Trentham Stormchasers 2010 USA Roadtrip
Day
7: 28th April, 2010: Another massive low pressure system is pushing into the
western USA today, extending from Oregon to California, bringing another foot or two of
snow to the middle and high Rockies. Lee of the Rockies, the trough gurgles into smaller
low pressure systems as it plays around with the upper bending jet digging down towards
Texas (lee wave troughing). Once free of the Rockies, a strong cold front gathers pace
over the western high plains and Wyoming, Montana and western Minnesota bringing freezing
temperatures and snow to higher elevations. The front is expected to move into western
South Dakota and west and south Nebraska late in the afternoon, with a weak triple point
moving through western Nebraska late afternoon. A strong surge of SW air is spreading into western Nebraska and South Dakota in the morning - unfortunately the air mass is rather dry. With the aid of the triple point and higher elevations in western South Dakota and western Nebraska, the outlook was for high based storm activity. We leave Mitchell on the I90 and head west turning south at Murdo onto Highway 83. At Mission we head west on Highway 18 for Pine Ridge. It's here we start to see high based convection early afternoon. Pretty soon a few towers poke high enough to glaciate. By mid afternoon, near Martin, a band of high based storms have become established along the cold front. Their bases are in excess of 15,000'. Cascades of virga are everywhere hiding bases. Soon we hear rumbles and our lightning detection system cranks up. The cold front overtakes us with 50mph gusts and large spots. 'Frontnadoes' spin along the boundary, some of them quite large...we head for Martin and strike south, heading for Nebraska. We spot a larger multicell sparking merrily. As we head into Nebraska, bands of high based storms are everywhere with great vistas. As we head south towards Hyannis, we note some of the storms are growing taller - there's a fair amount of sheet between 15 and 25,000'. High based storms in Nebraska have a curious habit of suddenly expanding into supercell status, despite the dryness of the surface airmass, and as we plod out of Hyannis towards Arthur, a linear solid base appears and grows into a photogenic multicell. It's now getting onto late evening, and we need to get accommodation and set up for the next day in Kansas, so we leave our picturesque multicell to drift east. We book into a hotel at North Platte and wander off to buy and evening meal. As we look north, we are bowled off our feet where we notice that our friendly multicell has gone supercellular
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High based convection starts SW Dakota. Bases near 15,000' |
Enhanced convection along the cold front. |
Virga was everywhere, and this storm was lightning active |
Dust racing past as the wind suddenly gusts |
The frontal line was narrow but impressive, complete with lightning and virga |
The high based storms moving quickly from the SW reminded us of northern Victorian storms in a dry summer |
The frontal boundary retained its identity as it moved further east, and generated 50 knot surface gusts |
We were fascinated with the ability of these storms to produce remarkable virga trails |
Arty farty stuff south of Martin |
Arty farty stuff south of Martin |
Towards the border of Nebraska, the frontal line started to generate larger multicells and heavier rain managed to make it to the surface |
Arty farty storm stuff, northern Nebraska |
Eventually, the Nebraska high based storms started to do their stuff - this was to be the precursor to a supercell
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Impressive backlit high based multicell |
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Late evening image of a receding supercell, central Nebraska |
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Stay tuned for tomorrow's episode... |