We’re still on track to receive a sizeable storm tomorrow as low pressure moves up the coast. The trends this afternoon have been towards low pressure being slightly farther east which would mean slightly cooler temps along with slightly less total precip. Overall, this leads to little shift in terms of how I think things play out but there are a few important differences. These differences mainly revolve around how things play out at the coast and just inland.
Looking at observations this evening, the forecast mainly looks good. A coastal front is forming across York County and will continue to sharpen up as low pressure develops offshore. The GFS shows this well. Keep in mind, models have had a very difficult time with this storm so don’t take any of the model graphics I post verbatim. They’re just to illustrate an idea not an exact figure or forecast.
Temps on the warm side of the coastal front are already above freezing over Coastal York county. Winds are off the water there and thus temps will continue to rise through the evening. Wherever that sets up, look for rain on the SE side and snow/freezing rain on the NW side. As always, snow amounts could be bumped up a few miles NW of the front as clashing warm and cold air will increase lift/forcing.
12Z GFS Showing Modest Forcing For Heavy Precip Tomorrow Morning. Credit: Accuweather
While dynamics don’t look crazy for this event, there is modest forcing for heavy precip tomorrow morning through midday. As this map shows, bands are likely to extend well into the mountains. Don’t worry at the coast, precip will be moderate to heavy there too but driven by different factors. The heavy precip will assist in dynamic cooling which will further assist cold air in moving southward tomorrow midday. I think everyone sees accumulating snow tomorrow afternoon/evening even areas that see rain for most of the event.
I’m sticking with my snow map for now as I don’t have the flexibility for adjustments and it still looks good. The jackpot will fall in the southern mountains and northern foothills with lesser amounts north and south. The one area to watch for higher amounts will be the southern end of things towards the coast. There is more liquid available at the coast but less cold air. If the cold air can show up, that extra QPF (Quantitative Precipitation Forecast) could allow for bust potential.
I’ll have updates when I can this evening on Twitter and another blog update will arrive tomorrow morning.
Not a lot has changed from this morning in regards to tonight’s forecast. Snow is ongoing across the area now but big accumulations will hold off until after around 9 PM when a very heavy band looks to sweep NE. As it does so, it will be intensifying and slowing down.
HRRR Model Showing Intense Snow Sweeping NE This Evening. Credit: Weatherbell
The farther NE you go, the heavier the band will be and the longer it will last. In this band, look for very intense snowfall rates of 2-4″ per hour along with gusty winds and potentially thunder. It won’t last terribly long for most, maybe an hour or two, but in that time, the snow will really pile up. If you are driving late tonight look for very dangerous driving conditions with near whiteout conditions. Thankfully, the worst of the storm will be from 9PM to around midnight. After that, the snow abruptly shuts off and NW winds pick up. Some snow showers could linger through tomorrow morning especially in the mountains and NE.
I still like my snow map from this morning. Remember, most of this falls in just a few hours late tonight. It will be quite a show if you happen to be awake for it!
Be careful tomorrow as winds will be gusting near 45mph which will blow around the new snow. The greatest threat for reduced visibility due to blowing snow is inland where the snow will be fluffier.
Initially there were concerns about coastal mixing and that is still possible but observations show cold air hanging tough for everyone but the outer peninsulas. Should this change between now and when the heavy band blasts through, areas east of Route 1 could see reduced accumulations.
Believe it or not, we got another storm lined up! More snow, possibly significant, could arrive Saturday. There are significant questions so the details will have to wait a while but know the potential is definitely there! Welcome to winter the way it should be!
A jucier than normal morning post today as the forecast for this evening is fascinating and very complicated. Before the snow arrives, look for increasing clouds with highs in the 20’s inland, low 30’s along the coast. Snow should arrive around 4 PM or a little after, then things get interesting.
0Z GEM Showing The Setup. Image Credit: Weatherbell
The setup from yesterday evening’s post remains largely the same this morning. Low pressure currently over Michigan will move E into southern Ontario this afternoon. Secondary low pressure will develop to our SW and move NE east of us. How fast this low develops is the key to the forecast. The general idea is that the combination of tons of upper level energy, warm ocean waters, and a favorable upper level setup (VERY negatively tilted trough for those that understand) will lead to rapid development just offshore.
