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Posted by Ray
on 7/31/2008, 6:24 am
72.230.154.40
During the course of this past week the models, and consequently the forecasters, have vacillated on which weekend day will be "better". At this point, for flying, it's clear Sunday wins the prize. The question for us is: how "bad" will Saturday be?
Details: As mentioned previously, small amplitude features riding on big Rossby waves are skitterish. The principle determining factor for how much precip will fall on Saturday, and how much of the day won't be VFR, is just such a feature. Serious readers are invited to loop through both the GFS and NAM 500 mb vorticity maps. Although discernable earlier, by 8 AM Friday (36 hour progs) both models show a vorticity max riding on the main flow (a huge Rossby ridge centered over Colorado) situated in Ontario province about 250 miles NNW of Duluth. Just 24 hours later (60 hours into the models), the Rossby ridge has barely moved. But both models have the vort max zipping towards us rapidly. The NAM has it moving about 550 miles to the south east by 1200 UTC Saturday, to over Lake Huron, and the GFS has it moving even faster, to right over western NY. Since this vort max is the main lifting mechanism for any precip, and since timing is everything, I'm still not sure how much of Saturday will be salvagable. Could be decent most of the day, or a washout. I hope for the former: I have to be there anyway, and want to fly. This needs updating, which I'll do tomorrow AM.
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