NGM MOS Forecast Bulletins  

The NGM MOS guidance bulletins, or the NGM Perfect Prog Forecasts, were first issued shortly after the April 1987 Technical Procedure only the stations three-letter identifier. The second is a POP/MN-MX line with forecasts of 12-hour probability of precipitation forecasts followed by a forecast maximum or minimum temperature. The third line is a WIND forecast identical to the LFM MOS wind forecast, and the last line is a CLDS forecast identical to the LFM MOS forecast. These bulletins are available under the MANOP series beginning with FOUS14 complete format should be very similar to the LFM MOS as well. At present, in situations when the NGM charts and forecast guidance are followed, the NGM MOS bulletins should serve as the primary forecasting aid for the informa-tion that is covered.

The trajectory bulletins provide 24-hour forecasts for parcels of air in the lower atmosphere. The objective of these forecasts is to provide greater accuracy and detail in the forecasting of moisture distributions below 700 millibars. These forecasts trace the paths of parcels of air that are expected to end up over the forecast station at the 24-hour forecast time. Table 4-3-10 shows a typical trajectory bulletin forecast for a single station. The first and second lines in the bulletin provide the MANOP header and product identification, as well as the date-time group. The third line in the bulletin gives the forecast times, with the first time being the actual analysis time. The fourth line is the headers for each block of data. The fifth line contains the station identifier and the 700-millibar data, while the sixth line contains the 850-millibar data. The last line provides surface information. The data represented in the columns are the following. The examples given are for the 700-millibar line, under the 030000Z analysis data column.  

LAT is the north latitude of the parcel of air at the specified time, to the nearest tenth of a degree. In our example, the parcel of air forecast to be over Miami at 040000Z was at 207, or 20.7N latitude at the 030000Z analysis time.

LON is the west longitude, to the nearest tenth of a degree, of the parcel of air at the time specified. The hundreds unit is dropped for longitudes greater than 100. The 700-millibar air parcel over Miami at the 040000Z forecast time was at 836, or 83.6W longitude at the 030000Z analysis time.

PPP is the parcels pressure, in millibars, at the time specified. The thousands unit is dropped for pressures over 1,000 millibars. The parcel of air at 700 millibars over Miami at the 040000Z forecast time was at 702, or 702 millibars at the 030000Z analysis time.

This same data format is followed for all three levels for the analysis time, as well as for the 6-, 12-, and 18-hour forecast times. The data in the 24-hour forecast column is different. The elements presented in that column are the MTP, TEMP, DEWPT, and K.

MTP is the model terrain pressure, or the forecast surface pressure (station pressure) at the station for the forecast time (040000Z). 008 means millibars.

TEMP is the temperature of the air parcel in degrees Celsius at the forecast time. 7.6 means the 700-millibar temperature will be 7.6C at the forecast time.

DEWPT is the dew-point temperature of the parcel of air in degrees Celsius at the forecast time. 5.3 means the dew-point temperature at 700 millibars will be 5.3C at the forecast time.

Following the trajectory paths not only will allow you to see where the air over your station

at the forecast time originated, but it will allow you to determine vertical velocities. For instance, the 700-millibar parcel originated at 702 millibars at 030000Z, and 6 hours later will have a pressure of 724 millibars. This implies a net downward vertical motion of 22 millibars per 6 hours. Some of the best uses of trajectory data is to forecast the changes on a Skew T, Log P MANOP for your location.

In this lesson we have discussed some of the charts and products used daily by Navy Aerographers Mates. We have addressed the minimum knowledge you must have in order to perform your day-to-day duties. You can acquire additional information by reading or reviewing some of the sources cited in this lesson. In time, through the continued use of the charts and products we have discussed, you will acquire the skill to "read" the charts and products as easily as you read a book. This skill can only be obtained through practice. As an exercise, in your weather briefing area, have your Chief, LPO, or Section Leader help you to locate some of the charts and products we have discussed. Interpret as much information as you can from each of the charts or bulletins. Your Chief or LPO will assist you with any difficulties in interpretation. Discuss your interpretation with them to ensure you are interpreting the information correctly.

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