A Pretty Good Fight

I get irritated when television meteorologists dumb-down the elegant complexity of atmospheric processes and tell viewers about "clashing air masses," and "battles between warm, humid air and cold dry air." I also get irritated when they wax idiotic about climate change (see here too), but that's a topic for a day when I have given up coffee.

So what gives...me using battle metaphors?

As of this writing, the TC area and much of the surrounding region is in a drought:




It's worth noting, too, that the many of the non-drought areas have been pretty wet (though the drought area is expanding slowly):

And this weekend, our established drought is in for its first real challenge of the 2009 warm season, as a sloppy weather system attempts to squeeze out big-time rains, right over Drought Territory. That's the fight. You can go to sleep now.

If you are still awake though, the always-loved and always-trusty models have been fairly consistent, in their subtly morphing way, about advertising significant rains this weekend. As of the evening model runs (Thursday evening), here is what the GFS model, which can get carried away, is depicting:




And here is the five-day total precipitation forecast from the Hydrometeorological Prediction Center, just to show what real forecasters are thinking:



Both of these forecasts (that is, in the heads of forecasters, and also in non-heads of the computer models) put a significant dent in the drought. In order to end the drought, we would need a thorough breaking of the pattern that has been in place for several months, and it's a bit early to call for that. But, 1-2 inches of rain would put water into the ground and into the soil, and some of that water would be available for the next system, making precipitation production at least a little bit easier.

Right now though, I would encourage readers to hold off on those "Yay, the Drought is Over!" parties that you may have (or almost certainly have not) been planning. While this system is the best-yet candidate to take the drought down, a few things make me suspicious. First, the GFS is clearly suffering from some "gridscale feedback," meaning basically, that it is inventing small features that produce small pockets of intense precipitation. This might be artificially balanced by the fact that the same model will generally under-forecast precipitation associated with thunderstorms, which operate on scales too fine for it to resolve.

I am also suspicious about the placement of the precipitation. The warmest, most humid air will be to our south, in Iowa, and while the conditions do support "overrunning" precipitation, which is found on the cooler side of the warm front (where we should be), I tend to think that storms are going to build towards the higher energy content of the warmer, more humid air...even if that means just barely being on the warm side of the warm front. Thus, I am concerned that the models might be driving the heaviest rains a bit too far north.

Lastly, any intense storms that do form in or very near the warm sector, will detract from moisture streaming to the north, and thus, would reduce--perhaps dramatically--the amount of rainfall we receive.

This will be interesting to follow, at least for me. I don't know if we should consider this weekend event a fight, or just the first round of a fight. If MSP ends up with a half-inch of rain or less between Saturday and Monday night, then I think we'll know this drought means business (has a tough chin, sticking with the fight theme). A half-inch, while potentially valuable, would be a real disappointment considering what this system has going for it (namely a good feed of moisture and a hang-around-the-region, slacker-ish attitude) On the other hand, if the event evolves as advertised, then the whole area would get a good soaking, indicating that the drought can be beaten, and soon (or that it had been wobbled...again, sticking with the fight theme).


As always, we shall see.