With the passage of an arctic front this afternoon, we have entered what looks to be a very active period, with two shots of very cold air and several storm chances expected. This discussion will primarily focus on the first of those storm chances, which is projected to arrive Sunday evening and last through Monday, but we’ll also take a brief look at the rest of the forecast period as well.
Colder air is currently filtering into the state as we speak, and tomorrow will be the first day of below-normal temperatures associated with this cold shot. Expect highs in the mid to upper 30s across the state, around five degrees below normal. It’ll be windy as strong northwest flow is established, and we could also see some snow squalls tomorrow as some remnants of the lake-effect snow going on to our west may make it into our area. Best chance for a quick bit of snow would be in the northwest corner of the state. Saturday should be cool and dry, with highs only topping out in the upper 20s to lower 30s, around ten degrees below normal.
A classic early-season Southwest Flow Event (SWFE) is expected to impact the state during this timeframe. The general framework for the event is clear; a weak to moderate system will move northeast out of the center of the country over the weekend, eventually running into an arctic high pressure over eastern Canada. As the system comes north, it brings warm air advection with it. Once the system runs into the block, it will weaken the primary low and most likely develop a secondary surface reflection, which serves to shut off the flow of warm air and lock in the cold over areas that have not yet warmed. SWFE’s are rarely enormous storms and are generally rather quick hitting, but can pack a punch during that time. It is rare to see one that is an all-snow event for the state, but they are a frequent producer of a heavy front-end dump for the state. How much of the event is rain vs. snow vs. ice/sleet depends on the antecedent airmass in place, the positioning of the Canadian high, and the strength/track of the system trying to run into the high pressure. A colder airmass in place and a well-positioned Canadian high both lead to colder systems, while a stronger low usually leads to a wetter system. Let’s take a look at the guidance and see how these variables play out on the models.
Here’s a look at the MSLP (Mean Sea Level Pressure) on the GGEM, GFS and Euro for 7 AM Monday morning.
So, which scenario do I believe? As of now, both are realistic possibilities; both the GFS and the Euro have the support of their ensemble packages, and SWFE’s can run the gamut from essentially being lakes cutters with a cold front-end to a full on snowstorm. However, at this point, I’m inclined to lean a bit more towards the Euro/GGEM combination for a few reasons. First, the GFS often has issues with the identification and strength of arctic highs. I’ve seen it time and time again where the model will try to ram a low-pressure system into a high, only to realize, as we get closer that the high pressure isn’t going anywhere and shift to a colder solution. Second, we have been in a generally progressive pattern, and it has been difficult to get anything to significantly amplify. The fast flow we have been seeing looks to continue, which would favor a weaker system. Third and finally, the model consensus excluding the GFS is for a weaker, colder system (UKMET has that solution as well), and I would rarely take the GFS over the Euro/GGEM/UKMET combo absent some good reason for doing so, which I don’t see here.
So, what does this all mean for our sensible weather? First off, we should see some snow showers Sunday afternoon and evening as an initial wave of overrunning snow arrives. This initial wave serves as the mechanism to allow the more impactful wave discussed above to move into the Northeast, but it should bring a bit of snow along with it as well. Heavier precipitation arrives overnight Sunday into Monday morning, likely making a mess of the morning rush hour. Initially, I expect snow to fall statewide and at least a light accumulation is expected everywhere. I do expect that the south coast will change to a mix or rain over the course of Monday morning, but right now, I would lean towards a mostly snow event for the interior, perhaps changing over right at the end of the system. Precipitation should move out Monday evening. As far as totals go, it’s too early to speculate on more specific amounts, but I would say that the entire state is in the game for a plowable snow, with warning level accumulations possible away from the shoreline and especially in the northern tier of the state. Assuming this threat does not completely fizzle over the next few model cycles, we will have a first call snowmap and discussion out on Saturday morning, with a final call issued on Sunday.
Overall, a classic early-season setup that looks to bring us our first significant snow event of the year!
Tuesday looks to be quiet and seasonable, with near normal to slightly below temps expected. Guidance then agrees on a Miller B system developing midweek (A clipper system transferring to a secondary low off the coast), but is widely divided on the track. The GFS is again the strongest and would be mainly a rain event for our area, the GGEM brings another round of accumulating snow, and the Euro is well south of the area and would just bring some flurries and cold temps. Considering the lead-time and the fact that we’ve already got one storm to deal with, will pencil in a chance of rain and snow for the dailies and let the next forecaster cover this one in more detail.
Here’s a look at this system on the GFS and GGEM.
Here are the dailies:
Friday: A chance of snow showers, otherwise, mostly cloudy, with highs in the mid 30s. Chance of snow is 30%.
Saturday: Mostly sunny, with highs in the upper 20s to mid 30s.
Sunday: A chance of snow showers in the afternoon and evening, otherwise, clouds building, with highs in the mid 30s. Chance of snow is 50%.
Monday: Snow likely in the morning, then rain, snow and ice likely in the afternoon. Otherwise, cloudy, with highs in the mid to upper 30s. Chance of precipitation is 90%.
Tuesday: Mostly sunny, with highs in the upper 30s to lower 40s.
Wednesday: A chance of rain and snow, otherwise, cloudy, with highs in the mid to upper 30s. Chance of precipitation is 40%
Thursday: Mostly sunny, with highs in the upper 20s to lower 30s.
Stay tuned to our website, Facebook and Twitter for updates on our upcoming system, and make sure to keep an eye out for our first call map on Saturday! Thanks for reading SCW. -SA