Model spread, mapped
Valid tomorrow evening.
Gap between the warmest and coolest of 4 models for the 00Z 30 Aug model run·42 hours out, valid 18Z 31 Aug
Widest gap 21.9 °F, 30 mi NE of Tucson, Arizona · unshaded ground is where all 4 land within 2 °F of each other
Thin lines are temperature itself, every 10 °F — the per-cell median of the 4, so a line no single model forecast.
Methodology
Across-model 2 m temperature spread from GFS, ECMWF, ECMWF AIFS, GEM — four models and three centres, named because a roster is a fact about a chart: two of these are ECMWF's, and where those two agree they agree partly for family reasons. Raw model output on every side — nothing here is bias-corrected, unlike the city forecasts elsewhere on this site, so the comparison is what it says it is.
The widest gap is read from the unsmoothed grid, because smoothing fills extremes, and from the drawn frame only — the store reaches further west than this map does, and naming a coordinate a reader cannot find is worse than naming a nearer one.
Valid at 18Z on purpose, and the same hour every day so successive maps compare: mid-afternoon is well mixed, and the models' own terrain heights explain a sixth as much of this picture then as they do at dawn.
Shaded ground is a disagreement rather than an error — none of these models is the truth here, and the map cannot say which is right. For who has actually been closest, the model leaderboards are the place.
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.