Heavy rain threat continues

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Thunderstorms with torrential downpours raked parts of Virginia on Sunday, dumping over three inches of rain in some areas in a short amount of time.  Flooding was reported throughout our viewing area as storm drains could not keep up with the rate and intensity of rainfall.

The threat of heavy storms will continue through mid-week as the remnants of Isaac slowly move through the area.  This area of low pressure is sitting over southwestern Indiana on Monday afternoon.  It continues to send little “spokes” of energy at us.  With high moisture and some instability in place, when those waves of energy enter the area, thunderstorms are able to erupt.

Ahead of Issac, humidity and dew point levels remain quite high and tropical.  Dew point values are quite muggy when they reach 70, and some dew points (both on Sunday & Monday) reached the low and mid 70s in some areas.

We also look at how saturated the column of air is from just above ground level up through a few miles above the surface.  This plot of atmospheric moisture indicates where the air is loaded with heavy moisture.  Note the area of dark green across central Virginia surrounding the I-95 corridor.

When a strong shower or thunderstorm taps into this muggy air, it is similar to wringing out a saturated sponge.  Downpours that can exceed an inch in less than 15 minutes can occur.

The set-up will not change much the next few days, but should break down when a front passes on Thursday.  Until then, localized flood-inducing rainfall will remain a threat.

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