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.
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