Thursday, 18 May 2017

Starting to gear up!


Long time, no post! But we've reached that time of year again where we get ready to head out to the USA for our storm chasing adventure. The anticipation is building!

Today, a nasty outbreak of severe thunderstorms is expected across the Central Plains - strong-violent tornadoes are possible, with portions of southern Kansas and northern Oklahoma at highest risk. This is due, in part, to a strong upper low/trough, which will move slowly east and then north-east from the SW'ern USA over the next few days.

By Monday, this looks like being located somewhere north of the Great Lakes, over Canada. A rather pronounced ridge is likely to be in place over the NW'ern USA, not a sight storm chasers like to see!

By around mid-week, a new trough/low is progged to drop ESE through the northern and central Plains - this should help drive a cold front down to the Gulf states, and perhaps into the Gulf, shutting down any flow of moisture into the Plains for a time (more below!).

Earlier in the week, within a somewhat cyclonic flow regime, SW of the Great Lake low, moisture should be in place over the southern states, and several areas of thunderstorms should be present. A few severe storms may be possible, given reasonable upper level winds, but it may be that it's quite a messy picture.

Back to mid-late week, indications are that, under a rather broad/nebulous westerly flow, without any real focus trough-wise, moisture should start to return northwards through SW and W Texas. This is when some rather large differences in model output creep in. GFS is 'keen' on keeping a broad ridge-trough pattern in place, somewhat detrimental to chasing, but not totally. *If* moisture can move back north through the Plains, then some 'north-west flow' events, including MCS development, are possible.

On the other hand, the trend of ECMWF, overall a better model, is to tend to flatten the pattern (nice rhyme!) towards the end of next week, and instead of bringing another trough SE'wards, keeps it towards the Pacific NW and, thus, a broad westerly or SW'erly flow over the Plains. This would encourage moisture return, and whilst not guaranteeing thunderstorms, certainly puts one of the key ingredients in place, should subtle perturbations move through.

It should be noted that the ensembles of both models are somewhat split between these two scenarios. Trying to be objective, it does appear that the ECMWF trend has some support from how the ensembles have trended too - a few more of today's runs support this than yesterday. Let's see!

Beyond that it's really up in the air, so to speak (indeed, even later next week is far from certain!). However, quite a few suggestions that by the turn of the month, if not a bit before, western troughing should be more prevalent, which could signal a more robust uptick in potential.

As always, though, the main chase philosophy is to take it day by day, appreciate being out on the wild, wide open Plains, enjoy the hospitality, and just soak it all up. And take pictures. And videos. And eat burgers!


  1. Love the explanations - have been trying to piece together the models and wonder if I'll see anything whilst out there. I'm keen to just be out in chase territory and take everything as it comes...

    1. Many thanks! What time period are you going out there for?