Taking a look at the Model Output Statistics (MOS)

| September 15, 2019 @ 9:00 am


(Photo Credit: National Weather Service)

DISCUSSION: The Model Output Statistics (MOS) is the output from models such as the Global Forecasting Systems (GFS) and the North American Model (NAM). MOS is often used to help with forecasting for elements near the surface such as temperature and wind, which are more applicable to civilians. The MOS in the U.S. is sent out multiple times a day with the Localized Aviation MOS Product (LAMP) going out every hour, the GFS MOS every 6 hours, the NAM MOS and the extended GFS MOS every 12 hours.
The MOS has several advantages compared to other models that are shown graphically. One such advantage is that the MOS is more point-specific to an airport as shown above (KSJC) or at some specific locations including a weather station at Central Park in New York (KNYC) instead of a grid, as is most typical displayed by other models. Another advantage that MOS has compared to other models is that the MOS is able to tell you how low of a cloud ceiling to expect as compared to the model graphics which only shows coverage but not height. Additional advantages are that the MOS is able to give you an indication of the probability of precipitation as well as being able to determine if fog will occur as compared to the model where the graphs are sometimes increasingly difficult to identify both. The output is often used by students and broadcast meteorologists to make forecasts with regards to temperatures, winds, clouds and precipitation.
Let’s look at the elements of the MOScast (MOS Forecast):
DT: Date of the month (in the diagram above: August 19/August 20)
HR: Hour of the specific day in Universal Time Coordinated (UTC) or Greenwich Median Time (GMT) (15)
N/X: Nocturnal minimum temperature and maximum daytime temperature in Fahrenheit (59 77)
TMP: Temperature in Fahrenheit
DPT: Dewpoint in Fahrenheit
CLD: Cloud coverage (no clouds=CL 0 to 2/8 of the sky=FEW 2/8-4/8=SCT 5/8-Almost 8/8=BKN and completely cloudy=OVC)
WDR: Wind Direction at 10 meters above the ground (Multiply by 10 to get direction i.e. 32 is 320°)
WSP: Wind speed in knots (nautical miles per hour) at 10 meters above the ground (1 knot is 1.151 mph)
P06: Probability of Precipitation (percent chance of rain and/or snow) in the 6-hour period ending at that time
P12: Probability of Precipitation in the 12-hour period ending at that time
Q06: The Quantitative Precipitation Forecast (QPF) (amount of precipitation forecasted) in the 6-hour period ending at that time [See Chart below for values]
Q12: The QPF for the 12-hour period ending at that time [See chart below for values]
T06: Probability of thunderstorms the 6-hour period ending at that time
T12: Probability of thunderstorms in the 12-hour period ending at that time
CIG: Cloud ceiling height forecasted (See chart below for values)
VIS: Visibility in miles (See chart below for values)
OBV: Phenomena which would cause obscuration to visibility (See chart below for values).

However, the MOS does have some disadvantages. Among the major disadvantages is that there is a temperature bias most of the time where the MOS is either too warm or too cold and needs to be adjusted. However, the MOS bias can be calculated and adjusted by comparing the temperatures to the METAR (Meteorological Terminal Air Report) temperatures of the specific location which some websites do such as here. In addition, the MOS goes out only 72 hours in the forecast and is not graphic so it is not an effective tool for forecasting for tropical systems as compared to the GFS which goes out for 384 hours and the NAM which goes for 84.
To find out more about MOS forecasts click here and to see other MOS products click here. To find out more about other educational topics in meteorology click here!’

?©2019 Meteorologist JP Kalb

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