500 mb heights, how far apart
GFS, ECMWF, ECMWF AIFS, GEM · Run 00Z 1 Oct · +18 h · Valid Thu 18Z 1 Oct
Gap between the highest and lowest 500 mb height of these models
Region Southern Plains
The readings under the map are for the whole map, not only the part shown.
GFS, ECMWF, ECMWF AIFS, GEM · Run 00Z 1 Oct · +18 h · Valid Thu 18Z 1 Oct
Gap between the highest and lowest 500 mb height of these models
Widest gap 7.7 dam at 20.0N 110.0W · unshaded ground is where all 4 land within 2 dam of each other
Thin lines are the 500 mb height itself, every 6 dam — the per-cell median of the 4, so a pattern no single model forecast. Read the troughs and ridges off them; the shading is where that pattern is in doubt.
Shows where the models disagree about the 500 mb pattern at 18Z 1 Oct — the day you choose, always at the same hour so that successive days compare.
Methodology
Across-model 500 hPa geopotential height 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. Uncorrected model output on every side.
Heights are in decametres (tens of metres), the unit every 500 mb chart uses: 582 is 5,820 m. The bands were cut against what this field actually does — over twenty valid times in early September the models sat within 2 dam of each other on two thirds of the frame, and past 8 dam on about one cell in eighty — so the scale is the disagreement's own, not a round guess.
The pattern at 500 mb steers the weather under it, which is why a forecaster looks here first: two models that agree on tomorrow's temperature and disagree by 10 dam on where the trough sits are not agreeing about the day after. Spread grows with lead — a day-1 map is mostly unshaded, and that is the picture.
Nothing here is smoothed. The shading, the contours and the widest gap are all read from the models' own grids at their own resolution, because averaging a cell into its neighbours fills in exactly the extremes this map exists to show — and a number printed over a colour has to agree with it. The widest gap comes from the drawn frame only.
Valid at 18Z and the same hour every day so successive maps compare — the temperature face's hour, kept so a reader switching between them compares one moment.
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.
This map is drawn from model output we store ourselves, not from anyone's picture of it, and is based on data and products of NOAA, the European Centre for Medium-Range Weather Forecasts (ECMWF) and Environment and Climate Change Canada. 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.
Sources and licences
- NOAA: GFS, from NOAA's NOMADS server. US government data, not subject to copyright (NOAA/NWS terms of use).
- ECMWF: IFS and AIFS Single, from ECMWF's open data. This service is based on data and products of the European Centre for Medium-Range Weather Forecasts (ECMWF). Source: www.ecmwf.int. This ECMWF data is published under a Creative Commons Attribution 4.0 International (CC BY 4.0). ECMWF does not accept any liability whatsoever for any error or omission in the data, their availability, or for any loss or damage arising from their use.
- Environment and Climate Change Canada: GEM, from the MSC Datamart. Data Source: Environment and Climate Change Canada, under its Data Services End-use Licence.
What we change: each field is cropped to the frame these maps share when we download it, and each map then smooths, contours, differences or ranks those numbers as its Methodology says. These are our maps of the providers' numbers, not their products, and none of them has reviewed or endorsed this site.
Coastlines, borders, lakes and place names: Natural Earth, public domain.