More Rain/Sleet Mixing In

This forecast was sent out to Premium subscribers just past 1 AM updating on the potential for more snow/sleet to mix in with the storm.  The update is now shared below:

Model guidance tonight has continued recent westward shifts with the storm system overnight into tomorrow.  Light snow will break out across the region in the next few hours if it has not already, and by 4 AM steady snow is expected.  Heavy snow is expected by 5 or 6 AM that will continue through the morning.

Most model guidance shows a high chance of mixing with sleet, freezing rain, or even rain sometime between 9 AM and 1 PM tomorrow.  This will be at the peak of the storm and limit overall snowfall accumulations.  Recent estimates have me looking more at the 8-16 inch range across coastal areas where we mix earlier and 10-18 inches further inland where snow holds on longer.  The storm between 2-5 PM likely ends as a burst of snow as well as the back end moves through.  However, from the late morning into the early aftenoon a mix of sleet/feezing rain/rain is quite likely to mix in with the snow, limiting overall snowfall accumulations.

The result is that I see current National Weather Service forecasts as a bit overdone for the region giving this recent mixing risk.  Additionally, some icy conditions could easily linger into Wednesday, but lower accumulations lessen the risk of significant impacts lingering into Wednesday.  The risk for serious travel impacts from wintry weather and wind tomorrow still remain, but a chance to other wintry weather may keep it from being as serious.

Another update will come tomorrow morning updating on the risk of lingering travel and school impacts into Wednesday.  The forecast is a bit lower confidence as models are divded as to whether we turn more to freezing rain or sleet.  Both will make travel terrible tomorrow afternoon into the evening, but the impacts from there are more uncertain.

Blizzard Expected Tonight Into Tomorrow

Below is the latest forecast for the upcoming blizzard:

Mostly sunny skies dominate for the rest of the day with high temperatures in the low 30s.  Overnight clouds rapidly increase, with a chance of snow arriving after midnight.  Snow begins light between 1 and 3 AM across the region, picking up in intensity by 4 or 5 AM by which point all travel will become dangerous and snowfall rates above an inch per hour can be expected.

Heaviest snow tomorrow falls between 7 AM and 12 PM with high tempeatures in the low 30s.  The heaviest snowfall rates could peak out at 3-4 inches per hour during this timeframe, at which points thundersnow would be a real possibility as well.  Between 9 AM and 12 PM sleet and freezing rain could mix in with snow across coastal regions as warmth moves in aloft.  This will compact snow a bit and keep snowfall ratios around 10:1, if even a bit less.  Snow quickly tapers off between 12 and 4 PM across the region, with lingering snow showers into the evening.

We could see a couple lingering snow showers Tuesday night on the backside of the storm as winds remain breezy.  Low temperatures drop into the upper teens with wind chills dropping into single digits, especially inland.

Wednesday looks to start mostly cloudy with maybe a few lingering snow showers, but most accumulating snow should have already ended.  High temperatures get into the low 30s as we clear out.

Model agreement on the storm is stronger on very significant snowfall accumulations across the region.  No longer does there appear to be that much of a risk of the storm sliding to our east, meaning we should see the heaviest precipitation at least partially across the region.  This means that there are two main things to track: banding and mixing.  Most models show 1.5-2.5 inches of QPF across the region, which on a 10:1 ratio with the sun angle in March that would lead to 15-25 inches.  However, there is going to be a risk of mixing across coastal areas, which could limit accumulations to around 12 inches.  That said, 12 inches across all guidance looks a virtual guarantee, with a maximum of 24-25 inches in the heaviest banding.  The new forecast now is for 12-20 inches of snow widespread across the region, with isolated amounts to 24 inches in the heaviest banding possible.  That banding is most likely to be further inland, as now it appears that accumulations may be a bit more limited by the coast where there will be some mixing with sleet/freezing rain at the peak of the storm.  The storm is fast moving enough that more than 2 feet looks unlikely, but even that would be enough to cause enormous problems.

As mentioned previously, the two things to focus on are mixing and banding.  If at the peak of the storm there is mixing along coastal regions, accumulations from 12-16 inches are more likely than from 16-20+ inches.  If there is no mixing at all we could even see more than 20-24 inches where the heaviest pecipitation occurs, but at least some sleet looks possible.  It will be important to track the mid-level atmospheric low pressure center that will move near the region and determine how far inland warmer air gets.  It is impossible to know the exact orientation until the storm really gets going, as short-range models tend to struggle with such features.  The same can be said with banding, which is hard to identify until inside of 12 hours.

