Frequently asked questions

Mostly about the daily temperature contracts, which are the most detailed part of this site. Some answers come from the daily letter this site accompanies, which compares ForecastEx against eleven public forecast tools; where an answer says “here”, it means that comparison. This site draws a narrower set (the National Weather Service forecast, the National Blend of Models, LAMP and GFS MOS).

What is a weather prediction market?

A market in which each contract pays one dollar if a stated weather outcome occurs and nothing if it does not, so the contract's price is the market's probability of that outcome. ForecastEx lists these on daily high and low temperatures at individual weather stations, on Atlantic named storm and hurricane counts, and on major hurricane landfall by location, among many others.

What are the four canonical forecast systems compared here?

All four commonly referenced forecast systems rely on physical numerical weather prediction models that solve the equations of the atmosphere forward in time. ECMWF (the European model) and GFS (the American model) are shown here in their raw form. Raw physical models are flexible and can handle weather situations they have never seen (they are not explicitly trained on historical data but rather adhere to the laws of physics), but forecasts apply to a relatively large discrete grid box that contains the weather station rather than the single point where the station sits, causing them to carry systemic biases relative to the stations.

The Aviation Forecast is a model output statistics system. It compares historical forecasts from physical models with what actually occurred and uses the errors to statistically correct systemic biases at the level of individual weather stations. The tradeoff is that a statistical fit is anchored in past situations and bends less readily to a genuinely unusual one. The National Weather Service's National Digital Forecast Database is undergirded by the National Blend of Models but layers on human forecasters' judgment, which is more flexible in dynamic weather situations but introduces subjective judgment.

What are all the forecast tools used here?

National Weather Service — the official public forecast, human judgment layered on model guidance; that judgment is subjective and can lag a fast-changing day.
Aviation Forecast — statistically corrected to each station and strong inside a day; reaches only about 25 hours and is anchored in past situations.
National Blend of Models — averaging many models cancels much of their individual error; a blend can be slow to commit when the models genuinely split.
European model — consistently among the most accurate global physical models; raw grid-box output still carries station-level bias.
American model — a global physical model updated four times a day; prone to systematic warm or cold stretches in conditions it resolves poorly.
German model — a modern global physical model with strong mid-latitude performance; the same grid-box limitations as its peers.
German statistical model — station-calibrated output built on multiple physical models; anchored in past relationships between forecast and outcome.
Canadian model — an independent global physical model whose errors differ usefully from the American and European models; raw station-level accuracy is middling.
UK model — a long-developed global physical model; coarser at United States stations than the domestic systems.
French model — an independent global physical model that adds diversity to the panel; raw station-level accuracy trails the leaders.
Japanese model — an independent global physical model; often the weakest of the panel on the daily-high standings, which is itself informative about model diversity.

How does a ForecastEx ladder become a single forecast temperature?

ForecastEx does not publish a single forecast temperature. It lists a ladder of contracts at different strikes, and each price is the ForecastEx probability that the day's extreme passes that strike. Comparing ForecastEx with the other systems therefore requires converting that ladder into a central estimate. The 50 percent level is the ForecastEx implied median, so where two adjacent listed strikes bracket that crossing, the central value is interpolated between them. Where the ladder does not bracket 50 percent, because every listed strike sits far in or far out of the money, no central value is recorded and ForecastEx is left unscored rather than extrapolated beyond the quoted ladder. That reflects how the strikes happened to be listed rather than anything about forecast quality, so it should count neither for nor against ForecastEx.

How the daily temperature displays are built

Every forecast cycle is archived as published, because no public endpoint returns an earlier forecast. “As issued” means the source’s last cycle before local midnight at the station. Day boundaries are the station’s local calendar day through its IANA time zone. The map shading is an inverse-distance interpolation of the listed stations’ NWS forecasts and is labelled derived; it is not an NWS product. Nothing here is an official National Weather Service product, and nothing implies endorsement by or affiliation with NOAA or the NWS.

Data sources

Every feed behind these pages. Weather content is US government data; the exceptions are named in this table.

Data	Source	Notes
Observed temperature	aviationweather.gov METAR	Hourly reports plus SPECIs. The contracts settle on METAR observations, so this feed is the matching one; api.weather.gov also serves the five-minute ASOS stream, and a daily maximum over five-minute data lands at or above one over hourly METARs.
NWS forecast	api.weather.gov gridpoint hourly and day/night products	The official National Weather Service forecast. The day/night product carries the official high and low.
NBM guidance	National Blend of Models text bulletins, NOAA Open Data	NOAA’s calibrated multi-model blend; forecasters start from it when editing the grids, so it is related to the NWS forecast, not independent.
LAMP guidance	NOMADS text bulletins	Observation-updated hourly guidance, 25 hours out. The best same-day trace; it cannot see tomorrow.
GFS MOS	NOMADS MAV text bulletins	A single-model statistical product with no forecaster editing; the cleanest independent comparison on the scorecard.
Hurricanes	NHC CurrentStorms.json, NOAA GIS service, NHC wind speed probabilities (PWSAT), ATCF best tracks	Roster, geometry, five-day wind probabilities at coastal locations, and season counts.
Basemaps	US Census Bureau boundaries; Natural Earth countries	Public domain.
Contract prices	ForecastEx public market-data endpoints	The best bids for the daily temperature, hurricane and climate contracts, read every 10 minutes. On this exchange there are no sellers. Every order is a bid to buy Yes or a bid to buy No, and the two sides of a contract sum to one dollar. Pages show the Yes bid and the No bid in cents, and a Yes price midway between the Yes bid and one dollar less the No bid; nothing is fee adjusted (the exchange charges $0.01 per contract to each side at execution). The “implied” temperature is the strike where the Yes price crosses 50¢, interpolated between strikes.
Live-storm wind probabilities	Reask (vendor), when enabled	Probability that the peak gust exceeds each threshold at the 163 reference locations the exchange’s wind contracts settle at, shown as published with the vendor’s mark. Off unless the site operator has enabled it with their own credential; the hurricane page says which.