Thursday, February 18, 2021 Winter Storm

 The active February continues as yet another winter storm approaches Connecticut. Like this past storm, this one has been rather challenging in the forecast department (though I must admit, I have not done much detail look into this due to other pressing weather issues around the country) as even now within 48-hours there continue to be inconsistencies within the forecast models regarding strength, overall track, and storm structure. All of these will play a crucial role into the evolution of the storm across Connecticut. 

Typically, I go into the science first then follow with my snowfall forecast, however, this go around I am going to start with my snowfall forecast and then explain the reasoning below it. Why am I doing this? No reason other than I feel its appropriate. So what is my snowfall forecast?

When looking at this, you're probably noticing...that is one helluva difference (gradient) between the northern part of the state and the southern part of the state. You also may be saying, "wait, since when does southern Connecticut do better in the snowfall department than the northern part of the state?". Well, this is why I've elected to do my snowfall forecast first. There is a reason why I believe we will see such a gradient across the state and why southern Connecticut will do better. 

First off, I have concerns about dry air which may eat away at the precipitation shield and these concerns increase as you move north across the state. Thursday morning starts with a fairly stout area of high pressure stretched from southeastern Canada through New England. This high pressure does slide to the north and east as the day progresses paving the path for the storm to continue its northward journey towards the state. I drew an arrow showing the counterclockwise flow around the high pressure (very important here):

Referring to the above image, at the surface, the winds are coming from a northerly direction. This is usually associated with drier air from Canada advecting into our area. Thursday morning, forecast dew points are only in the teens in Connecticut with 20's south of Connecticut and single digits and below-zero north of us. As long as the surface winds remain north, drier will will continue to drain into the state:

 But...before we call this dry air we need to reference this with surface temperatures. After all, if surface temperatures are going to be close to these dew point values, well the air isn't so dry anymore. Wednesday night, temperatures drop back into the teens after temperatures climb into the 20's to around 30 Wednesday afternoon. One thing to consider regarding temperatures Wednesday night, is increase in cloud cover. This could prevent temperatures from falling much back into the teens. Anyways, moving through Thursday morning temperatures should quickly rise into and through the 20's. Note: I am not a major fan of model output 2M temperatures. I often find them kind of low. So this does present a bit of a different (dew point depression) between dew point and temperature. Basically, the farther apart the two are, the drier the air is and the closer together the two are, the more moist the air is.

We can also visualize this by assessing a forecast sounding. Below, is a forecast sounding for Windsor Locks, CT Thursday morning. The green line indicates dewpoint temperature as you ascend through the troposphere (with the lower portion the surface) with the red line indicating temperature as you ascend through the troposphere. Notice how far apart the two lines are. That indicates dry air. Now, as you progress through the morning the column does moisten up a bit. This is due to the high pressure continuing to depart north and east and winds start to shift more easterly which slows down or shuts off the dry air drain from the north:

Anyways, without getting much more into this, I do believe dry air will be a bit of a concern across the northern part of the state and this results in less snow there. 

Towards the southern part of the state, there are decent signals for a band of pretty heavy snow (which may be on the wet side) which is enhanced from warm air advection as warmer air progresses northward. Note: Due to forecast storm track, the warmer air should not fully get into the state keeping the majority of the precipitation snow, however, there will likely be some sleet and freezing involved, especially during Thursday evening and overnight when precipitation intensity is more light. Forecast models indicate a strong push of warm air advection (just check out the scale at the bottom of the image...nearly maxed out!) racing north towards southern Connecticut as the afternoon progresses:

This will be associated with very intense frontogenesis with what will be a very heavy band of snow just north of it...and that would be right across southern Connecticut. The signals for getting this much farther into Connecticut are not very strong:

What to Expect:

• This will actually be a pretty long duration storm, however, the most intense part of the storm will not be that long-duration. Perhaps a 3-5 hour window of the most intense snow. Outside of this window precipitation is pretty light. 
• Starr time: Snow begins to move into the state between 7:00 AM and 9:00 AM Thursday across southern Connecticut and between 9:00 AM and noon across northern Connecticut. 
• Heaviest snow: Between 1:00 PM and 6:00 PM Thursday 
• This is where the long duration part comes in as there will be on and off precipitation which consists of light snow, freezing drizzle, or sleet Thursday evening through much of Friday. 
• Expect the Thursday afternoon and evening commute to be significantly impacted and this could continue through the Friday morning commute. Please allow extra time if traveling. 

Tuesday, February 16, 2021 Sleet/Freezing Rain Potential

 Saying the upcoming storm is going to be a mess doesn't do it justice. The storms we have dealt with this winter have been predominately easy in the precipitation-type department. This time, however, is not going to be the case. Despite Connecticut being such a small state, the differences in weather may vary significantly within the state. This adds immense challenges to the forecasting process and to the communication aspect of this storm. 

Before we get into our weather in Connecticut, let's take a moment to appreciate (meteorologically) what is transpiring across the majority of the country. Record-breaking Arctic cold (and prolonged cold) plunges well into the deep South with multiple winter storms impacting areas which aren't accustomed to winter weather. Why is this happening? We'll take a brief look below (well if you read my posts, you know I'm usually never brief with these things).

