Wednesday, 14 May 2014

Ramping up!


Well, once again it's the time of year where Helen and I are preparing for our annual trip to the central USA to go storm chasing. Despite the vagaries of forecasting beyond about 5 days, it's always too much of a draw to no look out as far as possible!

Currently, a major upper trough is moving across the USA, and a strong cold front has pushed into the Gulf of Mexico, shunting meaningful moisture (the 'fuel' for thunderstorms) well away from the US.

As the upper trough moves away and the flow aloft becomes more zonal (westerly), a lee trough will develop on the High Plains through the end of the week, the weekend, and into next week, and southerly flow will start to develop again. However, this 'return flow' will not (initially, at least), consist of deep, tropical moisture. Rather it will be a partially modified continental airmass. Thunderstorm chances will thus become low into the start of next week, but should start to increase from mid-week, especially across the western High Plains as moisture moves in - this may be most likely just north of a southwards moving cold front from around mid-week onwards, as some Pacific moisture may well be located just north of this front. Upslope easterly flow across Colorado may give a few thunderstorm chances, as an upper trough starts to move into the western USA.

Beyond this, there is some suggestion that this upper trough will cut-off across the SW'ern USA, with a big ridge developing up through the mid-section. This could prove detrimental to severe weather for a time. However, a week is a long time in meteorology, and once meaningful moisture makes a return to the Plains, even fairly subtle impulses can bring some nice surprises! Also, models can only even make a crude estimation of the amount of low-level moisture return more than a few days in advance.

Watch this space to see how it develops!

1 comment:

  1. Will be following with great interest as usual. Good luck-stay safe.