0Z GEM Showing Intense Banding Across Western Maine Tonight. Credit: Accuweather
Intense snow bands will begin to develop along with the low but when and thus where these bands develop is still an unknown. We do now have a slightly better idea of where to look for the heaviest snow, the lightest snow, and where it could go either way. This is a very complicated situation and I mean it when I say there is high bust potential here. With that being said, I doubt York County sees much more than 2-4 or maybe 5″. It looks like things pull together just a little too late down there. The Midcoast and areas NE of Augusta/Auburn are likely to see a solid 6-10/8-12″ snow. It’s the areas in between that are really tricky.
This is what I anticipate snow amounts to look like. Uncertainty is very high especially NE of York County and SE of Augusta.
Even in areas without much accumulation in terms of raw numbers, expect difficult travel as the snow will fall very heavily. There is also the chance that those in the heaviest bands see thundersnow this evening as well.
The immediate coast could mix with rain this evening before the heaviest stuff arrives. If this happens, watch for a rapid refreeze which would cause dangerous travel in those areas. Right now I think the peninsulas are most at risk for this but anyone east of Route 1 should be watchful.
Snow moves out tonight leaving a cold and gusty wind for tomorrow.
My apologies on this post for an uncertain snow event going out so late and being so short, cramming in something that usually takes 4+ hours into 2 is hard. With that aside, I’ll do my very best to look at the forecast for tomorrow night in some detail below.
Overview
12Z GEM Showing The Setup Tuesday Evening. Image Credit: Weatherbell
A clipper system is currently moving across Minnesota and will continue to dive SE tonight into tomorrow morning. It will end up over the Eastern Great Lakes by tomorrow afternoon. At this time, a new low will form near NYC/Long Island and move NE as it strengthens. The key to this forecast and why it is so uncertain is how fast this low intensifies. I want to stress that the difference between a widespread 3-6″ and a widespread 8-12″ event is a few hours. If the storm forms a bit earlier, there is more snow. If it is a bit late, there is less snow. Either way, a burst of heavy snow is likely tomorrow evening around or a little after the evening commute. Overall, impacts should be minor but after 7 or 8 tomorrow evening, roads are likely to become quite slick.
The Earlier Development Scenario
12Z GEM Showing Intense Upward Motion Leading To Very Heavy Snow Over Western Maine Tomorrow Night. Notice The Position Of The Red (Very Heavy Snow) Over Western Areas. Credit: Accuweather
This is the GEM model showing the earlier development scenario. At 11PM tomorrow night, an intense band of very heavy snow is located over Western Maine centered on a Portland-Lewiston line. In this scenario, intense snow bands develop earlier and farther to the west leading to higher totals across SW areas. Based on very warm SST’s offshore and the very high amount of energy blasting SE with the clipper, I think this is the more likely scenario. The 500mb trough will also be going sharply negative.
12Z GEM Showing The 500mb Factors In Favor Of Explosive Storm Development. Image Credit: Accuweather
A very negative trough with a ton of energy blasting over record warm ocean temps is a setup ripe for explosive storm development. The 12Z GEM shows this well. The other models show a similar setup and the GEM has shown itself to be very reliable when dealing with clippers and Canadian airmasses. It was the one model that caught the surprise no-show of the February 15 blizzard and I think it is on to something in terms of surprises with this storm.
This is what snow totals would look like if the low developed on the early side. Consider this my forecast.
The Late Development Scenario
12Z GFS Showing Snow Bands Firing Up More Along The Midcoast Than The ME-NH Border. Credit: Accuweather
It is also entirely possible things don’t pull together in time and the heavy snow bands really get going more over the eastern Midcoast than the NH-ME line. The GFS shows this well. This is the same parameter (upward motion) for the same time as the GEM map posted above. Compare them and look at how much farther NE the heavy snow bands (bright colors) are on the GFS compared to the GEM. This is the difference between 3″ and 8″ for most areas SW of Augusta. Where these snow bands set up is the entire forecast at this point. It is important to note that the GFS shows nearly the same 500mb setup. The trough on the GFS is the exact same as on the GEM with the only difference being the GFS is 30 or so miles farther NE. That is the difference between 3″ and 8″. I really want to stress how tiny the differences are in terms of the science. 30 miles is a tiny margin of error, it just so happens that this time that margin of error has tremendous impacts for a large swath of the area. Be prepared for either scenario despite the forecast being for more snow.