For the better part of the past few weeks a piece of the polar vortex has been displaced south and has become positioned in the vicinity of the United States/Canadian border. With the polar vortex being displaced from the Polar region, strong ridging has built into the Arctic and polar regions. Meanwhile, ridging has become established across the North Pacific. This is the perfect recipe for Arctic air outbreaks to sag south into the United States:

Flash forwarding to Monday morning (February 15) the jet stream will be digging extremely far south...pretty much into Mexico! With the jet stream displaced this far south combined with the configuration shown above, this is prime for Arctic air all the way into southern Texas:

At the surface, a very strong and robust high pressure (with central pressure greater than 1040mb!) is positioned across the upper-Midwest associated with the polar vortex lube. This is just funneling low-level Arctic cold into the majority of the country:

What does all of this have to do with our potential weather here in Connecticut? Well, quite a bit actually. There is something else I would like to illustrate and I am going to use forecast temperatures at 850mb (roughly 5,000 feet above the ground) for Monday morning. Off the Southeast coast of the United States is a large ridge (known as the Southeast ridge). The colors here can be correlated to warmer temperatures and colder temperatures. The brighter colors represent warmer temperatures while the darker colors represent colder temperatures. I've outlined in red the "battle" ground between Arctic cold and more tropical warmth with an orange arrow directed towards Connecticut. We are going to be in this "battle" ground between Arctic air and more tropical air. This is what is going to result in a slew of precipitation types across the state Tuesday:

By Monday evening, low pressure moves northeast up along the Eastern Seaboard and approaches Connecticut. Initially, temperatures at the surface will be below-freezing as winds out of the northeast (or east-north east) will funnel in low-level cold thanks to that extensive high pressure which stretches through eastern Canada:

 However, as the low pressure system continues to organize, we'll see temperatures between 3,000 feet and 7,000 feet above the ground actually warm above-freezing. This is due to low pressure up around 5,000 feet developing well to our west:

What can we expect? Well what we won't see much of is snow. In fact, outside of maybe the Northwest hills I don't think anyone sees any snow so this can be ruled out. The bigger challenges arise with sleet and freezing rain potential. In terms of sleet and freezing rain potential this will be determined by;

1. EXACT track of the surface low pressure. The closer to Connecticut this tracks and the earlier this strengthens, the greater the likelihood for warmer air to move in at the surface. This scenario would present more of a mix to rain for a greater portion of the state. Should this track not so close to Connecticut, there is greater potential to keep colder air locked in at the surface, resulting in higher likelihood for sleet and freezing rain. 

2. The configuration of the thermal profile (how temperatures are changing as you ascend through the atmosphere). This will be easier to explain with a visual, but the structure of the thermals will be a determent in sleet versus freezing rain. 

At this juncture, the potential exists for a quite a bit of sleet and freezing rain across the state (away from the immediate shoreline) with even the potential for significant icing (> 0.50'' icing) which would bring about power outages. All of these details are extremely complex and there is a quite a bit to resolve moving through Sunday. Below, is what we could be facing:

 

Super Bowl Sunday Snowfall Forecast

 The second significant snowstorm within a week impacts Connecticut Super Bowl Sunday as a potent coastal storm looks to track close enough to the coast to bring a band of moderate-to-heavy snowfall across the state Sunday. This will be a fast moving storm which will preclude the potential for even higher amounts. 

Forecast models are showing an intense band of heavy snow traversing the state from late Sunday morning through late afternoon. Snowfall rates once again could approach 2 to 3 inches per hour during this window:

There is pretty strong agreement in the 850mb low to track just south and east of Connecticut with very strong 60+ knots of inflow feeding moisture into the storm. This track is perfect for heavy snow across the state. Should also be noted the 700mb low tracks just south and east of Connecticut as well:

What to Expect:

• Snow starts 4:00 - 7:00 AM Sunday morning and quickly becomes moderate-to-heavy through mid-to-late morning.
• Heaviest of the snow falls in a window between 11:00 AM - 3:00 PM EST. Snowfall rates of 2 to 3'' per hour at times in this window. 
• Wind gusts 25 to 35 mph along the coast
• Snow rapidly tapers off by late afternoon and is out by evening. 
• Lowest confidence: Northwestern Connecticut

Super Bowl Sunday Snowstorm? Active February Ahead?

 We may be starting what could be quite an active month in terms of storm chances of Arctic cold shots. After getting our second major snowstorm of the season to start the week, there is potential for yet another significant snowstorm for Super Bowl Sunday. Below, are some of the piece to watch over the next few days.

The polar vortex across the southern Arctic is going to be heavily disrupted over the next couple of days when a piece (or multiple pieces) breaking off and becoming displaced across southeastern Canada:

There will also be confluence to the north of our region. This area of confluence could be a major determinant in whether the storm tracks close enough to the coast to give us snow or it stays out to sea and is fun for the fish:

 The key piece of energy which looks to be responsible for the potential storm quickly accelerates through the jet stream and is expected to move into the Pacific-Northwest region Thursday night:

There is very strong agreement within forecast model ensembles that the pattern (at least through mid-month) will be extremely favorable for Arctic cold shots and plenty of storm chances. Forecast models indicate in the Pacific-North American pattern (PNA) becoming increasingly positive as a large ridge builds across the eastern Pacific into the Gulf of Alaska. The Arctic Oscillation (AO) is expected to become extremely negative and favoring polar vortex (PV) displacement to southern Canada. Meanwhile the ridge off the Southeast coast holds strong:

This pattern screams Arctic cold blasts across much of the eastern-third of the country with numerous storm threats. In fact, the upcoming week features THREE different storm chances;

1) Super Bowl Sunday

2) Tuesday/Wednesday

3) End of week/next weekend

February is certainly no stranger to active weather and cold and it looks like February 2021 may deliver in both categories. Rejoice snow lovers, your time may be coming.