swctweather

And here we are again, just a few days after a previous snow storm, that came only days behind another one.  Each one slightly different, but this one is again taking a slightly similar path, but with secondary development of low pressure likely to become more defined, meaning that a warm tongue would not be as much of an issue.  It most certainly still can, but it’s not as likely to play as big a role with this storm like it did in the last one.

But before that I want to get into the details of the storm or anything like that, I want to give a summary of what I know and what is unknown, and just go over what’s going to be covered in this blog post tonight.

What we know is that this disturbance is coming.  The first piece of associated energy is coming onshore in the Pacific Northwest, and the next piece will move onshore in the next day or so.  This will increase forecasting accuracy, and once we have that better data sampling I will be able to offer up many more details with this storm.  Right now, there are generally two scenarios, one where the confluence over us and blocking in the atmosphere pushes the low pressure far enough south that we only get snow showers and flurries, similar to what we will get tomorrow, and there is not much of a significant storm.  The other one, which I find slightly more likely at this time, is that the storm strengthens and comes further north, far enough to impact the area with the heavier precipitation but not far enough to pull in a lot of warm air.  This could result in moderate or heavy periods of snow (maybe mixed with rain at the immediate coast or just offshore), with moderate to heavy accumulations on Monday.  It’s too early to talk amounts specifically, but I will be discussing what individual models show below for solutions.  So that’s the summary on the storm, and now I’m going to get a little more technical with regards to why I think a storm even this late in March could bring snow to SW CT.

First, I have been mentioning the AO a whole lot recently.  That’s because it is at record low levels, meaning that a direct injection of cold air straight from Canada is happening into the Northeast, hence the ridiculously cold temperatures the last few weeks.  It is approaching a value of -6, something it has not hit since 1985, to put that in perspective.  The NAO is also quite negative, as its current value is -1 but it is expected to drop down to -2 in a few days, again fairly low for March.  The couplet being a combined -6 or -7 is likely some type of record, and what this means is that blocking is ripe for storms to move up the east coast, and that plenty of cold air is in place for this storm.  So while climatology would completely argue against this storm, climatology also should not be weighted very heavily when we are talking about things that have not happened in decades, as climatology is not designed to help forecast for potentially extreme weather patterns.  What is being weighted heavily is the weather models that have been performing the best.  In order, that makes the CMC/upgraded GGEM, ECMWF, UKMET, JMA, GFS, NAVGEM.  Since its upgrade, the GGEM/RGEM has been extremely spot on with weather for SW CT, having correctly called the miss and then wrap around moisture with the storm system two Fridays ago, and then also calling for a longer period of moderate/heavy snow with this last storm.  The GGEM is also one of the most aggressive models with the upcoming snow storm, giving the coast around 6 inches of slush and further inland dumping over an inch of foot with a low pressure system that moves just east of New York City while going through rapid cyclogenesis.  Is this hypothetically possible?  yes.  Do I believe it will be the final solution?  Nope.  The GGEM has always had a bias of over-amplifying storms, and though it has done well recently, I think this could be one it is amplifying a little too much.  This means a weaker storm slightly further south would be more likely, so less snow further inland, but potentially more at the coast as there would be less warm air pulled up.  Most importantly, though, the GGEM shows a lot of moisture with this system, which is what to me screams the most potential.  The GGEM has support from its ensemble mean, too.

Next comes the ECMWF, which is further south than the GGEM and less amplified, but the 12z ECMWF did shift north and gives the region some light snow, and its ensembles are significantly further north than the operational, a sign that a shift north in the operational model is happening tonight.  Historically the most accurate model, should it begin to show a fairly significant storm a lot of people would begin to catch on and focusing in on this storm.  Until then, I don’t really expect that much hype around it.  The ECMWF ensembles are historically the most accurate, though, so it is very interesting that they are north and cold, and I will be looking closely tomorrow morning at what the overnight ensembles bring.  Then, we have the UKMET, which is further south still than the ECMWF, though has not performed very well as of late.  The JMA is similar to the GGEM except slightly less amplified, and amazingly I think the JMA could be the model that stands the best chance of verifying, as it keeps all of SW CT snow with moderate accumulations, but it does not go crazy with a bombing out low pressure.  The GFS, finally, remains fairly weak with the low, bringing only light precipitation to the area as the transfer happens too far out to sea for much more than light snow.  However, the GEFS ensembles support the operational GFS trending wetter, as they showed much more QPF than the operational, a signal that the GFS will likely be bouncing around a lot and is likely to trend stronger and wetter with this storm.  Those are really the only models at this point I’m using for the storm.