This is what snow totals would likely look like given the late development scenario playing out. This is not what I expect to happen but it remains a viable solution. In fact, new clues have emerged since the making of this map that indicate that totals could be slightly less than this if the low really fails to get going. Don’t be shocked if you wake up Wednesday to only a few inches SW of Augusta. Several inches look like a safe bet for the Midcoast and the NE mountains.
Coastal Mixing Concerns
12Z GEM Showing Near Freezing Temps At The Coast. Credit: Weatherbell
Winds ahead of the clipper will be onshore and thus temps will be marginal at the coast. However, winds will turn N/NE as the coastal low develops which will act to shut off the source of warm air. Also, heavy precip acts to cool the air and precip will certainly be heavy tomorrow night. All added up, I think this will be a wet snow for most coastal areas with only the peninsulas seeing rain. Again, this part of the forecast depends on the coastal low. The faster the low develops the faster cold air rushes in.
This is a VERY uncertain forecast so I’ll try to have an in-depth update tomorrow morning with details. I’ll have another update tomorrow evening as the storm is beginning. At this point, the details will be more clear (helpful, I know!).
Most of the heavy snow and sleet is off to our NE now as the mid levels dry out. Despite a lack of heavy precip, snow and sleet will still remain across the area this evening with another inch or so of snow and a coating of sleet and possibly a glaze of freezing rain as well. This continued light precip will cause roads to remain slick through the next few hours so continue to use caution if travelling.
Seeing as the storm is winding down, this will be my last update today. I’ll be back tomorrow morning with a look at tomorrow’s weather.
-Jack
10:30 AM Update
Heavy snow and sleet is ongoing across the region currently although the worst of the worst is now mainly NE of Portland. I expect moderate to heavy snow and sleet to continue for the next few hours with the worst gradually sliding NE. This afternoon, look for the second phase of the storm which is already beginning across southern areas which includes lighter mixed precip.
In Yarmouth, what I’ve been seeing generally seems to match up with other reports I’m seeing on mPING and on Twitter from folks across southern areas. Snow has been heavy here and is mixing with sleet. The sleet is piling up though, I’ve gotten about an inch of sleet on top of 4.5″ of snow as of 10:30. Keep in mind everything is still quite slick out there so use caution if traveling!
-Jack
7:45 AM Update
Snow continues across the region this morning. Here in Yarmouth, there was a period of sleet around 7 but the precip has since turned back to all snow as heavier precip moved in. As of 7:45, the precip remains all snow with very efficient accumulation. Due to cold temps around the area (10’s for most, 20’s coastal York county), the snow is dry and fluffy. I suggest shoveling/snowblowing now before the sleet turns the snow into frozen cement. Snow and sleet will continue with sleet moving north east through the morning. It seems that a middle of the road solution is playing out across areas north of York County with snow during times of heavy precip and sleet when precip is lighter. This will continue through the morning.
There are reports of many accidents across the are this morning and roads are very slick especially if your area is seeing sleet. Use extra caution on the roads today if you must travel. Also, remember to use your mPING app today! There has already been tons of great data flowing in and it’s really helping with the forecast!
-Jack
Original 6:15 AM Update
Hello everyone!
Today will feature a messy winter storm as low pressure moves through the Great Lakes. Warm air will be rising up and over a well-defined cold pool at the surface. This is the lifting that will produce moderate to heavy precip today. I’ve been digging into the depths of the forecast the past few evenings and now it’s time to bring it all together.
Morning Snow
HRRR Model IDEA On How Precip Unfolds This Morning. Keep In Mind This Appears To Be On The Cooler Side Of The Solutions. Credit: Weatherbell
Snow is falling across northern parts of New England this morning. Sleet has mixed in as far north as Manchester, NH as well indicating a warm layer already developing aloft. There are two possible solutions with this morning’s snowfall. Our first option is that the sleet line progresses as it has in the past hour unimpeded in its relentless march NE. This would result in sleet arriving during the heaviest of the precip, several hours earlier than last night’s forecast. Should this occur, look for totals lower or just under the lower end of the range from last night’s map (re-posted below). The other idea (this is the one you see above with the HRRR) is that the precip is so heavy that it dynamically cools the atmosphere. This has to do with the displacement of mass and is a topic for another day but the point is that if this occurs, the mid levels of the atmosphere could cool enough to allow for a little more precip to fall as snow thus resulting in totals more towards the middle or even upper end of the total ranges. Be prepared for either of these solutions. Remember even though it accumulates more slowly, sleet is icier and more slippery than snow. It is harder to drive in. Take it slow out there this morning.
