Friday 12/18/20

Good morning! After receiving 13.5″ of snow with yesterday’s storm – essentially a perfect verification of the 10-17″ forecast – cold conditions continue. With decreasing clouds, expect a high around 31 today, with a north wind around 5 mph. Tonight will be clear, with a low around 9, and a light northwest wind. Saturday will be mostly sunny and 31, with a calm wind. The next chance for snow is Sunday afternoon and evening with some snow showers in the area; however, accumulations are not currently anticipated. Highs will be in the upper 30s to around 40 through mid-week, cold enough to most likely preserve enough snow for a White Christmas.

The main surprise with this system is how far north the heaviest snow band ended up, and the fact that said band produced extreme snowfall rates of up to 5″ per hour (which is extraordinarily rare) in very cold air meant that some locations in south-central New Hampshire and Vermont got over 40″, with numerous locales getting 30″. Northern areas also had a secondary issue with the forecast where the Nashua to Manchester corridor eastward to Portsmouth got a little less than 10″ in most towns. I’m still planning on doing a “double analysis” of this storm and the December 5th forecast bust now that I’m through finals week.

Have a great day!

Wednesday 12/16/20 – AM Update

Good morning! Quick tweak to the forecast to account for continued trends favoring a major snowfall.

What’s Changed:
Not much. I moved the 10″ line further north, and made slight tweaks to the boundaries in southeast Massachusetts. The 10-15″ zone is now a 10-17″ zone.

Snow begins late this evening, just before midnight. The heaviest snow falls overnight tonight and into tomorrow morning’s commute, with the potential for over 2″ of snow per hour at times. Snow lightens in intensity some by late morning and ends completely by mid-afternoon.

Widespread 10-17″ snow, with the potential for isolated higher amounts. Where exactly we end up in the range depends on where bands set up, but this is about as clear-cut as it can get. This will be a light and fluffy snow for most locations throughout the storm, including the Dracut/Lowell area, where we will be in the teens to mid 20s throughout the storm. Areas closest to the coast as well as around Boston will start with a slightly wetter snow (but not a super wet snow by any means) but the bulk of the snow there will still be on the lightweight side. Mixing concerns do exist in southeast Massachusetts, where forecast snow totals are lower.


Not much uncertainty at this point. There are enough factors going our way that it would take multiple large failures for us to not reach 10″ of snow. An area of subsidence is being picked out by most models extending from roughly Manchester to Worcester with slightly lower precipitation totals, but the snow ratios should be high enough to more than compensate for that and get those places to 10″. Locally, the main question is whether we end up on the low end or the high end of the range, and only time will tell for that question. Get ready, everyone – this one looks like a hit.

Have a great day!

Tuesday 12/15/20: PM Update

Good evening!

Quick forecast update to reflect some significant trends throughout the day.

What’s Changed: I have increased snow totals for much of the region as a large northward trend in the system’s track has become much more apparent, as the relevant energy has become much better sampled and other small atmospheric pieces fall into place. Since last night’s model runs, the northward trend just keeps getting more obvious with this one. For the Merrimack Valley, the forecast certainty in a large snowstorm has increased significantly.

Timing: Snow starts late Wednesday evening, just before midnight. The heaviest snow falls overnight Wednesday night and into the Thursday morning commute. Snow begins to gradually taper off by mid- to late-morning Thursday, with all precipitation done by the early- to mid-afternoon.

Amounts: Expect a widespread 10-15″ snow for much of Massachusetts and southern New Hampshire, with a few spots potentially getting higher amounts. The potential for truly major amounts over 15″ will be limited by the progressive nature of the system, but given the very heavy snow banding as well as the cold air creating a dry, fluffy snow, we shouldn’t have an issue putting up around a foot of snow in the Dracut area as well as much of interior Massachusetts and southern New Hampshire. A few places may underperform if an area of subsistence sets up, but even then, given the amount of moisture and the cold air involved, those locales should sneak over the 10″ mark.

Elsewhere, central New Hampshire will see 5-10″ of snow (with locally higher amounts possible), with a quick drop-off further north as the northern edge of the precipitation shield will probably set up in northern New Hampshire. Southeast Massachusetts will also see around 5-10″ of snow, as the northward trend does mean that areas around and south of Boston will be warmer than anticipated. This means that rain will mix in for Cape Cod, the islands, and parts of southeast Massachusetts. For Boston as well as areas close to the immediate coastline and interior portions of southeast MA, the snow will start as a wetter consistency before gradually becoming fluffier Thursday morning. Cape Cod and the Islands likely see less than 5″ of snow.

