Sunday 1/31/21 – PM Update

Good evening! Here’s a full update on the upcoming snowstorm.

Amounts
Expect a widespread 10-18″ in much of interior New England, including the Merrimack Valley. There will be a sharp drop-off in totals at the immediate coastline. Most towns near the coast see 5-12″, with 2-6″ at some immediate shoreline towns (and 0-3″ for Cape Cod and the Islands). Also, a little less snow (5-12″) can be expected near the Connecticut River due to subsidence and the effects of being east of the Berkshires.

There is uncertainty at the coast, as well as for Boston’s southern suburbs. Trends today favored more snow, though it’s possible that the forecast could be under-compensating and that Boston could get over a foot of snow. On the flip side, trends could go the other way and favor less snow at the coastline, depending on timing of mixing. Regardless, this is a fairly safe forecast in most locations, including Dracut.

dracut-1

Timing
Once again, the timing shifts earlier. Snow begins midday tomorrow and will be heavy by the late afternoon/early evening. Heavy snow continues into the overnight hours, though gradually winding down. The accumulating snow is likely done by sunrise, though very light snow may continue occasionally during the day Tuesday.

Impact
The snow will be roughly average weight. It won’t be fluffy, but I also don’t expect anything unusually heavy and wet. There is a threat of downed trees and power outages, though, due to strong northeast winds of 10-20 mph, with peak gusts up to 40 mph. Blizzard conditions are possible at times with poor visibility. Driving will be extremely hazardous Monday evening into Tuesday morning, so stay off the roads if possible.

Uncertainty
This is a high-confidence forecast inland; the only major concern locally would be if the dry slot aloft moves in earlier than expected, which would undercut snow totals a little bit. Most of the uncertainty involves amounts closer to the coast. Trends today have favored more snow closer to the coast, but it will be a very delicate situation with the timing of mixing in those areas, so the forecast could bust in either direction at the immediate coastline, as mentioned earlier.

Have a great night!
-Nathan

Sunday 1/31/21 – AM Update

Good morning! Here’s a full update on the upcoming snowstorm.

Amounts
Expect a widespread 8-14″ in much of interior southern New England, including the Merrimack Valley. 4-8″ totals are likely a bit closer to the coast (especially inside of I-95 near Boston), as well as in parts of western New England further from the key moisture of this storm. Mixing will be an issue near the coast; 2-4″ can be expected at Cape Ann, as well as in much of southeastern Massachusetts (with 0-2″ for Cape Cod and the Islands). There is some uncertainty on snow totals near the coast.

Dracut

Timing
The system has sped up a bit since the last update. Snow begins midday Monday, and may impact the evening commute. However, the bulk of the accumulating snow will be Monday evening into Tuesday morning. The heavy snow ends by mid-morning Tuesday, but flurries and light snow may continue into Tuesday afternoon.

Impact
The snow will be roughly average weight. It won’t be fluffy, but I also don’t expect anything unusually heavy and wet. There is a threat of downed trees and power outages, though, due to strong northeast winds of 10-20 mph, with peak gusts up to 40 mph. Blizzard conditions are possible at times with poor visibility. Driving will be extremely hazardous Monday evening into Tuesday morning, so stay off the roads if possible.

Uncertainty
This is a high-confidence forecast inland; the only major concern locally would be if the dry slot aloft moves in earlier than expected, which would undercut snow totals a little bit. Most of the uncertainty involves amounts closer to the coast, as it’s not impossible that coastal locations (even south of Boston) could see up to a foot of snow with the initial band Monday evening and night before changing to rain.

I’ll have more info tonight if necessary. Have a great day!
-Nathan

Saturday 1/30/21

Good morning!

With sunny skies, expect a high around 19 today, with a northwest wind of 5-10 mph. Tonight will be clear, with a low around 2, and a northwest wind of 5-10 mph. Sunday will be partly cloudy and 28, with a light northwest wind.

We’re monitoring our first notable snowstorm in a while. It’s too early for precise details, but a widespread 6-12″ looks likely, with the potential for isolated higher amounts. Snow will likely start Monday afternoon or evening, but the bulk of the storm will be overnight Monday night and Tuesday morning, before winding down Tuesday late morning and afternoon. The main area of uncertainty is how far west the heavy snow shield extends. Most guidance indicates a hit for eastern MA and southeast NH, but it’s more up in the air to our west (though trends are looking favorable for snow to the west). More details will follow throughout the weekend.

Have a great day!
-Nathan

Friday 1/1/21 AM Update

Good morning and welcome to 2021!!!!

