12:00 PM (Saturday) | *****Long duration major winter storm for the Mid-Atlantic…6+ inches possible in DC...12+ inches in Philly, NYC…phase 1 “overrunning”…phase 2 “coastal storm”*****
Paul Dorian
There are many similarities aloft between the blizzard of January 1996 and the scenario that is unfolding for this upcoming major winter storm. That storm in January 1996 became the biggest snow storm ever for Philadelphia, PA with 31 inches between the 6th and the 8th - topping the prior leader of February 1983. Map on right courtesy Weather Bell Analytics, left courtesy Penn State eWall.
Overview
The stage is set…Arctic air is in place anchored by strong high pressure to the north and a major and complex storm system is coming to the Mid-Atlantic region and it will be a long duration event with impact from Sunday into Tuesday. Accumulations of 6+ inches are possible in the DC metro region with 12+ inches possible in the Philly and NYC metro areas. The storm will come in two phases with the first part associated with a process called “overrunning” and the second phase featuring a major coastal storm. The combination of the potential heavy snow and strong winds may prompt the need for “blizzard warnings” to be issued in at least parts of the Mid-Atlantic region for this upcoming event.
A blocking pattern in the upper atmosphere over eastern Canada will play a big role in the upcoming major winter storm for the Mid-Atlantic region. A coastal storm will become the dominant player on Monday and it will continue to impact the Mid-Atlantic region into Tuesday as it grinds to a halt off the coastline. Map courtesy NOAA, tropicaltidbits.com
Details
This upcoming major winter storm will likely produce the highest snowfall amounts in five years for much of the DC-to-Philly-to-NYC corridor when approximately two feet of snow accumulated in the late January 2016 blizzard. This looks like a long duration event in the Mid-Atlantic region that will last from early Sunday to late Tuesday and it can be best described in two different phases.
Phase 1 of the upcoming major winter storm will feature “overrunning” type snowfall which occurs when warmer air is forced up and over dense, cold Arctic air that will be in place in the Mid-Atlantic region. An initial or “primary” low pressure system will move over the Ohio Valley on Sunday then stall out and weaken as its upper-level support diminishes. A secondary storm system will then develop near the Carolina coastline and this will become the main player. Map courtesy NOAA, Pivotal Weather
“Phase 1” will be an initial outburst of “overrunning” type snow on Sunday and Sunday night as warmer air from the southwest is forced to ride up and over dense, cold Arctic air that will remain in place in the Mid-Atlantic region. This warmer air will be pushed to the northeast on Sunday by low pressure that will be headed towards the Ohio Valley from the central Plains. The Ohio Valley will turn out to be the most northward extent of this primary low pressure system and also the location of its demise as upper-level support will transfer to the east coast.
Phase 2 of the upcoming major winter storm will take place on Monday and Tuesday as a coastal (secondary) storm becomes the dominant player. The heaviest snow in places like Philly and NYC will take place during this second stage and winds will pick up noticeably perhaps prompting “blizzard warnings” for some spots. Colder air from the north will get wrapped into the system by later Monday and those places that change to a mixture of precipitation on Sunday night/early Monday are likely to change back to all snow by later Monday and the snow will continue on Monday night. Map courtesy NOAA, tropcialtidbits.com
“Phase 2” will take place from Monday into Tuesday as a storm system develops near the Carolina coastline and becomes the dominant player while the initial primary low fades away. This coastal storm will develop as upper-level energy swings around the base of a larger-scale trough and produces strong upward motion near the Carolina coastline. There is also a natural temperature gradient in this particular area between the warm waters of the nearby Gulf Stream in the western Atlantic Ocean and the cold air that will be situated over the nearby land mass. This sharp temperature gradient combined with upper-level energy will contribute to storm formation right near the Carolina coastline - an area known for the genesis of many east coast storms.
As the coastal storm intensifies on Monday, there will be a strong jet in the lower part of the atmosphere extending all the way from the eastern part of West Virginia to southern New England. This lower atmosphere jet streak should translate to strong winds at ground level during the height of the storm. As a result, “blizzard warnings” may need to be issued for this storm by NOAA’s National Weather Service in at least parts of the Mid-Atlantic region due to the likelihood of heavy snow and strong winds. Map courtesy NOAA, Weather Bell Analytics
As this system intensifies and moves north/northeast, it will come increasingly under the influence of a strong blocking pattern in the atmosphere over the eastern part of Canada. As a result, the coastal storm will ultimately grind to a halt and it could even “retrograde” or take a loop back towards the east coast during the early part of next week – all of which will result in a long duration event with impact lasting well into Tuesday for the Mid-Atlantic region.
