NOAA SPC REFSCT

GribStream Code: refsct

SPC REFSCT probability guidance

Calibrated REFS thunderstorm probabilities for one-hour, four-hour and full forecast periods.

Parallel guidance: These datasets are available in GribStream using NOAA’s parallel feed. NOAA plans to make SPC_POST v3 operational on or after 14 October 2026, beginning with the 12 UTC cycle. Severe weather may delay the transition. Read the implementation notice.

Cycles and probability periods

Runs at 00, 06, 12 and 18 UTC reach +60 hours. One-hour windows end every hour from +1 through +60 hours; four-hour windows end every hour from +4 through +60 hours. Full-period guidance starts every hour from +0 through +59 hours and extends to the end of the source’s convective day, up to a maximum lead of +60 hours.

Full periods can have the same end but different start times. Select their exact duration: full period; 24 hour probability; prob >0 differs from full period; 12 hour probability; prob >0. For example, the file labeled +24 in a 12 UTC run covers +24 to +48 hours. In the API, its forecast time is +48 hours, the end of that period.

Explore the SPC probability dashboard.

Querying probabilities

Values are percentages from 0 to 100. Select the exact name, level and info combination from the inventory. The ensemble information has already been combined into calibrated probabilities, so you do not select individual members.

{"name":"TSTM","level":"surface","info":"1 hour probability; prob >0","alias":"thunder_pct"}

Use this variable in a POST /api/v2/refsct/timeseries request, or /api/v2/refsct/runs to compare initialization times. forecasted_time is the interval end; subtract the selector’s duration to obtain its start. The text prob >0 is source GRIB metadata, not a user-selected probability threshold. Cycle times indicate when a forecast run was initialized; the data becomes available later.

Scheduled retirement of older SPC feeds

At NOAA’s SPC_POST v3 implementation, scheduled on or after 14 October 2026 at 12 UTC, the following HREF-based SPC products stop receiving new runs. If NOAA postpones the transition because of severe weather, retirement is postponed too. The replacements use different inputs and calibration, so applications need to select the new datasets and variables.

• spctor4hr, spchail4hr, spcwind4hr: migrate to GREFS four-hour TORPROB, HAILPROB and WINDPROB selectors.
• spctstm1hr, spctstm4hr: migrate to REFSCT TSTM, selecting one-hour or four-hour periods.
• spcltg4hr: no lightning-density replacement among these three datasets.

GEFSCT adds daily thunder guidance; it does not replace lightning density. This notice concerns SPC’s derived guidance; retirement dates for the underlying models require their own notices.

Archive and older datasets

GribStream retains runs initialized within the last two days, matching the existing SPC feeds. This limits how far back you can query runs, not how far ahead they forecast: each retained GEFSCT run still includes all eight daily periods. The older SPC datasets keep their identifiers, and their data expires under the same two-day retention policy. Query REFSCT separately; its values are not appended to the older series.

Source: NOAA / Storm Prediction Center. Guidance is public-domain NWS information subject to the NWS disclaimer. GribStream is independent of NOAA. These probability fields are forecast guidance, not official warnings.

Related guidance: GREFS severe hazards · REFSCT short-range thunder · GEFSCT daily thunder.

Dataset details

• Archive window: Last 2 days

Parameters