Sunday, 27 May 2012

Sunday thoughts

Only 3 chase days left to go now, and it looks like each will bring the potential for severe weather, so at least there is plenty to keep us occupied as we start to draw the trip to a close. However, let's not think about leaving yet as there are still 3 days to go!

Today, a cold front will move from the NW into central Nebraska and Kansas, as a powerful upper trough works in from the west. Strong southerly flow ahead of this is transporting reasonable moisture northwards although still not as high as one might expect at this time of year. Even so, with favourable kinematics and thermodynamics in place, another round of severe thunderstorms is expected. The main threat today, given strong instability and wind shear, is very large hail, perhaps 4 inches. Thus, today is not a day to get overtaken by the core, or have to approach the mesocyclone from the north or west!

The risk area is large, as you would expect from a frontal boundary. The tornado risk is low overall but one location which might be able to produce is extreme south central Nebraska into north central Kansas, where a surface low pressure area is progged to develop by early evening by several models, close to the cold front/dryline intersection. Cloud bases will be high during the afternoon due to the large temperature/dewpoint spreads, but cooling during the early evening, along with the increase of the low-level jet may be enough to get a couple of tornadoes going. Also, storms will modify the environment by producing cooler outflow, and sometimes other storms can ingest some of this air and have lower cloud bases.

As we're starting in Hays, and need to be in Oklahoma tomorrow for a severe threat there, we don't want to be heading way north. I don't think we'll have to go too far north, though, given my thoughts above.

A Norton - Smith Centre - Russell - WaKeeney square would be a good starting point, so until further analysis of both observational and short-range model data is possible, there's no reason to stray too far from Hays.

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