05/21/12 Forecast

Hey everyone! Let me start by saying this: we have more low pressure centers across the Southeast than Starbucks has coffee sizes. Lets start with a water vapor image.

And below is a fixed image with the centers located. This image comes from CIMSS Tropical Cyclone analysis page (along with the above animation).

All four low pressure systems are entirely different.
Low #1 (over Tennessee/Kentucky) is a frontal low associated with a building trough in the northern branch of the jet stream. This low is forming in the zone most favorable, which is slightly downstream of the trough axis.
Low #2 (near Virginia) is responding to a mid-level disturbance (from a very broad trough)
Low #3 (over Atlantic, east of the SC coast) is a frontal low associated with a trough in the southern branch of the jet stream.
Low #4 is a warm core tropical low, also known as Tropical Storm Alberto

So no wonder we have that continuing shower threat for this week! What do we have lined up for this week.

Today - thunderstorms will pop up rapidly this afternoon and evening. Weak winds even high aloft will limit damaging winds and storm longevity. The outflow from these storms are likely to fire up new storms nearby. Expect heavy rain and some hail today.

Tuesday - Wednesday - amplified split of the storm track (northern branch vs southern branch). We won't be seeing the northern branch very often this summer but the southern branch (subtropical jet) will be a nuisance for us this summer. This is typical for a neutral ENSO or an El Nino summer. A stronger subtropical jet brings more frequent southern tracking (weaker) storm systems to our area. This somewhat diminishes the chance of a powerhouse ridge forming over our area.

Upper level vorticity for Tuesday afternoon (from weather.unisys)

I don't see this upcoming cold front making it very far past the Blue Ridge before it stalls. This keeps rainfall nearby for Tuesday and Wednesday, but does put the High Country in a slightly more stable air mass. This means severe thunderstorms less likely. The building trough will accelerate the tropical storm away from the coast and lead to its demise.

Thursday - the strengthening trough in the northern jet "pinches" off the trough in the southern branch. This will leave behind a weak, broad upper level low for Thursday, which keeps showers in our area. The GFS has the upper level low being too strong but at least is on the right track of the areas of precipitation. We will just have some scattered showers then.

Friday - A ridge behind the southern branch of the jet stream will make it mostly clear and dry. There may be isolated showers along the coast due to a synoptic reinforced onshore flow. This won't be around Saturday. The ridge will force the southern branch far south of our area and will be weaker, thus keeping the weather drier for the weekend. It will be WARM this weekend