As discussed yesterday, a storm system will ride the gradient to our west between two areas of high pressure, bringing a round of mixed precipitation to the area. All precipitation looks to start as snow, but as the system comes north, it draws warm air further north with it as well given that there is no block or area of high pressure to provide resistance, and therefore most if not all areas of the state will eventually flip to mixed precipitation and/or plain rain over the course of the evening and overnight Saturday before precipitation tapers off Sunday morning. As always, this discussion is split into three parts; Models and Trends, Forecast and Timing, and Impacts. If you’re just looking for the snowmap, scroll down to the Forecast and Timing section, otherwise, read on and enjoy!
Models and Trends
All guidance in relatively good agreement on the track of the storm, however, some discrepancies remain related to surface temperatures and precipitation amounts. Most guidance keeps our area in the 33-35 range during the storm, however, I’m a bit skeptical of temperatures going much above freezing in interior areas during the duration of the precipitation. Models are typically too warm with surface temperatures when we are dealing with such a cold antecedent airmass, and the storm itself is relatively weak and hence does not have a strong mechanism to bring up warm air with it. We saw this in the 1/24 storm that kicked off this wintry bonanza where most guidance got the state into the 35-36 range and the end result was temperatures locked around freezing and an over performance of snow and ice as a result. Have leaned on that analog heavily for this forecast.
The one wildcard on temperatures is Sunday morning, where some guidance attempts to warm us up into the low 40s as the system clears out and the sun comes out, while other guidance says we rot at 33 for much of the day and then go back into the freezer overnight. Leaning towards the colder solutions for now due to the reasons explained above.
We have seen generally consistent runs from the models, and if anything, the trend has been towards a slightly colder and hence snowier solution. However, have not seen anything to suggest that models will dramatically trend colder or warmer and hence have essentially taken them at face value for the purposes of this forecast.
Forecast and Timing
Here’s a look at our forecast snowmap for this event.
We are also worried about some icing, especially away from the coastline in the traditionally colder spots. As of now, models agree that surface temperatures will get up into the 33-34 degree range once we flip to rain and as a result icing would appear to be no big deal, but I’m skeptical for two reasons. First off, models always overdo surface temperatures, especially in situations where we have a cold antecedent airmass like we do here, and secondly, ground temperatures are so cold from all the arctic shots that we’ve been experiencing that even if the two meter(the level at which surface temps are measured at) temperature is 33 or 34 degrees, the ground could still be well below freezing and as a result ice accretions would still be possible. As a result, I have included a chance for up to a quarter of an inch of ice accretion in the 3-6” zone of the map. In general, I think amounts will fall a bit lower than that, but we decided to be fairly bullish on the upper bound of icing because of the significant impacts that ice can have.
As far as timing goes, guidance is in relatively good agreement. . Precipitation approaches from the SW Saturday afternoon and overspreads the state from the mid afternoon on, increasing in intensity as we head towards the evening hours. By 7 PM or so, I’m expecting moderate snow to be falling across much of the state, with an inch or two on the ground for western areas and a bit less further east considering that precipitation will take longer to break out there.
As the storm moves northeast and gets us into the heavier precipitation, it will at the same time bring up a push of warm air from the south and begin to change areas over to rain. Generally, this transition will be from SE to NW, although likely a bit more dependent on latitude rather than longitude. By 10 PM at the latest, I expect that the transition to rain will have begun in the SE corner of the state, and it will continue to push NW through the evening and overnight. By 1 AM, most of the state except for possibly the far NW corner will have gone over to a mix or rain. Precipitation moves out over the early morning hours on Sunday, and by 7 AM, all we’ve got left is some rain showers, which move out soon after.
Here’s a look at the progression of the system on the RGEM model, which I think has a good handle as far as timing and precipitation types go. Times are in GMT, so subtract 5 to convert to EST(So 00:00:00 is 7 PM our time).
· A plowable snowfall for the entire state
· Tricky driving conditions later Saturday into Saturday night due to a combination of snow and ice.
· Potential infrastructure issues, especially on roofs, due to the combination of existing snowpack weight, additional heavy wet snow and ice, and melting. Ice jams and roof collapses are possible.
· Slippery surfaces Sunday evening from a flash freeze
· Minor flooding possible depending on the amount of rain that we get and how warm we get Sunday as a result of both melting snowpack and clogged drains.
We’ll keep an eye on the guidance and issue a final call tomorrow with a revised map if needed and of course will be updating continuously throughout the event as always. Thank you for reading Southern Connecticut Weather!