Temperature Anomaly

Sea Surface Temperature

Sea Surface T Anomaly

Precipitation & Clouds

Mean Sea Level Pressure

Precipitable Water

Surface Wind

Jetstream Wind

Sea Ice & Snow

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Data Source

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.

Additional Details

  • Sea surface temperaure (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 model bias compared to CFSR/CFSV2 in which very warm and very cold temperatures tend to be greater, leading to more pronounced temperature anomalies. In an effort to diminish the effect of this bias, a simple correction factor (CF) is applied to each regional temperature anomaly. Correction factors were derived by calculating the average percent difference between GFS-CFSR and CFSV2-CFSR using daily model output grids from June, 2015. The resultant correction factors are 0.49 (World), 0.46 (Northern Hemisphere), 0.64 (Southern Hemisphere), 0.53 (Arctic), 0.63 (Antarctic), and 0.54 (Tropics). The terms are applied in the form:
    Tanomaly region corrected = Tanomaly region * CF

    * 2/23/2016 — NEW GFS MODEL BIAS CORRECTION FACTORS calculated from winter (DJF) GFS-CFSR estimates: 0.7 (World), 0.75 (Northern Hemisphere), 0.5 (Southern Hemisphere), 1.1 (Arctic), 1.0 (Antarctic) and 0.5 (Tropics). GFS model bias appears to vary with the seasons due to snow/ice and albedo processes, and therefore season-specific correction terms will be applied from now on. As stated below, refer to the CFSR/CFSV2 Daily Reanalysis Maps interface for the most reliable daily temperature anomalies. CFSR/CFSV2 daily reanalysis maps are updated once or twice per month.

    Note that bias-corrected GFS-CFSR temperature anomalies will differ slightly from those calculated from CFSV2-CFSR (see these comparisons for June 30, 2015). CFSV2-CFSR is apples-to-apples; therefore, difference maps within the Daily Reanalysis Maps image archive should be considered reliable, and take precedent over the GFS-CFSR anomaly maps shown here as part of the current 7-day forecast.

    See this NCEP/NWS discussion for additional information on model bias.