Moving beyond the thaw...
Posted January 17th, 2013 by Bill Kardas. 21 comments
The streak of above freezing temperatures and days without measureable snowfall came to an end yesterday as a fast moving system grazed CNY with light snow. Today, a cold front sweeps in from the north and delivers a blast of colder air. The weather over the next few days will be rather unsettled as the stage becomes set for a blast of arctic air next week.
Our team is tracking a cold front this morning that's dropping in from the north. A fresh coating of snow can be expected between now and the early afternoon along with gusty winds. The air behind the front is quite chilly. As we've seen many times, CNY has NO problem drawing in cold air (unlike warm air). Temperatures will plunge into the teens for the evening commute. I think we will be lucky enough to catch some breaks in the overcast as cold air advection takes over today. Any sun today will only help 'mix out' the atmosphere, dragging cold air above the surface to the surface. In other words, there's no escaping the chill this afternoon.
High pressure builds in tonight and temperatures will likely into the single digits tonight. If skies clear out, the Adirondacks & cold pockets north of the valley will likely fall well below zero.
The cold air will stick around for the most part over the next seven days. Return flow on the backside of high pressure will allow a 'warm front' to cross through the area on Friday night. I say 'warm front' for two reasons - it's more like a 'break from the cold' front and it will likely bring more low clouds to the area Saturday morning. If the front does stall (which it will to some extent) we could linger around some flurries. The models aren't showing that, but we know better so we played it pessimistic on Saturday and kept the snow showers in the forecast. The front will swing north on Saturday afternoon as warm air advection cranks. Highs will climb above freezing.
For Sunday, two cold front swing through as low pressure passes to our north. Each front will be accompanied by widespread snow showers and accumulations will be dependent on the lakes. There could be some embedded squalls with the arctic front last Sunday night. We'll keep you posted.
The cold air next week looks plenty cold to generate lake effect snow. However, winds are going to be very light aloft as high pressure swings in from the north. This makes it very difficult to pin down the exact direction of wind early next week. In the given pattern, the reasonable foot forward is to assume the lake bands will stay close to the shore. We've seen that over the years with bitterly cold air. Based on observation, there seems to be a limit on the maximum extent of the band, particularly in very cold air masses. Note the graph illustrated here is not based on data but rather observation and is meant to give a general idea on how the system works.
Why does the band shrink if the air is colder?
If lake effect is generated due to the difference in temperature between the air and water, why wouldn't extremely cold air create epic lake effect events? There are two reasons. First, cold air can't hold as much moisture! In extremely cold scenarios, the lake band becomes limited by moisture availablity in the air. Second, really cold air is very shallow and dense. The inversion height, or height in which the air modifies aloft, is lower in arctic air outbreaks. This puts a limit to the overall height of lake effect clouds. In fact, during extreme cold, sometimes the doppler radar beam 'misses' the lake bands. We've had several scenarios over the years of moderate to heavy snowfall that have gone almost completely undetected by the three surrounding radar towers that encompass CNY. Hopefully that doesn't happen next week.
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