Re variables to use to assist in forecasting storms, I will be the first to admit that:
- I rarely look at TTs (but I probably should)
- I rarely use the K-Index (again, I probably should)
- For days like Sunday where the flow tends NW'ly, I like to look at the 850hpa RH/DP/streamlines to get an idea of how moist it is in the higher portion of the lower-atmosphere. If it's really dry then there's a good chance of that dry air mixing down through the lower levels as the day wears on, especially if the the westerly flow is more brisk (if it's only light then there's less risk).
- 2m/10m DP - to be used in conjunction with the above 850hpa DP/streamlines. Using surface dewpoints alone is a bad idea because you can't see what the rest of the lower-levels are doing
- 500mb temps - generally the sweet spot to identify temperatures in the upper levels
- MSLP + Precip - Can be useful to get an idea of how much precipitation the model is forecasting to reach the ground. If it's minimal across all models (1-5mm or something) then refer to other variables (maybe the mids are moist but the lowers have dry air through them restricting precip reaching the ground). Something to remember though is that I find each model handles this parameter quite differently? (Ken?) For example, ACCESS-C has had a few really good days this year where it'd show a good splattering of precip occurring across a region and it'd pretty much happen, all the while the others merely had 1-5mm. Then there was Wednesday when ACCESS-C again tried to do this (joined by GFS), but in the end it was EC's conservative approach that ended up being more accurate. There was also another day up here about a month ago where this turned out to be the case as well.
- CAPE (obviously).
- LI, although you still have to be careful not to take the pretty colours you so often see on BSCH as gospel. Be aware of other factors too because -8 LI does not necessarily translate widespread severe thunderstorms. I've seen BIG BIG LI days where absolutely nothing happens (for example, the cap might just be too strong for storms to initiate in the first place). So be very mindful when looking at LI on BSCH.
- One of the most important methods for me (and I'm so glad with the use of modern technology we are able to do this) is simulated soundings. Tropicaltidbits or BSCH for GFS, Windy for EC, and if you're using Windy, click the magnifying glass to zoom in your desired sounding). There are plenty of resources out there to help you learn how to read a sounding, one of my favourite ones is a three-page thread from the guys over at ASWA (site seems to be down right now, not sure if it's returning?)
http://www.australiasevereweather.com/forum/index.php?topic=1510.0. AC's thunderstorm forecasting guide is really good too:
https://www.downunderchase.com/storminfo/stormguide/
I probably missed some stuff but those are some of the main things I look at with thunderstorm forecasting (and please remember I am no meteorologist, just a self-learner with a wild dream of becoming a meteorologist some day).