Hi there!
As we have been working with the full version of the Forecast Builder, a couple of questions have come up regarding adding thunder and drizzle to the grids.
1.) As we enter fall,we want to add thunder with a lower probability than the PoP for rain. As we understand it, the only way to populate the PoTThunder grid is to use the SmartTool that essentially copies the PoP to the PoTThunder grid. We realize that you can cap the probability at a level and also lower the range. However, what we have wanted to do is essentially have a lower probability of thunder over only a small portion of the area where we have a probability of precipitation. For example, say we have a 50 percent of rain over the entire the CWA put only want a 20 percent chance of thunderstorms over the southeast quarter of our CWA. What we are currently having to do is assign a 20 PoP in the PoTThunder grid using the tool and then go back to the PoTThunder and editing it to remove 20s from everywhere except the southeast quarter. One could even come up with a more complex case where part of the CWA has the same probability of thunder as PoP while another part has no probability of thunder but still has a PoP In etiher case, at this point, we are finding it easier/faster to edit the Wx grid and add T to the grid than the multiple steps to edit the PoTThunder grid.
We would like propose two solutions - one an interim solution and the second a more complete solution. Our first suggestion would be to add the ability to subtract a value from the PoP and/or take the ratio of the PoP. I think this could be added to the current SmartTool with little additional coding but would allow more flexibility to the user during the cool season when the probability of thunder is typically lower than the probability of measurable precipitation. A more complete solution, which would be much more difficult to code, would be to have a set of slider bars that would assign probability as a function of MUCAPE or MLCAPE.
2.) Our second question involves drizzle. We have noticed that there does not seem to be a tool that allows us to put drizzle into the weather grid unless the PoP is greater than 15. For example, last night we had the PoTDirzzle grid set to 20 and our PoP was < 15. When the MergeWx Procedure ran (Step 6), patchy or slight chance of drizzle was not added to the Wx grid. So we had to edit the Wx grid directly to get drizzle into the WX grid. We were thinking that may be a bug in the MergeWx procedure.
Second, there does not appear to be a way to populate the PoTDrizzle grid unless the PoP is greater than 15.using a SmartTool.. Would it be possible to add drizzle to the Sprinkle/Flurries SmartTool so that the PoTDrizzle grid can be populated for PoPs less than 15%?
Thanks in advance for your help!
Phil Schumacher
SOO, FSD