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Oceanographic nowcast and forecast guidance are scientific predictions about the present and future states of a water body (generally including water levels, currents, water temperature and salinity). These predictions rely on either observed data or forecasts from large-scale numerical models. A nowcast incorporates recent (and often near real-time) observed meteorological, oceanographic, and/or river flow rate data and/or analyzed (e.g. gridded) meteorological and oceanographic products. A nowcast covers the period of time from the recent past (e.g., the past few days) to the present, and it can make predictions for locations where observational data are not available. Forecast guidance incorporates meteorological, oceanographic, and/or river flow rate forecasts and makes predictions about the future states of a water body. A forecast is usually initiated by the state of a nowcast.
NOAA's National Ocean Service (NOS) collaborated with the Great Lakes Environmental Research Laboratory (GLERL) in developing and transitioning the new generation of Lake Michigan and Huron Operational Forecast System (LMHOFS) to operations, to provide higher-resolution forecast guidance of water level, currents and water temperature. The upgraded LMHOFS uses the Finite Volume Community Ocean Model (FVCOM) as its core ocean circulation model and has extended the forecast horizon to 120 hours. It is expected to generate a more accurate model output than the former LMOFS and LHOFS, which have separate model domains based on the Princeton Ocean Model (POM).
The LMHOFS model grid has 90,806 nodes and 171,377 elements. The cell size ranges from 50 m to 2.5 km, with higher resolution along the shoreline and in the shallow western basin and coarser resolution for the open waters in both lakes. The grid has a minimum depth of 0.5 m and maximum depth of 271.4 m. The model has 21 vertical sigma layers.
Nowcast surface forcing are from NCEP's hourly updated High-Resolution Rapid Refresh (HRRR) atmospheric model and forecast surface forcing are from Global Forecast System (GFS) model output. USGS Real-time river discharge observations from 4 major river gauges are provided to drive the model. The unaccounted inflow/outflow due to combination of inflow from additional tributaries, runoff, and over lake precipitation and evaporation is estimated by the offset of the recent observed water level change (and the subsequent water volume change of the lakes) and the known water point source contributions. This unaccounted infow/outflow then will be imposed back into the surface forcing either as pseudo precipitation/evaporation depending on its positive/negative value. In addition, the observed water level at St. Mary River inlet is used as the open boundary condition to further secure water balance in the system.
LMHOFS runs four times per day with 6-hour nowcast and 120-hour forecast for each cycle on the NCEP's Weather Climate Operational Supercomputer (WCOSS).
The LMHOFS graphics archive is located at CO-OPS ftp server.
LMHOFS output files are in NetCDF format. An archive of LMHOFS NetCDF nowcast and forecast files can be accessed from CO-OPS THREDDS server.
All CO-OPS official real-time products, including nowcast and forecast guidance from LMHOFS are monitored by the CO-OPS's Continuous Operational Real-Time Monitoring System (CORMS). CORMS provides 24 hour per day, 7 day per week monitoring and quality control of sensors and data in order to ensure the availability, accuracy, and quality of water level, current, and other marine environmental information. CORMS is intended to identify invalid and erroneous data and information before application of the data by real-time and near real-time users.