Significant Rainfall Potential for North GA: 5/4-5/6

If you haven’t had enough of the cloudy, cool, rainy conditions we’ve had here lately, then you are in luck, because there’s plenty more on the way.

Earlier today, the NWS issued a hydrological statement due to flooding concerns this weekend, so lets take a look at what is on the way.

First, here is the current 500mb (way up in the atmosphere):

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As you can see, there is a powerful shortwave (the dip in the height lines) moving through the center of the country right now. This shortwave is expected to develop into a very stout, detached upper level low, as seen on the map below valid tomorrow afternoon.

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By the time this weekend rolls around, this low will deepen considerably and track right across Northern Georgia.

2AM Monday morning:

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This upper level low is expected to bring significant amounts of rain to the area through the first of next week. This will be thanks in part to an excellent feed of moisture from the Atlantic as is evident on this 700mb humidity valid 2AM Monday morning.

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This excellent moisture feed, along with the lift associated with the ULL and orographic lifting (moist air moving up mountains and getting squeezed out as rain due to cooling, same reason we get flurries in the winter), will lead to plenty of precipitation this weekend.

This is the forecast rainfall totals from the 18z GFS:

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As you can see, this run indicates a widespread 2-3″ across the entire area, and previous runs have been closer to the 3-4″ range. Ultimately, the track of the low will have an impact on exactly how much we get, but I expect to see a minimum of 2″ for everyone, and given the favorable moisture trajectory and low track, I wouldn’t be surprised to see some areas, especially the south/southeast facing slopes around Dahlonega/Cleveland/Cornelia/Dawsonville/Gainesville, see 3-5″ this weekend. Some areas of the NC/TN mountains could see much, much more.

Severe potential will also have to be watched with this ULL. as the GFS has been developing an area of increased lift on the northern side of the low.

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These types of lows are notorious for all types of weird weather, including low-topped (low cloud heights) severe storms that produce graupel, hail, and the occasional weak tornado. Potential for all of these will have to be watched closely as the models resolve the exact path.

And so, the forecast for the next several days is not particularly nice nor simple, but I will be monitoring the approach of this front closely and will keep you alert to all threats from the flooding to hail.

~TW 5-2-13

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