NOAA SPC HREF 4-hour Lightning-density Probability

GribStream Code: spcltg4hr

Scheduled source retirement: NOAA plans to retire this HREF-based SPC product when SPC_POST v3 starts, on or after 14 October 2026 with the 12 UTC cycle. Significant weather can delay the change. SCN26-77.

No lightning-density replacement is included in GREFS, REFSCT or GEFSCT. Thunderstorm probability is a different quantity. The new products use different inputs and calibration. Select the replacement dataset and the appropriate probability period in your queries. Existing data expires under the current two-day retention policy.

Description

SPC HREF 4-hour lightning-density probability is convective guidance aimed at lightning-sensitive operations. It is more targeted than a general precipitation forecast because it is built around thunderstorm electrical risk, which is often the operational trigger for outdoor venues, aviation ramps, construction, utilities, and recreation.

SPC describes its HREF calibrated thunder approach as combining ensemble evidence from simulated reflectivity, accumulated precipitation, and unstable thermodynamic profiles, then calibrating the probabilities against observed cloud-to-ground lightning. That design makes the product valuable when the practical question is whether an asset or point is likely to be close enough to lightning-producing convection to change posture.

Use this dataset alongside SPC Thunderstorm 4h and SPC Thunderstorm 1h for timing, and with HRRR sub-hourly when you need higher-frequency storm evolution around a site.

Detail

• Archive window: Last 2 days
• Source dataset: NOAA NOMADS SPC Post data
• SPC viewer context: SPC HREF ensemble viewer
• Coverage: CONUS
• Grid: SPC CONUS Lambert grid
• Forecast window: four-hour lightning-density probability fields
• Primary field: thunderstorm probability selector, TSTM
• Companion datasets: SPC Thunderstorm 4h, SPC Thunderstorm 1h, HRRR sub-hourly

Parameters