That’s really where we stand right now with the storm right now.  I will wait and go into more detail and get more technical tomorrow, but I do want to focus on the 500mb setup and the potential for the storm to stay stronger and trend north.  The potential here screams snow for SW CT, even in late March, and though this may not be a major event, chances are increasing of at least nuisance level snow across the region, if not more.  As always, make sure to keep it here for the latest on the storm.

The final update is out, and after running the latest data I have decided not to forecast a delay at the coast, however multiple coastal districts will likely end up delaying.  The above forecast means that I do not expect more than half of districts along the coast delay, though in a more general term it just means I think some will delay and others will not along the coast.  Further inland, I am more confident in delays across the board.  What is going into this decision?  Well, mainly new surface temperature data, as I have seen evidence that winds shifted more to a due east direction from the ENE/NE direction that they were in earlier, and this means that winds will be coming off of the Long Island Sound for the rest of the night, decreasing the amount of cold air that will be contained along the coastal plain and thus reducing the amount of freezing rain that is expected overall.  This shift will have minimals effects in inland communities where there is more elevation, as temperatures will be colder at the surface and roads more dangerous in the snow.  That’s why I am sticking with my chance of a delay there, as there remains a decent chance of icing overnight tonight.  As for snow days, I would be very surprised to see closures south of Interstate 84, though I guess it is possible if dangerous conditions persist through the morning. After the number of days already lost this year, most school districts should be scrambling to stay open, and with a marginal snow storm such as this where conditions will be much more favorable by morning, I would be very surprised if more than maybe one or two isolated districts close.  I often do err on the side of being more cautious, but this is a scenario when it likely won’t be necessary, and even inland I expect a delayed opening to be the best call for school.

As for current weather, snow is still dominating, with current amounts ranging from 2-5 inches across SW CT.  That’s the overall forecast as well, and I expect the region to turn to sleet in the next 30-45 minutes and for accumulations to really wind down.  So while a few regions will end up hitting 6 inches, the general range of accumulations in my snowfall forecast ended up working out quite well inland, with the coastal plain being underdone because of a stronger expected role from the maritime air.  Regardless, that transition to sleet will be happening soon, and that will be followed by a transition to a rain/freezing rain, with freezing rain dominating inland and rain dominating more at the coast by 1 or 2 AM still.  By 3 or 4 AM, I continue to believe that the entire region will turn over to plain rain, with isolated areas in valleys maybe staying frozen until 5 AM or so. That’s why I really don’t see many snow days, but rather see delays across a lot of SW CT.

Those are my overall thoughts for the night.  Stay safe, as the heavy snow does look to last a little bit longer, and even when there is sleet and especially freezing rain roads can be extremely dangerous.  Come sunup tomorrow, it’s unlikely we will actually see the sun for awhile, as there will be a second batch of precipitation trying to move through between 10 AM and 1 PM that will keep it cloudy as well, but temperatures should warm up enough to melt most ice and snow and road conditions should be much safer.  Then attention turns to a storm next Sunday into Monday that could lead to even more fun.  Check back tomorrow morning for the latest on the storm.

