Tag Archives: Winter storm

Major Winter Storm Tomorrow Night

Hello everyone!

A very interesting and exciting ~18 hours is in store from tomorrow evening through early Friday morning. During this time, look for torrential downpours along the coast, whiteout snows inland, and strong gusty winds for all. This will be brought to you by a rapidly intensifying coastal storm that will deepen roughly 20mb in 12 hours. This is double the rate of deepening needed for official bombogenesis!

Just a quick note before the fun… If you’ve been reading my storm updates for a while, you know I get into some fairly high level (and interesting!) meteorology while outlining what I expect to happen. If you’re new to my blog, this is how I like to operate as I think it gives you the reader a unique look “under the hood” of weather forecasting. I try to explain technical concepts in an accessible way so you too can become part weather geek. If you’re not into the “why behind the what” or just simply don’t have time to enjoy lots of weather geekery, scroll to the bottom where I’ll put my snowfall map and a concise forecast. Maybe you’ll even see a map interesting enough to read about on the way down!

The Pattern

Upper Air (300mb) Pattern At 7 AM This Morning. Image Credit: Meteocentre
Upper Air (300mb) Pattern At 7 AM This Morning. Image Credit: Meteocentre

The upper level pattern is relatively zonal today meaning that winds are mostly blowing west to east and there are no significant disruptions in the flow (storms, blocking highs, etc.). This will change to a certain extent in the next 24 hours but it’s important to remember that the overall zonal flow will prevent this storm from sitting and dumping. Also notice the lack of any substantial blocking high pressure over NE Canada. The zonal flow and lack of blocking means that this storm will be a fast mover and totals will be limited by the short duration of heavy snow. That doesn’t mean some hefty numbers will be recorded, it just means that this storm probably isn’t one for the record books.

Surface Pattern At 7 AM This Morning. Image Credit: NWS OPC
Surface Pattern At 7 AM This Morning. Image Credit: NWS OPC

At the surface, the setup isn’t quite ideal for a major storm but it does show that heavy snow is likely across the interior. The limiting factor for coastal Maine and New Hampshire will be the lack of deep cold air. This is a function of a) the zonal pattern discussed above, and b) the relatively weak high to the north and the relatively strong high to the south. This means the high to the south will be the primary driver of a) the flow ahead of the storm and b) the antecedent airmass. For big snows along the coast, we need a strong high to the N/NW to lock in the cold air and keep the cold air flooding south through the storm. This will not be the case tomorrow evening. As for the low pressure systems, the primary low was over MN this morning (it is now over SW Ontario) and the secondary low (our storm) was over northern OK (it is now over AR/SW OK).

The Onset

Kachelmann Swiss HD Model Showing Light/Moderate Snow Arriving Tomorrow Afternoon. Credit: Kachelmann
Kachelmann Swiss HD Model Showing Light/Moderate Snow Arriving Tomorrow Afternoon. Credit: Kachelmann

Snow will move into the area beginning in SW NH late tomorrow morning and ending up in the Augusta area by sundown. There are some indications precip will begin a little earlier in the Portland/Midcoast area as snow showers move in off the ocean but we’ll have to wait until mid afternoon for any more meaningful snowfall. Precip will begin as a period of snow for most if not all areas but will quickly change to rain along the immediate coast (east/south of rt 1). By sundown tomorrow, a couple of inches will be on the ground over SW NH with dustings elsewhere.

18Z NAM Showing Coastal Low Pressure Developing Thursday Afternoon. Image Credit: Weatherbell
18Z NAM Showing Coastal Low Pressure Developing Thursday Afternoon. Image Credit: Weatherbell

As the evening wears on, heavier bands of snow will begin to pivot into the area as coastal low pressure kicks into gear offshore. Guidance is hinting at two circulations being present initially. Which one becomes dominant will dictate which track the low takes and thus how much warm air can wrap into the coast. If the western circulation develops, the storm will track farther to the west and the coast will be warmer, warm enough perhaps for all rain. If the eastern circulation develops, the opposite would happen with the coast seeing slightly more snow. The difference here is not between 3 and 12″, it is rather between 0 and 3-6″. This is not a storm for the coast to see big snows but if the eastern track pans out, the coast would see moderate accumulations as opposed to light/nonexistent accumulations.

