Storm Trends Slightly East

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The updated snowfall forecast now calls for 1-3 inches of snow region-wide, which was the original forecast. As has been the case with most storms recently, expect the highest accumulations (around 3 inches) in eastern New Haven County while the least accumulations (around 1 inch) should be in Westchester County.  Accumulations of 3-5 inches are possible in heaviest banding in far eastern New Haven County, but most models have continued to trend east and show that the majority of that banding should miss the region.  This is why I do not like to change forecasts without significant confidence, as the models clearly headfaked us last night showing the potential for far more significant accumulations.

Confidence is increasing in this forecast as recent short-range models (HRRR and RAP) are agreeing well.  A couple models show the risk for more snowfall across eastern parts of New Haven County, while other models show the potential for a bust across inland Fairfield County and Westchester County with less than an inch of snow falling.  Both of these are real possibilities that I will continue to follow closely as the storm develops, but I am feeling better in broadly 1-3 inches of snow across the region.

Snow is now expected to start between 8 and 11 PM tonight as once again the storm has slowed down.  Temperatures at the coast may take until 11 PM or midnight to drop below freezing, so some snow could even struggle to stick at first even though the sun will have been down for hours.  By midnight temperatures should be dropping below freezing and light snow will be moving in.  A period of moderate snow is likely bewteen 1 AM and 6 AM, primarily across New Haven County.  Snow finally moves out sometime between 5 and 8 AM from west to east, and by 9 or 10 AM temperatures across Fairfield and Westchester Counties will be above freezing with the sun trying to come out.

Confidence Dropping For Sunday Night/Monday

The below forecast was recently sent out in more complete form to Premium subscribers, who also received our first school delay/closure forecast on Monday.  To begin receiving daily email updates before storms on potential impacts, forecast accumulations, expected timing, and school delay/closure forecasts, subscribe here.  Otherwise, below we detail the latest forecast update:

Generally, I do not like shifting my forecasts until the confidence is really there that the going one is going to be wrong.  However, here I do want to slightly jump ahead of the National Weather Service and overnight weather model guidance in upping forecast snowfall across Fairfield and New Haven Counties.  I am forecasting 1-3 inches of snow across Westchester County still, but now expect 2-5 inches across coastal Fairfield County and all of New Haven County.  Far inland Fairfield County is still expected to see just 1-3 inches as well as I am not yet convinced that moisture comes in far enough inland for sustained moderate snow.  Similarly, I expect eastern New Haven Counties to see the most widespread 4-5 inch regions.  Someone over there could see 6+ inches of snow if the storm jogs even a little bit to the west, which is certainly a possibility given the large trends we have been seeing on guidance recently.

One of the big things to note is that as emphasized yesterday, none of these impacts should be felt tomorrow.  It will be partly cloudy through most of the day with increasing clouds in the afternoon and evening.  Light snow will overspread the region between 4 and 8 PM, though temperatures will still be in the mid 30s.  This means that at first snow will struggle to stick on most surfaces.  It is not until at least 8 or 9 PM that I see snow sticking along coastal areas, and at that point already up to a tenth of an inch of liquid may have fallen (at least if the RGEM is correct).  From there we should see steady snow overnight, but guidance has shifted to show the core of steadiest snow generally being midnight to 4 AM across Westchester County and 1-6 AM across Fairfield and New Haven Counties.  This has significantly increased the chances that impacts linger into the morning commute, as snow finally will end between 6 and 10 AM from west to east.  Travel should rapidly improve by 9 or 10 AM on Monday as temperatures are relatively quick to rise above freezing and the strong March sun angle should quickly begin to melt the snow, but until then slippery conditions are expected, especially before 7 or 8 AM when temperatures across the entire region will be below freezing.

Light Snow Sunday Into Monday

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I’ll start with the scenario that has the least impacts, which would be the most recent 18z NAM.  This far out from a storm it can generally change rather dramatically, so I would not put too much stock in this output just yet.  However, it is a realistic scenario that a number of models are beginning to trend towards.  The model shows some flurries as early as 9 or 10 AM on Sunday, as seen here.  Surface temperatures will generally be near freezing.  However, at no point does it ever get heavier than that.  In the mid-afternoon light snow moves nearby again, as seen here.  But total snow accumulations here through mid-day Monday are less than a half inch across the entire region.  Essentially, the entire storm would miss with virtually no impacts.

