Threat Of High-Based Thunderstorms And Dry Lightning

The next two days will bring a threat of thunderstorms to the mountains of eastern Arizona tomorrow and to southern Arizona on Friday, May 23rd. Graphic above is the early WRF-NAM forecast of composite radar echoes valid at 2 pm MST tomorrow afternoon, while same graphic below is valid at 6 pm on Friday. The winds will still be strong tomorrow according to the WRF forecasts - second below shows 10-m wind forecast valid at 1 pm on May 22nd.

The storms will be high-based and won't put much rainfall on the ground - forecast above is total rain through 11 pm on Friday night (dark blue is 1/4 to 1/2 an inch; med blue is 1/10 to 1/4 of an inch; and light blues is < 1/10 inch). Thus, the threat will be to a large degree one of wind and dust and dry lightning flashes, posing a risk of more lightning-caused wildfires. The Skunk wildfire burning east of Globe has burned about 35,000 acres through this morning - this fire was started by lightning way back on April 19th.

Mike Leuthold ran an experimental version of the WRF model yesterday that included a lightning forecast algorithm developed by NASA/NCAR. The algorithm forecasts all lightning flashes, cloud-to-ground as well as in-cloud and cloud-to-cloud flashes (making quantitative validation a bit difficult). The graphic below shows a WRF lightning forecast valid for the hour ending at 4 pm MST tomorrow (color contours are for flashes/square km, with green indicating ~3 flashes), with the maximum threat centered on the White Mountains. This is certainly an interesting and potentially important capability of the WRF model.

Finally, the SPC Fire Weather Outlook for today is shown below - the area noted as ISODRYT is where the threat of isolated, dry thunderstorms exists. However, the outlook for tomorrow from SPC has not indicated the dry lightning threat forecast by the WRF runs at Atmo.