Uncertainty: For the Dracut/Lowell/Merrimack Valley area, this is now a high-confidence forecast, with the main uncertainty factor being the possibility of a slight over- or under-performance of the forecast. Even if we get 8″ or 18″, the point stands that we’re in for a respectable and impactful, but light and fluffy, Thursday morning snowfall. Uncertainty is higher in central and northern New Hampshire where the northern edge of the precipitation shield sets up, and uncertainty is much higher for points south of Boston where mixing may become an issue.

Have a great night!

Tuesday 12/15/20: AM Update

Good morning!

We have a significant snowstorm on our hands, but first, two days to get through. Today will be sunny and 32, with a northwest wind at 5-15 mph. Tonight will be clear and cold, with a low around 11, and a northwest wind around 5 mph. Tomorrow will have gradually increasing clouds, with a high around 26, and a north wind around 5 mph. Snow begins around midnight Wednesday night, with a low around 15.

weather 2020-12-15.001

And now for some more specific snow-related details.

Timing: Snow begins around midnight Wednesday night. The heaviest snow will likely be toward the morning commute hours, before tapering off around midday and ending by early afternoon. Over 1″ per hour of snow will be possible at times, but the higher risk for especially heavy totals is to our south (more on that in a moment).

Amounts: Given the sharp northern cutoff with this system (which I will get into in the “uncertainty” section), I am doing something a little unusual and going with overlapping forecast amounts. The good news with this system is the snow will be lightweight and fluffy throughout the area! Expect up to 4″ in central New Hampshire; the distance between no snow at all and several inches of snow may be very sharp. A narrow swath of modest 2-5″ is likely for most of southern New Hampshire, with the potential for isolated higher amounts if the stars align. From there, a widespread 5-10″ – with higher amounts possible – is likely for much of northern and western Massachusetts including the Dracut/Lowell area. This 5-10″ zone also encompasses extreme southern New Hampshire including the Manchester to Nashua corridor. Most locales along and south of the Mass Pike sit in an 8-12″ zone, with higher amounts possible. This includes Boston and Worcester, as well as all of CT, RI, and much of southeast MA. These zones are subject to change though, so stay tuned.

Uncertainty: The good news is this is nothing like the December 5th storm. There is lots of cold air available with this system, so precipitation type is not a concern. The main worry is with the northern cutoff of snowfall, which will likely be somewhat sharper than currently modeled, given the influence of high pressure over Quebec. If the system tracks slightly more to the north, this opens up a greater possibility of higher-end amounts over 10 inches. However, a tick to the south would give us a more modest snowfall than currently projected. Almost all data shows us having enough precipitation to get to 6″ of snow, and some show a fair bit more than that, but the margins are relatively narrow. Given the cold air with this system, the snow will be a dry, fluffy, lightweight snow, which will make snow-to-liquid ratios rather high (likely 15:1 or higher). This means that even if we get a little less moisture than anticipated, the cold air will compensate somewhat. The issue with the December 5th storm wasn’t available moisture or track, it was an issue with significantly overestimating the snow-to-liquid ratio due to the marginal and unstable nature of the cold air of that system. We won’t be in for that kind of a system, thankfully. I’m much more confident in this forecast than that one, but as I mentioned, the northern cutoff could still find a way to mess with us locally.


Once snow tapers off by early afternoon Thursday, cold conditions continue into the weekend. Expect mostly clear skies Thursday night and a low around 10, sunny skies Friday with a high around 27, clear skies Friday night and a low around 7, and mostly sunny skies Saturday and a high around 28.

I’m working around midday today and have a final tonight, so I may not have an update this evening. I have another student forecaster doing the UML update tonight so I may pass along his forecast this evening if I don’t have time to write my own.

Have a great day!

Sunday 12/13/20

Good morning!

With mostly cloudy skies, expect a high around 56 today, with a southwest wind at 5-10 mph.

There are two upcoming snow chances – read on for more info.

