Choosing among eight deterministic forecast models
Eight deterministic models publish through the same profile contract with different resolutions, lead times, pressure levels, optional capabilities, and field semantics. Choose by lead time and required detail, then use disagreement to locate sensitivity in the day.
Resolution versus horizon
Grid spacing and forecast reach trade differently across the catalogue; one number cannot stand in for model suitability.
HRDPS West: 1 kilometre grid and 48 hour horizon. HRDPS continental: 2.5 kilometre grid and 48 hour horizon. HRRR CONUS: 3 kilometre grid and 48 hour horizon. NAM CONUS nest: 3 kilometre grid and 60 hour horizon. RDPS: 10 kilometre grid and 84 hour horizon. NAM: 12 kilometre grid and 84 hour horizon. GDPS: 15 kilometre grid and 240 hour horizon. GFS: 25 kilometre grid and 384 hour horizon.
Choose by lead time and required terrain detail
Section titled “Choose by lead time and required terrain detail”| Question | Begin with | Then compare |
|---|---|---|
| What will the launch do today? | HRDPS 1 km / 2.5 km, HRRR or NAM nest 3 km | each other, then observations |
| How stable is tomorrow’s forecast? | the same high-resolution models | RDPS |
| Is the weekend worth protecting? | RDPS, NAM 12 km, GDPS | GFS trend |
| Is next week worth watching? | GDPS / GFS | wait for shorter-range guidance |
A global model can identify a ridge or trough many days out. It cannot resolve the launch cycle on a particular mountain face. Use long-range guidance to allocate attention, not to choose an hour.
Grid resolution controls terrain and local detail
Section titled “Grid resolution controls terrain and local detail”Each grid cell averages terrain and atmosphere across its footprint. A finer grid can place model terrain elevation closer to a launch and represent smaller weather features; a coarser grid describes the regional setup. Neither resolution guarantees the right answer.
Model terrain elevation changes pressure-level filtering and every height derived from the surface parcel. The windgram derivations define that dependency. Current grid spacing, domains, and verified model terrain elevations belong in the forecast model feed reference.
Time steps and pressure levels limit chart detail
Section titled “Time steps and pressure levels limit chart detail”Some windgrams contain hourly columns; others contain three-hourly columns. Their curves may look equally continuous, but the latter carry fewer observations of the model state. A narrow peak between three-hour steps is interpolation, not another forecast sample.
Vertical sampling imposes the same limit. Missing or widely spaced pressure levels reduce the detail available for lapse rate, wind shear, parcel crossings, and cloud layers. Compare the structure and sample positions behind a line before treating two smooth traces as equivalent evidence.
What each model declares
The discovery catalogue, rather than frontend assumptions, decides which fields and pressure levels exist.
HRDPS West (ECCC): publishes heat fluxes, 1 h max gust, CAPE, PBL height; 9 pressure levels from 925 to 600 hPa. HRDPS continental (ECCC): publishes heat fluxes, 1 h max gust, CAPE, PBL height; 14 pressure levels from 1015 to 600 hPa, with vertical velocity at 1000, 850, 700 hPa. HRRR CONUS (NOAA): publishes heat fluxes, instant gust, CAPE, CIN, PBL height, cloud layers; 9 pressure levels from 925 to 600 hPa, with vertical velocity at 925, 900, 875, 850, 800, 750, 700, 650, 600 hPa. RDPS (ECCC): publishes heat fluxes, 1 h max gust, CAPE, CIN, PBL height; 14 pressure levels from 1015 to 600 hPa, with vertical velocity at 850, 700 hPa. GDPS (ECCC): publishes heat fluxes, 1 h max gust, CAPE, CIN, PBL height; 14 pressure levels from 1015 to 600 hPa, with vertical velocity at 850, 700, 600 hPa. GFS (NOAA): publishes heat fluxes, instant gust, CAPE, CIN, PBL height, cloud layers, a cloud profile; 8 pressure levels from 925 to 600 hPa, with vertical velocity at 925, 900, 850, 800, 750, 700, 650, 600 hPa. NAM (NOAA): publishes heat fluxes, instant gust, CAPE, CIN, PBL height, cloud layers; 9 pressure levels from 925 to 600 hPa, with vertical velocity at 925, 900, 875, 850, 800, 750, 700, 650, 600 hPa. NAM CONUS nest (NOAA): publishes heat fluxes, instant gust, CAPE, CIN, PBL height, cloud layers; 9 pressure levels from 925 to 600 hPa, with vertical velocity at 925, 900, 875, 850, 800, 750, 700, 650, 600 hPa. REPS (ECCC): publishes heat fluxes; 5 pressure levels from 1000 to 500 hPa. GEPS (ECCC): publishes heat fluxes, CAPE, CIN; 5 pressure levels from 1000 to 500 hPa.
Generated from models.json; pressure columns share a 1015–500 hPa scale.
Use model disagreement to locate forecast sensitivity
Section titled “Use model disagreement to locate forecast sensitivity”Similar traces support the conclusion that the large-scale setup is straightforward. Separated traces identify sensitivity—to timing, moisture, initialization, terrain, or model physics—but a majority is not automatically correct. Related systems can share errors, and a coarse model can reach the right answer for the wrong local reason.
Use the comparison to locate the split:
| Pattern | First suspect |
|---|---|
| early timing split | boundary-layer development |
| persistent vertical offset | model terrain elevation or moisture |
| late-day fan | cloud development or collapsing surface heat |
The interactive timing comparison shifts development timing while holding its shape steady. Use the shared hour lens to expose the displacement, then inspect each model’s published profile.
The same development, shifted in time
Scrub one shared teaching hour across two controlled profiles whose daytime development starts at different times.
An interactive comparison of two profiles with matching daytime-development shapes shifted to earlier and later teaching hours.
Earlier development
Later development
Conclusion. Matching development shapes can occupy different teaching hours; reading only one instant hides that timing displacement.