Just as the calendar announces the arrival of Spring, our biggest winter storm threat all season is on the horizon. While it is still 3-4 days out, confidence is increasing that a storm will form in the Gulf of Mexico Saturday and move NE until it reaches somewhere near Cape Cod by Monday morning. This track is nearly perfect for heavy snow across the area with the storm being close enough to deliver a lot of moisture and far enough away so any warm air remains well to our SE.
It is important to note, however, that the storm is still a good 3-4 days away. While track changes are certainly possible, it is becoming more and more likely that we do see a high impact storm beginning Sunday afternoon and lasting through Monday afternoon. Here is the 12Z GEM showing the setup Saturday morning as high pressure builds in and low pressure begins to develop. We will have plenty of cold air to go around as Arctic high pressure builds south. At the onset of the storm, temps will be in the 20’s with dew points in the single digits. That will allow for this to be a mainly snow event. Should the low track a little farther west, some mixing could be an issue so we’ll have to keep an eye out for that in the coming days but as of now, this looks like an all or mostly snow event.
Confidence in track is reasonably good. Most guidance is indicating low pressure develops in the Gulf of Mexico and moves NE to a point right near Cape Cod. However, intensity and timing are the two variables that remain uncertain. The faster the storm is, the less it can intensify and the less snow it gets even if it takes an optimal track. The slower the storm is, the longer it has to intensify and the more snow we get, assuming the same track. This is why despite moderate-high confidence in track, it remains too early to issue accumulation maps. Uncertainty is still high as to exactly how much snow will fall. However, it is looking more and more likely that this is a 6″+ event. Should a slower/stronger solution play out, upwards of a foot of snow is possible. Should a slower/weaker solution play out, amounts would likely be closer to 6″. Currently, I am leaning much more towards the slower/stronger solution though this far out it is important to keep options open.
Yet another storm has decided to cut west this week as our pattern continues to disappoint for skiers and other winter enthusiasts. This storm will be a lot like our last storm and will, as with most inland runners, feature front end frozen precip, heavy rain, and high winds. Precip moves in Wednesday afternoon and moves out Thursday evening.
The storm will, as these storms usually do, take place in two stages. The first stage will be Wednesday afternoon into Wednesday evening with light snow changing to ice and rain. During this time, the warm front will be lifting north and cold high pressure will still rule with some weak Cold Air Damming in the mix as well. Accumulations will be on the light side, probably remaining under 3″ of snow though exact amounts are still yet to be determined.
A lull will occur Thursday morning as the warm front passes north. Winds will become strong out of the S/SE which will blast out any of the last cold pockets. Heavy rain associated with the cold front will approach and move into the area Thursday afternoon/evening and will bring with it the standard high wind/heavy rain threats with localized flooding and power outages possible. Exact winds are still to be determined but will likely be just a click below those of our last event which would indicate gusts to or around 50 mph along the coast with lighter winds inland.
Colder air moves in for next weekend along with another shot of snow currently centered around Saturday.
Cold air is firmly entrenched today but even colder air is on the way. Look for a cold front to smash SE tonight bringing behind it the coldest air all season and the first truly Arctic air we’ve seen all season. As the cold air moves in, an upper low diving to our south will set the stage for a Norlun trough event along the midcoast tomorrow. Beyond that, bitter and dangerous cold arrives Sunday followed by a messy storm midweek next week.
Saturday Norlun Trough
The front gets hung up along the midcoast as the upper low slides to our south. Winds out ahead of the 500mb trough will turn southeasterly and eventually easterly which will provide a mechanism for moisture to be transported into the region. Also, with southeasterly winds aloft, there will be nothing to move the trough once it sets up. Most of us will see the moisture transport aloft in the form of light snow/snow showers during the day tomorrow with light accumulations. The midcoast will be the only area to really capitalize on that. To understand why, read the next paragraph about how Norlun troughs work. If you’re more interested in the forecast, skip on down to the next picture and read about the cold coming Sunday.
A Look Behind The Scenes At Norlun Troughs
Because it’s been so warm recently, the ocean is still quite toasty. This sets up a very large difference in temperature between the warm ocean and the cold air. The warm water will heat the lowest level of the atmosphere creating warm air which wants to rise. Above this very shallow layer of relative warmth lies an entire atmosphere of very cold air which wants to sink. Somewhere in the impenetrable fortress of cold, there will be a weakness. The warm air will rush upwards through this weakness generating tremendous upward motion and leading to warm moist air crashing into cold dry air. This violent collision will produce snow.
As the new trough takes up the energy immediately near it, warm air trapped under the cold air all across the Gulf of Maine will rush in to take its place so it too can rush upwards and cool. As the trough is using up the existing warm air, new warm air will keep being created as the water continues to warm the lowest levels. This warm air will rush to the weakness in the cold and rise up, depositing its moisture along the way. This is what we call a Norlun trough.
One of those will form over the midcoast and deposit heavy snow tomorrow. Totals are likely to come it at around a foot in the core of the trough but it remains to be seen exactly where that sets up. These events are notoriously fickle and can set up wherever they please or not at all. One good example happened just last night when a weak Norlun formed over Portland out of left field causing major issues. Bottom line: expect the unexpected.
Expected snowfall for tomorrow. Upslope snow showers in the mountains are likely to produce 1-3″ in the usual spots. Farther south, a dusting to as much as 2″ is possible with isolated snow showers/flurries. In the core of the Norlun, thundersnow is possible as there will be a solid amount of instability associated with the temperature falling dramatically with height from the warm ocean to the bitter cold air moving in aloft (technical: lapse rates will be very impressive).
NW winds will be howling tomorrow beginning in the afternoon. While blowing and drifting snow will initially not be an issue, by Saturday night, those who saw snow will also see it blowing around leading to more slick spots and reduced visibility. It will also add an extra sting to the air if you happen to be out and about Saturday night.
Dangerous Cold Sunday
Very cold air is still on track to come into the area behind the storm on Sunday. Actual temps will drop well below zero and as NW winds howl at over 25 mph, wind chills will drop even lower. This is the image I used for last night’s post and it still applies as wind chills approach -40 to -50 in the north with -20 to -30 degree wind chills in the south. Bundle up for the Valentines Day dates both Saturday and Sunday nights. Thankfully, the extreme cold is out on Monday.
Messy Midweek Storm
As the cold retreats, we have another storm threat. We are virtually certain to see precip the question is of what variety. Right now, it looks like a mess with all precip types possible for everyone. It is far too early to nail down exact impacts or amounts but total accumulation of whatever falls could be significant. My thinking from yesterday still applies in that uncertainty remains large here. One group of forecast models leans towards a colder, farther east solution with more snow than mix while another camp of models leans towards more rain and mix than snow.
Another storm is on the horizon late next week but we have to get the first two resolved before we can dig into that one. Just know that there is the potential for a storm and as always, ignore any hype you may see.
I’ll have more updates in the coming days as the midweek storm becomes clearer. I’ll also be on Twitter watching the Norlun trough evolve tomorrow @JackSillin.
A powerful storm is bombing out over the ocean near the Carolinas this evening and we will be on the far western edge. At the same time, a complex upper low is diving SE across the upper Midwest. They will form a connection of sorts that will transport warm moist air over the cold air moving in tonight following today’s cold front.
The coastal monster will stay mainly offshore but it will throw a ton of moisture back to the NW. There is a clipper to the NW which is ready to receive this moisture and will help draw it back NW. Bottom line: there will be a feed of moisture over the area tomorrow as moisture from the coastal low gets pulled back into the clipper. If you watched my video discussing the Friday storm, you know that we need three things for snow: moisture, cold, and lift. We got the cold today with that Arctic front and above is the moisture. The problem though is the lift.
As the warm air providing the moisture rises up and over the cold air at the surface we got today, it will rise, cool, and condense into precip. Sometimes, this mechanism for forcing (getting air to rise) can be quite effective in producing heavy precip. Not so much this time. If you’ve followed along for a while, you’ll know that I use Vertical Velocity to show how much air is rising and thus how heavy precip will be. In the big storms, you’ll often see bright purples and reds (notice scale on right of image). This time, we see yellows and oranges. This is indication that there will be less mesoscale banding and more broad lighter precip. Therefore, look for lighter snow though it will last long enough for fairly heavy accumulations.
This snow will be light and dry which is nice for shoveling but will be unfortunate because the gusty winds will have no problem blowing around the light, fluffy snow. For this reason, expect blowing and drifting snow to cause visibility issues especially tomorrow afternoon (map valid 1PM tomorrow). Winds are likely to range from near calm in the mountains to over 30mph at the coast.
Here’s what I expect in terms of total snowfall. Keep in mind, this falls over a near 30 hour period from late morning tomorrow through Tuesday afternoon. Slow and steady is the name of the game for this one.
We’re heading into a period of active weather this week and our first storm is up tomorrow. This one is tracking to our west and thus we’re on the warm side. This will be an all rain event with temps soaring into the 40’s. Winds will also be extremely strong gusting near 60mph at the coast.
Low Pressure is developing over Arkansas right now and will move NNE tonight through tomorrow while strengthening. This storm will drive a cold front through the region tomorrow night. Ahead of the front, look for heavy rain, strong winds, and warm temps. Conditions behind the front look cold and windy as arctic air moves in. Now that we’ve set the stage, lets dig into the details.
Rain will move in tomorrow morning and will become heavy by early afternoon. In terms of amounts, a general 1-2.5″ is expected with the highest amounts falling in areas where heavy rain is enhanced by upsloping SE winds. Any SE facing slopes are at risk for the 2-2.5″ totals. With the snowpack being marginal at best, widespread flooding isn’t likely but some rivers and streams could run high enough to cause minor issues in any usual trouble spots. A flood watch is out for much of the area due to this threat.
