Just like on Monday, Day #2 of the Big Spring Experiment in the NOAA Hazardous Weather Testbed began with a briefing on the day's weather conditions, and the areas that were most likely to become severe. It was not looking like an active day in their belief, with a miniscule tornado threat and low chance of hail, too. However, as the afternoon wore on, we started to see some strong convection (clouds growing tall due to instability) in the mountains of West Virginia. My forecasting partner and I decided to keep an eye on this area, and we used some of the products at our disposal. One of the really cool things we have in the Testbed is visible satellite imagery that updates once per minute. This allows us to see clouds growing and moving in stunning detail. When clouds are moving very fast, the image can look jumpy, but with this type of resolution, the jumpiness is completely gone!
We also used a product called convective initiation. In the picture with this post, the CI are the multicolored blobs. Each color represents a percentage range, and that percentage represents the likelihood of convective cloud development in the region. This can be helpful when you have a whole bunch of clouds and you don't know which ones to focus your attention on. The high-percentage colors can help you spot clouds that could become severe thunderstorms.
As it turned out, the area in red in the Shenandoah Valley was looking particularly volatile in this computer analysis. We continued to watch its progression, and as the CI values fluctuated, the cell began growing and heavy rain fell. A Flash Flood Warning was issued soon after. This tool saw the potential for heavy convection well before the storm intensity grew, but it didn't tell us what the threat would be- wind, rain, hail, etc.
We also tracked the area in yellow, which you see up near the panhandles of West Virginia and Maryland. This is the area that produced several Severe Thunderstorm Warnings on Tuesday afternoon. I saw some reports of quarter-sized hail out of those cells! This computer data helped us pinpoint the areas that we should keep a close eye on, but it didn't help us determine what type of severe threat we might be facing. For the rest of the week, we'll continue to watch how this model handles different types of severe events, and compare it to other data that we have available to see what products give us the best advance warning for dangerous weather.