•Clouds increase tonight ahead of a storm system that will spread warmer air and precipitation into our region for Sunday into Monday
• We have concerns that the models may be under estimating the cold air at the surface, meaning a short or long duration freezing rain event is possible
Will need to keep a very close eye on things over the next 24 hours, we have devised three possible scenarios of what might happen on Sunday into the overnight:
1- A brief period of freezing rain on Sunday morning that could quickly change to rain in the valley with very little impact. (Some of the sheltered valleys in the Catskills being exempt) Low impact/Medium Probability
2-Cold air could be a bit more stubborn, in which case freezing rain would linger throughout the day before finally changing to rain with minor icing. Moderate Impact/Medium Probability
3-Cold air hangs tough for almost the entire duration of the storm, causing a prolonged period of freezing rain resulting in more significant impacts. High Impact/Low Probability
•Rain or Freezing Rain, changes back over to snow early Monday as cold air rushes back into the region.
•Dangerously cold air returns by Monday night
•Another chance of snow returns by Thursday
Details as to how we came to the above forecast, and a lesson-
On Sunday a storm system will track through central New York State, putting the Hudson Valley on the warmer side of its system. In the winter, this typically means the warm-up will cause all rain, or a snow to rain scenario. The one key difference this weekend, is that we will be at the tail end of one of the most impressive arctic invasions in years, not to mention a fresh snow pack. These two factors may spell potential trouble, and are the key ingredients for one of winters biggest headaches: freezing rain.
As the storm approaches us from the Southwest, it will be driving warmer air into the region. Remember, the flow around a low pressure system is counter-clockwise, so this puts us in Southerly and Easterly winds, (i.e. tropical air) and warm air off the Atlantic Ocean. Now, keep in mind how cold it is here currently. The snowpack we have accumulated acts as a protector of that cold air that is down at ground level, and gives it an added staying power. Warm air is lighter than cold air; the hot air rises and cold air sinks. Cold air sinks because it is heavier and denser. As the warm air moves into our region it runs over top of the remaining cold air that is trapped at the ground. The warmer air is invading the upper atmosphere where the precipitation is forming. The rain that is falling, is spending most of its time in the warm air, and thusly in liquid form. When it hits the ground, it freezes on contact, because that shallow layer of cold air is keeping ground surfaces at/or below freezing temperatures. This is what glazes the roads, trees, signs, electrical lines and anything else at the surface.
At the moment, most of the models are not picking up on this warm air/cold air threat. The models are possibly overlooking or underestimating the staying power of the cold air. This would cause the region to warm faster with only a brief period of sleet and freezing rain, that would quickly turn to plain rain. Now this may indeed be one of the outcomes, but its important to highlight the potential for this to turn into a much icier scenario.
Below is the NAM model which shows the possibility of a brief period of freezing rain on Sunday morning, but quickly changes to rain in most locations by late morning, with the exception of some pockets in the Catskills. This model shows precip type in three different colors, blue is snow, pink is ice and green is rain.
Next is the GFS model, showing the track of the storm, which I have marked with a black arrow. As aforementioned, this track puts the HV on the warm side of the storm as it drives air from the Atlantic and the tropics into the region (red arrows). (*Blue Arrow: A key component for next week’s forecast is the cold air that will sweep in behind the storm as is continues north.)
Pretty cool right? Now lets take a look at just how much a track like this can warm the temps: Below is the Euro model’s forecast for max temps as this storm passes to our west. (Keep in mind that we feel this model is a bit overdone on the high temps, as it’s forecasting us for about 50 degrees on Monday)
Seems overdone, but considering lows on Saturday night are forecasted to be between 10-14 degrees, this is an impressive warm up. But, feel that it will not get this warm. So what happens next is as this storm pulls away, that counter clockwise flow around it switches the winds back to the NE and opens the door for the cold air to pour right back in behind it. Check out the GFS model below and see when compared to its earlier image how the cold air just wraps right back in behind it, look for the zero Celsius line, as thats the freezing line.
Yeah I know, its pretty awesome, if your into this kinda stuff. So, are you curious as to how much this will drop the temps? Well, remember the Euro model temps had us at about 50 degrees on Monday? Lets see where it has the temps by Tuesday night shall we?
Single digits to below Zero! Yup! That is a fifty degree drop in temps in about 24 hours. This is part of the reason we feel the models may be struggling on the handing of surface temps. Nevertheless, whether it’s freezing rain or rain falling on Sunday night, it will all change to a period of snow Monday before it ends.