WeatherFanatics: Warmup to Bring Flooding, Roof Collapse Risk Midwest, East

Tuesday, February 18, 2014

Warmup to Bring Flooding, Roof Collapse Risk Midwest, East

By Alex Sosnowski, Expert Senior Meteorologist

February 18,2014; 9:37PM,EST

In addition to the warmup bringing a break from winter this week, rain and rising temperatures will also bring the potential for flooding and roof collapses.
Temperatures will climb into the 40s over much of the Upper Midwest, New England and the upper part of the mid-Atlantic on multiple days during the balance of this week. Some locations in the Ohio Valley and the lower part of the mid-Atlantic will reach the 50s to near 60 degrees for a day or two.

However, due to the snow on the ground, mild air and rainfall expected, some problems are likely.
According to National Weather Service Hydro-Meteorologist Ted Rodgers, "We do not anticipate enough rain and natural melting for major flooding at this time, but sporadic minor flooding incidents are possible."
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The warmup will be of rather short duration and rainfall will generally average 0.50-1.00 inch later this week. Only if much more rain falls than expected would there be more substantial problems.

In most cases, the thick snow cover will absorb the rainfall and hold back some of the warmth.
"The snow cover is so extensive and the ice is so thick on area streams and lakes that it will work against very high temperatures and will not melt all at once in this case," Rodgers said.
Most of the problems will be associated with street, highway and poor drainage area flooding, where storm drains have been blocked by piles of snow.
A few incidents of ice jam flooding cannot be ruled out, but widespread flooding associated with ice breaking up is not expected.

In portions of the Ohio Valley and from West Virginia, Virginia to the lower mid-Atlantic coast, the risk is slightly greater, since temperatures will be higher longer than up north.
While flooding is likely to be minor and sporadic, the warmup and rainfall will bring the risk of roof collapses.
This risk is greatest on flat roofs.
"A deep snow varied by drifting, combined with rainfall, natural melting and blocked drainage systems on the roofs can lead to uneven weight distribution," According to Forensic Weather Expert Steve Wistar, "When this weight exceeds the design of the roof, a partial or total collapse could occur."
Property owners may want to consider removing some of the snow from the roof, only if they can do so safely. If any doubt, consult a properly-insured private contractor.
In some cases, strained roofs that survive the added weight from this week's rain could succumb to additional storms later this season.
Cold air is expected to return in stages this weekend, and additional storms with heavy snow are possible beginning next week. The return of cold air will cause slush and runoff to freeze.
"The lingering snow cover and added moisture from the rainfall and additional snowstorms will carry the flooding forward through the remainder of the winter and perhaps into the spring," Rodgers said.
As of Tuesday, Feb., 18, 2014, there was as much as 6 inches of water locked up in the snow over parts of the Upper Midwest and northern New England. Farther south in the Midwest and Northeast, there was between 1 and 3 inches of water contained within the snow on the ground.

Over a surface area of one square foot, an inch of water (approximately 10 inches of snow on average) weighs about 5.2 pounds. However, the weight of the snow can vary, depending on its water content when it first fell and how much rain it absorbed later.
Steve Wistar is one of the nation's leading experts on roof snow loads.

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