Sunday, July 03, 2005

another chase, another 2 tornadoes

yesterday didn't look all that impressive for tornadic storms, although it looked like a solid supercell producer. there was plenty of moisture and instability, a surface trough was swinging through southern manitoba (lift), and the left exit of an upper jet was to impinge upon the area in the evening, providing some speed shear. and more lift.

the surface winds, however, were southwesterly, lessening the directional shear.


i say "mostly" because this has a bit of an impact on what happened.

around 5 pm i was at home watching the radar show a pretty neat little supercell west of brandon, but the environment wasn't great for tubes. the winds there were west, and they were west all round. the instability was pretty much the same all over southern manitoba, and so it was a matter of waiting for the shear. using the satellite pictures you could actually see when the influence of the left exit region of the jet/stronger area of lift was being felt on any given area. first near regina, then estevan. i timed it out and decided that we should leave at around 5:30 to get to the area of influence in time--morden-ish. what heightened my interest, though, was the wind observation from carman--it was northwest all day, but at 5 pm it suddenly turned to southerly. directional shear. let's go!

we got to carman and saw some towers going up to our southwest. we decided to chase the most southerly of the bunch, and it turns out it was southwest of morden. we tried to get to it for a while, but then 2 things happened: first, we came to the pembina river valley just west of highway 31 (who knew the roads in manitoba ever got that steep?) and couldn't cross safely. second, the storm itself petered out. so we only had one choice left. go north back toward highway 3 and see what was what. as we approached the highway, wxdog called me and asked where we were, and was happy to know that we were there. he told me that radar was showing a monster supercell just off to our west-northwest, and there had been reports of golf ball hail with it. as well, radar showed some very strong rotation within it. storms farther toward the saskatchewan border were dropping tornadoes sporadically, so this provided added chance for a tube. we saw the storm and it wasn't that far away, so we bombed off in that direction.

as we approached it, near pilot mound, we saw the wall cloud. it was pretty low to the ground, ragged, and slowly rotating. at this point wxdog called again and relayed our report to environment canada.

at this point we were almost due south of the storm, and a gift from the heavens in the form of highway 34 going north appeared to us. we took it, only to be foiled of a view of the wall cloud by trees alongside the road.

then it happened.

all of a sudden, from light and variable, the winds picked up to easterly 20 to 25 knots. my conceptual model ideas kicked in and i realised that this could be only one thing: an inflow jet. i pinned the accelerator and told my chase partner why i was doing it; in essence, with this inflow jet, i figured the storm could/would put down a tornado anytime.

we got past the trees and stopped. the wall cloud was about 3 km to our west. no sooner had i put the car in park than it happened. tornado on the ground. no wait, 2 tornadoes. okay, now 3, all rotating about one axis. yes, folks, we had a multiple vortex tornado. i called it in to environment canada and was glad to hear that they were already in the process of drafting up a tornado warning for the storm.

we sat there for about 10 to 15 minutes watching this thing go multi vortex to elephant trunk to no condensation funnel but still debris, and back through the cycle again. the storm was barely moving and so we were able to take numerous pictures. i called environment canada back to let them know that the tornado was still on the ground.

then it started to move. it wasn't moving to our left, and it wasn't moving to our right, but it was getting bigger. we hightailed it out of there, back south on 34 to highway 3. we stopped a couple of times for quick pictures, but all of a sudden this thing was cooking. we had to drive through the hook echo of the storm, that is, the wraparound precipitation in the downdraft, and i was a little worried about this. we had no other choice, but sometimes extremely large hail is embedded in this part. luckily, though, not this time. it was a 1 km wide swath of light to moderate rain and winds 35 to 40 knots.

when we were on highway 3, the tornado was passing about 5 to 7 km to our north, and the contrast was pretty bad. we could barely see it, but when we could, it was evident that this was a wide tornado, what some would call a wedge. my estimate was that it was about 3/4 of a km wide, but that's just the estimate of a guy hopped up on adrenaline.

there were 3 bright flashes in the tornado, spaced apart by about a minute each. one was pinkish and the other 2 were blue. the duration and location (and colour of one!) were pretty wrong for lightning, so i figure it was probably transformers exploding. this is something you usually only see in kansas or oklahoma. amazing.

finally the tornado lifted but there was still violent rotation in the cloud. again i called environment canada to let them know that the tornado had finally lifted (after about 25 minutes!) but the storm was still very capable of producing another tube.

we continued east, toward home, when my partner pointed out more stuff to the northwest. we were just entering the town of la riviere when we saw a condensation funnel 3/4 of the way to the ground, and a bit of a dust cloud being picked up. tornado #2! we got a couple of pictures but this one didn't last very long--maybe 20 seconds. we got back out of la riviere (pretty town, but horrible cell coverage and brutal for storm chasing visibility!) to see that the original wall cloud had occluded out, but a new one was forming. its rotation was a bit more lazy, and the scud being sucked up into it was a lot more ragged. at this point, because of darkness and seemingly less vigourous rotation, we called it an evening and drove the hour and a bit back to winnipeg.

a successful chase!

i hope to have pictures up on weather central today (sunday) or tomorrow.


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