The visible satellite image from around 26,000 miles in space shows yet another Mesoscale Convective System (MCS) to our West at sunrise today heading in this direction, the radar presentation below:
These MCS usually “peter out” before reaching us (because they leave their source generator behind as they move East away from it and enter different more stable air mass).
But importantly, they also send out an “outflow boundary” ahead of them. Plus thunderstorms in our area yesterday will have left some “outflow boundaries” in our area. Think of these as ‘mini-cold fronts’ which often are invisible to our data net until mid day or late afternoon.
New thunderstorms often form along these old outflow boundaries. Yet at other times the ‘cold pool of air’ behind an outflow boundary can stabilize the atmosphere and prevent storm development. So you can see these patterns are tricky sons of guns.
For this reason it’s not unusual for the thunderstorm odds to end up much higher OR much lower than expected the day before or even at the start of the day compared to reality.
Frequently at the end of the day a cluster or line of storms will become concentrated in one area where all the “outflow boundaries” end up, leaving the rest of the area high and dry. I’ve seen that the past three days across the Northern two-thirds of Georgia.
I expect today will have plenty of dry hours before and after any thunderstorm even if you do get one. Some places can get hit hard or twice while another place nearby gets brushed by a light shower or doesn’t get a drop. NOT every thunderstorm will be severe!
The Storm Prediction Center (SPC) is putting us in the STANDARD risk for storms with damaging winds and hail with a RISK LEVEL OF 2/5:
So with a potentially unstable air mass in the heat and humidity of the afternoon we can expect scattered showers and storms to pick up and a few may be heavy or severe, but like the past three days some places can get pounded and others don’t get a drop.
Here’s a radar estimate of thunderstorms yesterday and last night:
I’ve pointed out hundreds of times in the past on the radio and in blogs that UNLIKE other forecasts, SOME types of THUNDERSTORM FORECASTS must be updated every 2-4 hours. Because of the mixed plus and minus factors I explained in the text above.
The type of thunderstorm forecast that does NOT have to be updated every two hours or show are the types that involve a specific well-developed “synoptic-scale” front or upper-level disturbance.
Then it looks like a little less humid and a little more stable air mass tomorrow and Wednesday so MOST of us will stay hot but storm-free on these days.
After that the typical summertime Atlanta pattern of hot and humid with scattered afternoon or evening thunderstorms and a mix of sun and clouds resumes Thursday through next weekend and probably into early July.
For more Follow me on Twitter @MellishMeterWSB and on the radio at WSB AM750 and 955FM, or download the WSBRADIO APP here.