Oftentimes, the high definition version of the NAM model will be more amplified and present scenarios that are more realistic.  All winter it has also been performing better.  With this storm, however, it is relatively similar.  Over the next 60 hours, it shows less than an inch of snow across the region, as seen here.  Some parts of SWCT/NY could see no accumulating precipitation at all (especially inland) while Long Island and points further south could see slightly more, seen here.  But this agreement is worth noting, especially as the storm has continued to jog off to the south on most models this afternoon.

Meanwhile, the closest model suite to the NAM, the SREFs, disagree.  As seen here, they show widespread amounts of 3-4 inches of snow across the region through Monday.  A couple members have the storm entirely miss, but most show at least a decent hit.  Through 8 PM on Sunday they have around a 65% chance of an inch or more of snow and a 23-35% chance of 4+ inches of snow, as seen here.  These are relatively impressive probabilities, though it is worth noting that by 2 AM or so they are declining as the storm is generally shown moving out slightly earlier than before.  Here, the consensus appears to be that 2-4 or 3-6 inches of snow region wide should be considered most likely.

Next, we have the GFS guidance which has continued to gradually trend southeast in line with the NAM.  The model has light snow overspread the region by 9 or 10 AM on Sunday, as seen here, with temperatures generally right around freezing.  During the day, however, the strong March sun angle might melt a majority of this.  A brief burst of moderate snow is seen from 2-5 PM, as seen here, but again temperatures are right by freezing, and much of this snow is likely to compact.  From there the storm moves out of the region by 2-3 AM at the latest, with only light snow showers after 5 PM.  As seen in the bottom middle here, this scenario generally brings .1-.3 inches of liquid, some of which would likely melt on impact as almost all precipitation would fall during the day.  This would thus amount to around .5-2.5 inches of snow on Sunday that would be relatively low impact, struggling to stick to roads and never getting all that heavy.  The worst impacts would be across coastal New Haven County, where the slightly higher accumulations would be possible, but again no real lingering impacts into Monday would be expected besides potentially delays from icy roads should any snowmelt freeze over.

Next we have the Canadian model guidance, which is notorious for overdoing snow storms and moisture.  Here on the bottom right we see that total amounts of liquid from .5-.8 are shown across the region, amounting generally to 4-7 inches of snow with much falling overnight Sunday night as the storm takes longer to get its act together but is much stronger.  However, the higher resolution RGEM version of the Canadian model is less convinced on this widespread snow, though admittedly it is not entirely in range.  Generally, the model shows only snow showers that don’t stick on Sunday, with moderate snow Sunday evening and heavy snow from 10 PM Sunday through 4 AM Monday.  Snow then moves out between 5 and 9 AM on Monday with 4-7 inches region wide and schools closing with travel significantly impacted.  This scenario is the worst case scenario overall, but at this time is not seen as all that likely.

Finally, the ECMWF appears to be split between the GFS and the CMC.  It does show the storm strengthen far more rapidly than the GFS does, but does not have it quite as strong or west as the CMC.  The result is a strip of 3-5 inches of snow across New Haven and parts of Fairfield County, with instead closer to 2-3 inches of snow inland.  The timing is a little quicker than the CMC as well, but regardless the snow clears out by Monday sunup, which models are very consistent in.

As I mentioned yesterday, I do not love this storm setup.  The upper level pattern just does not look primed for a large snow storm, and alongside that unless things look perfect in March it is hard for it to really come together for significant snow.  With much of the accumulation poised for Sunday afternoon, I feel much of it could melt on impact, limiting total accumulations and impacts from the storm and not making it much of a deal at all.  I said yesterday that most of the crazy snowfall amounts of 8-10+ inches were likely overdone, and today we saw just that as a bunch of models backed off the storm.  I even think there is a chance that the NAM could be right, and we see nothing more than flurries and snow showers through the day Sunday into Sunday night with no real accumulations, but I am not yet ready to forecast just that.

Instead, I think 1-3 inches of snow starting Sunday afternoon and winding down overnight appears most reasonable.  It seems quite likely that we do see light snow starting between 9 and 11 AM on Sunday across much of the region but it is unlikely to stick or cause much trouble.  Any steadier snow likely waits until Sunday evening when it should begin to stick, but whether that is just for a few hours or for a more extended period of time is unclear.  I do not see the CMC scenario with widespread amounts of 4+ inches verifying, though the fact that the SREFs do have such a high chance of 4+ inches being widespread has be concerned that there does remain some upside risk to the forecast despite the southeastern trend today.  Similarly, my forecast is below the National Weather Service, which appears to be forecasting anywhere from 2-6 inches across the region, but given that surface temperatures at first are only marginal, some models show the storm entirely missing, and it is going to be late March, I just do not see much coming together for widespread amounts of more than 2-3 inches.

