Computer forecast models continue to show strong consistency and strong agreement that a significant blizzard is about to unfold across a large portion of southern New England and yes, this includes Connecticut. A low pressure system developing off the Southeast coast through the day Friday will undergo very rapid cyclogenesis (strengthening) as it works up the mid-Atlantic coast. The biggest question is/was exact track, however, this is starting to become more clear, but not yet set in stone so deviations in the track will result in deviations within the forecast. Adjustments will be made as needed. Note: Just because I am using output from a particular forecast model does NOT mean I am favoring that model or creating a forecast solely based on that model. The output is just used for illustrative purposes.
Low pressure is expected to form right along the baroclinic zone Friday evening just off the Southeast coast. During this time an amplifying (strengthening) trough, southern stream shortwave energy, and strong upper-level jet dynamics will favor rapid cyclogenesis of the low pressure as it moves north-northeast just off the coast:
From this point, the one million dollar question is, how does northern stream shortwave energy interact with this system. This will play a substantial role in the evolution and overall track the low pressure system takes. There are some differences in this within forecast models. Some forecast models indicate a greater and earlier involvement of this northern stream shortwave energy, resulting in an earlier rapid strengthening and a closer to the coast track while some forecast models have this occurring a bit later, resulting in a slightly more east track. One of these models is the GFS forecast model. Given how close the baroclinic zone is to the Southeast coast, I believe the GFS is developing the surface low too far east and as a result, tracks the storm farther east (even though the interaction of the northern stream being later favors an already east track).
Given the combination of upper-level dynamics and interaction of all pieces mentioned above, surface low pressure should strengthen incredibly rapidly as it moves north-northeast just off the mid-Atlantic coast, likely bringing major snow totals to portions of the mid-Atlantic. Forecast models are also indicating as much as 80+ knots of wind at 850mb (about 5,000 feet off the ground) feeding into the storm. This will result in copious amounts of moisture being fed into the storm:
As the low pressure system rapidly strengthens, low pressure centers develop at 850mb and 700mb (about 10,000 feet above the ground) indicating a very strong, mature system. Where these low pressure begin to develop, strengthen, and track are extremely important as historically, the bands of heaviest snowfall occur northwest of these low centers. In more developed lows this is about 30-50 miles northwest of the centers, in more poorly organized or just developing centers this can be as much as 60-70 miles northwest. This will also be tied into exact storm track, but the indication is this process will occur south and east of Connecticut and close enough to result in a band of extremely heavy snow traversing much of the state. The NAM forecast model (along with the European model) are very aggressive with this. The NAM in fact indicates an extremely powerful band of snow across the state
Given the very cold airmass with this storm, snow ratios should be fairly high, perhaps on order of 18:1 to 20:1 (1'' of liquid would equal about 18-20'' of snow). Our average is about 8:1 to 10:1! This would be especially true under the band of heaviest snowfall where the degree of upward vertical motion into the dendritic snow growth zone would be maximized. The 12z/26 NAM bufkit for IJD (Willimantic, CT) indicates as much as 40-50 units of omega tapping into the dendritic snow growth zone (purple/yellow contours). That is incredible lift. This would indicate the potential for snowfall rates of...3-5'' per hour!!!! along with the potential for thundersnow:
With such an intense low pressure not far off to the southeast, this will translate to very strong winds thanks to a very strong pressure gradient. Winds along the shoreline could become sustained as high as 25-35 mph with gusts 60-70 mph. Winds just inland could become sustained as high as 15-25 mph with gusts 40-60 mph. 12z NAM/26 bufkit for Groton, CT shows very high wind potential. This would result in blizzard conditions, significant drifting of snow, very low visibility, and scattered-to-numerous power outages:
So with the meteorology/science fun out of the way let's break the storm impacts and timeline down:
What to Expect:
- Light snow showers throughout the day Friday.
- Light snow may develop during the evening and overnight well ahead of the storm. This snow will have potential to produce 1-3'' of snow locally.
- Saturday...
- Heavy-to-extremely-heavy snow overspreads a large portion of the state moving through Saturday morning and continuing into late afternoon before gradually beginning to taper off.
- Under the heaviest banding snowfall rates could approach 3-5'' per hour!!!
- Thundersnow possible.
- Strong-to-damaging winds are expected statewide with sustained winds of 25-35 mph and wind gusts of 60-70+ mph along the immediate shoreline. Sustained winds of 15-25 mph with gusts 40-60 mph inland. This will create blizzard conditions, significant drifting of snow, and extremely low visibility.
- Scattered-to-numerous power outages are likely, especially along the shoreline. Power outages may last a few days in some areas.
- Major-to-devastating coastal flooding along the immediate shoreline.
- Travel will be very dangerous and perhaps near impossible Saturday. due to the extreme snowfall rates, plow operators will not be able to keep up with the snow. While travel is highly not recommended, if having to travel, prepare a necessity kit in the event you become stuck or stranded.
Below is my initial snowfall forecast. Please keep in mind, given the high uncertainty and low predictability which exists with determining where the heaviest banding will set up and traverse, it's very difficult to highlight that on a map right now. Also, anytime you see such an intense band of heavy snow you get an area of subsidence (sinking air) this will result in less totals in areas under subsidence and that is also very difficult to illustrate on a map. As we get closer, these details can be ironed out:
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