I think the biggest story will be the winds. The map at right is the winds just above the surface, NOT winds at the surface. The numbers on the map are knots so the winds between 2,500 and 5,000 feet are hurricane force. NOT all these winds will mix down to the surface by any means. That being said, winds will be very gusty as heavy rain helps to transport winds aloft down to the surface. Winds along the coast especially NE of Portland are likely to gust over 55mph. This could cause a few isolated power outages so watch for those if you usually see darkness during storms like this. All in all, not a massive windstorm but some branches are likely to come down and could cause a few issues. Also be sure to secure anything that might blow around outside (sleds, shovels, etc).
There could be some thunder in the heaviest precip. Nothing crazy but that’s not something we usually hear here in Maine in January especially with rain (thundersnow happens sometimes with strong Nor’easters but rarely to we break enough into the warm sector for thunder).
On the back side of the storm, cold air will be rushing into the region on strong NW winds. Look for subfreezing air to blast into the area Monday and any leftover puddles will freeze. As a result, look for slick roads Monday and Monday night.
SE winds will be strong tomorrow but won’t last for a long time. As a result, coastal flooding impacts should be minimal. Some splashover/erosion is likely and the usual trouble spots could see some issues but no major impacts are likely.
Cold air moves in Monday and lasts through the week with snow threats midweek and next weekend. Those are still far out so details will have to wait to be figured out.
I’ll have another update tomorrow morning. I’ll also have updates through the day over on the Facebook page.
Last night between 8 and 9 PM, something really cool happened all across southern Maine. Several hours after dark and following the passage of a cold front, temps spiked between 4 and 6 degrees in less than an hour going against all logic that temps should fall after dark especially without any large scale weather system to draw warm air north. Let’s see what happened.
At 8:00 last night, a cold front was crossing the area from west to east with SW winds ahead of it and W winds behind it. Temps were already pretty warm, in the 60’s, as southerly winds ahead of the front brought warm air into the region. Colder air lurked behind the front and temps in the 30’s were being reported in the upper Great Lakes with west winds bringing those temps right to us. So what happened? Shouldn’t temps have dropped after the passage of a cold front with an actual cold airmass behind it?
The answer lies in downsloping. This is a term I’ve used a lot but really want to explain here. Winds after the cold front were
westerly/northwesterly and thus the air over southern Maine came from New York/Quebec and then up and over the Appalachian Mountains. When the air rose up the west side of the Appalachians, it cooled but not a lot of the moisture was rung out as shown by the lack of precip at the time.
Because the air was still pretty saturated at the time, the sinking air on the east side of the mountains warmed at the saturated adiabatic lapse rate of roughly 5.5F for every thousand feet. The 5.5 degrees per 1,000 feet figure is for fully saturated air with relative humidity of 100%. The relative humidity in Portland at the time was 73% so the air could be expected to warm at 73% of the moist (partially saturated) adiabatic lapse rate. 73% of 5.5 degrees is 4.015 degrees, very close to the 4 degree rise measured at PWM.
At Augusta, the same calculation works. The temperature rose 5 degrees from 59 degrees at 9 PM to 64 degrees at 11PM. With a relative humidity at 9PM of 90%, that works out to a moist adiabatic lapse rate of 4.95 degrees, again, darn close to the 5 degrees observed in actuality.
Another contributing factor to the suddenness of the spike in temps was warm air aloft suddenly being mixed down to the surface. The 7PM sounding up in Gray showed warm air just above the surface which promptly mixed down with the turbulence caused by the passage of the front.
The air just above the surface was being downsloped to just the right temperature with westerly winds just above the surface and when the surface front came through, the turbulence broke the inversion and sent those warm temps crashing to the ground.
I’ll be back in the morning with tomorrow’s weather. A sneak peek reveals cooler but still not chilly temps in the 50’s with mainly sunny skies.
Our long-awaited storm is here and heavy rain is falling across the area with the expected strong winds as accompaniment. The heaviest of rain is north and east of Portland as of 5:15 this morning and this area of intense rain/wind will continue to move NE in the coming hours. Behind that lies a batch of very heavy rain over SE MA and lighter showers over eastern NY. The SE MA rain is moving NE and will likely impact the midcoast with another round of torrential rain and gusty winds. More showers lurk back in NY associated with cold front #1 today and expect one last shot at intense rain and driving winds as this moves through.
Behind those showers, which arrive 9-10 AM, expect clearing skies and warming temps. By mid/late afternoon, temps in the 70’s are likely under partly sunny skies. Another cold front moves through this evening which touches off some showers and possibly a few thunderstorms too. For a minute, it just may feel more like August than October. Temps drop a bit behind the front but a continued stretch of very mild weather looks to be on the way for the next week or so.