Additional updates to this forecast will come as necessary.  Premium subscribers will receive updates as soon as they are made, and another Free update will be released Saturday evening if necessary.

Snow To Rain Tomorrow Night

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TIMING: Most models agree that light rain/snow will be starting across the area from south to north between 10 AM and 1 PM.  Please note that especially at the coast, it is likely to start as light rain with surface temperatures in the upper 30s and temperatures aloft close to freezing as well.  As the heavier precipitation moves in, sometime between 1 and 4 PM the entire region looks likely to go over to moderate snow and begin to stick as temperatures drop into the mid and low 30s.  Inland snow will stick sooner, especially as it is slightly colder aloft and there is more cold air to pull down.  Snow should mix with sleet between 4 and 7 PM at the coast and between 5 and 8 PM inland.  Snow will also be heaviest across the entire region from 4-8 PM.  Rain comes in at the coast around 7 PM, while freezing rain is mixing in further inland by 8 PM creating a true mess with the evening commute.  Light rain continues at the coast through the night, while around and north of I-84 freezing rain could continue into early Wednesday morning before temperatures finally rise significantly above freezing by 7 or 8 AM Wednesday.  Rain then continues through the day on Wednesday.

ACCUMULATIONS: Coastal areas are expected to see a coating to 2 inches of snow.  Though up to .3-.4 inches of liquid will fall as wintry precipitation, some may be sleet and the initial snowfall may struggle to stick.  2 inches of heavy, wet, slushy snow will still be possible through around 5 or 6 PM in some coastal areas, which will be enough to cause trouble.  Inland, I am expecting more like 1-3 inches of snow, as almost all guidance shows enough cold air and precipitation for at least an inch of snow, and some guidance shows the potential for more.  Isolated regions of 4 inches of snow are possible where temperatures both at the surface and aloft are the coldest, but generally it looks like around 3 inches should be the cap.  A glaze of ice is possible in patchy regions at the coast, and up to a tenth of an inch of ice around or slightly north of I-84 is possible with surface temperatures right around freezing.  North of Fairfield and New Haven Counties we could actually see more significant icing where the cold air traps.

An additional update will come later this evening should the forecast significantly shift.

 

Light Snow/Freezing Rain Possible This Evening

The below forecast is part of an update sent out to Premium clients regarding chances of school and travel impacts from the upcoming light winter weather event.  To see the latest school forecast, subscribe here.  Otherwise, the update is contained below:

Steady snow is still expected to begin around 4 or 5 PM this afternoon, though scattered light snow showers are possible before then.  Overall, expect 1-2 inches of snow to fall across the region before we mix with freezing rain, sleet, and rain.  Temperatures rise through the day to be in the low 30s by evening.  Steadiest snow can be expected between 4-8 PM, with travel beginning to deteriorate by around 6 PM.  Conditions should improve rapidly once temperatures rise above freezing overnight.

The entire region should turn from snow to freezing rain and then rain between 7 and 10 PM.  The first sleet should mix in along the immediate coast by 7 PM, and we could see about an hour of freezing rain sometime between 8 and 10 PM at the coast.  Further inland, freezing rain could last slightly longer, and north of I-84 we could see icy patches linger through midnight or slightly longer depending on just how strong the cold air damming is. Confidence is high that the coastal plain turns to plain rain by 10 PM, and travel conditions there improve rapidly.

Travel is likely most treacherous between 7 and 10 PM across the region.  Snow will be light, so that will not impact travel much.  Instead, the period of sleet/freezing rain is when I am most concerned about travel.  Once temperatures at the surface rise above freezing (around 9/10 PM at the coast and around 11 PM further inland) roads return to normalcy rather quickly.

Rain will continue through the day on Tuesday.  Around 1 inch of rain is expected, and it could be heavy at times.  There is a slight chance of thunder as well between 2 and 5 PM when the heaviest rain is expected to move through.  Luckily, there is minimal snowpack across the region, so flooding is not expected to be too serious of an issue.  Generally, only scattered showers are expected through the morning with foggy conditions.  Scattered showers will be possible into the overnight hours as well.  High temperatures Tuesday get into the low 50s with low temperatures overnight into the low 30s.