A delay is now forecasted for all inland school districts, with a chance of a snow day still remaining but not being very likely.  The chance of a delay at the coast has also risen fairly dramatically throughout the day, and there is a chance that in the final update around 11 PM one may be forecasted all the way down to the coast as well depending on precipitation type and surface temperatures.  As I mentioned before, the latest RAP remains very cold, and this is something that needs to watch very closely, as freezing rain still could be an issue into the morning, and that’s why the chances are higher for everything.  Along with that, at this point the storm has dramatically over-preformed in terms of snowfall, as some regions are already reporting upwards of 2-3 inches of snow and it is just past 9 PM.  We still have at least another hour and a half to two hours of snow before sleet begins to mix in, meaning up to 5 inches of snow remains possible all the way down to the coast.  This extra snow will take more time to remove and is making for some very dangerous road conditions tonight.

I am going to keep an eye on the latest RAP at the surface, as well as other data regarding surface temperatures as well.  Precipitation timing is important too, and with precipitation looking to last through 7 or 8 AM and potentially being frozen at the surface inland through that point, it means delays continue to look more likely, and the RAP does support the idea that roads will be dangerous tomorrow morning.  The ice is not something to really mess around with, and I think districts, especially with elevation, will delay to play it safe, but also do everything they can to open to not lose another day of school in a year where many districts have lost more days than any year before.  I think this is the most realistic decision, and this could be extended all the way down to the coast in the next forecast update, so check back for that.

Other than that, the forecast remains on track.  Sleet will begin to mix in with the snow over the next few hours, and then by midnight or 1 AM it should be all rain.  We only have a few more hours of snow accumulations, but it is coming down heavy enough that that could mean another few inches, as snowfall rates are ending up being even heavier than most models showed in this time frame.  Surface temperatures dropped fairly quickly from the heavy snow as well, and I am interested to see if they stay there or try and slowly rise throughout the night.  The immediate coast is right at freezing and everywhere else is below freezing, meaning that the stage is set for some ice accumulations even down to coastal areas, and thus delays remain very possible.  Check back at 11 PM for the final call though, as there is a chance that delays will be forecasted down to the coast depending on the latest short range guidance.  Stay tuned.

Things are beginning to ramp up.  We have heavy snow across the region falling at around an inch per hour, and by 8:30 or 9 PM that first inch of snow will have fallen across SW CT.  I don’t expect to see snowfall rates as heavy throughout most of the night, but in some bands they will be heavy.  However, what most people are curious about is how this impacts schools and businesses tomorrow, which I am going to try and address here.  The earlier snowfall actually didn’t do much to change the snow day/delay forecasts for both inland communities and the coast, but rather the latest RAP with very cold surface temperatures did a lot for that.  It showed a fairly stead ENE wind and yet surface temperatures down to I-95 staying below freezing into the early morning hours before slowly warming up.  This is something no model has shown for days, and even though the RAP was awful with the precipitation timing, it does have a warm bias, making me believe it may be on to something being  so cold at the surface.

The warm tongue is currently on track at 800mb, and is gradually beginning to become more defined across the area.  As it becomes more and more defined, it may become harder for snow to stick on pavement, even with surface temperatures below freezing.  Once the snow turns over to sleet, though, it will be very easy for the sleet to stick on roads and make them even icier.  The timing looks the same, with the first sleet mixing in to hold down accumulations around 11 PM, and a full turnover to sleet occurring between 12 PM and 1 AM, with a mix of freezing rain and rain likely after that.  The freezing rain will generally be inland, with the rain at the coast.  It is the length of that freezing rain that will determine whether schools open on time or not tomorrow across SW CT, and the amount of snow that falls now won’t make much of a difference because it will be quite easy to clean up come morning.  Ice, however, is a much different story, and though the ice threat seemed to decrease throughout the past 36 hours, the RAP just brought it back.  This has led me to increase totals, now giving a 65% of some impact for inland SW CT communities, and a 35% chance of a delay at the coast.  I don’t see any scenarios by which inland communities are not completely above freezing by 7 or 8 AM, so as of right now no chance of a snow day is included at the coast, but should a few scattered communities remain below freezing through the day or get hit especially hard with more than a quarter of an inch of ice, then closures are possible.

