Nowcasting Solar Flares from Ca II K Peaks: Dunn Solar Telescope Pilot Results

We evaluate a straightforward flare nowcasting approach using chromospheric Ca II K intensity peaks from small, fixed regions in high-cadence imaging at the Dunn Solar Telescope. For a compact set of recent non-X events, we compare the time of each Ca II K peak with the corresponding maximum in the GOES soft X-ray record for the same active region. Region light curves are averaged over pixels, detrended to remove slow seeing and transparency changes, lightly smoothed, and peaks are selected by prominence. We track the signed time difference between the chromospheric peak and the soft X-ray maximum. Most cases show the chromospheric peak arriving earlier or essentially at the same time. Typical lead times are on the order of a couple of minutes, with occasional later peaks by about a minute. A near-simultaneous case indicates tight chromosphere-to-corona coupling, while later cases likely reflect extended chromospheric brightening or overlapping sub-flares. The procedure requires only fast imaging and simple processing, which supports real-time telescope-side alerts. I will outline the region-of-interest pipeline, show timing overlays for representative events, quantify uncertainties dominated by cadence and catalog rounding, and present an operational recipe with basic quality control. Results indicate that compact Ca II K brightenings provide an immediate and practical indicator that a soft X-ray maximum is imminent, offering actionable guidance for space-weather operations.