Thursday, June 25, 2015

Today's Soundings

I am having internet connection problems this morning and am just going to take a quick look at several skewT plots of upper-air soundings.

Above is the 12 UTC skewT for TWC on campus, which I have modified and annotated. Winds in the BL are light and variable this morning, but with a layer around 500 mb having east winds of about 20 kts. Upper-level winds are southwesterly, giving a nice shear profile. I have estimated well-mixed moisture in the afternoon BL to be a bit less than 8 g/kg. This gives a lifted condensation level of 600 mb. But there is a nasty inversion above 500 mb that, if it persists, severely limits CAPE (red shading) for the low elevations. The black "dot" and "x" indicate estimated T and Td during early afternoon up on Mt. Lemmon. The high elevation BL parcel has substantial CAPE and is not impacted by the inversion - so more storms likely on the mountains today.

Shown here are forecast soundings for TWC from the 06 UTC run of the WRF models at Atmo - both valid at 2:00 pm MST this afternoon. Above is the forecast from the WRF-NAM model. This forecast indicates mixed moisture in the BL of about 10 g/kg, which results in substantial CAPE for the low elevations. This appears to me to be too moist, especially since conditions are drier off toward Phoenix.

Below is the same forecast from the WRF-GFS model. The GFS BL is drier (a bit over 8 g/kg) which appears more realistic when compared to the NAM version. The CAPE in the GFS forecast is only 487 m2/s2, about a third of the NAM version's CAPE. 

So there is considerable difference between conditions forecast by the two model variants. The NAM version forecasts storms to persist longer into lower elevations, but still keeps strongest storms to our east and south. However, both forecast soundings have mostly smeared away the nasty inversion that the morning observations show. Will this actually happen? There is slightly cooler air at 400 mb upstream over New Mexico, but advective winds are light. So, the fate of the inversion aloft is probably a coin flip.

My feeling is that it will likely be another frustrating day for us desert rats. Certainly chances of storms and rain are better closer to the mountains, and I'll hope that if storms develop over the Catalinas they move in our direction today.

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