Early forecaster comments on the nearcasting revealed a general difficulty comparing the vertical theta-e difference and related algebraic representations of the mid-tropospheric instability forecasts from the Lagrangian trajectory model to other stability parameters and other sources (model forecasts and analyses, etc.).
In response to this, product developers Jordan Gerth (University of Wisconsin) and Robert Aune (NESDIS/STAR/ASPB Madison, WI) participating in the testbed this week formulated a simple convective available potential energy (CAPE) calculation using nearcasting model output with the 780 hPa equivalent potential temperature (theta-e) as the parcel and 500 hPa theta-e as the environment.
With CAPE (units of J/kg or m2 s-2), users can easily understand the physical significance of the information provided by the GOES Sounder and watch the evolution. It is believed that this will be ideal for following the growth and decay of elevated instability. Even though this is not a full-profile CAPE calculation, the 780-500 hPa layer potential energy is particularly important for storm development and updraft strength.
The CAPE calculation was recently implemented in AWIPS II for the remainder of this year's Hazardous Weather Testbed. Furthermore, the new layer CAPE output from the nearcasting model is available online at http://cimss.ssec.wisc.edu/model/nrc/ in the "Under Development" section. It was recommended that forecasters compare to fields in AWIPS II and on the SPC mesoanalysis web page.
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