Final call: Near record storm for Mid-Atlantic, questions elsewhere

Good afternoon.

We are staring at what could be the biggest weather event for our region since Hurricane Sandy, and one of the biggest winter storms we have ever seen. Such is especially true in the mid-Atlantic, from central Virginia through the Washington DC and Baltimore regions into southern Pennsylvania, including Philadelphia, and into central New Jersey. North and south of that region, confidence is much lower as models are not nearly in consistent in either defining the northern envelope of heavy snow or dry slots and changeover zones in the southern mid-Atlantic coast. Regardless, this will be a storm to remember for years, if not generations, up there with last year’s New England storms, the 2010 “Snowmageddon” storm, the Blizzard of 1996 and the Superstorm of 1993.

If you haven’t prepared in the mid-Atlantic, time is almost up, if not up. Make sure you have at least 5 days, ideally 7 days (especially in rural areas) worth of supplies since you likely are not going anywhere at least until early next week, possibly longer. It will likely be late Sunday before even the main roads and Interstates become passable, and then it will take through Monday and Tuesday at least to get the collector roads and urban streets drivable or walkable again. Rural side roads and isolated locations will take even longer, hence rural residents should be prepared to stay where they are for up to a week. Stay off the roads – we need to keep the plows working clear and available to lead emergency vehicles if necessary (it is possible even they may not be available Saturday). Airports will likely be shut down in that area well into Sunday, and it will take until late Sunday or Monday just to re-establish a skeletal mass transit network.

As for snowfall amounts, there remains key questions on the northern fringe. The NAM and its derivatives (such as SREF) insist on bringing enormous snow totals into the New York City region, central Pennsylvania and southern New England as well. The GFS, ECMWF and CMC insist on a cutoff south of them, resulting in much lesser amounts (although wind and coastal flooding remain threats). This forecast, which is our final call, leans heavier towards the latter group, but is a bit more aggressive on the northern edge out of deference to the NAM. It is, however, low confidence there. The heaviest snow in the mid-Atlantic is of much higher confidence, but mesoscale banding could make the difference between records being broken or smashed and a near record (but still paralyzing) event. In general, these are probably conservative for that region with locally higher (possibly much higher) amounts possible – the hardest hit areas may easily exceed 40 inches and even approach 50 inches of snow!

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Regional synopsis:

 

Note that these are general amounts for each region. Check with local offices and media for more specific local impacts.

  • Northern New England and northern New York: No impact. Confidence: High
  • Coastal southern New England: Little or no impact near Boston; 1 to 4 inches most other areas with locally up to 8 inches in SW Connecticut. Confidence: Low to Moderate
  • Interior southern New England and Catskills: Little or no impact. Confidence: Moderate
  • Central valleys (Mohawk, lower Hudson, upper Susquehanna, Lake Ontario shore, etc.): Little or no impact for most; maybe 1 to 4 inches in southeastern areas. Confidence: Moderate
  • New York City region: 5 to 10 inches north, 8 to 18 inches south. Confidence: Low
  • Northern Mid-Atlantic coast (NJ, DE, Philadelphia area): 5 to 12 inches on the immediate coast with significant mixing, rain or ice, 10 to 24 inches inland with highest near and west of I-95. Confidence: Moderate to High
  • Central New York and northern Pennsylvania highlands: Little or no impact north, 1 to 4 inches south. Confidence: Low to Moderate
  • Interior southern Pennsylvania: 3 to 8 inches north, 8 to 16 inches near PA Turnpike, 14 to 24 inches along Maryland border; locally to 30 inches possible along Blue Ridge front near Maryland border. Confidence: Low to Moderate
  • Chesapeake and Potomac region (DC, Baltimore): 14 to 22 inches near Chesapeake Bay, otherwise 20 to 32 inches; locally 40 to 50 inches possible along Blue Ridge front. Confidence: Moderate to High
  • Central Appalachians/Blue Ridge: 18 to 26 inches; locally to 40 inches possible along Blue Ridge front. Confidence: Moderate to High
  • Southern Piedmont/valleys (Shenandoah, James, New River Valley, etc.): 14 to 24 inches except 8 to 16 inches in southeastern areas near North Carolina border. Confidence: Moderate
  • Southern Mid-Atlantic coast (MD, VA): 2 to 6 inches south (most falling as rain, sleet or ice), 4 to 10 inches north plus some mixing or ice. Confidence: Low