Lingering Precip This Afternoon
After the initial burst of snow comes through this morning, precip will shift to a lighter more spotty type. This will fall any number of ways depending on your location. A mix of snow, sleet, and freezing rain is likely across the south with snow and sleet farther north and all snow up in the mountains. The freezing rain expected across the south will continue to cause very slick roads. Slick travel is expected everywhere today but in terms of a complete lack of traction, nothing beats .1-.3″ of ice on top of an inch or two of sleet on top of 4-6″ of snow.
Help Forecasters Track The Storm!
Given the plethora of precip types incoming with this storm, tomorrow would be a great time to give the mPING app a workout! Over the past few days you’ve seen how hard it is to forecast multiple precip types. Here’s a chance for you to help forecasters out! Simply download the free app and take a look outside! Send in your report of snow, sleet, freezing rain, or rain and you can help forecasters like me with forecasting multiple precip type events! The data is sent to the National Severe Storms Laboratory to help with radar development which gives models better data which improves forecasts. Read all about it over on the NSSL webpage. Also through that website, you can view your report and everyone else’s reports to track the rain/snow/sleet line in real-time! This is one of my most valuable tools for tracking the mix line to verify the forecast/make adjustments if needed. Happy reporting!
Totals
Forecast Total Snow/Ice Through Tuesday Night
I keep my map the same this morning as I think each solution (warm or cold) is equally likely. There are interesting radar trends that indicate the colder solution is playing out though you can’t go against hurricane force winds 10,000 feet up blasting in warm air.
Live Blog
We’ll know more as the morning goes on and I’ll keep updating this post as I see changes happening. Keep checking back right here through the morning and I’ll have new info at the top of the page as it comes in. I will also be on twitter with updates all morning @JackSillin.
Here is the link to last night’s post as the information there more or less remains the same.
A cold front is currently moving east through the region and will push offshore this evening. Behind it, a sprawling high pressure system will build in straight from Western Canada bringing with it our first real shot of cold air. On Tuesday, warm air from the tropics blasted up the coast by the storm currently causing trouble in Texas will smash into the cold air and a good burst of snow will result. Here’s how I think it will play out and why.
The Cold Air: Tomorrow
12Z GFS Model Idea Of High Temps Tomorrow Showing Very Cold Air In Place. Credit: Weatherbell
Highs will remain below freezing tomorrow for everyone except maybe far southern York County. Highs near the international border will struggle to get out of the single digits. That doesn’t include the NW breeze which will definitely be felt. This is our source of cold air for Tuesday. Prepare for January like temps and wind chills which compared to this torch of a December will feel quite chilly!
The Moisture: Monday Night
12Z GFS Model Showing Moisture From The Gulf Of Mexico Plowing Northward Monday Night. Image Credit: Weatherbell
At the same time, the storm that is bringing a slew of problems to Texas will be moving North through the Ohio valley. This will set up a feed of warm moist air from the Gulf of Mexico right up the coast to Maine. This will cause some concerns as the moist air also comes with warmth which will cause concerns for mixing towards the end.
The Collision: Tuesday
The cold air comes tomorrow and the moisture arrives on Tuesday. The collision is what will cause the snow. At the moment this looks like a front end thump of snow during the day Tuesday followed by a lighter period of mixed snow/sleet/freezing drizzle/drizzle on Tuesday night. Let’s dig into the snow first.
12Z GFS Model Showing Strong Plenty Of Energy To Produce Heavy Snow Tuesday Afternoon. Credit: Accuweather
As warm air plows northward, it will run into the cold air that arrives tonight into tomorrow. This will allow for heavy snow to form on the leading edge of the warm air as it is forced up and over the cold air. This map from the 12Z GFS shows strong forcing (that’s how the moisture in the air is squeezed out) Tuesday morning. Expect slick roads and heavy snow starting Tuesday morning and lasting through Tuesday afternoon/evening. This is when most of the snow will fall. A general 4-8″ is expected with some seeing more and some less. See the snowfall map below for more details.