MONDAY: This is a minor “mood snowfall” event. Snow showers are possible tomorrow afternoon with a coating to an inch possible throughout much of New England. The snow may be mixed with rain at times. Overall, this is a minor event; not much to worry about here.

WEDNESDAY NIGHT/THURSDAY: If everything goes right, this could be a blockbuster snowstorm. That will depend on the exact track. What we do know at this point is a storm system will pass in our general vicinity. There is also strong support for cold air, so someone in the Northeast is likely going to get smoked by this one. At this point it’s just a question of where and how much. This is a completely different situation than last weekend’s storm where temperatures were very marginal and the whole storm depended on it “making its own cold air”, per se. The support for cold air will make this a light, fluffy snowfall.

The main point of uncertainty for our area is the northern edge of the precipitation shield. Most ensemble and operational guidance has us seeing at least some snow, but we could get nearly shut out if the system ticks a bit too far south. However, if we do get in on the precipitation shield, the high snow-to-liquid ratios will likely compensate somewhat, as this will likely be in the coldest air of the entire system. If we get in on the heavy precipitation, we could get absolutely slammed with snowfall. The guidance has fairly high confidence (especially for being 3-4 days out) on the storm taking place, as well as the cold air aspect of the system; and moderate confidence on the track (high confidence on the vicinity of the track but much lower on the precise location). We’ll likely know more by tomorrow, so stay tuned.

Have a great day!

Saturday 12/12/20 AM Update

Good morning!

With mostly cloudy skies and rain likely this afternoon and evening, expect a high around 42 today with a northeast wind around 5 mph.

I’ll have a more complete forecast update hopefully this afternoon or evening, as we are tracking a potential winter storm around the middle of next week. It’s too early for details but we will likely have more cold air available than the last storm a week ago. Speaking of a week ago, I’m still working on that post-storm analysis. It’s hit a bit of a snag due to final exam preparations.

Have a good day!

Sat 12/5/20 – Evening Update re: Forecast Bust

Interesting exercise in marginal-temperature snow setup forecasts today. Myself (and most other forecasters, FWIW) significantly overestimated snow-to-liquid ratios. It already looked as if they would be well under 10:1 with 7:1 or 8:1 seeming more likely, but they ended up somewhere between 3:1 to 6:1 instead, which is why we got glorified water today.

As a student of science I’m doing some research on how exactly the forecast went wrong (it appears the snow to liquid ratio was the main culprit, as the liquid forecasts were fine and the changeover timing forecast was fine). Assuming I don’t get sidetracked watching NFL RedZone tomorrow, I’m going to try and do a more technical write up to post tomorrow or Monday on the subject.

Let’s keep this forecast bust positive: at least we didn’t get widespread power outages!

Have a great night!

Saturday 12/5/20 AM Update

Good morning!

Rain has overspread the region early this morning as forecast. The forecast has become more favorable for higher snowfall amounts; the details are below.

Amounts: Expect a swath of 10-15″ for south central New Hampshire into central and interior northeastern Massachusetts, as the heaviest snow bands should set up around here. I have the Lowell/Dracut area within this range as the interior portions of the Merrimack Valley (including the Lowell to Manchester corridor) should be subject to some of those very heavy snowfall rates. The jackpot will likely be just north of Worcester, though. This 10-15″ range extends off the map into a large area of central New Hampshire and Maine.

Elsewhere, a large swath of 5-10″ surrounds the 10-15″ zone, though some spots in the 5-10″ zone may overperform. This zone includes most of coastal northeastern Massachusetts, Boston and its immediate northern/western suburbs, northeast Connecticut, northwest Rhode Island, and continues northward into much of New Hampshire and Maine. There is some uncertainty at the immediate coastline on amounts, though. I have 2-5″ forecasted for the southern suburbs of Boston, the Providence area, the Connecticut River valley, and the very immediate shoreline from Cape Ann to Boston. Amounts decrease further west and south, where rain will be more prevalent and flooding may even be an issue.

Timing: Rain changes to snow first in the Worcester Hills, later this morning. Other interior areas, including the Lowell/Dracut area, change around midday to early afternoon, with the coast changing to snow during the late afternoon to early evening hours, as temperatures cool to around freezing. The heaviest snow locally falls during the late afternoon to mid evening hours, during which 1-3″ of snow per hour is possible. Snow winds down this evening and ends completely around midnight.

