Domain Decisions

When severe weather is imminent across the country, forecasters at the SPC must consider all of the possible areas. However, here at the SFE where we are considering multiple experimental NWP ensembles, we have to select our domain of interest. When the severe weather is spread across an area larger than a single domain, we must choose which region we want to focus on. To do this, the facilitators consult not only our experimental numerical weather prediction models, but also the upper-air data collected by radiosondes. Typically, the domains have quite a bit of overlap, but on days like last Thursday (17 May), a decision must be made between two very different areas.

After evaluating the previous day’s forecasts, the first forecasting activity for the current day that participants do is the hand-analysis of upper air maps at six different levels: 250 mb, 500 mb, 700 mb, 850 mb, 925 mb, and the surface. This activity ensures that participants get their hands onto the observed data, and develop a thorough understanding where a convectively favorable environments will occur. A map discussion follows (pictures of which can be found on the NSSL Flickr account) where participants share what they’ve learned through their contours. On Thursday, the conversation was far-reaching, as we had to decide between two domains that had very little overlap:

The two potential areas of interest for 17 May 2018, with the eventual selected domain highlighted in green.


I know it when I see it and other discussions

We had many discussions over the last two days. One was regarding CI definitions. Of the variety of opinions we heard, a storm was defined by:
1. Whether lightning occurred,
2. a coherent, continuous thunderstorm that eventually reached a significant low level reflectivity threshold (40-45 dBz) within 30 minutes,
3. any combination of 1 or 2, which also produced severe weather (e.g. it was just a storm, but a severe storm)

These variations on the theme are exactly what we were considering for the experiment, the experimental algorithms from the model, and the forecast verification we had played with prior to the experiment.

Another conversation involved what forecasters would use from the experimental suite of variables. The variables would need to be robust, easy to interpret (e.g. quick to interpret and understand), and clear. This is a tough sell from the research side of things, but it is totally understandable from a forecaster perspective. Forecasters have limited time in an environment of data overload in which to extract (or mine) information from the various models. They have very specific goals too, from nowcasting (e.g. 1-2 hours; especially on days like today where models miss a significant component of what is currently happening), to forecasting (6-24 hours), to long lead forecasting 1-8 days.

We also spent some time discussing the Tuesday short wave trough in terms of satellite data and radiosonde data.  I argued that many people believe that satellite data and its assimilation is much more important now (Data volume, coverage, and quality control) than radiosondes. It was mentioned that radiosondes are very important on the mesoscale especially in the 0-24 hour possibly 48 hour forecasts. Still more opinions were expressed that some forecasters have questioned the need for twice a day soundings. Opinions in the HWT ranged from soundings are important, to soundings should be launched more often, to sounding should be launched more often at different times. It is plausible that some of our NWP difficulty may be due to launching soundings at transition times of the boundary layer.

I am of the opinion that if model suites are launched 4 times per day that soundings should be launched at least 4 times per day, especially now where cycling data assimilation is common practice. This would return our field to the 1950’s era where 4 times per day soundings were launched at 3,9, 15, and 21 UTC.

Lastly, we discussed the issue of what happens when a portion of the forecast domain is totally out to lunch? Like today where the NM convection was not represented. I think I will talk about that tomorrow once we verify our forecast in the OK area from today. Stay Tuned.