Saturday, June 27, 2015

Forecasts Indicate Significant Shift In Activity Today

The NWS has issued perhaps the largest blowing dust advisory that that I've ever seen down here, as per above graphic. The advisory states:
Conditions this afternoon are favorable for strong thunderstorm outflow winds across south central Arizona. A Blowing Dust Advisory is in effect from 3pm this afternoon until 8 pm this evening for Pima and South Central Pinal counties. Thunderstorms frequently produce strong downward rushes of air, called downbursts. These gusty winds can generate areas of dense blowing dust that may limit visibility and cause health concerns. Individuals with heart disease and respiratory sensitivities may want to limit exertion and reduce exposure today. If driving and a dust storm approaches, remember: PULL ASIDE · STAY ALIVE! (Pull off the road, put vehicle in park, turn off lights, take your foot off of the brake).
The SPC has also issued a slight risk area for severe thunderstorms for this afternoon - below. The area is similar to the dust advisory region but extends a bit further east.

Both of these forecasts indicate a significant shift of thunderstorm activity toward the west and northwest, extending into the Phoenix metro area. Unfortunately, there was no upper-air sounding taken at PHX this morning. In fact, there are no soundings this morning from Guaymas, Yuma, Phoenix, nor Flagstaff, making diagnosis quite difficult.

The 12 UTC sounding for TWC is shown above. Things of note: the LFC/LCL continues to be around 600 mb with a mean mixed layer moisture of 8 g/kg - again an excellent situation for strong winds; steering winds appear stronger than any time this week, as 500 mb anticyclone remains very strong over the Great Basin; warm air above 500 mb continues to restrict the amount of CAPE. Preciitable water has continued to slowly increase due to both a steady, but weak influx from the GoC and re-cycling due to downdrafts and outflows. The blended PW analysis from CIRA (below at 12 UTC) now indicates highest PW over south-central Arizona. The 15 UTC visible image below at bottom indicates clouds thinning quickly over southeast Arizona, so reduced heating will apparently not be an issue today.

The 06 UTC versions of the WRF model both forecast strong storms initially over the Tohono O'odham Nations to the southwest of Tucson, and then both models run storms from the Catalinas northwestward toward the Phoenix area - would cetrtainly have been nice to have a sounding from Phoenix on what could possibly be their first big haboob day of summer 2015. Here in the Tucson metro area the two variants of the WRF model have different outcomes this afternoon: the NAM version keeps thunderstorms off to west, northwest and north of Tucson, while the GFS version brings some storms westward across parts of the metro area. Another day to keep an eye on the sky. 

1 comment:

  1. Anonymous9:28 AM

    The Phoenix NWS office has temporarily relocated to the Tucson NWS office this weekend....due to some work being done at their office in Phoenix. That's probably why there was no sounding today....and if that's the reason, why there probably won't be a sounding tomorrow either. I think they're back in their office late Sunday night (10 pm).

    Scott D.
    Pinal County AQ