We are in a new weather pattern now called a “NW flow regime”. (side note: my Senior Thesis included this as part of a wider paper on severe weather)
The above chart is the model forecast 500mb jet stream level with “vorticity” shaded depicting upper level disturbances in the wind flow valid Tuesday August 6th 2pm.
It’s not the worst pattern in the world to be in for this part of the country, especially considering the alternative is usually a Great Smokies heat wave pattern with stagnant air and highs 95-100.
In NW flow aloft the general chance of thunderstorms is usually less than most other summertime weather patterns, not zero but quieter.
It usually also results in a little less humid weather at least for a few days before the air mass modifies and upper level heights slowly recover to more typical levels. It sometimes will allow for good penetration of a cold front more to the South than is typical, something we saw happen recently. But before and after such fronts you get at least normal heat or above-normal heat especially in the Southeast where downslope compressional heating is added as the air comes down over the Appalachians.
This happens as the center of upper level high pressure and the core of heat shifts to the West or “4 corners” area, the counterclockwise flow around that high pressure ridge in the jet stream places our region along with much of the Midwest, NE and Mid-Atlantic in NW flow aloft.
The bugaboo in this type weather pattern are what are known as “short-waves” bits of swirling energy within the long-wave jet stream flow and/or cold pools of air aloft. They are tricky to time, especially the small ones, and small ones may go undetected. The large ones are fairly easy to detect and time.
The relevance of this? MCCs or MCS (unique thunderstorm clusters) often can be sparked in the NW Flow Aloft aka “the ring of fire”. The worst of this usually occurs to the West and North of Georgia but sometimes we get in on it, too.
They can bring flooding, severe storms, Derechos (special thunderstorm wind type) and occasionally a rare summer day thats cloudy cool and showery.
Here’s an example I Tweeted last week of what an MCC/MCS looks like on Satellite:
So while most days will be largely dry with just a stray thunderstorm or two, if one of these upper-level disturbances comes along, and if it’s strong enough it can really change things. You can end up with an MCS unexpected surprise anytime of the day or night. Models typically do not handle these well.
But getting the timing and location of those correct much in advance is hard, unless they are large.
We may get a front to move through by Monday but without much effect, with another chance of a cold front by mid-month.
SEE the pattern evolve slowly over the next 10-days or so. Keep in mind the maps below do NOT show possible upper-air disturbances just the jet wind flow pattern (parallel to the black lines). Blue shading shows cooler than normal at that level and yellow-orange warmer than normal at that level, white is near-normal:
PROTIP: The 588mb line is a rule of thumb for a high of at least 90F.
The Atlanta NWSFO forecast discussion from yesterday afternoon laid it out nicely:
I’ll update my forecast as needed through the week so stay tuned for last minute updates and specific daily forecasts and my 5-day forecast on 95.5 WSB on all platforms.