The Blitz

12Z GFS Showing Intense 500mb Dynamics Thursday Night. Image Credit: Accuweather
12Z GFS Showing Intense 500mb Dynamics Thursday Night. Image Credit: Accuweather

Precip will begin to fall very heavily as powerful mid/upper level dynamics move into place Thursday night. At 500mb, it’s hard to imagine a better setup for rapid cyclogenesis. The shortwave trough is negatively tilted and a very strong vortmax is racing NNE out ahead of it. Winds ahead of both the vort and the trough are strongly divergent which favors intense upward motion across the entire area.

12Z NAM Showing Strong Jet Dynamics Contributing To Rapid Cyclogenesis Thursday Evening. Image Credit: Accuweather
12Z NAM Showing Strong Jet Dynamics Contributing To Rapid Cyclogenesis Thursday Evening. Image Credit: Accuweather

Another factor aiding in explosive cyclogenesis will be favorable jet dynamics in the upper levels of the atmosphere. The polar outflow jet of the storm is forecast to be situated in such a way that its right entrance region will overlap with the left exit region of the inflow jet to the south/south-west. This overlapping of zones favorable for divergence will allow the storm at the surface to rapidly strengthen, deepening around 20mb in 12 hours!

12Z GFS Showing Extremely Intense Upward Motion Thursday Evening. Credit: Accuweather
12Z GFS Showing Extremely Intense Upward Motion Thursday Evening. Credit: Accuweather

What does all this divergence mean? Upward motion Thursday night will be truly incredible. When the scale ends at 20 and values are forecast to exceed 70, you know the event is highly anomalous. The rapid deepening of the surface low, the intense vort at 500mb, and the jet dynamics at 300mb will combine to lift the air at a very high rate. What does this mean for us? Precip will be falling and it will be falling hard.

NAM 3km Simulated Radar Showing Very Heavy Precip Thursday Night. Credit: Tropical Tidbits
6Z NAM 3km Simulated Radar Showing Very Heavy Precip Thursday Night. Credit: Tropical Tidbits

A band of precip will set up Thursday evening across eastern NH and western ME that will feature whiteout snow falling at rates of 1-3″/hr+, torrential downpours along the coast, very strong winds, and possibly thunder. The fact that precip will be falling so heavily is important because of a phenomenon known as dynamic cooling. When there’s so much upward motion and so many snowflakes melting into raindrops, the atmosphere (especially the above freezing parts) will cool rapidly. This is the key to snowfall east of I-95 and N/W of the peninsulas. The next paragraph explains dynamic cooling and is borrowed from last evening’s update.

As snowflakes melt, the water they contain goes from solid (frozen) form to liquid form. This phase change requires outside energy to energize the water molecules into moving around more, thus changing the phase from solid to liquid. Where does this energy come from? The air around the melting hydrometeors (a fancy word for water (hydro) that falls from the sky (meteor) ). What happens when you remove energy from the air? It cools because, by definition, air with less energy is colder. If you have tons and tons of snowflakes melting at the same time, the temperature will continue to cool and eventually, the entire column will cool below freezing and snow can reach the ground. This process is aided by the intense lifting as air rises, cools, and is replaced at the surface by colder air moving in from the NW.