Wind gusts in the storm look to get up to near 50 mph.  Luckily, surface temperatures in the upper 20s/lower 30s through much of the storm will keep the snow from being quite as sticky, so concerns about downed tree limbs are not quite as high, but some downed limbs are possible.  Isolated power outages by the coast are also possible Tuesday.  The strongest winds will be near the coast from Tuesday mid/late-morning through the evening as the storm rapidly intensifies.  Moderate coastal flooding is likely as well as water gets pushed up along the coast, as the storm looks likely to be very strong.  However, winds will be worse across the Mass coast than in SWCT/NY.  Winds peak in intensity between 9 and 11 AM when most power outages would occur.

The National Weather Service has upgraded the entire region to a Blizzard Warning, as expected.  They are similarly calling for 12-20 inches of snow now, with decent agreement overall.  It is hard to see significant changes to the forecast unless there is a warmer trend with more mixing that would limit accumulations.  Otherwise, at least a foot of snow looks like a guarantee with impacts lingering into Wednesday.


Heavy Snow Expected Tomorrow Morning

A major snow event will impact the region tomorrow.  Premium subscribers have been receiving email updates and forecasts regarding expected accumulation, timing, and impacts from the upcoming storm.  Below we summarize our latest Premium forecast in all those categories.  Additional forecast updates through the storm will be emailed out to Premium subscribers with parts posted freely here as well.  To read our more in-depth and frequent forecasts, subscribe here.  Otherwise, please enjoy the free forecast below:

Precipitation begins to break out late overnight into early tomorrow morning.  Isolated to scattered rain/snow/sleet showers will be possible between 1 and 5 AM overnight, but nothing all that steady is expected.  The main precipitation shield looks to move in from west to east between 4:30 and 7 AM based on the most recent guidance.  By this point all precipitation will be turning over to plain snow as the entire column rapidly cools and temperatures down to the coast fall below freezing.

The period of heaviest snow and most significant impacts looks to be 7 AM – 12 PM tomorrow.  In this timeframe, snowfall rates of up to 2-3 inches per hour are not outside the realm of possibility, with thundersnow also a possibility.  Up to 75-80% of accumulations are expected to come in this 5 hour window, indicating just how heavy snow will be in this timeframe.  All precipitation will be snow, and recent indications are that areas south of I-84 have the highest chances of getting into the heaviest banding in this timeframe as well.  However, steadier snow may be able to start just a bit earlier further inland thanks to better lifting with the higher terrain.  Models are mixed on how much of an advantage far inland areas may receive from this still.

Between 1 and 5 PM snowfall gradually winds down across the region from west to east.  Most significant accumulating snow will be out of the region by 1 or 2 PM, but wrap-around banding could allow for some lingering light snow showers through the afternoon as gusty winds continue as well.  Some blowing snow will be a possibility and could keep travel conditions poor through the afternoon as snow will end very light and fluffy with cold flooding in behind the storm.  Then overnight tomorrow night we will see temperatures drop into the single digits inland and low teens at the coast with wind chills down to around 0 degrees.  Snowcover helps to sustain the cold for one of the coldest nights of the winter.

The accumulation forecast is as follows: South of I-84 expect 8-15+ inches of snow rather widespread and around/north of I-84 expect 7-13+ inches of snow.  The “+” in each forecast highlights the potential for isolated amounts significantly higher in the strongest banding, as the dynamics with this storm are such that we are seeing a very intense amount of snow for a short amount of time, and widely varying accumulations are a real possibility.  Additionally, snow may be hard to measure due to its increasingly light nature and the increasing threat of drifting through the storm as winds pick up as well.  If anything, I may have to raise the forecast a bit inland, as some modeling guidance shows the potential for widespread amounts in the 10-12 inch range or higher there, but a couple models show the heaviest snow confined to the coast which seems quite possible given the expected track of the storm and best dynamics.  Snowfall ratios start around 10:1 but rise up to around 15:1 through the storm as cold air floods in behind the low pressure center.  Intense banding will allow for highest accumulations likely across southeastern areas, though it is exceedingly difficult to try and nail down exactly where the strongest banding will be.

Gusty winds are expected with the storm as well.  Strongest winds are expected at the coast, where gusts up to 40 mph are expected, while inland areas could see gusts up to 30 mph.  These gusty winds will create blizzard-like conditions at times in the late morning and early afternoon and severely reduce visibility while also allowing snow to drift.  At this point I am not too worried about power outages as the winds will not quite get to that level and the snow should be light and fluffy enough to avoid really sticking/accumulating to branches and power lines, but blowing snow into the evening tomorrow will be an issue.

