Gaston- the storm, not the lake.

Most folks around here get nervous when they hear the term "hurricane". Rightly so after Isabell. I think from now on they will get nervous when they hear the term "tropical". Being somewhat of an amateur student of meteorolgy, I offer my explanation of what happened. One of my favorite weather sites is the Storm Prediction Center in Norman, OK. They are the agency responsible for issuing hazardous weather outlooks and warnings. Their site is very educational. Anyway, one of the factors that they look at when determining T-storm or tornadic activity is "convective available potential energy" or CAPE. Their definition:

Surface-Based CAPE/CIN (J/kg)

SBCAPE (Surface-Based Convective Available Potential Energy) is a measure of instability in the troposphere. This value represents the total amount of potential energy available to a parcel of air originating at the surface and being lifted to its level of free convection (LFC). No parcel entrainment is considered. The CAPE calculation uses virtual temperatures, but the CIN value does not. SPC forecasters have noted that non-virtual CIN calculations tend to define areas of weak cap more accurately than if the virtual temperature was considered.

CIN (Convective INhibition) represents the "negative" area on a sounding that must be overcome before storm initiation can occur.

This is what the local tv weather man is talking about when they mention "lift" in the atmosphere. Back to what happened. The CAPE levels that day were very high due to a cold front moving in from the west. Colder air is heavier and rolls in under the warm air, thereby generating lift.The couple of hours of sunshine we had added to the lift since warm air rises. Now here comes Gaston, a tropical spinning low pressure area. Its spinning motion pushed it fairly quickly across Carolina since CAPE levels there were relatively low. Now all of a sudden it hits all of this lift. The warm moist air rises and as it does, precipitation is enhanced and its motion is stalled. Tornadoes break out. Rain becomes deluge. 10-14" across the Richmond Metro area. So that's my explanation. Who knows, maybe a real meterologist will read this blog and tell me I'm full of crap. If you haven't seen the pictures, Times Dispatch has a slide show. A very weird event, one that I hope doesn't happen again.