12Z GFS Showing Poor Dendritic Growth And A Deep Warm Layer In Portland Thursday Night
12Z GFS Showing Poor Dendritic Growth And A Deep Warm Layer In Portland Thursday Night

The problem along the coast is that the dynamic cooling has a lot of warm air to overcome. The warm layer in Portland is modeled to be around 5,000 feet deep by most guidance. Some models are colder but not by a lot. While melting and lifting will cool the atmosphere a bunch, it likely won’t be enough to get significant accumulations. The accumulating snow along the coast will come at the very end as cold air rushes in from the west while precip moves out. IF the easterly track pans out, the warm layer would be shallower and the dynamic cooling would have a chance at cooling the column enough for more substantial snows near the coast. As I mentioned above, there is a cap on snowfall potential east of I-95. I’d say this is about 6″ which would only fall in this area if a) the storm tracked a little east, b) the dynamic cooling worked out as strong or stronger than forecast and c) moisture aloft continued to keep snow falling longer as cold air rushed in behind the storm Friday morning. If none of that happens, most coastal areas would only see an inch or two at best and parts of the midcoast could see no snow at all.

The Wind

NAM Model Showing Two Rounds Of Strong Winds Thursday Night. Image Credit: Weatherbell
NAM Model Showing Two Rounds Of Strong Winds Thursday Night. Image Credit: Weatherbell

Besides the heavy precip, the other big story with this storm will be the wind. There will be two rounds of very strong winds, one on the front side of the storm and one on  the back side. On the front side, winds will be out of the ESE along the coast with gusts to 60mph possible along the midcoast. Gusts to 50-55 mph are likely in the Portland area and points along the coast SW of that. On the back side, winds will flip to the west and begin blasting at similar speeds. While the front side winds will be mostly a coastal issue, the westerlies on the back side will impact everyone.

12Z NAM Showing Two Blasts Of Wind Along The Coast Thursday Night
12Z NAM Showing Two Blasts Of Wind Along The Coast Thursday Night

Here’s another visualization of the winds at a single point (Rockland) through time. Much like a hurricane, there will be front side winds, a calm period as the center of the storm passes overhead, and then back side winds. Winds will not be of hurricane strength though a gust to hurricane force can’t be ruled out offshore and possibly at an exposed Midcoast point. These winds will definitely be strong enough to knock down trees and power lines especially those anchored in soggy ground (midcoast) or those weighed down by heavy snow (inland). With colder air moving in behind this storm, it will be important to be prepared for a night or two in the cold should your power go out.

Snowfall Forecast
Snowfall Forecast

Here’s the latest snowfall forecast. The main adjustment was to trim back totals a bit near the coast as guidance has shifted towards a warmer solution. The bullseye of around 2 feet in the Whites/Mahoosics still looks good. The area with the sharpest gradient (near the coast) still has a bit of uncertainty attached as some guidance still wants to hang onto a colder solution. This will be watched and any adjustments needed made tomorrow.

To summarize: snow will arrive from SW to NE midday tomorrow and will change to rain along the coast tomorrow evening. Heavy snow and rain will arrive tomorrow evening and last through tomorrow night with whiteouts possible in areas of heavy snow. Thunder will also be possible as dry air moves in aloft and instability is created with warmer and moister air near the surface. Winds will be strongest along the coast and will blast the area in two parts. The first will be along the coast with ESE winds gusting up to 60mph. The second will be enjoyed by everyone with WNW winds gusting up to 50mph. These winds will be strong enough for power outage concerns.

No coastal flooding concerns are expected as tides are astronomically low though a few instances of minor splashover are possible along the midcoast where onshore flow will be strongest.

The pattern doesn’t stop here, more snow is in the forecast for New Year’s Eve night and mixed precipitation may threaten to begin the first week of 2017. I will have an update on those storm threats later this evening or tomorrow.

-Jack

 

High-impact storm to impact the area Wednesday

Hello everyone!

As you all have heard, confidence is increasing rapidly that the area will feel significant impacts from an early season winter storm. I will publish my first shot at a snowfall map but I encourage you to read the discussion as well which is where I explain the reasoning behind the snow map. This will be a little on the longer side just so you’re prepared. I have a timeline at the bottom should you want to skip to that part.

The Setup

We have a complex pattern out there right now that will have significant implications for snowfall on Wednesday. Lets start not on Wednesday, not on Tuesday, but night now.

current obs
10:00 AM observations from around the area.

