Temperature Market Platform Differences

Platform Overview

There are currently four major platforms offering temperature prediction markets in the United States: Kalshi, Polymarket, Robinhood, and Interactive Brokers (IBKR). While all four let you trade on daily high (and sometimes low) temperature outcomes, they do not all use the same resolution source. This means that the same city, on the same day, can technically settle at a different temperature on one platform compared to another.

Resolution Sources: NWS vs Weather Underground

The resolution source is the official data used to determine the outcome of a market. It is the single most important thing to understand before placing a trade, because it determines what the "correct" high or low temperature is for any given day.

Kalshi → NWS Climate Report (CLI)

Kalshi resolves its temperature markets using the next-day Climate Report (CLI) issued by the National Weather Service. The CLI is the official daily climate summary for an ASOS weather station. It is produced by NWS meteorologists and undergoes quality control before publication. The final CLI for a given day is typically released the following morning. For a deeper dive into what a CLI is and how it works, see the NWS Data Guide.

Polymarket, Robinhood & Interactive Brokers → Weather Underground

Polymarket, Robinhood, and Interactive Brokers all resolve their temperature markets using the "History" tab on Weather Underground (wunderground.com). Weather Underground displays historical observation data for airport weather stations, and the high and low values shown on their History page are what these platforms use for settlement.

The Trading Day Window

The "trading day" defines the time window during which observed temperatures count toward that day's high and low. This is where the two resolution sources diverge significantly.

Weather Underground (Polymarket, Robinhood, IBKR)

Weather Underground reports temperatures in local clock time year-round. This means the trading day always runs from 12:00 AM to 11:59 PM in whatever time the local clocks are showing — whether that's standard time or daylight saving time. It's simple and intuitive: midnight to midnight, matching the calendar day as most people experience it.

NWS Climate Report (Kalshi)

The NWS Climate Report records the high and low temperature in Local Standard Time (LST) year-round, regardless of whether daylight saving time is in effect. This is a critical distinction. During the months when clocks have "sprung forward," there is a one-hour offset between clock time and the NWS reporting window.

In practical terms for Kalshi markets:

• Outside of Daylight Saving Time (November – March): The trading day runs from 12:00 AM to 11:59 PM local clock time — identical to Weather Underground.
• During Daylight Saving Time (March – November): The trading day runs from 1:00 AM to 12:59 AM local clock time. Because LST is one hour behind DST, the NWS "day" starts and ends an hour later on your clock.

The Daylight Saving Time Wrinkle

The DST offset is not just a curiosity — it can directly affect which temperature reading counts as the high of the day. Consider this scenario:

In this scenario, the Weather Underground high for the new day could start at 82°F before any daytime heating even begins, while the Kalshi/NWS high for that same calendar date would not include that reading. This type of edge case is most relevant on nights where temperatures are changing rapidly between midnight and 1:00 AM local time during DST months.

Data Sources & Why They Differ

Beyond the trading day window, there is another significant difference between the two resolution sources: the types of raw weather data they consider.

NWS Climate Report (Kalshi)

The NWS CLI is comprehensive. It draws from all available data products for the station, including:

• High-frequency METARs — special observations triggered by rapidly changing conditions
• Hourly METARs — the standard once-per-hour reports (e.g., at :51 or :53 past the hour)
• 6-Hour High/Low — max and min temperatures over the previous 6-hour window, derived from one-minute observations (OMOs)
• Daily Summary Messages (DSMs) — interim summaries issued throughout the day
• Intra-day CLI — preliminary climate reports issued before the final end-of-day version
• 24-Hour High/Low — the max and min over the prior 24 hours, also derived from OMOs

Because the CLI considers all of these data points, it can capture temperature spikes or dips that occurred between standard hourly reporting times. A brief spike at, say, 2:37 PM that was only captured in the 6-hour max would still appear in the CLI — even if no hourly METAR recorded it.

Weather Underground (Polymarket, Robinhood, IBKR)

Weather Underground's History tab is simpler in scope. It considers only:

• Hourly METARs — the standard once-per-hour observations
• Special METARs (SPECIs) — observations triggered between standard reporting times by significant weather changes

Weather Underground does not incorporate 6-hour highs, 24-hour highs, DSMs, or one-minute observation data. This means short-lived temperature spikes or dips that happen between standard observations — and are not significant enough to trigger a special METAR — may not be reflected in the Weather Underground data.

When Do These Differences Actually Matter?

NWS and Weather Underground frequently report different high and low temperatures for the same station on the same day. These are not rare edge cases — they happen regularly, and in prediction markets, even a 1°F difference can flip the outcome of a contract. Here are the situations where you should be most alert:

• Fast-moving cold fronts or warm fronts — temperature can swing quickly in a narrow window, potentially getting captured by OMO-derived products (6-hr max) but not by a standard hourly METAR.
• Late-night temperature changes during DST — the 12:00–1:00 AM window belongs to different calendar days depending on which platform you're trading on.
• Brief afternoon temperature spikes — a spike between hourly METARs may appear in the CLI (via the 6-hour max) but not on Weather Underground.
• Markets sitting right on a strike price boundary — when the temperature is near a contract threshold, even 1°F of difference between sources can flip the outcome.

Using the Wethr.net NWS / WU Toggle

On Wethr.net, every city dashboard includes a toggle switch that lets you select between NWS and WU (Weather Underground) as your reference source. This toggle adjusts the data and calculations shown on the chart to align with the resolution rules of your trading platform.

This ensures that the Wethr High and Wethr Low values displayed on the chart match the rules your platform uses for settlement. It also adjusts the trading day window accordingly — so during DST months, the NWS setting will reflect the 1:00 AM – 12:59 AM window, while the WU setting will always reflect midnight to midnight.

Related Articles

• NWS Data Guide — Deep dive into CLI, DSM, METAR, and the ASOS rounding process.
• Basic Trading Guide — How prediction markets work, limit orders, and resolution timing.
• "The Temperature" — Understanding what "the temperature" really means in weather markets.
• City Resources — Data release schedules and external links for all markets.
• Wethr.net Chart Guide — How to read the temperature chart and all its layers.