Storm HQ

Saturday is not going to be a pretty day around here, but most of you already knew that. There are some changes to our forecast though. Once again, we’ll start with the basics (which really haven’t changed), then work our way into the details (which have changed a bit).

Low pressure will develop off the Southeast coast this afternoon and will head up the Eastern Seaboard tonight and Saturday, rapidly intensifying as it does so. The system will likely pass just south and east of Nantucket Saturday night, and pull away from the region on Sunday. A few snow showers are possible today as a cold front moves through, completely unrelated to the storm. What that front will do is bring colder air back in, so that we’ll be dealing with all snow across nearly all of the region, except possibly Nantucket and Outer Cape Cod.

OK, let’s get to the details. We’ll start with temperatures. North and west of Boston, temperatures will likely be in the teens for much of the storm, resulting in a fluffy snow. This will make cleanup easier, but also make it easier for accumulations to pile up quicker. South of Boston, temperatures will be in the 20s to start, but will drop during the day, so we’re also looking at a fluffier snow here as well. Across Cape Cod, temperatures will be closer to freezing, so it’ll be a wetter snow, with the possibility of rain mixing in, depending on how close the storm actually tracks. The general rule is that 1 inch of liquid equals about 10 inches of snow, which works fine with temperatures close to freezing. The colder you get, the higher the ratio gets. When temperatures drop into the teens, the ratio can get to 20:1, which means 1 inch of liquid results in 20 inches of snow. We’re not sure it’ll get that high, as there are other factors involved beyond the temperature at the ground, but it is certainly possible. The other thing to keep in mind is that the temperatures, combined with strong winds (see next paragraph), will result in very cold wind chills, so keep this in mind if you’re heading outside to do some shoveling during the storm.

Next, we’ll get to the winds and coastal flooding. As the storm gets cranked up south of the region, winds will pick up on Saturday. Sustained winds of 15-25 mph are likely inland, with sustained winds of 20-40 mph along the coast. Wind gusts of 40-50 mph are likely inland, but along the coast, wind gusts of 50-70 mph seem likely, with higher gusts possible, especially across Cape Cod. Some trees and power lines could come down, so be prepared for power outages, but with a fluffier snow, there might be less widespread than you’d normally expect. The winds, combined with astronomical high tides, will result in some coastal flooding, especially at northeast and north-facing coastal areas during both the morning and evening high tides on Saturday.

With strong winds and heavy snow (more on that in a moment), blizzard conditions are expected on Saturday. If you don’t have to go out, then don’t. Whiteout conditions will make travel nearly impossible during the afternoon and evening. The National Weather Service has issued a Blizzard Warning for most of eastern Massachusetts and Rhode Island, as well as the New Hampshire Seacoast and coastal Maine.

Sustained winds or frequent gusts ≥ 35 mph AND considerable falling and/or blowing snow frequently reducing visibility < ¼ for ≥ 3 hours.

Blizzard conditions need to be the predominant condition over a 3 hour period.

Official definition of a Blizzard Warning from the National Weather Service

Now to the part that you’ve all been waiting for – how much snow is going to fall? If you read our Weekend Outlook yesterday, or are a regular reader of the blog, then you know that we are normally very conservative in our snowfall forecasts – no hype here. Well, many of the forecast models continue to forecast insane snowfall totals, and most of the guys on TV are buying in. With that in mind, we are issuing an Extreme Hype Warning.

When an Extreme Hype Warning has been issued, it means you’ll see blanket coverage from the network stations around here, hourly updates even when they go to regular programming, and of course, obligatory live shots from (take your pick):

• The side of an Interstate
• Logan Airport
• A local DPW salt pile
• A beach showing the rough surf and coastal flooding
• A Dunkin Donuts where they are talking to a plow operator
• All of the above

You’ll also get network reports about how the snow is creating chaos in New York City, how it put Washington at a standstill (due to the 1-3 inches they’ll get), and possibly how it dumped heavy snow (a.k.a. 1 inch) on parts of the Southeast.

As for our forecast? We’re going to raise forecast amounts from what we had yesterday, but not to the levels that most of the media is forecasting. Light snow may develop by midnight along the South Coast, spreading northward over the ensuing few hours, reaching southern and central New Hampshire and southern Maine by 3-5am. Between about 10am and 7pm, it’s going to snow rather heavily. Snowfall rates of 1-2 inches per hour will be likely in many areas. However, there will be some embedded bands of intense snowfall, with snowfall rates of 2-4 inches per hour. If you’re under one of these bands for any length of time, your totals may end up higher than our forecast, while areas outside the band a few miles away have significantly less snowfall.

OK, we’ve rambled on enough, let’s go to the actual forecast totals:

Central NH (Lebanon/Laconia): 4-8″
Southern NH/Central MA (Concord/Manchester/Nashua/Fitchburg): 10-15″
Merrimack Valley/495 Belt/NH Seacoast (Portsmouth/Haverhill/Lowell/Framingham): 15-20″
I-95 corridor (Beverly/Boston/Providence): 18-24″
Southeastern MA/Cape Cod (Brockton/Weymouth/Plymouth/Taunton/Fall River): 20-26″ with some totals in excess of 30″ possible.