The year starts off with clear skies, along with a low temperature around 22 to take place closer to sunrise. Today’s high will be 40, with a few clouds developing toward the afternoon hours, but otherwise sunny skies will rule the day. Winds will be mainly light and calm. Clouds increase further after sunset; the Friday night low will be 30 as we see a mixed precipitation event in which every main precipitation type – snow, sleet, freezing rain, and rain – may fall.

Expect a widespread coating to 2″ of snow and sleet and a trace to 0.05″ of ice/freezing rain. Precipitation begins around midnight, likely starting as snow (or as rain and quickly changing to snow) before becoming a difficult to predict mess overnight. Confidence is high in this being a mixed bag event, but the exact timing of changeovers and when a certain precipitation type will be falling is tougher to nail down. In any case, regular rain should begin to prevail for good not long after sunrise, and rain ends in the early afternoon as temperatures rise to around 38 degrees. Driving will be difficult in the overnight hours into tomorrow morning, so be careful.

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weather 2021-01-01.001

We get a brief rest Saturday night (low 24, mostly cloudy) before our next storm chance Sunday. The morning looks to most likely be dry, but precipitation likely develops in the late afternoon and evening. Most likely this will be a mix of rain and snow, with the possibility of several more inches of snow overnight Sunday night into Monday morning. Given I am forecasting a high around 39 Sunday, precipitation likely starts as rain, probably flipping to snow at some point Sunday night, and changing back to rain Monday morning, but there is still a lot to figure out so stay tuned. Precipitation would be favored to end by early afternoon Monday, with a high around 37. Monday night will be mostly cloudy and 27; Tuesday will be mostly cloudy and 41.

weather 2021-01-01.002

Have a great day! I’ll have more storm info if needed later.
-Nathan

 

Thursday 12/24/20 AM Update

Good morning!

With skies turning cloudy, expect a daytime high around 53, with a south wind of 5-10 mph, along with potential gusts up to 25 mph.

Expect rain to develop well after sunset and continue overnight; with heavy rain at times, flooding is possible in urban and low-lying areas, as well as smaller streams, especially considering that significant snowmelt is expected. For this reason, the National Weather Service has posted a Flood Watch for the area. Make sure your drains are clear of snow! Over 2 inches of rain may fall overnight tonight and into tomorrow. Rain will end during the evening tomorrow. Additionally, a few strong to severe thunderstorms are possible during the morning tomorrow, which would only enhance the wind damage threat (more below); a line of thunderstorms appears possible.

Additionally, high winds are also a significant hazard with this system. A High Wind Warning is in effect as southeast to south winds of 10-20 mph, with peak gusts over 60 mph, are expected tomorrow morning. Expect the most likely time for the strongest gusts to be just after sunrise into mid-morning, although strong gusts are expected throughout the night as well. The wind will calm down during the afternoon tomorrow. Power outages are likely for some folks; take care to make sure devices are charged and the like.

As for the snowpack, most or all of it will be gone by tomorrow. The definition of a “White Christmas”, as per the National Weather Service, as having 1″ or more of snow cover on the ground Christmas Day. It’ll be a race against the clock. It used to be said that it had to be 1″ at 7 am, but the National Weather Service does not reference this any longer. 7 am is a good marker of “Christmas morning” though. Whether we have 1″ left on the ground at 7 am is an open question, especially because fog is possible which could further eat away at the snowpack, but we should have more than enough to have a White Christmas if you use midnight as the definition. Either way, I’ll follow up on how much snow I have left tomorrow morning.

Temperatures will rise through the 50s overnight, with the Christmas daytime high being around 60 during the morning. It won’t be nearly as warm as 2014 (when a Christmas Eve/Day storm brought heavy rain and temperatures in the low 60s) and 2015 (when an abnormally warm pattern brought the Christmas Eve and Day that most of us probably want after putting up with this nonsense of a year – a high of 71 Christmas Eve and 64 Christmas Day with dry conditions throughout).

Temperatures fall back into the 50s during the afternoon tomorrow. Friday night will be mostly cloudy, with a low around 29, and a south wind at 5-10 mph, with gusts up to 25 mph possible.

weather 2020-12-24.001

Saturday will be mostly sunny and much colder, with a daytime high around 35 (although for technical purposes, the official high will be somewhere in the 40s at midnight Saturday morning). Saturday night will be mostly clear and 21. Sunday will be mostly sunny and 38; Sunday night will be mostly clear and 24; and Monday will be mostly cloudy and 46.

weather 2020-12-24.002

I will have an update later today if changes in the forecast warrant. Otherwise, Merry Christmas Eve to those who celebrate, and enjoy your day!
-Nathan

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!
-Nathan

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.

Timing:
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.

Amounts:
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.

dracut-2

Uncertainty:
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!
-Nathan

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!
-Nathan

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.

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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!
-Nathan