Upslope flow mark 2

05 June 2014

It’s always good when the two days follow a similar pattern, particularly for the bank balance as it tends to mean there’s not a huge drive involved. Today would be our second day in eastern Colorado with a setup very similar to the day before. Quasi-zonal flow remained over the US from a wide high pressure sitting over northern Mexico into southern Texas. Meanwhile a low forming in response to a jet streak was encouraging moist air from the Gulf of Mexico into an upslope flow regime over eastern Colorado. A couple of upper impulses moving over Colorado would introduce some strong upper level support for convection. Once again sheer profiles appeared adequate for supercells however mean 0 to 6km flow was forecast to be east southeast, which would give our storms an unusual heading of south southeast. The road network in the southeast of Colorado leaves something to be desired, particularly when you’re not able to do many farm roads in your hire car. This is doubly tricky when you have a storm motion like SSE – I don’t think there is a single road in the area that will take you on that track.

A setup like today’s can be made a little easier with the fact that some of the models which try to forecast where convection will start are likely to be accurate enough to work from for positioning. They’ll rarely get it exactly right, but when the setup is fairly simple you know their outputs are probably better than your own judgement (unlike other, more complex setups, where they are no more useful than poignantly pouring dust from your hand and staring into the distance…).  We knew the storms would be a little further south than those yesterday, and the HRRR model was breaking them out a south of Denver. We positioned in Limon and waited for kick off.

We’d barely had time to start making a sandwich before some storms had fired to our west. Thankfully, they were tracking east and we had a good road on which we could head straight out towards them. We managed to reach the young storm in time to get a good view of its early development before it started to gather strength and began moving on a much more southerly trajectory. We met our UK chaser friend Nathan at Limon and again under this storm so we all set up to burn through our memory cards and batteries together.

Supercell thunderstorm

Storm Friends

We drove south to stay ahead of it, through many roads we shouldn’t, and managed to get onto it again on a tarmac road. Staying ahead of the storm was getting us directly into its gust front, which was unusually cold and stacked full of tumbleweeds. Probably due to the previous surface heating, followed by this cold blast of air, there were dust devils that could be described as nothing short of rampant. It was pretty entertaining viewing – if a little on the chilly side. One such circulation became so big that even experienced chasers were questioning whether it was a land spout. In the absence of better information we reckon it was a dust devil as there were so many around, but don’t mind calling it a tornado!

Landspout or dust devil

Mammatus

As this cell continued into an area with next to no good roads to follow it we elected to head to the next cell behind it which looked pretty good on radar, leaving behind this storm, which still looked pretty strong.

Cumulonimbus

Unfortunately it was dying as we approached it, likely because the cell we’d left behind had become the dominant feature in the whole area and had undermined this one. Nevertheless we caught some nice structure in its low precipitation halcyon days.

Weather photo: decaying supercell

As we were now left out of position to have any chance to get back on any more bad weather we decided to call it a day and head for a motel in Eads, Colorado, grab a couple of beers and wait for a new line of storms to come over us. Unfortunately they made an effort to break into two pieces and go either side of us…story of our day really!

Key points:

SPC Day 1 Weather Outlook as at 06:00UTC (01:00 Central Time the night before)

SPC 01:00UTC day 1 forecast for Thu June 2014

SPC Day 1 Weather Reports for the day.

SPC storm reports for Thu June 2014

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