Mixing Concerns
12Z GFS Showing Warm Air Aloft Creeping In Tuesday Afternoon. Credit: Accuweather
Southwest winds bringing the warm moist air into the region will eventually bring in warm enough air to start causing mixing problems especially in Southern New England. My current thinking is that Warm air aloft gets as far north as the MA state line during the tail end of the steady precip. Lighter precip will linger through the evening and areas as far north as Portland could see some light sleet/freezing rain overnight Tuesday. If warm air moves in earlier/farther north than forecast which is a possibility, totals could be cut down in SW ME and NH. Northeast of route 26 is likely safe from any impactful sleet.
12Z CMC Showing A Tight Temperature Gradient Along The Coast Associated With The Coastal Front. Image Credit: Weatherbell
The other concern for precip type will be along the immediate coast where a coastal front is likely to form. There will likely be a tight temperature gradient along this front and if you end up on the SE side, temps could rise high enough to change the precip to a rain/snow mix. This threat is greatest along the coast south of Portland and along the tips of the peninsulas. Wherever this sets up, look just to the NW for heavier precip associated with the warm ocean air moving up and over the cold locked in at the surface. Warm air rising over cold air is what is causing this whole mess on a large scale, the same thing happens on a small scale.
After the main snow event moves east Tuesday evening, lingering low level moisture will contribute to light mixed precip lingering through the first half of Tuesday night. As warm air completes its invasion aloft Tuesday evening, this could fall any of a number of ways, snow, sleet, freezing rain, or rain. The precip will be light so the impact on snowfall totals will be limited.
I’m thinking that because the moisture is below the warm layers, it stays mostly snow. The warm air moves in at 700mb (10,000 feet or so) but the cold stays tough below that (the blue lines on the map above indicate subfreezing temps at 5,000 feet). The moisture is in the low levels (where the cold air is) and thus even though 700mb is warm, I could definitely see another inch of snow as the snow falls in the low level cold layer. Regardless, this will keep roads slick through Tuesday night despite the heavy precip being gone.
Expected Snowfall
Expected Snowfall
Looking at the final snowfall amounts, I expect a general 4-8″ for Northern New England with less to the south. I think someone sees 10 or 11″ and the best chance looks to be either in the mountains where deep cold stays really locked in contributing to a drier snowfall that accumulates faster or near the coast where the coastal front contributes to more liquid falling from the sky. The coastal ‘jackpot’ area largely depends on the ocean air staying farther SE and the sleet being kept at bay. The northern Jackpot is dependant on enough moisture moving that far north. A coastal low developing Tuesday evening will try to steal some of the moisture from NW areas.
I’ll have another update tomorrow evening on the storm, details on tomorrow’s weather will come tomorrow morning.
Winter is making a big offensive push against the torch this week and Maine is right on the front lines. We have three storm threats this week, tomorrow, Tuesday, and Thursday/Friday. This post will focus mostly on tomorrow. I’ll have full updates on Tuesday’s storm threat starting tomorrow evening. Due to how far out the New Year’s storm threat is, I’ll save that for after we clear the first two.
Tomorrow’s Storm
18Z HRRR Model IDEA On How Precip Overspreads The Area Tonight. Credit: Weatherbell
Rain and snow will move into the region late tonight into tomorrow morning. Look for initial mix for most areas turning to rain first at the coast and then inland. Everyone is at risk for slick spots in the morning even the coast. Major issues aren’t expected but just use extra caution and remember, roads start to get slick around 35 degrees so even if your car thermometer says 34, that doesn’t mean that roads can’t slick up.
6Z GFS Model IDEA Of Where The Mix Line Could Be Tomorrow Afternoon. Image Credit: Accuweather
The rain/snow line will creep northward tomorrow and cold air will become entrenched just east of the mountains. As a result, this becomes a 3 part storm. Coastal/Southern rain, foothills/inland mix, and mountain/northern snow. Look below for a complete impact map. My biggest concern here is the weak winds aloft. I think the models are too quick to warm the mid levels of the atmosphere given a lack of strong winds to blast warm air in. If there are surprises with this storm one of them very well could be areas near/just south of Route 2 stay snowier for longer.