One final thing I am monitoring is a quicker movement of the precipitation as well, and this is something most models seem to be catching up on.  By 8 AM, all precipitation now looks to move out of the region, another reason why school closures are unlikely, but delays possible.  Precipitation will continue into the early morning hours per the latest RAP, but it will then move on out before getting later in the morning.  This should allow for a fairly easy cleanup from the storm during the day, though then by 10 AM a second batch of precipitation moves through associated with the original cold front trailing the forming secondary low pressure system.  By this point, all of SW CT should be above freezing, so that second batch of precipitation should be all rain, and most threats will be gone thus by 9 or 10 AM.  Overall, as of right now I am seeing increasing evidence that a delay is going to be the correct call for most of SW CT, with the coast now looking to be a harder call because of surface temperatures, even though originally it looked like inland would be a harder call.  Make sure to keep it here for the latest on the storm, and the next update will come between 9 and 9:30 PM, with constant updates on Twitter as well.

Let the fun begin.  First snow is now being reported in Greenwich, and this snow will very slowly overspread SW CT from west to east over the next few hours.  Once it begins, it won’t take long to stick as surface temperatures are generally at or just below freezing, though it is light enough to start that it will take a decent amount of time for that first inch to fall.  Still, that snow is beginning now and will be covering the entire region within the next few hours.  It will start as all snow down to the coast, and will remain that way through around 11 PM tonight.  Between 11 PM and 1 AM tonight we see a warm nose between 775mb and 825mb begin to work in aloft, and even though temperatures around 900mb will be very cold, snow will be melting further up in the atmosphere.  It will then refreeze, producing sleet in that time frame, so even though frozen precipitation down to the coast is possible even through 1 AM, most accumulations will end by around 11 PM when the sleet really mixes in.  Then, between 1 AM and 3 AM there could be a period where surface temperatures in coastal areas (but away from the IMMEDIATE coast) are below freezing, and that is where up to a tenth of an inch of ice accretion is possible, but likely in pockets, and I don’t expect much more than a coating of ice or so along the coast.  It could briefly cause problems, but as temperatures rise above freezing that ice should melt and by 3 AM I can guarantee that the coast will be plain rain.  This is why the delay percentage chance at the coast is so low, as there will only be residual cleanup from the snow/ice overnight that will be left by morning, and assuming that goes well there will not be more dangerous conditions coming for the coast during the day tomorrow.  There really is not much new to cover with that forecast.

Further inland it begins to get a little bit more complex.  They will remain generally snow as well through 11 PM, and I expect most inland areas to have seen around 3 inches through 11 PM.  Sleet may begin to mix in, but it will take slightly longer, with most areas being sleet by around 1 AM.  By that point snow accumulations will cease, and the region will peak with a general 4 or 5 inches of snow.  Then, freezing rain will dominate, possibly mixed with sleet, through 3 AM, similar to the coast.  It is after that where things get interesting.  Winds will generally be ENE, helping warm things up slightly just south of I-84, but not by much.  Through 6 or 7 AM the region will generally be between 32-34 degrees, and it is that small range that is ever so hard to forecast.  This means that icy patches could last into the morning rush inland, and that worries me regarding schools.  The current forecast for inland SW CT is that there is a 45% of some impact to schools tomorrow, 40% being a delay and only a 5% chance of snow days south of I-84 because precipitation is guaranteed to go over to all rain at some point between 5 and 7 AM if it does not earlier.  Patches could remain icy, and whenever dealing with an extended period (more than an hour or two) of freezing rain, it is often better to play it safe rather than sorry.  Freezing rain is the most dangerous form of precipitation because it creates black ice almost instantly on roads, which is difficult to see.  It will likely come down to a town-by-town and valley-by-valley basis which districts end up delaying tomorrow further inland, as that one to two degrees in the morning will be the difference between wet roads and very slipper and dangerous roads.  By 8 or 9 AM conditions across all of SW CT should be much safer for travel.

That’s really all I have for right now, but I do plan on releasing another update around 8 PM tonight, and of course more will follow that as well.  Make sure to keep it here for the latest.