Lets take a look at the current observations across the area right now. Notice all the 50’s with some 40’s and some 60’s? These temps have been here for a while (since last night) and are expected to continue through tomorrow morning. What we have with this type of setup is a very warm boundary layer (boundary layer is the layer of the atmosphere right next to the ground). This prolonged period of warm weather is thawing out the ground and causing both the ground, and the air right next to the ground, to be quite warm. Both of these factors will have significant implications down the road with potential snowfall.

With a wind off the water, ocean temps are another important factor that many overlook. At bouy 44007 (~25mi off the coast near Portland), the ocean temperature this morning was 50.3 degrees. Other bouys in the area confirm ocean temps right around 50 degrees. If the wind turns more easterly (even NE winds could be a problem especially in MA) then the warm air would be pushed onshore and the whole snow operation would be shut down.

Let’s look now to the upper air pattern and step forward in time. All images come from Accuweather with text/lines/shapes added by me.

0z CMC Model IDEA of 500mb pattern 7PM tonight.
0z CMC Model IDEA of 500mb pattern 7PM tonight.

Notice the two pieces of energy marked off on the map. They will round the base of the trough and form a storm off the Carolinas. The key to this forecast is the exact track of the storm and that will be determined by two pieces of energy diving down across the plains.

cmc---conus-72-C-500vor_white
0z CMC Model IDEA on 500mb pattern 7PM Wednesday

They key to this forecast as I mentioned above will by the piece of energy pushing east across the Carolinas Wednesday. If this energy is faster, like the GFS, NAM, and CMC are saying, the storm tracks closer to the benchmark and a snowier solution ensues. Should this energy lag behind a little more, like the Euro says, the storm tracks farther west and a rainer solution ensues.

Right now I am leaning towards a compromise with a slight GFS bias due to the lack of blocking over the Atlantic. It is important to note that without strong high pressure in the western Atlantic, the door is open for the storm to slide a little farther east. This is the main reason why I favor the GFS solution over the Euro solution. However, with the Euro’s track record, it is very important to not discount it. A western track is still very possible.

The Action

Now that we’ve looked into the larger scale setup and some of the caveats to the forecast that only humans can pick up on, let’s get into what will really happen.

There are still differences between the models regarding the exact track and thus the westward progression of the rain/snow line. right now, I think it is safe to say that all coastal areas mix for at least some time. The greatest threat for mixing will be around 1 Am Thursday Morning and should come as sleet since the only nose of above freezing temps comes at 700mb. Everything above and below that is blow freezing.

There are a few things that are going in favor of coastal snow in this scenario. First off, this storm will be rapidly intensifying. The Euro has a pressure drop of 22mb in 24hours (7am Wed to 7AM Thu) so not quite an official ‘bomb’ but close enough (to be an official bomb, the pressure must drop 24mb in 24hrs). When storms intensify like this a few things happen. First, they tend to suck in cold air due to their rapidly expanding wind field. This could be a contributing factor in keeping coastal areas snowier for longer.

They also tend to manufacture their own cold air through a process known as dynamic cooling. This is a rather complicated process that can be boiled down to the cooling of the atmosphere in response to upward motion. We have a lot of upward motion associated with this storm due to its rapid intensification. This means that despite the fact that there will be little in the way of cold air at the onset of the storm, there will be a supply of cold air and that could potentially keep some coastal areas in the snow for longer.

Early thoughts on snow accumulations for the area. Subject to change.
Early thoughts on snow accumulations for the area. Subject to change.

I have opted to go conservative with the snowfall amounts especially at the coast to allow for the possibility of a westward track. I will continue to refine this and post revisions either here or on Twitter @Jacksillin.

Here is a timeline of how I expect things to unfold across the region. Highest impacts from heavy snow are expected to be felt Wednesday evening into Wednesday night.

Wednesday Morning: Snow approaches from the south, no travel impacts. Get travel and any storm prep done now.