Additional threats

  • Storm surge/coastal flooding: This is another significant threat especially from the Maryland coast northward to southern New England. In fact, for some areas (especially on the Jersey Shore) the impacts at the coast may rival that from Hurricane Sandy in 2012, and according to a news report last night by WPVI meteorologist Cecily Tynan, the beaches could face their biggest test. My overall thinking is unchanged from last night here. In terms of surge amounts, I believe 2 to 4 feet is a reasonable guess south of Delaware Bay, with 4 to 6 feet possible along the Jersey Shore and around New York City and in Long Island Sound, decreasing northward from there. Given the high tides, at least 3 to 4 feet of tidal range can be added to those numbers, resulting in a peak water rise of 6 to 10 feet. For most areas that is not at the levels of Sandy, but still very dangerous. South of Atlantic City, this storm could rival or exceed Sandy though. Regardless it is a dangerous threat that must be prepared for as well.
  • High winds: In general, many areas – particularly from the I-95 corridor cities eastward to the coast (much less so inland) – can expect sustained winds of 25 to 35 mph inland and 30 to 45 mph near the coast. Gusts will likely be higher – up to 50 mph inland and up to 60 mph near the beaches (locally to 70 mph especially along the southern Jersey Shore and Delmarva coastline). The strongest winds especially will likely lead to significant power outages and tree damage in those coastal areas. Areas that experience those winds along with heavy, wet snow or ice (particularly along and east of the I-95 corridor, although the threat will exist at least up to the Blue Ridge front) will be at even greater risk for such, and may also combine for structural damage as well. It is likely that hundreds of thousands, or even millions, of customers will lose power and possibly for an extended period. Regardless of power issues, the wind and snow will likely combine for blizzard or near-blizzard conditions and zero visibilities, making driving extremely dangerous if not impossible.
  • Freezing rain: This is not a major threat in our region, but a significant risk that is underway in parts of the Carolinas, particularly from central North Carolina into upstate South Carolina. Those areas are currently experiencing widespread ice amounts which may total 1/4 inch or greater with the heaviest amounts of 3/4 inch to 1 inch possible. Combined with strong winds, that will likely lead to widespread power outage problems and given the larger area to be affected, slow down recovery as power crews will need to spread out more this weekend or will be stressed. Most likely relief crews will need to travel long distances to reach the mid-Atlantic.

Confidence: High on the general synoptic setup, variable (see above) on the amounts and their locations. It is a very tough forecast on the northern flank, and the numbers could rise or fall greatly, so it is good to be prepared for much more than forecast there as well.

Final thoughts: This storm has been forecast for several days. At first I was cautious but it became clearer and clearer that this would be a historic storm. All indications are it will indeed be for many areas. I have previously posted several other articles including one on how to be prepared. Now for the mid-Atlantic the ultimate test is coming, something we haven’t seen in over 3 years since Sandy in 2012. New England experienced a brutal winter last year with multiple crippling storms, and now that experience is spreading farther south. This looks to be one to remember for years, if not generations, for some. However questions remain to the north and mesoscale factors will dictate what happens there, especially in the New York City region.

One last thing: if we are wrong, remember it happens. Even the experts are wrong sometimes. This great article posted by Becky Elliott of AccuWeather on the Washington Post explains the challenges even the pros face and the potential backlash – forget amateurs and students like us. In a low confidence situation for millions of people, that possibility certainly exists here that they get the sense of being hit “without warning”. On the flip side, some areas may receive less than forecast and this may have been seen as overblown. It’s a tough balancing act.

For everyone in the area of greatest risk, my thoughts and prayers are with you. Stay home, stay off the roads and you will do just fine. Most importantly, stay safe!!!

Forecaster Craig Ceecee – @Ceecee_Wx

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