Winter is making a last-ditch effort to fill in the Philadelphia to Boston snow-hole along the I-95 corridor less than two weeks before an expected warm-up ends chances for significant snow. The snow will last just under 12 hours for most of the Northeast, but this will be long enough to pack quite a punch as over 6″ of snow will fall in this short time span. Although the snow should fall short of a foot for most areas, this quick-hitting, plowable snow will be the most disruptive of the otherwise paltry 2018-2019 winter season as it causes havoc on the Monday morning commute.
The storm will materialize over the Southern Plains and Mississippi River Valley overnight Saturday as a storm originating in the Pacific Ocean interacts with a boundary along the Gulf Coast. Heavy snow will develop lee of the Rocky Mountains Saturday night through Sunday morning as the system taps into abundant Gulf moisture. Snow will accumulate 6-8″ across western and central Kansas with lesser amounts of 3-6″ extending into southern Nebraska, northern Oklahoma, and western Missouri through early Sunday afternoon. Snow will be less disruptive in the middle Mississippi and Ohio Valleys, where 1-4″ of snow is expected to fall through early evening as the storm intensifies over the Southeast.
While heavy snow pounds the Southern Plains and middle Mississippi River Valley, heavy downpours and severe thunderstorms will develop over the Deep South. A complex of thunderstorms will develop Sunday morning over the western Gulf States ahead of the primary storm’s cold front. By early afternoon the storms will have organized into a squall line capable of producing tree-toppling wind gusts. Ahead of the squall line, discrete supercells may develop in southern Alabama and western Georgia during the afternoon hours. These severe thunderstorms will be capable of producing destructive tornadoes and golf-ball sized hail before the arrival of the squall line.
The same energy fueling severe thunderstorms in the Deep South will help overspread heavy snow from southwest to northeast across the northern Mid-Atlantic and New England Sunday afternoon and evening. By early evening the snow will have begun moving out in the Ohio Valley while just beginning across the entire state of Pennsylvania, southern New York State, and the I-95 corridor from Baltimore to New York City. The snow will hold off in Boston and Northern New England until later in the evening.
Precipitation may actually begin as light rain along and east of I-95 in the Northern Mid-Atlantic. For southern New Jersey, rain may never completely changeover to snow. Instead, there may be a brief period of sleet and snow mixing with rain late in the evening. But north of New Jersey’s I-195 corridor, the availability of cold air matched with latent heat absorption by melting snowflakes aloft will quickly transition rain to snow.
Snow will intensify during the late evening into the overnight hours as the low pressure system develops further over the Atlantic Ocean. Snowfall rates will reach or exceed 1″ per hour earlier in the night in south-central Pennsylvania, northern New Jersey, and southeastern New York and later in the night in southern New England. Plummeting visibility matched with increasingly more snow on roads will make driving extremely dangerous.
Warm air will gradually work northward during the height of the storm such that snow in areas south of New York City eventually mix with and change over entirely to rain and sleet, including Philadelphia and the Jersey Shore. This transition will generally occur after 10pm. Snow will eventually mix with rain and sleet on Long Island and in southeastern New England, but a complete transition to either is not expected, except on Long Island’s twin forks and on Cape Cod. After mixing with or changing over to rain, a rush of cold air on the storm’s departure will change precipitation back to snow briefly before ending for these areas. Precipitation is expected to stay entirely snow elsewhere north, west, and northeast of New York City.
Snow will clear everywhere south and west of I-91 by 7am Monday, including all of the northern Mid-Atlantic and western New England. Snow will linger in Boston through the morning, clearing by noon. Further north, snow may continue in Maine until early evening.
Snow will be heaviest along and east of I-91 in southern New England, where 6-10″ of snow will fall over cities like Hartford, Worcester, Boston, Manchester, and Portland. A general 4-8″ of snow is likely along a swath covering central Pennsylvania, northern New Jersey, the lower Hudson Valley, and most of western and central New England. Cities along and just east of the I-95 corridor may undergo brief mixing and lower snowfall rates, so snowfall of 2-4″ in Philadelphia and central New Jersey and 3-6″ in New York City and Long Island will be most likely.
Like most coastal storms, the snowfall forecast is highly sensitive to the storm track. Any slight wobble to the south and east could bring additional snowfall to areas between Baltimore and New York City currently forecast to undergo mixed precipitation while cutting amounts north and west of I-95. Regardless of storm track, the Monday morning commute will be highly impacted by snow. Snow is only expected to end in New York City and points south in the late overnight hours with little time for roads to be cleared before the morning commute. North of New York City, snow may continue into the morning commute. The heavy, wet snow and slush on roadways will make for treacherous driving conditions, even if the snow had stopped falling.