Three Sources to Answer "Is It Gonna Thunder Today?"
- NOAA Storm Prediction Center day-1 outlook — categorical severe-storm risk (Marginal → Slight → Enhanced → Moderate → High) for the next 24 hours. spc.noaa.gov.
- Local NWS forecast — chance of thunderstorms expressed as a percentage by 12-hour period. forecast.weather.gov.
- Live lightning map — confirms whether storms have actually materialised. Browse our state and city lightning maps.
How to Read the SPC Day-1 Outlook
| Category | Meaning |
|---|---|
| Marginal (MRGL) | Isolated severe storms possible, limited duration / coverage. |
| Slight (SLGT) | Scattered severe storms expected, short-lived, not widespread. |
| Enhanced (ENH) | Numerous severe storms possible, more persistent or intense. |
| Moderate (MDT) | Widespread severe storms likely, including significant tornadoes / hail / wind. |
| High (HIGH) | Severe-weather outbreak expected; long-lived, widespread, intense. |
Most storm days are MRGL or SLGT. ENH+ days are uncommon but high-impact. HIGH-risk days are rare (a few per year nationally) and worth taking seriously.
Reading "Chance of Thunderstorms" Numbers
Local NWS forecasts express thunderstorm probability as a percentage. The number means: of 100 historical days with similar atmospheric conditions, on how many did measurable thunder occur somewhere in the forecast zone.
- 0–20% — storms unlikely; carry-on with outdoor plans but stay aware of changing conditions.
- 30–50% — storms possible; have a shelter plan and monitor the sky / radar.
- 60–80% — storms expected; postpone vulnerable outdoor activities or be ready to take shelter quickly.
- 90%+ — storms near-certain; assume you will be affected, plan accordingly.
Combine Forecast + Live Map for Best Decisions
A 60% chance of thunderstorms tells you the day is risky. A live lightning map tells you whether the risk is materialising right now. Combine both:
- High forecast + active map = stay sheltered, expect lightning. Use the alerts setup guide to get push notifications when strikes hit your radius.
- High forecast + quiet map = storms haven't fired yet but conditions are right. Watch over the next 1–3 hours.
- Low forecast + active map = mesoscale convection caught the forecast off-guard (common with afternoon Florida sea-breeze cells and Gulf Coast outflow). Trust the map; the forecast is stale.
- Low forecast + quiet map = today is genuinely a low risk day. Outdoor plans are fine.
By Region: When Today Likely Has Thunder
- Florida + Gulf Coast — sea-breeze convergence makes summer afternoons (June–September) almost daily storm days.
- Great Plains (TX, OK, KS, NE) — dry-line storms April–June produce the most violent supercell days.
- Midwest (IA, MO) — frontal storms May–August.
- Mountain West (CO, AZ, NM) — afternoon monsoon storms July–September.
- Northeast / Pacific Coast — fewer storm days; check forecast on case-by-case basis.