Forecast 05/22/12

Well, we will be singing our swan song for Tropical Storm Alberto. Wind shear has been displacing the convection away from the warm core surface low and the upper level component has detached from the surface low. This storm is on its way out the door and the surface low will soon lose its identity. Lets have a moment of silence for this storm.

Water vapor imagery from CIMSS.

So what's the swirl over Alabama/Georgia? That is actually the soon to be upper level low, forming at the base of the trough.

Palmer Drought Index (from U.S. Drought Monitor).

Let the rainfall commence...well, not really. We do not need anymore rainfall. In fact, the High Country and the immediate surrounding regions are completely out of drought conditions. The rainfall is more welcome farther south, which has been relatively dry except for sporadic thunderstorms. While the High Country has gotten both steady rain events and short "burst" convective thunderstorms, areas farther south have gotten just the latter. That's not a good thing when all of the water runs off before the soil has sufficient time to absorb the water!

Convective Available Potential Energy (CAPE) for tomorrow afternoon (from twisterdata.com)

As expected, thunderstorms peaked early today and remained semi-stationary over the mountains, aggravating the already rain soaked regions. Today is the peak day for thunderstorms this week. Tomorrow thunderstorms and showers will still be present in the afternoon but the spatial coverage will be slightly less than today. I think the proximity of the front (just east of the Blue Ridge) will keep showers nearby. In this very broad trough (in the southern storm track) we will have a weak upper level low form tomorrow. The next few maps are from www.weather.unisys.com.

300mb winds for tonight. The trough in the southern jet stream is in its peak phase

Tomorrow 300mb level (winds). Notice the trough has become more broad, with an upper level low over the Mid-Atlantic and another zone of vorticity over the Gulf.

This upper level segment of the trough (image above) for tomorrow, along with the proximity of the stationary front (just east of the Blue Ridge) will again fire up showers and thunderstorms in the afternoon. Again I think the rain chances will be high (higher than 50%) but the areal coverage of rainfall will be lower (not as much green covering the weather map).

Thursday 300mb winds.

Notice on Thursday that the upper level portion that was over us Wednesday has degenerated. We will look at a lower level to show this. The heaviest precipitation will be across Florida. Sporadic showers will still be around our area.

Thursday 500mb level VORTICITY map. This is not a wind map, but a map that shows absolute spin in the atmosphere.

Question that may get asked: Why is this map disproportionately covered in positive values?
Answer: Absolute vorticity = relative spin + planetary spin. The farther north one goes, the greater the planetary spin effects weather systems. This is the same reason why we do not get tropical cyclones forming along the equator. Tropical cyclones need some input from planetary spin (coriolis).

See the yellow off the coast of New Jersey? This is what is left of the upper level low that will be over the area tomorrow. Shower chances decrease to a moderate level on Thursday. The trough quickly accelerates away from the Southeast coast, giving us clear weather on Friday - Sunday, as a ridge builds to our southwest. It will be VERY warm this weekend, however I think the hottest weather will be to our west.

I blame Pete Soule (professor at Appalachian State) for my frequent use of weather.unisys. This site is run by several guys over at Purdue and in terms of making weather map products that are easy for the common person to read, this is it. We will save the more complex variables for another day!