Daily high
The highest temperature each point reaches over the whole of the day you choose.
Tuesday 1 September · GFS run 12Z 31 Aug4 × 6 h
Warmest 109.2 °F · coolest 44.6 °F
Methodology
A day here runs 06Z to 06Z. The model files its maxima in six-hour blocks, so this is the highest of 4 of them, and each column takes the four covering its own local day rather than one window for the whole continent. Six hours is coarser than the four and a half hours of solar time the map spans, so in practice almost every column lands on the same four blocks — the per-column choice is what keeps that true rather than lucky, and it is what starts mattering when a finer field arrives.
GFS only. Of the four models on these pages, two file a daily extremum at all: this one and ECMWF. The other two publish temperature at instants, from which a daily high cannot honestly be recovered.
Every map on this page is drawn from model output we store ourselves, not from anyone's picture of it. The per-city read of the same day — which cities the models are fighting about, and what the discussion makes of it — is on the national page.