SPC severe weather forecasts for event security are the most underused planning input in outdoor production. The NOAA Storm Prediction Center publishes categorical convective outlooks for the next 24 to 72 hours that tell you, in geographic polygons, where tornadoes, large hail, and damaging straight-line wind are most likely. Production teams typically look at the SPC map once on the morning of the event — by which point the load-in trucks have already been parked and the rigging crew is in the air. SignalGuard checks the polygons every scan and tells you when your venue's coordinates sit inside one.
What this signal monitors
The SPC signal reads NOAA's day-1 and day-2 categorical risk polygons (TSTM, MRGL, SLGT, ENH, MDT, HIGH) and tests whether your venue's exact latitude/longitude is inside any of them. It's a planning signal, not a real-time alert — its job is to tell you 12 to 36 hours in advance that your event is in the bullseye, so you can pre-position lightning detectors, brief the structural engineer, and coordinate with the venue's emergency manager before the day-of cellular network gets congested.
Data sources
SignalGuard's spcClient.js pulls two GeoJSON files directly from NOAA: day1otlk_cat.lyr.geojson and day2otlk_cat.lyr.geojson on spc.noaa.gov/products/outlook/. Both are free, no API key, refreshed several times per day as the SPC forecasters update their analysis. The client uses a ray-casting point-in-polygon algorithm on the venue's coordinates and returns the highest-rank tier the point falls inside. SPC also publishes day-3 through day-8 outlooks; we currently surface day 1 and 2 because operational decisions outside that window are typically driven by other planning inputs.
How SignalGuard scores severity
SPC categorical tiers map directly to threat levels: TSTM (general thunderstorms) and MRGL (marginal risk) are low; SLGT (slight risk) is medium; ENH (enhanced risk) and MDT (moderate risk) are high; HIGH is critical. The signal returns whichever of today or tomorrow is worse — so a clean Saturday inside an Enhanced-risk Sunday outlook still triggers the high level on Saturday's scan, giving operators a 24-hour decision window. The 2011 Indiana State Fair stage collapse occurred during an SPC Slight Risk outlook with a high-resolution mesoscale discussion calling out the threat; in retrospect, the NIST after-action report noted that earlier escalation of the SPC signal could have changed the evacuation decision timeline.
Use cases for event security
- Pre-event hard-stage decision. When tomorrow's outlook is ENH or higher and the venue is in the polygon, production weighs delaying load-in by 24 hours rather than risking a strike crew at altitude in a storm.
- Rigging inspection escalation. A day-1 SLGT risk inside the polygon raises the inspection cadence — riggers walk the truss every 4 hours instead of every 12, and ground crews stage de-rigging contingencies.
- Shelter capacity audit. An MDT or HIGH outlook within 24 hours forces a sit-down with the venue on covered shelter capacity. Outdoor festivals routinely overcommit on attendance vs. shelter — SPC gives you the lead time to publish a clear "no shelter for crowds of this size" decision before doors.
Pairs well with
- Weather monitoring — day-of alert layer that fires inside the outlook polygon.
- Air quality monitoring — convective downbursts blow dust and reset PM2.5 readings.
- FAA TFR monitoring — SPC-driven hazard TFRs sometimes appear over a venue during outbreak days.
Premium upgrade path
The free NOAA SPC feed is authoritative and refreshes faster than most paid products can republish. For event teams operating internationally, the free SPC data doesn't apply — connect DTN MetService Pro, Tomorrow.io's Severe Weather Insights, or Baron Lynx on the Integrations page for region-specific convective forecasts. SignalGuard's premium AccuWeather connection also adds severe storm probability scores at the forecast-period level worldwide.
Frequently asked questions
What is an SPC severe weather forecast? The Storm Prediction Center is a NOAA branch that issues categorical risk outlooks — geographic polygons ranking the likelihood of severe thunderstorms, tornadoes, and large hail across the contiguous US for the next 1 to 8 days.
Does SPC publish day-2 forecasts? Yes — SignalGuard pulls both day-1 and day-2 categorical outlooks and reports the worst-case of the two as the headline severity.
How is SPC different from a National Weather Service warning? NWS warnings (tornado warning, severe thunderstorm warning) fire when a storm is happening or imminent (minutes to an hour). SPC outlooks fire when the conditions favor severe storms (hours to days ahead). Use SPC for planning, NWS for response.
What does an "Enhanced Risk" mean for an event? ENH is the third-highest of six tiers. Historically, Enhanced Risk days produce numerous severe reports across the polygon — for an outdoor event inside one, operational posture should already be elevated.
Does SignalGuard alert me if the SPC outlook changes during the day? Pro and Enterprise plans support refresh on SPC polygon updates. See SignalGuard pricing and the docs hub.
==========