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Low risk of flash flooding for Saturday, July 23

July 23, 2011

A significant thunderstorm continues to generate prolific lightning and rainfall totals at this time. Although convection is weakening behind this system, it is possible that 2-3″ of rain may fall in the 24-hour period ending 7:00 AM. The Hydrometeorological Prediction Center has placed the area in a moderate Update 9:51a: low risk (5% chance) of flash flooding for today.

More concerning is that this convection is expected to repeat, with 1-3″ of rain falling this afternoon and tonight. This would bring the total rainfall amounts up to 3-6″, and may cause street closures. Higher amounts would bring worse damage.

Although we have not had meaningful rain for 16 days prior to tonight’s storms, the amounts noted are significantly more than the ground is able to handle at once, particularly with rainfall rates occasionally exceeding 3″ / hour (for durations of less than an hour). This will result in excessive runoff, and resultant flash flooding.

Precipitation totals will be posted here as the rain is measured.

Update 2:54a: Storm totals are as follows: Since 9:00a, 0.84″. 2:05a-2:45a, 2.36″. 24-hour storm total, 3.20″. This is (should be) sufficient to bring the creek above bankfull.

An additional 0.50″ is possible in the next hour. An additional 1″ is possible around 6:00a. The HPC is forecasting an additional 1-2″ this afternoon, but with low confidence, as storms may fire on the southern periphery of this current system, as opposed to in our area.

Update 9:51a: The 24 hour storm total as of 9:00a was 3.48″ of rain. This is not enough to cause flooding issues, although Lake George is full and the creek is a few inches above bankfull. Another couple of inches are expect before the end of the day, which would aggravate these conditions. Due to uncertainty regarding where the heaviest rain will fall, the HPC has downgraded today’s flash flooding possibilities to “low” from “moderate”.

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