Cities to the south and east of Buffalo are digging out from up to 88 inches of snow this morning after this week's double lake effect snow events. To make matters worse, warm temperatures and potentially heavy rain will cause a rapid snowmelt, bringing the potential for major flooding.
A low pressure system will develop over the central Plains this weekend and quickly scoot towards the Great Lakes as it deepens into a potent cyclone with a minimum central pressure possibly reaching 970 millibars. The strong gradient associated with this low will cause significant warm air advection across the eastern United States, which means that air from the Gulf of Mexico will briefly pump directly north through the East Coast and straight up into Canada. Highs will jump up into the 70s as far north as Virginia, with maximum temps in the 60s into New York and even Ontario.
While it's great that it's going to feel comfortable for a day or two, this is not good news for areas that just saw epic amounts of snow. According to the latest snow water equivalent analysis—which measures how much water would result from all of the snow in particular area completely melting—the snow over a large swath of western New York holds more than six inches of water, with areas that experienced those seven feet accumulations seeing eight to ten inches of water in their snow pack.
This high water content will create some pretty significant problems once the snow starts melting, which is expected to begin tomorrow and quickly pick up through early next week. This rapid melt will be the result of three factors: warm temperatures, high dew points, and heavy rain.
The combination of mild temperatures (highs in the upper 50s and low 60s on Monday) and elevated dew points will mean that the air is relatively warm and moist for a region that just saw a Shaquille O'Neal's worth of snow. This will allow for an efficient snow melt (as NWS Buffalo calls it), with water sinking down through the snow pack, solidifying it into a thick slab of heavy slush.
If and when it does rain on this snow pack, it will exacerbate the melting and cause even more of the snow to turn into a heap of slush. Virtually all drainage systems that aren't cleared and kept clear will likely be blocked, causing water to pool up anywhere it can. This flooding could endanger homes and businesses in low-lying areas, including those buildings that are caught on the wrong side of a solidified snow bank.
The biggest story we'll hear out of this snowmelt might not be the flooding, but rather the structural damage that comes from water-logged slush pressing up against walls and sitting on roofs. We will see roof collapses from this event. Box stores are notorious for suffering from structural failures when rain falls on a dense snow pack, but the amount of snow on residential roofs will also pose structural problems.
Most homes with gabled roofs should be okay if the roof is in good condition and the home doesn't have any underlying structural issues. The most likely damage we'll see is in buildings with flat roofs or in older homes that can't withstand the weight of water-logged snow. The best way to prevent structural damage and a potential roof failure from the weight of the impending slush is to get it off of your roof (by climbing up there with a shovel or using a very long tool from the ground), but even for healthy individuals that's not always a practical option.
If you live in the areas that got hit the hardest by the snow this week, make sure you're aware of the potential for significant flooding next week, and make plans in case you need to evacuate in a hurry. Warm temperatures and up to half an inch of rain is the last thing the area needs after seeing almost 90 inches of snow.
[Images: WeatherBELL, NOHRSC, Associated Press]