Overall, travel tomorrow will be brought to a standstill as schools should close with major impacts from a strong snow storm.  The storm is quite intense but also quick-moving, preventing it from having impacts quite as severe or long-lasting.  At this time, the main questions revolve around exactly where we would expect banding to set up with the storm and what snowfall ratios will be like, as these will answer the questions of whether this is a moderate snow storm with accumulations in the 8-10 inch range or a major storm with accumulations in the 12-15 inch range.  The shortest-term model guidance should get in range this evening and help to answer these questions.

Light Snow Expected Tomorrow

The below update was part of a recent Premium forecast relating to a light snow event expected to hit the region tomorrow.  Minor travel and potentially school impacts are expected, as outlined in the forecast.  To see the potential school and travel impacts, subscribe here.  Otherwise, below is the forecast timing and accumulations for the light snow tomorrow:

Tomorrow will start partly cloudy with increasing clouds through the morning.  Very light snow showers break out across the region between 9 AM and 11 AM, likely remaining quite light into the early afternoon.  The largest change in short-range guidance has been to show that any snow through 1 or 2 PM will be quite light as over-running precipitation struggles to accumulate.  No more than half an inch of snow is expected through 1 PM now, with questions as to what exactly happens after.  Following that light snow, coastal areas could see a pause in snow between 1 and 3 PM as a dry slot moves across the region; light snow may still continue inland with slightly better orographic lift.   A moderate burst of snow between 2 and 6 PM is still a possibility though not a guarantee, as some modeling still shows almost all steadier snow further inland.  Then, lingering snow showers look to be a possibility through much of the evening, finally winding down between 10 PM and 2 AM.  We clear out from there into Wednesday morning.

Accumulation forecasts have become a bit more complicated as it appears the front end of the storm will bring a bit less snow than currently forecast.  It is hard to find evidence of widespread amounts of 2-3 inches like the National Weather Service is calling for, and even though there may be decent snowfall ratios this appears overdone.  Instead, I am calling for a coating-2 inches of snow regionwide now.  Most regions will likely see around an inch falling primarily in the afternoon and early afternoon.  Inland and far inland areas could still see isolated areas of up to 3 inches where the best lift is, but those look to be isolated much more so than widespread, as generally an inch or two of snow is expected.

Accumulation Forecasts Raised For Today’s Snow

In an email just sent out to Premium subscribers I highlighted the risk for more snow than was forecast across the area and have accordingly raised accumulation forecasts.  The latest forecast is available below:

Light to moderate snow is breaking out right on time across the region.  It will start light initially, though over the next hour or two we could get a couple of moderate bursts.  From there it will still begin to pick up in intensity between 12 PM with steady moderate to briefly heavy snow until 4 PM, with lingering snow showers through 8 PM.  Models overnight showed a slightly higher threat for bursts of heavy snow any time between 11:30 AM and 4 PM, with eastern and coastal regions the focus.  High ratios may allow snow that does not seem particularly heavy to add up rather quickly.  Snow should end by 9-10 PM across the region as the storm pulls out, though a couple models show a couple snow showers across New Haven through around 11 PM.

A snowfall gradient is still expected, though it may not be quite as sharp as previously expected.  Snow to liquid ratios up to 20:1 continue to look possible with the storm moving through, which is why I am becoming increasingly concerned about moderate accumulations into Fairfild County.  Later in the storm winds will pick up a bit so we could see some dendrite shattering more so by the coast (depending on exact snow growth regions) that may bring ratios down a bit, but at least 15:1 ratios seem reasonable throughout the entire storm.

The forecast has been tweaked with more location specificity.  5-8 inches of snow is expected in southeastern and coastal New Haven County, with 4-7 inches of snow expected across inland New Haven County and coastal and inland Fairfield County.  Far inland Fairfield County (north of I-84) can expect to see 3-6 inches of snow, as can costal Westhchester County, while inland Westchester County will see 2-5 inches of snow.  In this way the gradient is best reflecter, but overnight guidance shows less intense banding and moderate snow extending further to the west, increasing confidence that some of higher accumulations across New Haven County will be possible in Fairfield County as well.  Recent short-range guidance has shown the possibility of widespread amounts even further west of 6-7 inches of snow, so a slight tweak higher may be needed as the storm develops, primarily because of just how light and fluffy the snow is going to be as it adds up quickly.