The air flow just above the surface level (900 mb) by later Monday will be pushing lots of Atlantic Ocean moisture back into a very cold air mass in the Mid-Atlantic region…translation…the potential for some heavy snowfall. Map courtesy NOAA, Weather Bell Analytics
As the coastal storm intensifies, the pressure gradient surrounding it will tighten and winds will increase markedly later Monday and Monday night; especially, across eastern Pennsylvania, New Jersey, and southeastern New York. Another key point here is that once the coastal storm stalls out over the western Atlantic Ocean, it will pull in some very cold air from the north/northeast and those areas that change from snow to a mixture of precipitation during the initial phase of the storm will change back to all snow later in the day on Monday and additional accumulations are very likely with this “wrap around” snow all the way down to the DC metro region. In fact, the intrusion of cold air on the back side of the coastal storm will result in significant accumulating snow all the way down to the coastal sections of New Jersey and the Delmarva Peninsula. “Blizzard warnings” may need to be issued for the storm system by NOAA’s National Weather Service due to the potential combination of heavy snow and strong winds with the most probable regions for these warnings in eastern Pennsylvania, New Jersey, and southeastern New York and perhaps even across the northern half of the Delmarva Peninsula.
12Z Euro forecast map of “total snowfall amounts” in the upcoming major winter storm. Map courtesy ECMWF, Pivotal Weather
Here is a breakdown by metro region in the Mid-Atlantic’s I-95 corridor as to what to expect during this upcoming long duration major winter storm:
DC metro region:
Snow develops early Sunday morning in phase 1 of this upcoming event and continues for much of the day with several inches of accumulation likely during this “overrunning” stage. In fact, phase 1 could turn out to be the time period with the “best” accumulating snows in the DC metro region although I do expect some additional accumulations from “wrap around” snow associated with the coastal storm (i.e., during phase 2). The snow will tend to lighten up at day’s end or by early Sunday night and the precipitation will also become mixed with ice or rain and it should continue in a spotty fashion into Monday morning. Any mixed precipitation will then likely change back to all snow later in the day on Monday as colder air wraps around from the north/northeast and it should continue as snow into early Tuesday with some additional accumulations likely. Total snowfall estimates for the DC metro region: 6-12 inches.
Philly and NYC metro regions
There can be a snow shower or two in the morning on Sunday, but the steadier snow should develop during the mid-to-late afternoon hours for the Philly metro region and by early evening in the NYC metro region. The snow will continue tomorrow night, but it could become mixed with sleet and/or rain late at night and into the morning hours on Monday. As colder air wraps in from the north/northeast, any mixed precipitation on Monday morning will change back to all snow by later in the day and should continue as snow on Monday night and into the day on Tuesday. In fact, the heaviest snow is likely to take place from later Monday into early Tuesday with significant accumulations. In addition, the winds will increase markedly as well later Monday resulting in some blowing and drifting of the snow and those strong winds will continue through Tuesday. Total snowfall estimates in the Philly and NYC metro region: 12-18 inches and there can be isolated higher amounts. These potential isolated higher amounts would be in those spots that experience “mesoscale” or small-scale banding containing brief bursts of intense snowfall and possible thunder.
Comparisons with the blizzard of January 1996
This unfolding scenario has many similarities in the upper part of the atmosphere to the blizzard of January 1996 which became the biggest snowstorm ever for many locations in the Mid-Atlantic region including Philadelphia, PA where 31 inches fell between the 6th and the 8th. The January 1996 blizzard featured a “closed-off” upper level low over the Ohio Valley, strong energy rotating through the base of an upper-level trough, and the formation of an intense coastal storm with entrenched Arctic air in place and so should the upcoming storm. In addition, the January 1996 blizzard featured strong ridging of high pressure across the western US - a key component to east coast snowstorms - and this upcoming storm should as well.
Stay tuned for further updates as this is a complex storm system, but get prepared for a major winter storm of long duration in the Mid-Atlantic region.
Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com