I had advertised a Cold Air Damming setting up across portions of the southeast. That didn't really happen. Yes, we did see some cool and cloudy mornings, but we saw partly to mostly cloudy skies in the afternoon allowing us to get into the middle 80s Friday and Saturday. Here's the current situation from space this morning:
There's a pretty good layer of cloud cover over most of Georgia, extending into east central Alabama. This has been the view the past few mornings, but the clouds haven't been thick enough to hold up with the heating of the day. You may ask yourself, what heating? There's a ton of clouds, there's no heating! Au contraire fellow reader. The atmosphere extends miles into the sky. Here's a view of the soundings to illustrate the points I'm about to make:
Peachtree City, GA 12Z Sounding from this morning:
The green, dew point, and red, temperature, lines are very close together near the surface. That's the cloud deck we are seeing across much of Georgia! Now, here's the 00Z Sounding from last night (technically today but I'll say last night since it was from 8PM Sept. 17, 2011 ;))
There's the same inversion, where the red line starts going back to the right as you go up, near the same pressure level, but notice the temperature line near the surface is WAY right of the dew point line. This is why we didn't see much cloud cover yesterday afternoon. The atmosphere mixed itself out bringing slightly drier air from aloft. Another reason the NWS pointed out was the absence of confluence, where air flows inward toward an axis parallel to the general direction of flow. We've had zonal flow, west to east winds, aloft, meaning the atmosphere had a chance to mix itself out and dissipate the clouds.
That's a look back at the weekend, but what about the upcoming work week? Well, Monday appears mostly dry with the better rain chances to our west. The rain will likely move in sometime Tuesday and be off and on through Friday. Here's the model output in a nice graph for you:
The NAM, which only goes through Wednesday afternoon, or 84 hours, has the rain moving in early Tuesday morning. I feel it brings it in a TAD early and will forecast better rain chances by early afternoon Tuesday. As we look at the GFS, it gives us almost 1.5 through Friday night/Saturday morning. This appears plausible, the good rain chances that is, with a cut-off low developing over the Ohio River Valley. A cut-off low just means it's not in the jetstream anymore and got left behind. Here's a picture of what I'm talking about:
The low just sits over the state of Illinois for a day or so before being nudged to the northeast by the end of the week. It should be noted that a quick glance at the 06Z GFS has the cut-off low a little further to the northeast. Overall, I don't think we'll get as much rain as the GFS is putting out, but somewhere between 0.5" to 1.0". Of course, there could be locally heavier amounts in thunderstorms, but that's just a generalization for the area.
It will be interesting to see all of this develop the next few days. As always, I'll keep you updated with my latest thoughts!
Thank you,
David Reese
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