OCTOBER 2026 NOR'EASTER — DELMARVA FORECAST COMPARISON

Forecasts initialized October 18 and 19, 2026 at 00 UTC. Main checkpoint:
October 20 at 06 UTC, or 02:00 EDT. Wind components are m/s; pressure is Pa.
Calculations convert wind speed to knots. All CSV timestamps are UTC.

Recompute the article's numbers with Python 3 (standard library only):
  python reproduce.py

Regenerate the comparison figures (numpy and matplotlib required):
  python plot_figures.py
Figures are written to regenerated/ as PNG and SVG. The packaged web PNGs are
the figures used in the English review. Layout and typography can vary with
Matplotlib and font versions.

requests.json records each exact GribStream MCP query, associated source CSV,
row count and byte size. It contains no credentials or expiring download links.
Rows are sorted by location, initialization, valid time and member before
analysis. Native coordinate metadata is retained for map and sampling checks.
The full useful native output cadence is retained: hourly HRRR/GFS, 3-hourly
IFS and 6-hourly AIFS. The HRRR map retains 53,200 sampled native 3 km cells.

The main sample is 38.50N,74.75W; the Cape Hatteras comparison is 35.00N,75.50W.
All 51 AIFS ensemble members are included at each selected valid time. The
previous ensemble request covers the five six-hourly outputs at leads 48–72
needed for the revision check. HRRR's horizon is 48 hours. The spatial mean
uses native cell centers within 38.375–38.625N,74.875–74.625W.

These fields describe forecast disagreement and evolution during an active
event. Ensemble percentiles are raw member distributions. Independent,
appropriately exposed observations are needed to establish forecast accuracy.
The farther-west GFS pressure minimum is a plausible contributor to its stronger
coastal wind band; a causal decomposition has not been established.

Forecast sources: NOAA HRRR and GFS; ECMWF IFS, AIFS Single and AIFS Ensemble,
retrieved through GribStream MCP. Model/catalog and source references:
  https://gribstream.com/models/hrrr
  https://gribstream.com/models/gfs
  https://gribstream.com/models/ifsoper
  https://gribstream.com/models/aifsoper
  https://gribstream.com/models/aifsenfo
  https://gribstream.com/docs

Meteorological context read for the article:
NWS Mount Holly, FXUS61 KPHI 191020 AFDPHI, October 19, 2026 at 10:20 UTC:
  https://forecast.weather.gov/product.php?format=CI&glossary=1&highlight=off&issuedby=PHI&product=AFD&site=PHI&version=1
NWS Newport/Morehead City, FXUS62 KMHX 182350 AFDMHX, October 18 at 23:50 UTC:
  https://forecast.weather.gov/product.php?format=CI&glossary=1&issuedby=MHX&product=AFD&site=NWS&version=1
These bulletin URLs serve the latest version; the issue headers identify the
editions used for the October 19 article.

Coastline: Natural Earth 1:50m, public domain.
  https://www.naturalearthdata.com/about/terms-of-use/

The original review package was attached to its private Page. For repository
integration, the same fixed historical runs/fields were retrieved again through
GribStream MCP, and the headline values, spatial checks, ensemble ranges and
revisions were independently recalculated. The recovered review figures are
retained here with the reproducible data and regeneration code.
