This is probably a fitting way to end March 2017. The month has been nearly 5 degrees below average compared to January 2017 which was 6.6 degrees above average! As I wrote about yesterday late March/early April is full of weird storms (2016 April freezing rain and 2014 morning commute surprise snow) that have given forecasters fits and ticked off the vast majority of Connecticut residents ready for spring.
A storm is going to dive south of southern New England and produce a period of rain, sleet, freezing rain, and even a bit of snow. If you're excited for a big snowstorm - temper your enthusiasm immediately! This storm is looking more and more like a slushy/icy mix for areas north of I-84 and a mainly rain event south of there. Even in the Hartford area a lot of what will fall will likely be in the form of rain.
The "snow/sleet" forecast is actually fairly straightforward. Plenty of mid level warmth will limit the amount of snow we can get. In fact most areas see very little. The bigger question is what form the ice takes Friday evening and Friday night. Is it ice pellets or freezing rain. Ice pellets (or sleet) is the bouncy stuff that is a nightmare to shovel and not great to drive on but it sure beats freezing rain which clings to powerlines and trees and can result in all sorts of problems.
The key to figuring our what we'll see is how thick and how warm the warm layer is aloft AND how cold temperatures are right at ground level. First we'll start at the ground. This product from the NCAR ensemble shows the probability of temperatures below 32F at the surface at 8 p.m. Friday. There are good odds for <32F temperatures for the hilltowns later Friday.
Upstairs the forecast is a bit more convoluted. I can look at the 850mb pressure level (about 5,000 feet up) and see what the temperatures are doing there and you can see a significant spread between the NAM and the GFS. The NAM is warmer with a low farther north and the GFS is colder thanks to a low farther south.
So which one's right? The truth likely lies in the middle and that's where the European model has been. The Euro shows a warm layer Friday night and Saturday morning which is enough to preclude snow and likely deliver a period of sleet and freezing rain in the hills north of I-84 and rain farther south.
Here's the bottom line on the Friday/Saturday storm...
- Mainly light mix of snow, sleet, and rain on Friday with little if any road issues given strong March sun angle, temperatures generally above 32F, and light rates of precipitation. There is still a small chance for a bit of snow accumulation around daybreak if we get an unexpected heavier birst around the morning commute.
- Heavier rain, sleet, freezing rain mixture Friday evening and Friday night.
- 1"-2" of liquid precipitation expected with a few slushy inches of accumulation possible in the hills.
- A prolonged period of icing (freezing rain) remains possible in the hills though I think prolonged sleet is more likely. If we get a lot of freezing rain it could lead to tree and power line issues. This would also result in minimal accumulation (i.e. the 2"-4" won't happen). In this event the valley locations around Hartford will just see rain as surface temperatures will be above freezing.
- An icy mix lingers into Saturday morning and tapers off by mid morning. A flip back to snow from the wintry mix is possible even in the valley/Hartford area - this is one thing we'll watch closely.