Forecaster Thoughts – Jonathan Guseman (2013 Week 1)

Posted in Forecaster Thoughts on by Greg Stumpf.

Here is what I took away from the experiment last week.

Out of the MRMS products, the Maximum Estimated Size of Hail (MESH) one was the most useful since many of the storms we evaluated were primarily hailers. It did underestimate hail size by around 0.50 inches some of the time, especially within colder airmasses (e.g. the cutoff low that lingered across the eastern CONUS early last week). However, it did prove to be effective most of the time across the plains. Plotting the 30, 60, or 120 minute accumulated MESH was nice in extrapolating the storm’s track and subsequently finessing the extent of a warning polygon. Several other products were also useful, including the height of 50 or 60 dBZ cores above the 0 or -20C level as well as isothermal reflectivity products.

POD was very high, but FAR was also high when evaluating the HSDA. The spatial extent of giant hail was overdone at times, but a hail event was rarely if ever missed.
The OUN WRF showed utility in forecasting convective initiation in the short term, but it missed Wednesday’s event as it forecast a complex to develop near the Red River Valley. Switching to the RAP for initial conditions will likely be a benefit for the model. The variational LAPS analysis was useful in the 0-3 hour forecast timeframe, providing 15 minute forecasts in the short term. Lower resolution extended guidance was also available but not used as much.

Lightning jumps using total lightning data were evaluated with the Flash Extent Density product. The 8 km resolution is pretty coarse for evaluating discrete areas, but the product does give a good general idea of where to focus. The idea of drawing a polygon to evaluate a specific area for total lightning data will benefit the Total Lightning Trending tool. Simulated IR and WV imagery look very similar to real-time data and are very useful in getting a feel for convective evolution throughout the day. They do underdo the spatial extent of features, such as MCCs, quite a bit, but the idea is certainly there. Fields like convective instability and PWAT difference using the Nearcast product can be evaluated to aid in short term convective forecasting. The UAHCI product can be sporadic at times showing low probabilities of CI where flat cumulus fields exist, but the larger values usually do well, especially along boundaries (i.e. dryline). Cloud top cooling via the UWCTC product is also very helpful in diagnosing storms capable of becoming severe. Values of -20C/15 min of cooling have shown to provide extended lead times, sometimes on the order of one hour. Both the UAHCI and UWCTC products do suffer from cirrus contamination. They both suffered on one shift when convection was ongoing early, but they were very helpful prior to CI where skies were mostly clear.

Thanks again for the opportunity to participate and hopefully I’ll see you in upcoming experiments!

Jonathan Guseman
General Forecaster
NWS Lubbock, TX
2013 Week 1 Evaluator

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