2/28/09 Forecast: AL GA SC FL

[Andrew Butler]

Can't believe no one has started one for tomorrow so I will take the plunge. Being really weak at this I'll rely on others to add expertise.

Set up to me is reminiscent of 2/18. As usual this time of year, moisture return/clearing is key so the threat seems very conditional. Nevertheless, if things get going I can see a repeat of last week. Very strong helicity values will be in place across northeast Georgia. Looks to be a daytime event for any discrete stuff.

Please elaborate on my weak forecast.

 

[Paul Austin]

Yeah, I was debating starting a thread, but I couldn't add much to what SPC had already put out in its forecast.

Pros: Td's in the mid 50's to mid 60's already from central MS to AL. Today's lack of cloud cover south of the convective cluster is promising for tomorrow. With some decent daytime sunshine and strong (30-40kts @ 925mb) continued return flow, I'd say instability will not be a problem with potential SBCAPE AOA 1500 J/Kg over southern AL/GA. The sfc low should deepen and track across MS/AL/GA providing some forcing and enhanced sfc convergence. Also, lapse rates should steepen a bit at least in the mid levels with the developing low. If the trough can become a little more neutral-tilt before exiting the SE, a little backing of sfc winds from SW to a more SSW or S direction would help in developing low-level shear. The low itself should provide vorticity to the mix. Upper air dynamics also appear favorable for storm rotation with modestly large clockwise curved hodographs. And the approaching jet max appears to hint at a split or spreading leading edge, developing lift from divergence. Perhaps the overnight convection will result in a quasi-stationary E/W boundary focusing higher helicity values over building instability (more or less a hopeful speculation )

Cons: Conditional nature of return moisture and cloud cover. It's hard to predict exactly how today's convection will affect tomorrow's setup. How far south will the MCS develop overnight? How worked-over will the air become? How much cloud cover will be left to burn off? Will sfc winds back much with approaching trough/low? As with the 2/18 system, will it matter much? Of course, any comparison to last week's system would be incomplete without acknowledging the slightly weaker H3/H5 wind flow. Also, with SE systems typically sporting veered sfc wind profiles and at least semi-uni-directional vertical profiles, Any dicreet cell development often develops toward a more linear/bowing line segment/LEWP mode with time.

I will probably be chasing this setup and hoping for some discreet/semi-discreet action from southeast AL to the west central GA area.