atlantic, spreading northward into southern New England by evening. Winds will strengthen throughout the day especially along the coast where coastal flooding will become possible. If this coincides with the heavy snow bands, conditions could approach blizzard criteria in parts of southern New England and New Jersey coast. By Thursday, the snow and winds will impact coastal New England into Maine but conditions will improve as the day progresses when the nor'easter begins to move away into the Canadian Maritimes. Meanwhile, an energetic and moisture-laden frontal system is approaching California. This system is forecast to interact with a large upper-level low dropping down from the Gulf of Alaska over the next couple of days to spread unsettled weather into the western U.S. The heaviest rainfall is forecast for central to southern coastal California where flash flooding is quite possible. Heavy snow is expected for the Sierra Nevada where snowfall accumulations of 2 to 4 feet are expected with localized amounts up to 5 feet possible! By Friday morning, the northern edge of the moisture could reach northern Plains with wet snow likely. Kong Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php