The driver behind this event is a vigorous piece of shortwave energy at 500mb (~18,000' above the ground), surface low pressure moving northward up the eastern seaboard, and an anomalously cold airmass currently in place over our region. The low pressure and an associated warm front moving northward will advect warmer and more moist air northward. As this warmer and more moist air interacts with the anomalously cold air the result will be a band of extremely heavy snowfall developing. We will explore this is in further detail below.
As stated above, a vigorous piece of shortwave energy will be positioned across the Ohio Valley tomorrow morning and this will be moving right overhead overnight and during the day on Friday:
Temperatures at 850mb (~5,000' above the ground) will be about -5C with surface temperatures down well into the 20's tomorrow morning...plenty cold enough for snow (to save time, the temperature profile throughout the atmosphere is plenty cold for snow to reach the ground and the production of snow).
With warmer/moist air moving northward into this cold airmass, this will end up resulting in intense warm air advection:
This intense warm air advection moving into an anomalously cold air mass will result in very strong frontogenesis (indicating a strong horizontal temperature gradient):
A bufkit sounding for Waterbury, CT from the 0z run of the NAM from Wednesday evening shows rather intense upward vertical motion within the dendritic snowgrowth zone. While not shown here, there is sufficient moisture within this zone. This indicates and further strengthens the thinking of a very intense band of snowfall:
Now getting into storm specifics...
- Light snow begins to breakout between 2:00 PM and 5:00 PM tomorrow afternoon.
- Given what was described above, we can expect a band of extremely heavy snowfall to work south-north across the state with the heaviest snow occurring between 6:00 PM and 11:00 PM.
- During this time, snowfall rates may approach 2-3'' per hour at times, but this will be in brief bursts.
- After this band moves through, warmer air will begin working in within the lowest 10,000' of the atmosphere, not only will snow intensities vastly reduce, but we'll begin to see a mixture of sleet/freezing rain across the interior and rain along immediate shoreline. This will persist into the overnight.
Originally, I was thinking we would see snow on the backside Friday morning across western CT, however, that idea doesn't look as probable. With this said, we'll continue to see rain through midday Friday before the system clears out, however, some mixing of snow/sleet is certainly possible across extreme western CT. Below is my latest thinking:
