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Posted by Ray
on 5/16/2009, 6:10 pm, in reply to "Re: Weekend of May 16, extended"
69.205.81.50
Mark,
One user friendly site is NCAR's RAP (= research applications program). Here's the link:
http://www.rap.ucar.edu/weather/model/index.php?model=ruc
If the above link doesn't work just Google "rap weather maps". You will get a screen which defaults to the RUC (rapid uptake cycle) model, whose data field selection does not include vorticity. So switch to either the Eta or GFS model. First, decide which forecast times you want, or check the "loop all times" box and you get them all. Second, in the second column of data fields, about halfway down you will see "500 mb vorticity"...click on that. The map or maps you get show positive vorticity increasing from slight to strong as the colors go from green to red.
There isn't space here to mathematicaly define or discuss in any detail what vorticity is....but: essentially it is swirl on the synoptic scale. Clockwise swirl is negative vorticity, converesly counter clockwis swirl is positive. Generally for "good weather", i.e. VFR, you want negative. When positive vorticity comes at you (trade term is PVA or positive vorticity advection), you generally get clouds, over development, and precip. Right now I'm looking at the 48 hr prog "valid" for 1200 UTC Monday. I still see a lump of PVA right over NY state, but not as intense as yesterday's prog. So Monday could still be quite good, although probably not super.
Good luck tomorrow.
Ray
--Previous Message--
: What are the vorticity maps Ray? Where can I
: view these?
:
: Mark
:
: --Previous Message--
: Saturday: obviously the worse of the two
: days.
: We may get in some morning instruction or
: demo flights during the "dry slot"
: , that is, after the passage of tonight's
: warm front and before the afternoon strong
: cold front. Hopefully the dry slot won't be
: MVFR as sometimes happens. The cold front
: will eventually shut us down in the
: afternoon, there is even a modest potential
: for all hell breaking loose (read: hail).
: Too bad we don't have metal ships rated for
: +/- 10g and IFR instruments, ‘cause if you
: took a 4,000' tow you would probably contact
: wave, the forecast has winds more or less
: perpendicular to the ridge all the way up to
: 39,000', speed 38 kts @ 6,000 increasing to
: only 58 kts @ 39,000. A most unusual, and
: ideal for wave, vertical profile. If you do
: have the equipment and cojones, better have
: your wool knickers too, temp at 39k will be
: ~ minus 76 F.
:
: Sunday: obviously the better pick. Cold
: front well downstream, VFR all day. Soaring
: will be good but probably not great,
: depending on how much rain the front dumps
: on us. We could get > half an inch,
: meaning the ground will generate
: "sucker cus" early on, but
: improving in the afternoon, with stronger
: conditions at 5 PM ("go-home time) than
: at noon. But nothing like last Tuesday.
: Morning NW wind is forecast to back to west,
: and brisk, in the PM, so ridge should
: work... and will surely kick off thermals to
: cloud base.
:
: Monday: normally I would have expected
: another diamond day like last Tuesday, since
: by then the ground will have dried out, and
: a 700 mb ridge is forecast to be upstream (=
: continuing cold advection aloft). Fly in
: the ointment is the evolution of flow at the
: all-important "level of non-
: divergence". Interested readers are
: invited to scroll thru the 500 mb NAM
: vorticity maps, starting at 0000 UTC
: Saturday: you see a trough over the midwest
: which deepens thru Sunday, then instead of
: passing to the east by Monday, has a big
: chunk of vorticity shearing off and sitting
: right over us on Monday afternoon. And if
: that 72 hr prog (at this time) verifies,
: kiss a really super day goodbye. Hope I'm
: wrong, still should be decent for the
: weekday flyers.
:
: Ray
:
:
:
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