Once the storm pulls away, dry and colder conditions settle in for Sunday and Monday, before temperatures start to moderate. There are some indications for a big warmup late-week and a storm that will bring in rain, but it’s still several days away, so we wouldn’t put too much stock into that just yet,

Yes, the rumors are true, a storm system is on the way for the weekend, and there is the potential for some significant snowfall. Nothing is definite yet though, so let’s separate the truth from the exaggeration. First, we’ll set the table for what’s going to happen.

Low pressure will move out of the Gulf of Mexico and up the East coast Friday into Saturday while rapidly intensifying. (You’ll hear the word bombogenesis used for sure.) Before that happens, a cold front will move across the Northeast on Friday, producing some snow showers. These are unrelated to the storm system, and could drop an inch or less on the region. That front will likely dissipate south of New England as the approaching coastal storm overwhelms it. Meanwhile, behind that front, a large high pressure system will build into southeastern Canada, locking cold air into place.

OK, now that we have the basic setup, let’s delve into a few things that we’ve heard or read today and how truthful they are.

Statement: An historic blizzard could set records across the Northeast this weekend.
Truth: Yes, some models are showing a rather extreme storm system with the potential for extraordinary snowfall totals. But, it’s still 4 days away, and a lot can change. This is far from a given. We’ll explain below.

Statement: This will be all snow for the entire region.
Truth: Again, given that there is still some uncertainty in the track, a mix or change to rain can’t be ruled out, especially for Cape Cod, and possibly eastern Massachusetts of Rhode Island. Again, read on for more details.

Statement: Significant coastal flooding is likely.
Truth: This one rings true. With a New Moon on Tuesday (we were that close to a Duran Duran song), tides will be running astronomically high. Add in strong east to northeast winds pounding the shoreline for 2 and potentially 3 high tide cycles, yes, coastal flooding is likely, especially the normally vulnerable locations.

OK, now let’s get into what could happen on Saturday. A rapidly intensifying storm system will head up the East Coast, producing strong winds and heavy snow ahead of it. While most of the models are fairly similar to each other with a track close to the “benchmark” (40N/70W), this is far from definite. The storm could end up farther offshore, which would limit the how far inland the heavy snow extends. The storm could also track closer to the coast, which would allow milder air to move in and change the snow to rain, how far inland the change could occur would be determined by the track obviously. This is the type of the detail that won’t become clearer for another day or two at best.

One factor in determining that track? The upper-level energy responsible for the storm is just moving into from the Pacific tonight. Why is that important? Let us explain. Every day around the world, we send up weather balloons twice a day to sample the upper atmosphere. This is done at 00UTC and 12UTC everywhere (7am/7pm in EST). This data is then fed into the models. The upper-level energy that will create our storm has been over the Pacific for the past several days, where there is little data. In the past, we would get observations from planes as well to supplement the balloons, especially over the water, where there are no balloon launches obviously. Well, since the pandemic, air traffic is less than half what it used to be, so there are a lot less of those aircraft observations. So, we are basically at the mercy of the balloon data. Once that upper-level energy moves over land, as it is doing now, it will be into the balloon network. The models should now start to have a better idea of its structure and converge on a solution.

Complicating things is the fact that some models show the system being captured by the upper-level trough of low pressure, or even getting stuck underneath a “cutoff” upper-level low pressure system. (It’s called that because it becomes cut off from the jet stream.) This would potentially allow the low to stall out south of New England for a while, prolonging the impacts to the region. How strong the storm gets (also up for debate) could determine whether or not this scenario occurs, but will also impact how strong the winds will be and in turn the amount of coastal flooding that may occur. Right now, the timing of the system looks to be generally between midnight Saturday morning and midnight Sunday morning, but obviously, this is far from definite.

As for how much snow will fall? Well, we’re not even going to attempt to put any numbers down yet. There is still FAR too much uncertainty. In addition to all the factors we talked about above, another one is temperature. Some models keep the cold air locked into place, with temperatures in the teens and 20s for much of the region during the storm. This would result in a much fluffier snow, making it a little easier to clean up, but also allowing it to pile up a lot quicker. If the warmer air does move in, especially near the coast, then temperatures could be near or even above freezing in spots. The general rule is that 1 inch of liquid precipitation equals 10 inches of snow. This holds true at temperatures close to freezing. With temperatures in the lower 20s, that 1 inch of liquid could result in 20 inches of snow. Most of the snow maps you may see online are ones that use the 10:1 ratio only, so in colder scenarios, like this one could be, they will underestimate the amount of snow.

If you really want, there are plenty of people all over Facebook, Twitter, and the web, who are more than happy to share all of those various model forecast maps, no matter how far-fetched they may seem. We’re not going to do that. We’ll just say that the potential is there for this to be a significant snowstorm.

Given all of this, we are issuing an Extreme Hype Watch for the StormHQ viewing area. An Extreme Hype Watch is issued when conditions are favorable for media hype of an event to reach extreme levels within the next 48-72 hours. If conditions warrant, a Hype Advisory or Extreme Hype Warning will be issued as the event draws nearer. We’ll hazard an initial attempt at amounts when we publish our Weekend Outlook Thursday afternoon. In addition, well do another full blog post on Friday.