The Worst of the Rain is Over
By Erica Grow on July 28, 2012, 9:20pm
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The heaviest rain has moved out of Connecticut into the Atlantic Ocean, but we're not completely out of the woods yet. As you can see on the map above, an area of low pressure is situated right over Philadelphia, and the counterclockwise rotation around the center is keeping low clouds and drizzle in place. High pressure will come in from the Great Lakes region, replacing today's clouds and rain with sunshine by Monday. But what about tomorrow? What happens during this transition period between low and high pressure?
The low pressure on the map is in association with a shortwave trough, which is a smaller feature embedded in a larger trough. Shortwaves usually have small concentrations of high energy, which leads to rain and thunderstorms. This particular shortwave is progged to move out very slowly, so we'll still be feeling its effects on Sunday. All 3 models I looked at (NAM, GFS, and Euro) show the shortwave trough very clearly defined, moving from upstate NY into the open ocean water by 12Z Monday. But in the meantime, the vorticity maxima in the shortwave will provide an extra spark of energy for the lingering moisture from today's rain and plenty of 700mb moisture, too. I expect that we'll see another round of showers with some rumbles of thunder tomorrow afternoon into the early evening, but it won't rain as hard as it did today, because the bulk of the upper-level moisture has moved out to sea. These systems tend to carry their heaviest rainfall bands in front of the vorticity maximum, and I see no reason why tomorrow would be different.
The temperature profile on Sunday looks pretty stable; a look at a skew-T prog for tomorrow around noon shows that the temperature drops very slowly (less than moist adiabatic) all the way up to 700mb, which is typically viewed as the "cloud layer". So while it will be cloudy for a good chunk of the day tomorrow, the other affect of those clouds will be stable conditions that are not conducive to convection. Thunderstorms will be widely scattered tomorrow, instead of forming in a a strong line like the storms we had today.
The good news, of course, with the wet weather is that we are eating away at our rainfall deficit. I believe by the end of the week the entire state will be out of drought conditions, and we will be pretty close to normal rainfall totals, year-to-date.
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