Wednesday, May 11, 2005

practice makes perfect...

today was another severe thunderstorm day across the united states. this time it was a classic setup in kansas and nebraska.

i got into the office this morning and did my analysis, and right away a couple of things jumped out at me. first, there was a 65 knot jet streak over new mexico. next, there was a strong wind shift at 850 and 925 mb over northern kansas. add in solid dewpoints at 850 and 925. sprinkle in a sharp warm front at the surface and a dryline in western kansas, and the ingredients were set up for an afternoon of severe deep moist convection. (i'll talk another time about why and how all these things are so important, but for now, trust me--they are.)

at about 9 this morning i drew a box of maximum threat for the day--i decided that today was a day to chase virtually. i figured, okay dave, you have to decide where you would drive to for the afternoon initiation. where would it be?

i decided that a good place would be in northwestern kansas, just south of goodland.

in all fairness, chasing a day like this, in terms of where the threat of severe storms is going to be, is easy. it's figuring out which storm to stick to that's the difficult part.

well, in the afternoon, spc issued a pds (particularly dangerous situation) tornado watch--actually 2 of them, and the one farther west was centred pretty much on my "location".

storms ended up firing in the area, and numerous tornado and very large hail reports occurred.

what does all this mean?

well, first, that a good forecast starts from a good analysis. i'll say this over and over and over again. all the models in the world won't help you if you don't start with a good analysis and diagnosis, and only then can you make a judgement call as to whether the model guidance is good or whether it's out to lunch.

second, it's easy to forecast on synoptically evident days. this seems like an almost absurdly obvious statement, but it must be made. i've been forecasting weather of all sorts as my career for a few years now, and i've made quite a few severe weather forecasts--both for the job and for chasing. on days like this, you can almost sit back after your morning analysis, issue the bulletins, and know that pretty much everything is going according to plan. it's on the less obvious days that you have to mine the data for that one crucial piece of information that may lead you in the right (or wrong) direction.

third, it's easy to sit back and say "yeah, i'd go here". but to put in the real miles, to stare at a long road, to gaze upon (and glaze over at the sight of) field upon field of corn, wheat, flax, sunflowers, or canola, is an entirely different matter. trust me on this.

once the storms did fire up today, though, they were moving pretty quickly. this was something i had neglected to take into account this morning. fast-moving storms can really be tricky to chase. you have to be in the right place, you have to have good road options, you have to have good visibility, and you have to have eyes in the back of your head, to make sure another storm isn't bearing down on you. i must always remember to keep storm motion in mind. i much prefer the supercell that sits almost stationary or moves toward the east at about 5 km/h. they're easy to stay away from and nice to view--especially if you want to tripod your videocamera and leave it for a while.

sometime soon, i'll talk about severe thunderstorm forecasting. a primer, if you will, for those interested. especially for those enrolled or hoping to enrol in the course.


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