Hurricane Henri - What to Expect here in Connecticut

As we move through the remainder of this Saturday, all eyes are on Henri and just how much Henri strengthens as it now moves into a more favorable environment for strengthening. For the past few days Henri has been impacted by very strong wind shear to the north. Henri, however, is moving away from this stronger wind shear and is moving over the very warm waters of the Gulf Stream. As of this writing, Henri was not looking particularly great, but it is slowly trying to strengthen. 

Below, is the latest forecast track with cone of uncertainty from the National Hurricane Center (NHC):

The NHC is forecasting Henri to make landfall across the eastern tip of Long Island as either a strong tropical storm or a low-end category 1 hurricane with the center then passing over Madison, CT with maximum sustained winds of 70-mph with gusts upwards of 85-mph and tropical storm-force winds (my estimation of gusts 40-60 mph) across the majority of the state. However, notice there is still a quite a bit of spread in potential landfall with the cone as far west as western Long Island and as far east as eastern Rhode Island. This is due to the questions regarding exactly how strong Henri gets today and interactions with an upper-level low to our west:

My anticipation is that Henri will make landfall across central or eastern Long Island (more likely eastern Long Island) and then swing northwest into the Connecticut shoreline. I am unsure of strength but if it is as strong as what the NHC is suggesting...we will see big problems statewide. Below are my thoughts on each storm phenomena:

Wind: The latest GFS computer forecast model, with it's forecast track of Henri, forecast winds anywhere from 50-70+ knots about 2,500 feet above the ground east of the Connecticut River as Henri moves into southeast Connecticut. 

It is my estimation this would result in widespread wind gusts of 40-60+ mph across much of the state for a solid 3-5 hours. Wind gusts along the shoreline just east of the center could approach 80-90 mph. 

Power Outages: These winds would cause extremely widespread wind damage, some structural damage, and power outages along the shoreline just east of the track with widespread power outages and tree damage across a large portion of the state. Hardest hit areas should prepare to be without power for upwards of several days.

Storm surge/Coastal Flooding: Forecasts are for 3-5 feet of storm surge along the Connecticut shoreline and this would bring about significant-to-devastating coastal flooding. 

Rainfall/Freshwater Flooding: The heaviest rain and highest totals would occur just west of the track and that places the highest rainfall totals along and west of the Connecticut River. Rainfall of 4-8'' with a narrow swath of 8-12'' is likely. This would promote widespread significant flooding. 

Tornadoes: Isolated tornadoes are possible with embedded thunderstorms, especially just to the east and northeast of the storm track. This would likely be northeast Connecticut into Rhode Island and into southeast Massachusetts. 

Timing: It is very possible we see some bands of torrential downpours and embedded thunderstorms move into the state later tonight (which would carry a isolated tornado risk). Weather conditions begin to rapidly deteriorate moving through late Sunday morning. The worst of the winds happen late morning through late afternoon but the rain/flooding threat should persist well into the evening.  

Let's be very thankful this is not a much stronger storm or that it is not approaching us at a faster speed.

Wednesday, April 21, 2021 Low Topped Squall Line Potential

 A cold front is set to sweep across southern New England early Wednesday evening. Combination of marginal instability and rather strong dynamics and forcing from the front will promote the development of a low-topped squall line ahead of the cold front. While the greatest overall potential for damaging winds and even hail exists across New York and Pennsylvania, localized embedded damaging wind gusts and hail will be possible across southern New England (particularly western and central sections). 

Instability is not the driver here with temperatures predominately in the 60's with dewpoints into the 40's and lower 50's, however, steep mid-level lapse rates (~7 C/KM) will aid in the development of marginal instability characterized by about 500-750 J/KG of mixed-layer CAPE. 

The driver is going to be the strong forcing associated with the cold front and very strong jet stream dynamics which are characterized by 50-60+ knots at 500mb (~18,000 feet above our heads) and 35-40+ knots at 850mb (~5,000 feet above our heads). These shear values are more than enough to support the development of organized convection. 

The line initially develops across western New York and central Pennsylvania and rapidly progresses east through the afternoon and evening. Combination of dry low-level air and strong low-level winds will support the potential for damaging wind gusts on the leading edge of the squall line. Wind damage may be more scattered across New York and Pennsylvania but then become more isolated across New England. Given cold mid-level temperatures characterized by -20C at 500mb (~18,000 feet) some of the more robust convection within the line could even produce some small hail. The line is likely to move across Connecticut between 5:00 PM and 8:00 PM Wednesday evening likely causing some localized damaging wind gusts on the leading edge and even potential for some small hail:

Vigorous Upper-level Low Pressure to Bring Accumulating Snow to Parts of Connecticut Overnight 04/15/21 to 04/16/2021

 A vigorous upper-level low pressure system across New England prompts the developments and strengthening of a surface low pressure right in the vicinity of Connecticut moving through Thursday night. If the processes involved with this system occurred say another 50-75 miles farther south and east..at least the northern part of the state would be looking at a pretty significant winter storm, however, looks like the most significant snows occur across parts of western Massachusetts, southern Vermont, and perhaps around the Worcester Hills in east-central Massachusetts. 

