General Meteorology Laboratory #11. Forecast Models

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1 General Meteorology Laboratory #11 Name Partners Forecast Models Date _ Section Purpose: Develop the ability to contour two dimensional data and use the resulting information to locate a cold front. Equipment: Station Thermometer Anemometer Psychrometer Psychometric Tables Min./Max. Thermometer Barometer Rain Gauge Barometric Correction Tables I. Surface observation. (Optional) Begin the first 1/2 hour of lab performing a surface observation. Make sure you include pressure (station, sea level, and altimeter setting), temperature, dew point temperature, wind (direction, speed, and characteristics), precipitation, and sky conditions (cloud cover, cloud height, & visibility). From your observation generate a METAR and a station model. A. Generate a METAR for today's observation B. Generate a station model for today's observation. II. Forecast Model Data In this lab we will look at the forecast model data available at There are several web sites that have similar data to this one; however, I will use this one due to familiarity and due to the fact that I know Dan Vietor, who was a principle developer of this software. From this site you can obtain current weather data, radar and satellite images, as well as forecast model data. All of these data sources are useful when making a weather forecast. We will spend today becoming familiar with the data and reading the maps. Next week we will use this information to see why weather systems behave as they do. Today we will look at the Model Output Statistics (MOS) and the Aviation Model (AVN). Once you learn to read data from the AVN model, it is easy to understand any of the other models present at this web site (NAM, Eta, and ECMWF). Ohio State also has a web site with forecast model data links. You can find this data at You will note that the data is the same as the Unisys site. It is just organized differently.

2 General Meteorology Page 2 Lab Experiment #11 A. MOS (Model Output Statistics) The MOS Forecast product is generated from a numerical weather prediction model. It provides forecasts for specific locations in the country using a computational interpretation of the model data. This process is objective and can be improved upon by a human forecaster. An experienced forecaster will learn how the MOS differs from actual weather experienced at their location and will naturally provide more accurate forecasts. MOS forecasts are generated for different weather models, such as the Eta and NAM models. You can visit to find these weather products. It is useful to compare forecasts of various models since each have their strengths. A comparison of various models with respect to precipitation forecasts is available at NAM MOS Data From the web page, click on the link Model Statistics under the label Forecasts in the left column. Next click on NAM MOSPlots in the right column. There are NAM MOS Plots for 12hr, 24hr, 36hr, 48hr and 60hr forecasts. In the spaces below draw the station model forecasts for ton, OH for the next 60 hours. Also indicate the local day and time for these forecasts. ton is not included on the national map, so you will need to visit the Atlantic region (designated with Alt) to get this data. Also indicate whether any precipitation will occur. 12 Hr 24 Hr 36 Hr 48 Hr 60 Hr Time Time Time Time Time

3 General Meteorology Page 3 Lab Experiment #11 Go back to the original MOS web page and click on the Meteogram link. ton is not available, so we need to choose stations close to the ton area. The three closest stations are IND (Indianapolis), CVG (Cincinnati) and CMH (Columbus). Go to these three locations and chose the INV option and then print. You only need to print the first page for each station. In the space below summarize the differences you see in the forecasts and then make your own forecast for the morning low in ton and the high for tomorrow. Summarize the differences between the 3 forecasts. Forecast: Tomorrow morning low temperature Tomorrow afternoon high temperature B. AVN (Aviation) Model The AVN model is one of the oldest operational models and has forecasts available for not only the US, but also Europe, east Asia, South America and Australia. Each of these regions is the result of separate computer simulations. Unisys makes these results available in different formats. The domestic forecast products have more options for displaying the data than the foreign forecasts. SL Pres/Prec Click on the GFS/Avn Model link at Next click on the image displayed in the middle of the screen. This will send you to the 4 panel plot of the sea level pressure and precipitation forecast. At the top of the page are a number of options. Selecting a particular time will give you a more detailed image of the United States forecast. Using this data determine if there will be any precipitation in ton over the forecast period. Also record the amount of precipitation expected during each of the 12 hour forecast periods. Does the AVN forecast match the NGM MOS results obtained earlier? 60 hr 72 hr Precip (in) How do the precipitation forecasts differ between the AVN and NGM MOS model results?

4 General Meteorology Page 4 Lab Experiment # mb Plot This plot represents a portion of the atmosphere that is about 5,000 ft above the surface (~1 mi or 1.6 km). This is the top of the atmospheric boundary layer and, therefore, is not affected by the daily heating and cooling cycle. From the available plots determine the 850 mb air temperature and wind direction for ton, OH. Also locate where the high and low pressure systems are over the United States. Just indicate the state over which they are located. Temperature Wind Direction High Pressure Low Pressure 500 mb Plot This plot represents the middle of the atmosphere. The wind at this level dictates the motion of most weather systems and precipitation and is, therefore, called the steering level. The winds tend to follow the height contours giving geostrophic winds for straight contours and gradient winds for curved contours. Vorticity is an indication of rotational or eddy motion in the atmosphere. High vorticity can strengthen surface low pressure systems. From the available plots determine the 500 mb height and wind direction for ton, OH. Also locate where the regions of high vorticity are present over the United States. Just indicate the state over which they are located. Height Wind Direction High Vorticity

5 General Meteorology Page 5 Lab Experiment # mb Plot This plot represents the upper troposphere. The key features on this map are the high speed upper winds or jets. Jets are locations where the wind speed exceeds 100 knots. Locate the jets over the United States and indicate their maximum wind speeds. Jet location and wind speed C. Comparison of Models There are a number of different weather models available and they each have their strengths and weaknesses. From the two web links given below record the resolution and length of forecast for these different models. Also note any aspect of the model that may make it better than other models for forecasting purposes. Model Resolution Length of Forecast Advantageous Features NGM Eta AVN MRF ECMWF