We're tracking yet another winter storm, Winter Storm Liam, that will impact our area and the greater region this Wednesday as an area of low pressure with a large shield of precipitation tracks into cold air. In this article, we break down the timing, forecast, and the setup of this likely snowstorm. Keep in mind that this forecast may change, so it's important to stay updated with us (and not the weather app).
Timing of Snow:
Snow starts: Around 9am
Snow peaks in intensity: 9am-11pm
Snow ends and changes over to rain/freezing rain/sleet: 11pm and 12pm
Timing of Freezing Rain:
Freezing rain is the most difficult to predict
Coast: Starts around 11am, and lasts as late as 3:30PM
Inland: Starts between 11am and 1pm, and lasts as late at 5PM
Inland locations will be the most impacted by freezing rain, where over 0.1 inch of ice is possible
Wednesday morning: Low to mid 20s inland; mid to upper 20s at coast
Wednesday early-afternoon: Between 25 and 30 degrees
Wednesday late-afternoon into evening: Rising from upper 20s/low 30s to mid 30s, cold air may remain stubborn north of Danbury at around 30 degrees
Heaviest inland; lightest at coast
Most areas receive 1-3 inches
North of Danbury may receive up to 4 inches
A weak but strengthening area of low pressure will develop Tuesday night, developing near the central Gulf Coast as a piece of energy from the Northern Tier meets up with this second piece of energy near the Gulf Coast. Whenever this process occurs, it's called phasing. In short, two storms are basically combining into one. First of all, this will not be a monster storm or a nor'easter. It will remain as a relatively weak area of low pressure tracking from the Gulf Coast through the interior Northeast. Meanwhile over the Northeast Tuesday into Wednesday, there will be a strong area of high pressure with pressures near 1035 millibars. This high pressure will funnel in low-level cold air into much of the Northeast, which is the main ingredient for snow. If we didn't have this high pressure near the Northeast, then we will be talking about an all-rain event.
So now that we talked about the basic setup, let's chat about the forecast and how you are actually going to be affected. Precipitation will begin to stream into the south and west Wednesday morning. This precipitation will move in during the late-morning with snow falling for the entire region. With cold temperatures in the 20s, not only will the snow be able to stick or accumulate to all surfaces, snowfall ratios will be higher than the typical 10:1 ratio. This typical ratio means that for every 10 inches of snow, there is one inch of precipitation or liquid water. In this case due to the colder temperatures, ratios will likely be around 15:1, or 15 inches of snow for every one inches of liquid. We will not be receiving an inch of liquid with this storm, but we will receive enough to possibly produce as much as four inches to inland locations, especially in the hills north of Danbury.
Now during the midday hours of our Wednesday, I'm thinking conditions will be at their worst with moderate snowfall rates. This is the time period when the most amount of snow will fall in the shortest amount of time. Now between 11am and 2pm, warmer air is expected to begin to erode the air column of cold air. Therefore, while temperatures are still below freezing at the surface or the ground where you live, temperatures a few thousand feet aloft, or in the atmosphere, will actually be above freezing. This is a conducive set up for freezing rain, especially inland and away from the coast. This is a hard precipitation type to predict, but a couple hours of freezing rain is not out of the realm. Below, you'll see the forecast atmospheric profile for the early-afternoon in our area. It's a bit too complicated to explain, but the x-axis of the graph shows temperatures and the y-axis is height or altitude. The right line on the graph shows the predicted temperatures as you go up in height in the atmosphere. Notice how the line actually goes right or toward a higher temperature first, then it takes a left turn toward colder temperatures in the upper-levels of the atmosphere. In order to get freezing rain, which this atmospheric profile shows, you need a thick layer of freezing rain aloft. If this freezing rain ends up verifying, then a glaze to up to a tenth of an inch of ice is expected to accrete. The chances of freezing rain occurring has increased and several hours of it is possible, which will make roads treacherous.
By the late-afternoon to evening, all of the wintry weather is expected to come to an end as the cold air erodes in all levels of the atmosphere, including the surface. This will allow for a plain rain to fall during the evening before ending around 8pm Wednesday night. That rain will then refreeze, making for a slippery morning commute.
Based on this complicated forecast, our snowfall accumulation forecast still has some uncertainty, although most of the modeling is in great agreement. It's a tough call because it depends on how long the snow lasts before the changeover to freezing rain.
Stay tuned to Jackson's Weather leading up to and during this storm for continuous updates. Also follow our LIVE Twitter feed below.