As of Thursday afternoon moderate-to-heavy rain has overspread much of Connecticut. As we move into the overnight and the low pressure system really gets its act together, anomalous cold will transpires within the lowest levels of the atmosphere. In fact, surface temperatures look to even dip as low as the mid-30's and even colder across the hills. As this occurs rain begins to transition to snow across the hills and even parts of northern Connecticut. In fact, the majority of the state could even some some snow mix in with the rain. 

This is a highly complex setup due to the features and processes involved, however, forecast models have been zeroing in on a solution which features a band of heavy snow which becomes established across southern Vermont through the Berkshires of western Massachusetts even extending into extreme northwestern Connecticut. This would result in a several-hour period of moderate-to-heavy snow overnight. Snowfall rates could approach 2'' per hour so despite the warm ground, these rates, combined with it being overnight would result in snow accumulating, though taking a bit longer on paved surfaces. Another band of moderate-to-heavy snow looks to originate across the Worcester Hills of east-central Massachusetts with this band pivoting and clipping parts of northeast Connecticut Friday. 

Given this snow will be wet in nature and very heavy, the potential exists for downed tree limbs and power lines. In fact, scattered-to-numerous power outages could be expected in areas which receive greater than 4'' of snow...power outages could even be on the widespread side. 

This is a very dynamic storm and add in the time of year and you get a very challenging forecast which is ultimately going to come down to nowcasting...meaning we won't really know how the situation unfolds until the processes involved get going. 

What to Expect:

• Moderate-to-heavy rain persists through the overnight
• Around midnight, rain begins to mix with and change over to snow across the northwest and northeast hills with snow becoming moderate-to-heavy through the overnight. 
• The heaviest of the snow across the northwest hills winds down between 6:00 - 8:00 AM Friday morning, however, moderate-to-heavy snow may persist through much of the morning across parts of northeast Connecticut. 
• The majority of the state may see some snow mix in, however, most people will probably be counting cows when this happens. 
• Gusty and cold Friday with temperatures only into the lower 40's with a stiff northwest wind gusting 20-25 mph.

Below is what I am currently expecting in terms of snowfall accumulations:

Burst of Moderate-to-Heavy Snow Thursday Night (March 18, 2021)

 A strong Arctic cold front arriving from the northwest moves across Connecticut early Thursday evening. Meanwhile a low pressure system (responsible for the ongoing tornado outbreak across the deep South) approaches from the southwest Thursday morning. As the low pressure approaches, heavy rain pushes into the state early Thursday afternoon. The combination of the approaching cold front and strong Arctic high pressure behind the front helps to push the approaching surface low south of the state Thursday evening.

By early Thursday evening, the Arctic cold front rapidly pushes through the state resulting in much colder temperatures quickly overspreading the state. Despite the cold front moving through the state, lift will remain rather strong (thanks to the surface low passing south of the state) and ample moisture will be thrown into the colder airmass. This results in rain changing over to a period of moderate-to-heavy snow by late evening Thursday before exiting during the late overnight or early pre-dawn hours Friday. 

Forecast models indicate some pretty strong lift across the state during the early overnight hours Thursday night with forecast soundings showing a thermal profile favorable for snow:

Breakdown of what to expect:

• Heavy rain moves into the state early Thursday afternoon.
• Temperatures get into the lower 40's, but during the evening begin to drop rather quickly with increasing winds as the cold front moves through. Wind gusts of 30-40 mph are possible overnight Thursday 
• Snow begins to transition to rain during the mid-to-late evening Thursday with the changeover occurring more quickly across the northwest hills. 
• Snow end during the late overnight or early pre-dawn hours Friday morning. Some parts of the hills could see as much as 4-5' of snow.
• Majority of the snowfall accumulations occurs on the grassy/colder surfaces, however, roads will become slick, especially as temperatures drop below-freezing. Give yourself extra time for the Friday morning commute.
• Sun comes out through Friday morning, but a cold/breezy day with temperatures only into the 30's.
• Snowfall Forecast:

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