Model Output Statistics (MOS) is a program that incorporates output from the LFMII model and compares this output with historical condi-tions since 1969 for a region or station to produce a forecast for that region or station. Different parameters are considered for the warm season (April through September) and the cool season (October through March). In some cases, the model distinguishes differences for four seasons. Output from the LFM MOS model is available in bulletin format out to 60 hours, citing best chances for maximum and minimum temperatures and probabilities for different types of weather occurrence, such as low ceilings, fog, and thunderstorms. Output is also available as a computer-worded forecast for a region or a specific location. It is also available as graphic charts out to 48 hours; these charts indicate various parameters for the United States, such as probability of precipitation, maximum and minimum temperatures, surface winds and winds aloft, and cloud cover.

Implemented in April 1987, the NGM Perfect Prog is very similar to the LFM MOS output in both graphics and bulletin products. The main difference is that Perfect Prog uses the forecast situation from the NGM model, vice the LFMII. The situation is then compared to the historical conditions, and probabilities for various types of weather occurrences are calculated. NGM Perfect Prog forecasts are referred to as NGM Probability listings.

Learning Objective: Identify parameters on the most frequently used National Weather Service facsimile charts.

PARAMETERS ON NWS FACSIMILE CHARTS

Although the National Weather Service produces numerous facsimile charts to distribute oceanographic and meteorological information to its own forecast support offices, DOD, and public users, we cannot describe all of those charts in this training manual. To do so, we would need to publish a separate volume dealing with nothing but the NWS facsimile products. In this section, we will discuss some of the most frequently used products.

Surface Analysis  

The NWSs NMC produces four Northern Hemisphere surface analyses and eight North American surface analyses daily at synoptic and synoptic intermediate hours. All of these analyses are plotted and roughly analyzed by the computers, then reanalyzed by trained analysts. Figure 4-3-2 shows a typical section of a Northern Hemisphere analysis as transmitted on facsimile. It is very similar to the North American analysis in the type of information presented.

The depiction and coding of various elements on these charts is as follows:

Fronts and instability lines as indicated in figure 4-3-3. Frontal type, intensity, and character are indicated near each front in a three-digit code followed by a bracket (]). It may help you to remember this as the "TIC" codefor Type, Intensity, and Characterbut these codes are actually World Meteorological Organization (WMO) codes 1152, 1139, and 1133, respectively. These codes are given in table 4-3-1. Pressure troughs are also labeled with the phonetic abbreviation trof.

Isobars (lines of equal pressure) are drawn as solid lines, usually using a 4-millibar interval and a base value of 1,000 millibars. Intermediate isobars may be shown as dashed lines. All isobars are labeled with two figures, for tens and units of millibars.

Pressure centers are indicated by Hs (for high pressure) and Ls (for low pressure) with central pressure values given in two figures, for tens and units of millibars.

Date and time of the analysis are printed in an identification block in the lower left (and upper right on the Northern Hemisphere analysis) corner of each chart.

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