Daily high

A day here runs 06Z to 06Z. The model files its maxima in 6-hour blocks, so this is the highest of 4 of them, and each column takes the 4 covering its own local day rather than one window for the whole continent. These are the model's own maxima, so a high here can read a little warmer than the same model's on a city's forecast, which is the warmest of its hourly values. The dashed line, when it appears, is 32 °F.

How far out is it worth reading? Scored against 30 years of each city's own records for the same date, this model's daily high beats simply knowing what is normal out to about day 7 — measured on 7,148 forecasts across 30 cities since 2026-08-22, and re-read every day rather than written down. Those 39 days ran +2.0 °F from normal, which makes the almanac a weaker opponent than usual — so expect the day to move as the record lengthens.

At six hours the blocks are coarser than the four and a half hours of solar time the map spans, so in practice almost every column lands on the same ones — the per-column choice is what keeps that true rather than lucky. It is the ECMWF map, over the nearer days where its blocks are finer, that changes the picture.

GFS. Of the four models on these pages, two file a daily extremum at all — GFS in 6-hour blocks; ECMWF in 3-hour blocks out to day 6 and 6-hour beyond. The other two publish temperature at instants, from which a daily high cannot honestly be recovered. The switch above draws the same day from the other one.