May 20: Forecast update - One more day

The NAM (ETA) model is one that we haven't been paying much attention to, since it is a shorter-range model that only goes out four days. Well, today our first storm photography day (Tuesday) is in the NAM's window, and it looks very good. What's better, the NAM's forecast is in agreement with the GFS for Tuesday, and Tuesday is looking like a possible banner storm photography day if the models verify. Lots of upper level energy overspreading strong instability and moisture at the surface, good directional shear (wind direction turning with height) with backed winds at the surface. A classic tornado setup if it comes to pass.

The problems for the upcoming week could be the 'cap' (capping inversion). The 'cap' is a layer of warm air above the surface that suppresses convection/bouyancy of the surface air. The cap can be a good thing or a bad thing. We need *some* of a cap to keep storms from going up everywhere. Too many storms contaminate each other, and usually prevents any individual storm from organizing. However, too much of a cap and no storms will form at all - a 'clear sky bust'. If the cap is just the right strength, it will let a only few storms go up that will stay isolated, allowing them to feed off of the avialable energy sources without 'competition' from other storms close by. The models seem to be showing high cap strengths for next week, which would tend to mean storms might have trouble forming on some days. But if convection can start, the storms that do form will be isolated monsters!

After Wednesday, the bulk of the upper level energy shifts away temporarily, but good moisture and instability remains at the surface. Wednesday-Friday of next week could either be 'down days' or possible storm photography days if there is enough energy to break the capping inversion. Too soon to tell.

Memorial Day Weekend through next Tuesday looks very good on the GFS, with a big western trough moving into the Plains. Of course, that is too far away to get excited about, but the gist is that the patterns seem to be moving along nicely and not stagnating like they were the past 2 weeks. This means that even though we might get a few 'down days' with little activity, the inactive patterns will move out quickly to make way for the next active setup.

So, the Monday departure is still on, Lord willing and barring any drastic short-range model changes. Monday is the 'long haul' trip to get to the Plains from West Virginia (12 to 16 hours of driving). David's train arrives here in Charleston tomorrow morning, and we'll probably go ahead and leave as soon as Matt arrives from Raleigh on Sunday night, stopping somewhere between Lexington and Louisville for the night. This gets us a couple of hours' jump just in case our Tuesday target is far away, like in Colorado or South Dakota. If our target ends up being closer, then that will give us some breathing room for Monday night-Tuesday morning.

Based on the current outlook, this probability table charts the chance of our trip starting on a particular date:

2006 Storm Photography Expedition - Departure Date Probability as of May 20

May 20

May 21-27

98%

May 28-June 4

No trip