Joe Lundberg

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Record Rains in the Northeast; Tracking a Wet Disturbance from Arizona to the Midwest

August 13, 2014; 11:29 AM ET

Wednesday, 11:59 a.m.

There are rains, and then there are rains. I had rain and thunder on and off in my back yard yesterday afternoon then again for a time last night. So did much of the mid-Atlantic region. And some of the rain was exceptional, like over 6 inches around Baltimore and over 2 inches in Wilmington, Delaware. The 3.40 inches in Williamsport, Pennsylvania, set a new daily rainfall record, as was the 2.55 inches in Harrisburg.

That's a lot of rain in 24 hours, and it did cause some flooding, but all of that pales in comparison to the torrent of rain that literally inundated Islip, New York, late last night and this morning. The grand rainfall total was a stunning 13.26 inches at Macarthur Airport, with over 10 inches of that falling in three hours this morning heading into the morning rush hour. That total obliterated the old daily rainfall record for Islip, but it also appears to have eclipsed the New York state rainfall record of 11.6 inches in Tannersville, set on Aug. 27-28, 2011, during Hurricane/Tropical Storm Irene.

These tropical downpours came courtesy of the upper-level low we've been talking about this week, still in the process of forming over southwestern Quebec. It managed to draw high dew point air northward into the eastern Ohio Valley and mid-Atlantic region, effectively pushing a warm front into the region. Clusters of rain and thunderstorms developed along this boundary and moved downstream to the east and northeast, but some locations were hit multiple times.

In the case of Islip, a band of rain set up over them early this morning and barely moved, dumping heavy rain on them for several hours before finally moving on by midmorning. Here's a look at the radar estimated storm total precipitation to this hour:

This area of heavy rain is now soaking New England ahead of a slow-moving cold front, and that's going to mean areas of flooding this afternoon into tonight before the rain exits from south-southwest to north-northeast across the region.

I mentioned in Tuesday's post about an upper-level low rolling through the Northwest, and that some of the moisture tied to it will be pulled from the Southwest into the upper-level storm's circulation. That feature is a separate entity unto itself. Look at the latest visible satellite imagery:

Combine that with 500mb forecast for this evening:

This upper-level disturbance will track around the upper-level ridge positioned over the eastern Rockies and western Plains, where it will be relatively hot this afternoon and again tomorrow. As this feature moves north-northeastward, and then crosses the northern Rockies toward the northern Plains, it will pull a lot of moisture up from the Southwest, and that's going to mean numerous showers and thunderstorms along the way, and the potential for locally severe weather and flash flooding.

By Friday, this disturbance will come out of the northern Rockies and cross the Plains. The bulk of the rain and thunderstorms associated with it will be north of any weak surface low pressure area, helping to tamp down the temperatures from Montana through the northern Plains, then into the Midwest Friday night, then the Great Lakes and Ohio Valley Saturday into Saturday night. The mid-Atlantic states and parts of New England Sunday. The bad news is that the rain can be heavy in many places, and it will wipe out at least one of the days of the weekend. On the other hand, the good news is that none of the rain will be as excessive as it was over parts of the mid-Atlantic and southern New England in the past 24 hours.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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Joe Lundberg
Joe Lundberg, a veteran AccuWeather.com forecaster and meteorologist, covers both short and long-term U.S. weather on this blog.