Another thing to be worried about here is Cold Air Damming and associated icing threats right up near the mountains. Winds will be southeasterly and will thus warm air at the surface will flood most areas. Temps will cool this evening setting up a pool of cold air. This will easily be pushed NW for the most part by SE winds. The cold pool of air will run into issues near the mountains though as it can’t really go anywhere. Cold dense air doesn’t like to climb mountains and I think that while eventually the SE winds will gather the energy to get the cold air out of there but I think it could take a while. Don’t be surprised if there is a little more freezing rain/sleet/snow than forecast.
A Look At What To Expect For Tomorrow’s Storm
Tuesday Storm
12Z CMC Model Showing The Major Players In Tuesday’s Event. Image Credit: Weatherbell
Behind tomorrow’s storm comes a large area of Canadian high pressure. This will ensure a steady supply of cold dry air to do battle with a steady flow of Gulf of Mexico moisture. This battle is what will produce our snow. With such massive, powerful, and cold high pressure close to our north, I have a hard time believing there will be any widespread intrusion of warm air for Northern New England. Rain could make an appearance at the immediate coast but it’s about 5,000 feet above our heads that warm air could present the most problems.
18Z NAM Showing Warm Air Moving In Aloft Allowing For Snow To Mix With Sleet In SW Areas. Areas In Green Are At The Greatest Risk For Sleet According To This Model Depiction. Image Credit: Accuweather
Here is the 18Z NAM temps 5,000 feet up Tuesday Evening. By this time most of the heavy snow will be out of the way but This map shows how warm air will be rapidly approaching the region as precip is rapidly leaving. It is too early to tell exactly who will change to sleet and for how long but just be aware of the potential especially for SW areas. If totals come in a little lower than expected, this might be why.
18Z GFS Showing The Players In The Forecast Tuesday Evening. Image Credit: Weatherbell
This event looks like a heavy burst of snow followed by a lighter, drizzlier precip. The exact timing is still to be determined but sometime during the day looks like the most likely time for a 6 hour or so burst of heavy snow before the mid levels dry out enough to shut off the steady precip. After the first burst of snow, look for lighter snow/sleet/freezing drizzle. This remaining light precip should taper off Tuesday night before fully clearing out Wednesday morning.
A coastal low will also develop and move east Tuesday evening bringing with it the tropical moisture connection. Its development will also help keep cold air locked in inland and will intensify a coastal front that is likely to develop along the immediate coast. The GFS also shows the light and showery nature of precip Tuesday Evening.
18Z GFS Showing The Development Of A Sharp Coastal Front As Low Pressure Develops Off The Coast. Image Credit: Weatherbell.
In terms of amounts, too early to tell is the name of the game for now. The most I could see out of this event is 6-10″ probably across the foothills into the western mountains. The coastal low will likely keep the moisture SE enough so that Jackman north won’t see as much liquid. The coast is at the mercy of the coastal front and warmer temps while SW areas could see sleet mixing. I’ll have more details tomorrow evening on amounts but a general 4-8″ seems likely with some 10″ amounts definitely possible.
We get a quick break Wednesday but never really clear out fully before our next storm arrives Thursday. That one looks like mainly rain with a mix up north as of now.
4:15PM Radar Shows Rain Slowly Expanding NW. Image Credit: Accuweather, Annotations By Me
Rain is already spreading across the area this afternoon as a plume of moisture moves north. The immediate coastline and the inland portion of the midcoast is currently seeing light to moderate rain and this will continue through the evening with rain slowly expanding NW. Light to moderate rain should continue throughout most of the early part of the night mainly east of the Turnpike.
12Z GFS Giving Us An Overview Of The Storm, Map Credit: Weatherbell, Annotations By Me.
The main feature of this storm will be a sharp gradient on the back side of the system with 5 or 10 miles making up the difference between a few sprinkles and a half inch of rain ending as an inch of snow. As a result, the forecast is especially touchy for areas west of the Midcoast where 1-4″ is likely depending on elevation. Once you get to the I-295/I-95 corridor, a very sharp dropoff in snow totals is likely with some areas seeing up to 2″ and others but a few midnight flakes.
20Z HRRR Model IDEA On How The Storm Winds Down Tomorrow Morning. Map Credit: Weatherbell, Annotations By Me
All precip, rain or snow, comes to an end early tomorrow morning with everyone west of I-95 dry by sunup and everyone else soon thereafter. The rest of tomorrow looks cool but nice with clearing skies and NW winds bringing in cooler and drier air.
