Frequently asked questions

The forecast

How far ahead does SevereWX forecast?

Seven days, in two tiers. Days 1-3 get the full analysis: Day 1 uses the high-resolution HRRR model, updated every hour, plus NadoCast machine-learning tornado probabilities, and Days 2-3 use the GFS. Days 4-7 get a shorter extended outlook built from the GFS, the European (ECMWF) model and the Storm Prediction Center's Day 4-8 outlook. Severe weather that far out is uncertain, so an extended day never goes above Slight and says how confident it is. We'd rather be honest about uncertainty than show you a tornado icon for next Tuesday that has no scientific basis.

How often does the forecast update?

• AI analysis: every time new model data arrives (up to 8× per day)
• GFS model data: every 6 hours (4 runs a day)
• HRRR model data: every 3 hours
• SPC outlooks: every 15 minutes
• NWS forecast discussions: every 2 hours
• NadoCast ML tornado probabilities: 3× per day (1:30, 13:30, 15:30 UTC)

Why does my threat level sometimes say No Threat when storms are nearby?

SevereWX shows the threat for your specific location, not the broader region. A Moderate risk in Oklahoma City doesn't mean Tulsa is under the same threat. Severe weather is highly localized. If you're concerned about a broader event, check the Outlook Map to see SPC risk areas and your locations in context.

What does confidence mean?

Each forecast says how sure it is: High, Fair or Low (signed-in forecasts add the percentage). It reflects certainty in the forecast, not how active the weather is. A calm, stable day with no severe weather expected should score very high confidence (90%+), because that's an easy call to make. Low confidence means the atmosphere is in a transitional or uncertain pattern where small changes in timing or storm track could significantly change the outcome. On low-confidence days, check back: the picture often clarifies within a few hours as new model runs come in.

How SevereWX works

What does "WX" mean?

WX is shorthand for "weather": a two-letter brevity code with roots in Morse telegraph communication. In the mid-1800s, telegraph operators developed shorthand codes to compress common words and save transmission time over the wire. These codes were standardized and adopted across the military, maritime, and aviation industries. WX for weather was part of that system. It survived the end of the telegraph era because meteorologists, pilots, and emergency managers kept using it. You'll find it in NWS forecast discussions, aviation METARs, ham radio storm spotter nets, and military weather briefings today. SevereWX is short for Severe Weather.

How is this different from Weather.com or the NWS app?

Those apps show general weather: rain chances, temperature highs, wind speed. SevereWX is specifically built for severe weather threat assessment. We pull the same model data meteorologists use, combine it with official SPC outlooks, have an AI model write it up under fixed forecasting rules and anchored to the SPC outlook, and give you a plain-language answer to the question that actually matters: should I be concerned today?

What is the SPC?

The Storm Prediction Center is NOAA's office responsible for severe thunderstorm and tornado forecasting across the continental United States. When SevereWX shows an Enhanced or Moderate risk, it's because the SPC, staffed by professional meteorologists, has issued that outlook for your area. We don't override their judgment. SPC outlooks are treated as authoritative in our analysis.

What is the Area Forecast Discussion (AFD)?

The AFD is a technical discussion written by your local NWS office meteorologists, published multiple times daily. It's the same document professional forecasters, emergency managers, and storm chasers read. SevereWX surfaces it alongside the AI analysis so you can read the meteorologist's own words if you want the full picture.

What models does SevereWX use?

• HRRR (High-Resolution Rapid Refresh): 3km resolution, updated hourly, best for Day 1 short-range forecasting
• GFS (Global Forecast System): 0.25° resolution, 4 runs a day, used for Days 2-7
• SPC Day 1/2/3 categorical outlooks: issued by NOAA professional forecasters, treated as authoritative
• NWS Area Forecast Discussions: local office meteorologist analysis, updated multiple times daily
• NadoCast ML: machine-learning tornado probability model trained on historical severe weather data, provides EF0+ and EF2+ tornado probabilities for Day 1

Threat levels

What do the threat levels mean?

• No Threat: No organized severe weather expected. Go about your day as usual.
• Marginal: Isolated severe storms possible. Low coverage, brief in nature.
• Slight: Scattered severe storms possible. Be weather-aware.
• Enhanced: Numerous severe storms possible. Have a plan.
• Moderate: Widespread severe storms likely, some intense. Take shelter plans seriously.
• High: Widespread, long-lived or intense severe storms expected. A particularly dangerous day.

These match the SPC categories. Is that intentional?

Yes. SevereWX uses the exact same categorical scale as the Storm Prediction Center. When the SPC issues a risk level for your location, SevereWX reflects that. The AI analysis fills in the plain-language explanation of what that risk means for your specific area.

Can SevereWX override an SPC outlook?

No, and it won't. If the SPC has issued an Enhanced risk for your location, SevereWX will show at minimum an Enhanced threat level. The AI may add context or nuance to the analysis text, but it never downgrades below what the SPC has officially issued. Professional forecasters have the final word.

Alerts and notifications

What email alerts does SevereWX send?

Two types of emails:

• Forecast ready: sent once when a full model-based forecast is generated for a newly added city.
• Threat alert: sent when your city reaches a Slight risk or higher. If the threat later escalates (e.g. Slight → Enhanced), you'll get a follow-up for that too. We only send when the threat level goes up, never for the same level twice.

When does the threat alert email go out?

Threat alerts are sent after each analysis run when Day 1 or Day 2 reaches Slight risk or higher for your location. If the forecast has already been at that level since the last run, no duplicate is sent. If the level escalates to a higher category, a new alert goes out.

How do I unsubscribe from email alerts?

Every alert email includes an unsubscribe link at the bottom. Clicking it will immediately stop that type of email for your account. You can unsubscribe from forecast-ready emails, threat alerts, or both independently.

Can I choose which emails I get?

Yes. In Profile you can switch off forecast-ready emails, threat alerts and occasional reminders separately, and every email has an unsubscribe link. Threat alerts are forecast-based: they go out when our analysis reaches a Slight risk or higher for your city. SevereWX does not send push notifications.

Roadmap

What's coming to SevereWX?

Recently shipped: the 7-day outlook, radar on the outlook map, live storm tracking pages, and NadoCast machine-learning tornado probabilities on Day 1. Coming next:

• Lightning strike data
• Historical severe weather events for your location
• Significant tornado and hail parameters
• Sharing and embedding forecast cards
• Pro tier billing

Can I request a feature?

Yes. Use the contact form at the bottom of this page. We read everything. SevereWX is built by weather enthusiasts for weather enthusiasts, and the roadmap is shaped by what users actually need.

Is SevereWX free?

SevereWX offers a free tier that covers one location. Pro tier unlocks up to five locations and will include additional features as they ship. Pricing is designed to stay accessible: this is a tool for people who take severe weather seriously, not a subscription trap.

Threat level reference

• No Threat: No organized severe weather expected.
• Marginal: Isolated severe storms possible. Low coverage.
• Slight: Scattered severe storms possible. Stay weather-aware.
• Enhanced: Numerous severe storms possible. Have a plan ready.
• Moderate: Widespread severe storms likely. Take shelter seriously.
• High: Widespread, long-lived or intense severe storms expected. Take action now.