The weather maps shown here are generated from the
NCEP Global Forecast System (GFS) model. GFS is the primary operational model framework underlying U.S. NOAA/NWS
weather forecasting. The model is run four times daily on a global T1534 gaussian grid (~13 km) to produce 16-day
forecasts. Here, we use 0.25°x0.25° (~30 km) output grids available from
NOMADS, and calculate daily averages from eight 3-hourly timeslices starting at 0000 UTC.
- Sea surface temperature (SST) and SST anomaly maps are generated from
NOAA Optimum Interpolation SST version 2 (OISST V2).
OISST is a 0.25°x0.25° blendend dataset derived from satellite, ship, and buoy measurements. The SST anomaly
is based on a 1971-2000 NOAA climatology.
- Temperature refers to air temperature at 2 meters above the surface. The temperature anomaly is made in
reference to a 1979-2000 climatology derived from the
reanalysis of the NCEP Climate Forecast System (CFSR/CFSV2) model. This climate baseline is used instead of the
1981-2010 climate normal because
it spans a period prior to significant warming of the Arctic beyond historically-observed values. For context,
see this timeseries plot showing how various
climate baselines compare against the NASA GISS
1880-2014 global land-ocean temperature index.
- GFS Model Bias Correction — GFS has a systematic model bias compared to CFSR/CFSV2 in which the diurnal
cycle has greater amplitude over areas of snow/ice and hot desert. A correction term, calculated from the difference
between GFS and CFSR/CFSV2 on average per month from June 2015 - May 2016, is therefore applied such that
regional temperature anomaly values are consistent with CFSR/CFSV2. A timeseries plot showing the bias corrections
for each region is shown here. Temperature anomaly maps showing uncorrected and corrected GFS vs. CFSR/CFSV2 can also
Note that bias-corrected GFS-CFSR temperature anomalies will still differ slightly from those calculated from
CFSV2-CFSR. The most reliable temperature anomaly estimates can be found in the
Daily Reanalysis Maps image archive.
The archive is updated once or twice per month.
See this NCEP/NWS discussion for
additional information on model bias.