NE Flooding: I`ve Got Good News and Bad News...

(MARCH 12, 2010)

UPDATE: A lot more "major flooding" forecasts have popped up in Maryland and "Moderates" are stretching across New Jersey onto Long Island now.

The impact and severity of flooding in the Northeast (caused by a combination of heavy rain and snow melt) is still in question this morning. Here are a couple tidbits brought up in our morning News Team meeting here at AccuWeather. For more information on the threat for your area, consult our news story. And remember: Street & stream flooding will come first tonight and Saturday; river flooding will come later -- Sunday or Monday.

THE GOOD NEWS:

The good news is: It may snow. I know, this may be bad news for those who are tired of snow this winter, but it will be good news meteorologically because snow won't run down the mountains and will stop further snow melt from happening. The latest run of the GFS computer forecast model says that snow, not rain, will fall in the higher elevations of Pennsylvania & New York Sunday morning during the latter part of the storm. This won't completely stop the flooding because there will be heavy rain and some snow melt in advance of that, but it could cut down on the severity of it.

The NMM model disagrees with this, saying that all the heavy precipitation will fall as rain, and will end before Sunday morning. Joe Bastardi says:

Another piece of good news is that the highest rain amounts will fall east of the location of the highest snow cover in southwest Pennsylvania.

THE BAD NEWS:

The bad news is twofold. One, the government (NWS) has increased the area covered by Flood Advisories (shown in green below) today, which means they are more worried than they were yesterday. (UPDATE: They have issued even more and I have updated the image below (original here). You can get a real-time version of this image on AccuWeather.com MapSpace.

They have also considerably raised their River Flood forecasts. Yesterday morning they were projecting the Conemaugh River @ Seward, PA to be about 11 feet. Yesterday afternoon, as I reported in J's Breaking Weather News" (see below) they raised that to 16 feet. That is significant because that changes it from "below flood stage" past "moderate flood stage" to over "major flood stage." According to the stats on that page, that would make it the highest that it has been since 1996! (Another piece of good news: As you can see from the graph, it is not as high as expected this morning).

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Several other rivers are projected to be over major flood stage this weekend as well, though none are as historically significant as Seward. Seward is next to Johnstown, home to three major floods including one in 1936 that was also caused by (a lot more) heavy rain and snow melt.

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