Forecasting SE AZ Convection using Unreliable Upper-Air Sounding Data from NWS/TWC

The last two soundings taken at TWC illustrate how frustrating it can be trying to use unreliable data from the new NWS Sippican sondes. The sounding from 00 UTC on 11 August is shown in Fig. 1, and the 12 UTC sounding on 11 August is shown in Fig.2.

The FSL time series comparing GPS IPW with TWC sounding IPW is shown in Fig. 3. The sounding last evening was too dry by 5 mm wrt GPS IPW and this morning's sounding is too wet by 5 mm wrt GPS IPW. The forecaster apparently didn't notice this problem this morning:

AREA FORECAST DISCUSSIONNATIONAL WEATHER SERVICE TUCSON AZ945 AM MST SAT AUG 11 2007 DISCUSSION...THE TUCSON 12Z UPPER AIR SOUNDING INDICATED A MORE MOIST BOUNDARY LAYER COMPARED TO YESTERDAY. THIS ADDED LOW LEVEL MOISTURE COMBINED WITH GOOD SURFACE HEATING SHOULD YIELD MODERATE TO STRONG INSTABILITY FOR THIS AFTERNOON...ESPECIALLY NEAR TUCSON AND WESTWARD.

RE: Fig. 1

The afternoon sounding yesterday is particularly difficult to resolve meteorologically.
First, the surface super-adiabatic contact layer seems to extend upward to 900 mb. Possible I guess, but it also may be because a dry-spike data point was eliminated by the person who processed the sounding. I have no way to determine whether this was the case.

Second, where is the missing moisture located in the vertical? Since the well-mixed BL in theta extends up to 700 mb and the well-mixed q BL extends only to about 780 mb, I suspect that the "missing" moisture was likely in the upper-part of the BL. This sounding was taken in proximity, in both time and space, to a severe thunderstorm, I think that the CAPE was probably greater than the 314 indicated by the sounding analysis software. These sounding problems may have affected the timeliness of the severe thunderstorm warning that was issued at 6:22 pm.

Obviously, unless this sounding is somehow flagged as suspect in the data archives, a future researcher could consider it a valid severe thunderstorm proximity sounding, leading to………..

RE: Fig 2

This morning's sounding is also very difficult to analyze wrt to the likelihood of afternoon storms. Question is where is the "extra" moisture hiding in this sounding?
It is probably not in the spikey (noisy) data above 620 mb (some Sippican soundings are characterized by extremely noisy T and q data points for unknown reasons). The strange layer from 900 to about 840 mb is my guess for the layer that is too moist. I estimate that a BL well-mixed in q this afternoon would be one with q of ~ 11 to 12 g/kg.

While the mountains will have storms today, it is not clear how the lower elevation BL may evolve. It will likely have CIN above it's top, and if warming occurs in mid-levels, may end up not supportive for storms trying to move to lower elevations. But this is all guess work - since I don't know what the thermodynamic structure is below 700 mb to begin with, it is very difficult to try to predict what the afternoon structures are likely to be.

As for my forecast for our house - that's much more simple. Regardless of what happens to the south, unidirectional southerly flow is very unfavorable for storms and measurable rain at this particular spot. So, I would say that POPs here at our house are near zero today.