18Z NAM Showing The Negatively Tilted Trough And The Winds Out Ahead Of It Directing The Storm Westward Up The Coast. Map Credit: Weatherbell, Annotations By Me
Every storm has a surprise and by virtue of surprises, they largely remain unknown but if there was one place I had to guess there would be a surprise, it’s where there’s been one already. There were indications that the trough at the 500mb level would be negatively tilted with this storm for days. Finally, the surface forecasts caught up to that and in the past 24 hours the forecast has gone from ‘chance of a flurry midcoast’ to ‘many people get their first accumulating snow’. This trend has smoothed out with the afternoon guidance today but don’t be surprised if this thing comes a tad farther west and instead of a dusting, you end up with 2″ of snow. After all, it would really only take 25 miles to make that big of a difference for some.
12Z GFS Showing NW Winds Bringing In Colder (And Drier) Air Which Could Shut Off Precip Early
The other, equally possible surprise is that the same cold NW winds bringing in the cold air to change things over to snow also come with enough dry air to shut off the precip early, especially because NW winds downslope off the mountains which dries the air even more. For a full explanation of downsloping in relation to temperature, check out my neat weather tidbit from a few weeks ago. While that post talks specifically about temperature, the same principle applies to moisture in that when air rises, moisture condenses and forms clouds/precip etc. just like it cools and when it sinks, the opposite happens. The post also includes a general overview on downsloping which applies to this forecast.
While the last two paragraphs could reasonably be perceived as me covering myself in case the forecast goes wrong, my hope is that in case it does, you can at least know why. As I’ve said several times, part of my goal here is to educate you about why weather happens as well as to tell you what’s likely to happen.
Speaking of what’s likely to happen, here’s a look at how much snow to expect when all is said and done. All in all, not a big deal but it still will be nice to see the flakes flying in November.
I’ll have another update on tomorrow’s weather in the morning.
I tweeted this afternoon about a neat phenomenon I observed known to the weather community as virga. Very cold air aloft and some slight daytime heating at the surface combined to create some instability clouds/showers today across the area. Many areas saw their first flakes today but here in Yarmouth, extremely dry air at the surface prevented any flakes from making it to the ground though plenty were seen falling high above.
Virga occurs when precipitation falls out of a cloud into a very dry atmosphere below the cloud. The precip then evaporates leading to a dry surface while a healthy shower occurs above. This phenomenon creates a neat visual effect similar to a paintbrush running out of paint mid stroke as the precip gradually fades away.
Here are some more pictures of the Virga here in Yarmouth.
Another chilly night is on the way so keep fragile plants indoors through tomorrow.
Quick update this evening to bring you up to date on the latest info regarding our next storm system arriving tonight and hanging out through tomorrow afternoon. For the most part it will be a fast-mover with precip ending in the early afternoon but while it’s here, the mountains could pick up some decent snowfall for this time of year.
Click around on the map to view precip types and approximate changeover times for your local area.
Rain moves into the region in the wee hours of the morning tomorrow and will start as all rain but will quickly change to snow in the higher elevations before dawn. Snow levels will drop as the low intensifies in the Gulf Of Maine and pulls in cold air on the NW side. Expect everyone to see flakes in NH and ME by early afternoon with western MA likely seeing a few flurries as well. It will be a race against time as the cold air rushes SE to try to get to the coast before the precip departs and just who wins is still a bit up in the air.
In every storm there is bust potential and while forecast confidence is pretty high, the exact extent of the rain/snow line as the precip leaves is still an unknown. As of now, it looks like the Maine coast with the exception of a few of the peninsulas will see at least a few flakes with most of coastal MA and all of RI missing out on the white but don’t be surprised if the snow comes in a little earlier than expected and totals are a little higher. Models have tended to place lows to the NW of their actual positions so if this low ends up a little farther SE and a little colder, I wouldn’t be too surprised. With this in mind, while coastal areas don’t look to see any accumulations, a quick coating is possible should a colder solution occur.
A rumble of thunder is also likely across MA RI and CT and some small hail is possible in some of the stronger cells.
Winds will kick up tomorrow as the storm moves out and gusts over 35 mph are widespread so watch for some isolated power outages especially in areas where snow has accumulated on branches and power lines.
I’ll have another update in the morning as the rain/snow line sets up.
Forecasterjack 