Wednesday Afternoon: Snow overspreads the area and becomes heavy especially interior MA and CT. Snow changes to rain coastal SE MA. Travel impacts: Moderate

Wednesday Evening: Heavy snow moves into interior sections. Coastal areas south of Portland Maine inland to about 5 miles mix with sleet/rain. Midcoast Maine likely mixes as well. Travel impacts: High

Wednesday Night: Heavy snow continues especially interior NH/ME. Coastal Maine still stands the chance for mixing with greatest mixing potential still south of Portland. Rain/snow line starts collapsing in CT/SE MA. Travel impacts: High

Thursday Morning: Heavy snow moves into eastern Maine and snow starts to taper off. Mix line moves offshore of coastal Maine but still impacts SE MA. Snow ends CT/MA/NH. Travel impacts: Moderate, improving

Thursday Evening: Snow ends for everyone. Travel impacts: None

I will have more updates on Twitter this afternoon as well as all day tomorrow and throughout the storm itself. I’m @JackSillin. I will have a video out later today and will post the link to Twitter. I may or may not have another update on here tonight depending on how things play out. Next definite update will be tomorrow morning.

-Jack

 

Morning update

What a wild ride this has been in regards to amounts, source of amounts, low placement etc. We now have a low pressure center moving ENE that is located about 150 miles SE of the Cape. Regardless, its associated trough will bring snow. This trough will set up over the region today and sit there not moving until evening. Due to the non norlun nature of this trough (thank goodness!!), I am confident with my amountsthat have been upgraded and are shown below.

snow 2222
Snow Map.
ptype 2
Precipitation type map.

The upgrade in snow totals was due to the trough being slighly stronger than expected. As a result, the snow rates will also be higher than expected leading to reduced visibilities and slick roads.
-Jack

What a change…

What a change over the past few days! First we were looking at the potential for a foot of snow from a powerful ocean storm and now we are looking at 6″ from its wicked inverted trough. Remember that inverted or norlun trough from earlier this winter? They are impossible to predict where they will set up until they actually do set up. Now I am thinking it will set up right near Portland or maybe a little south. Either way, there should be snow breaking our today from “ocean effect” or lake effect snow but over the ocean. Ocean effect snow tends not to be as heavy as lake effect and that is what we will see today.
There is a developing low off the Carolina coast that is moving ENE. This low will skirt too far offshore to have too much of an effect. its norlun or inverted trough however will. This troughs are notoriously impossible to predict as we saw earlier this year. Right now my thoughts are that it will dump a sufficient amount (6″) to many across southern Maine. My snow map is below.
snow111
Snow map.
Check out my other two sites for town by town forecasts for the snow. Those will be updated with the 18z runs tonight. They can be found at the right of my page.
-Jack

Models agree now on only a very minor snow event for many

Models now agree this morning that the comination or phasing of these two storms will occur too far to the south and east to give us much snow. I expect a widespread 4-6″ from an inverted trough. Remember what happened with that last time? We all expected 8-12″ but we got 0. These things are absolutely impossible to predict so confidence is super low. Snow map coming with 12z models midday.
The area of low pressure will develop and move to the ESE today into tonight. It will then rapidly deepen South of the Maritimes. The inverted or norlun trough will hang around behind giving us minimal snow. Check back later for the snow map.
-Jack

Wintery pattern ahead…

After a week of extremely mild temps, old man winter is really hitting us with his cane later this month. Just to clarify This WILL NOT BE THE CHRISTMAS BLIZZARD OF 2010!! But there will likely be some northeast snowstorms and colder temperatures.

glb 1a

This image shows a “Greenland Block” setup for the 16-21 of this month. This is the setup we had in the winter of 2012-2011. This will be a major factor in bringing in the coastal storms as well as the cold air. In the 2010-2011 winter, there was also an ultral-positive PNA which is not present, an ultra strong MJO for most of January, again this year, there could be a time when everything comes together at the right place at the right time and creates a large snowstorm.

I am seeing some model development of a snowstorm in about a week from now. Stay Tuned for the latest!!!

-Jack