Friday, August 08, 2014

Bit More Moisture But Fairly Dismal Setting Continues

It has been a rather dismal five days since the brief burst of storm activity last Friday and Saturday. The time series above of T and Td at the airport says it all with the continued low dewpoint temperatures. Low-level moisture is up a bit more this morning, with PW values in southeast Arizona coming in at about 1 1/4 inches. There were some isolated showers yesterday, mostly out in central Pima County, pretty much as forecast by the WRF models. In a regional sense, thunderstorm activity over northern Mexico was much diminished yesterday (as indicated below by the plot of CG flashes through 1 am MST this morning) - so little in the way of mesoscale outflows to push higher moisture around.

The TUS morning sounding from the campus NWS Office is shown above (skew-T plots from University of Wyoming upper-air page). Winds below 500 mb are essentially light and variable, while winds above are westerly and the upper-level air mass is quite dry. Very little to be excited about in this observation. If it mixes out in the BL to 650 mb, there is a sliver of CAPE present during late afternoon, although conditions will be a bit better for storms on the mountains. The skew-T plot of the 00 UTC sounding last evening (below) shows that the BL was mixed out to 600 mb, with essentially no CAPE present.

The early WRF model forecasts from Atmo continue with isolated showers and thunderstorms, mostly over central Pima County, where low-level moisture values are a bit higher. All of the models ramp up thunderstorm activity over the weekend and into the start of next week.

The 12 UTC 500 mb analysis from NCAR RAL is shown below. The main feature of interest is the cyclone south of Brownsville, Texas. This is the reflection of a fairly strong, upper-tropospheric cyclone/inverted trough. This feature is forecast westward by the models, with its north end brushing southeast Arizona Sunday and Monday, so we will remain hopeful for some more rain in the gauge during next few days.

No comments:

Post a Comment