Impacts: Travel will be extremely dangerous with extremely heavy snow this afternoon. When combined with strong wind gusts exceeding 35 mph, periods of blizzard conditions are possible. Additionally, this will primarily be a heavy wet snowfall; the weight of the snow may cause downed tree limbs and wires. Some power outages are likely with the potential for widespread power outages and significant property damage. The snowstorm of March 7-8, 2018 also featured a band of intense heavy wet snow and the result of that storm was huge percentages of people with no power (94 percent of Dracut out), as well as countless trees, wires, and tree limbs down. I’m not saying we’ll see a similar outcome today, but be prepared for the possibility that we do.

Have a great day!

Friday 12/4/20 AM Update

Good morning!

We have a storm on our hands, so let’s quickly run down the next day and a half or so first. With mostly cloudy skies, expect a high around 53 today, with a southwest wind of 5-10 mph. Tonight will be mostly cloudy, with a low around 39, a light southwest wind, and a chance of rain late. Expect heavy rain tomorrow morning, with the high temperature of 43 occurring around mid-morning.

weather 2020-12-04.001

Temperatures then fall to around the freezing mark by midday as heavy rain flips over to heavy snow. For a time during the afternoon and evening, snow rates well over 1″ per hour are possible. This will make for poor driving conditions, and whiteout conditions are possible at times with a northwest wind of 5-15 mph gusting up to 35 mph. Snow wraps up by around midnight or so Saturday night. Power outages will also be possible due to the weight of the snow. My going forecast calls for 5-10″ of snow for much of northeast Massachusetts and southeast New HampshireMore details regarding uncertainty follow.


There is increasing confidence in significant snowfall amounts as guidance is settling in on a classic “benchmark” track that is favorable for snowfall in interior eastern New England. However there is still some uncertainty here. Given the likelihood of an especially heavy snow band setting up, it’s possible we could over-perform even the 5-10″ forecast; when all is done, some places may see over a foot of snow, but confidence is not high enough to add a 10″+ tier. Depending on trends, such an update may be necessary this evening (such an update won’t happen until after 9 pm, because of work).

The other end of the uncertainty stick is with amounts at both the immediate coastline as well as in western New England. The obvious caveats always apply at the coast regarding warmer temperatures, but temperatures will be marginal everywhere and this storm is reliant on very heavy snow rates, so it’s possible that heavy snow could occur right up to the coast – likely not to the same degree as inland, but the northeast MA coast will likely approach the 6-inch snow mark.

As for western New England, the system’s eastward trend is leaving less overall precipitation for that region, and some guidance is now indicating a near-shutout out that way. There is still some guidance on board with heavy snow out that way, so while the odds are decreasing, there is still tons of uncertainty in western New England that should resolve soon.

While this now seems very unlikely, it’s also not entirely impossible that this ends up being an underperforming system locally as well. Overall, this forecast is much less stable than we typically have so close to the onset of a storm. 

The system’s departure gives way to temperatures falling to around 26 Saturday night, with a northwest wind of 10-20 mph, gusting up to 35 mph, and mostly cloudy skies. Skies turn mostly sunny Sunday, with a high around 35. Sunday night will be mostly clear and 21. Monday will be mostly sunny and 35; Monday night will be mostly clear and 17; Tuesday will be 35 and mostly sunny.

weather 2020-12-04.002

Have a great day!

Wednesday 12/2/20

Good morning!

With partly cloudy skies, expect a high around 42 today, with a chance of an afternoon shower and a southwest wind of 5-15 mph. Tonight will be mostly clear and 26, with a west-southwest wind of 5-10 mph. Thursday will be mostly sunny and 48, with a southwest wind of 5-10 mph. Thursday night will have increasing clouds, with a low around 32, and a southwest wind of 5-10 mph.

weather 2020-12-02.001

Friday will be mostly cloudy and 50; Friday night will be cloudy and 37, with a chance of showers. Saturday will be cloudy and 45, with rain likely, especially toward the later stages of the day. Saturday night will be cloudy and 32, with rain likely, perhaps changing to a mix late. Sunday will be mostly cloudy and 38, with a chance of rain and potentially mixed precipitation in the morning.

weather 2020-12-02.002

Have a great day!