Saturday, May 26, 2012

A tale of two heatbursts

In the Hazardous Weather Testbed we have a ton of data coming in showing all kinds of unique phenomena and yesterdays models had a few strong heatbursts. This was expected given the very strong capping inversion and the likelihood that storms would initiate along the dryline and move into the capped region. As it turned out the storms in Texas/Oklahoma moved North and not Northeasterly thus putting the residents of western OK into jeopardy for Heatbursts. And indeed there quite a few damage reports from the high winds generated by the heatbursts.

The models did a nice job in simulating that dew points would drop to 40 or lower, and temperature would be around 95-100 if they occurred.

Here are two examples, one from Woodward:

And one from Arnett:

The one in Woodward come directly from overhead from the lofting of precipitation particles. As the precipitation likely evaporated, a strong downdraft was created. As this local area of at first cooler air descends, it warms adiabatically and given the initial momentum it eventually reaches the ground as strong winds without rain or cooler temperatures. I am sure the residents of Woodward were none to happy with temperatures climbing back up into the 90's late at night, but at least it wasnt humid as dew points dropped to below 40 for 30 minutes. The whole event lasted nearly 3 hours (the dew point drop and subsequent rise).

The story in Arnett is a bit different. Here the thunderstorms produced, again, no rainfall, but some cooler outflow temperatures probably from the gust front from where it was raining. Winds gusted to above 70 mph from that outflow and the dew point dropped into the 50's. And then the heatburst came and drove temperatures back up to the mid 90's and dew point down below 40.

In both instances it appears that the heatbursts produced the days high temperature at both locations.

Here is a snapshot from a few of the models of the surface temperature field. Note the initial cooling in most of them from the storms after 00 UTC, and then small isolated pockets of much higher temperature within that initially cooler area.

It would appear these hi-res models have a bit of skill in producing these phenomena but you still need to know where the storms will be and predict their motion and demise.