Second round of storms possible 

Posted: 11:10 am Saturday, July 21st, 2018

By Kirk Mellish

After a lot of predawn and post sunrise action with the MCS (Mesoscale Convective System) squall line a more stable air mass is left behind in the wake of the morning storms which moved to South Georgia. “Convective” refers to thunderstorms.

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Surface based thermodynamics show the high CIN (convective inhibition) factor in blue shades over North Georgia with the higher CAPE (convective available potential energy) red lines in South Georgia and Alabama, CIN is a negative for storms CAPE is a positive:

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Daytime heating from solar energy and transport (advection) by wind flow will both serve to slowly destabilize the atmosphere during the afternoon as the air mass “recovers” from being “worked over” (cooled and stabilized and temporarily slightly drier).

However, the air mass is unlikely to be as unstable as it would have been late today had the morning storms not rolled through. This changes the area of greatest severe weather threat from this:

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TO THIS:

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[EDIT:] AFTERNOON UPDATED TO THIS NOW:

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But any storms that do pop around Metro Atlanta late in the day will still pack a punch! However the tornado risk is LOW but hail or damaging straight-line winds still a possibility in a few storms.

Rather than a squall line like this morning any that pop will be less organized and more cellular in nature. (At least that’s the current thinking). Whether that happens and how scattered or numerous they will be will depend on just how much the air mass can recover before sunset. Sometimes they never recover.

I point out over and over that thunderstorm forecasting is not like forecasting other types of weather and thus sometimes require updates every few hours.

[EDIT:] Since the morning blog post there has been an update, here’s SPC thinking:

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The approaching front trailing from low pressure over northern Indiana is still to our Northwest heading to the Southeast:

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AFTERNOON RAINFALL ESTIMATE:

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TONIGHT RAINFALL ESTIMATE:

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AFTERNOON AND EARLY EVENING THUNDERSTORM OUTLOOK:

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OVERNIGHT:

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Go about your weekend plans, but unlike some folks in Branson, Missouri be weather aware, be able to receive warnings, and keep an eye on the sky.  No reason for needless tragedy in the information age.

See previous blog post on this unusual weather pattern and if it will last.

I now return to my rare scheduled weekend off.

Follow me on Twitter @MellishMeterWSB.

 

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