Saturday, August 07, 2010

Quite Messed Up Setting Today

The early morning rains have left behind a messy synoptic situation for Arizona today. The 500 mb vorticity maxima that yesterday's NAM made an important player for today has vanished and been replaced by a new convectively-induced vortex that is situated just off to the east of Tucson. The visible satellite image (top) shows that all of Arizona was covered by heavy cloud at sunrise, and that a nice slug of moisture will be moving into Utah later today. Much of northwest Mexico has cleared out though, and this will essentially be the wild-card in how today's weather evolves over southeastern Arizona. The large clear area over northwestern Mexico is exactly where this morning's NAM has initialized a large moisture maximum at 700 mb, leaving the model starting out with a dubious analysis.
The morning Tucson sounding from SPC (middle graphic) indicates no CAPE and is of an onion character, having been highly modified by the MCS debris and light rain. This sounding, with heating later today will have to build a new boundary layer surface upward. The sounding will develop some CAPE but will require a good outflow kick to release the CAPE - thus the important question of what will develop over northern Mexico and Sky Islands of southeast Arizona. The SPC had outlooked a very large area with a risk for severe thunderstorms today, but the latest update has wisely dropped that. However, things could become interesting later today in the Canyonlands of Utah and perhaps along the Borderlands. Winds remain mostly south-southwesterly with some speed shear in upper-troposphere; the sounding's north-northeasterly winds around 700 mb reflect the convective vortex to Tucson's east. Today's NAM forecast for precipitation ending at midnight tonight (bottom graphic) has become a mere shadow of what it was forecasting for this period the last several days - so, we'll have to watch carefully how things evolve later today, and I look forward to seeing what the WRF runs come up with this morning!

1 comment:

  1. John Diebolt12:43 PM

    Skies cleared rapidly across southern Arizona by late morning after all. Surface Temp/TD at noon was 88/60. Noted some small cumulus but the apperance of the small cumulus thus far have been very flat indicating the warm air aloft just above the condensation layer. Vertical development over the Sky Islands around Tucson not very impressive either at 12:20 MST. From my vantage point west of the Tucson Mountains I can see one CB tower to the distant SW..which radar shows out west of Sells. Visible image south of the border shows Sonora pretty suppressed in terms of vertical cloud development except along the eastern border. Action might well develop focus out over central/western Pima County where differential heating boundaries exist. Spreading anvils may then obsucre westering sun and further limit heating across the Tucson Basin late afternoon.
    Current PoP forecast for Tucson NWS Zone 33 (70% this afternoon and even 60% tonight) looking very shaky at this point. I could be very wrong..but my instincts are telling me this will be a very supressed day for the Tucson Basin..unless we get something to dramatically assit vertical lift.