HOW TO DECODE THE MODEL OUTPUT STATISTICS GUIDANCE MESSAGE

INTRODUCTION

The Hydrometeorological Center of the National Environmental Prediction Centers (formerly National Meteorological Center) produces a short range (6 to 60 hours) MOS (Model Output Statistics) guidance package generated from the NGM (Nested Grid Model) for over 300 individual stations in the continental United States. These alphanumeric messages are made available at approximately 0400 and 1600 UTC for the 0000 and 1200 UTC forecast cycles, respectively.

To indicate snow and precipitation type forecasts, the message varies between the cold (16 Sep through 15 May) and warm (16 May through 15 Sep) seasons. Snow and precipitation type forecasts are never issued for certain Florida and California stations.

DECODING THE MESSAGE

Each line in the body of the message begins with an abbreviation of no more than five alphanumeric characters identifying the particular forecast sequence of the weather element appearing in that line. These abbreviations are noted in the description of each part of the message below:

MESSAGE HEADER

This message heading accompanies each forecast message and serves for identification purposes:

The first line of the message includes a WMO header used for communications purposes:

FOUS14 KWBC MMDDHH

The second line of the header includes:

STATION LOCATION IDENTIFIER

• A three-letter FAA/NWS identifier is the first entry of the second line and is used to identify the station for which the forecast has been prepared.

NWS REGIONS:

• Immediately following the station locator, a letter indicates the NWS Regions where this message is transmitted over the AFOS network; more than one letter indicates that the message will appear in more than one region. The NWS Region code is:

E                   Eastern              C                   Central              
S                   Southern             W                   Western              

"NGM MOS GUIDANCE" Identifies the message contents.

MM/DD/YY Identifies the date of model production:

MM = month (1 - 12)

DD = day (1 - 31)

YY = year

0000 UTC or 1200 UTC Identifies the NGM forecast cycle, or the initial data time.

• The third and fourth lines (DAY, HOUR) are header lines for the columns in the message text and denote the day of the month and hour (UTC) at which these forecasts are valid ("specific time forecasts") or the time corresponding to the end of a particular interval, such as those intervals used for forecasting precipitation accumulation.

MAXIMUM/MINIMUM TEMPERATURE FORECASTS: MX/MN

• The anticipated maximum and minimum surface temperature forecasts (MX/MN) are the extreme temperatures expected to occur within consecutive 12 hour intervals. These forecasts are listed directly under the appropriate forecast time header for 24, 36, 48 and 60 hours after the initial data time (0000 or 1200 UTC). The order depends upon the time of the forecast production run in relation to the local day/night cycle. For reference purposes, daytime is defined from 0700 to 1900 Local Standard Time (LST), while nighttime runs between 1900 and 0800 LST. Hence, the order of the MX/MN sequence for the 0000 UTC cycle starts with the maximum temperature for the calendar day (today), tonight's minimum, tomorrow's maximum and tomorrow night's minimum. The sequence for the 1200 UTC cycle is tonight's minimum, tomorrow's maximum, tomorrow night's minimum and the following day's maximum.
• Each extreme temperature forecast is tabulated in whole degrees Fahrenheit, with a maximum of three characters, thereby permitting temperatures of 100°F or more to be included. Temperatures below 0°F contain a minus sign. A missing forecast is indicated by "999".

SURFACE TEMPERATURE and DEWPOINT FORECASTS:
TEMP and DEWPT

• Forecasts of the surface air temperature (TEMP) and dewpoint (DEWPT) for each specific three hour forecast time are provided from 6 hours to 60 hours after 0000 or 1200 UTC. These forecasts, listed on two separate lines, are in whole degrees Fahrenheit. Temperatures below 0°F contain a minus sign. A missing forecast is indicated by "999". Consecutive forecasts of 100°F or more (or -10°F or less) will appear without intervening spaces separating the forecasts.

OPAQUE CLOUD AMOUNT CATEGORICAL FORECASTS: CLDS

• Specific time forecasts of opaque cloud cover categories are made at 3 hour intervals from 6 to 60 hours following 0000 or 1200 UTC. These categorical forecasts, appearing under each forecast time header, use the following two letter designators identifying the best category:

OPAQUE CLOUD COVER CATEGORIESCL                  CLEAR               0/10 of opaque clouds                    
SC                  SCATTERED           1/10 to 5/10 of opaque clouds            
BK                  BROKEN              6/10 to 9/10 of opaque clouds            
OV                  OVERCAST            0/10 of opaque clouds or totally         
XX                  MISSING             obscured                                 
                                        Missing                                  

SURFACE WIND DIRECTION and WIND SPEED FORECASTS:
WDIR & WSPD

• Forecasts of the 1 minute-average near-surface wind direction and wind speed at the specific 3 hour forecast times are listed starting with 6 hours after 0000 or 1200 UTC and ending at 60 hours. Each variable is listed on a separate line.
• The wind direction (WDIR) forecasts are coded as two digits, in units of tens of degrees measured clockwise from true north (01 = 10° to 36 = 360°); calm conditions are coded "00".
• The two-digit wind speed (WSPD) forecasts are given to the nearest knot, with a maximum speed of 98 knots; calm conditions are coded "00".
• Missing WDIR and WSPD forecasts are coded as "99".

PROBABILITY OF PRECIPITATION: POP06 and POP12

• The forecasts of the probability of measurable precipitation (0.01 inch or more of liquid equivalent) occurring within a 6 or 12 hour period are included as the Probability of Precipitation (PoP) in a 6 hour period (POP06) and Probability of Precipitation in a 12 hour period (POP12), respectively. Two lines are employed. The 6 hour PoPs are valid for intervals of 6-12, 12-18, 18-24, 24-30, 30-36, 36-42, 42-48, 48-54 and 54-60 hours after the initial data times. The 12 hour PoPs are valid for intervals of 12-24, 24-36, 36-48 and 48-60 hours after the initial data times.
• In the message, the PoPs are tabulated at the end time of the noted time interval. The numeric values of the PoPs are given to the nearest percent, ranging between 0 and 100%. A missing forecast is indicated by "999".

QUANTITATIVE PRECIPITATION FORECASTS: QPF

• The forecast of the liquid-equivalent precipitation amount accumulated during 6 hour and 12 hour intervals are identified as the QPF. These forecasts are displayed in the FOUS 14 message as a categorical format with a single digit. The appropriate code for each of the eight QPF categories appears in the accompanying table; these categories depend upon the interval length. The QPF forecast for a 6 hour accumulation appears to the left of the diagonal entry at the end of each 6 hour interval corresponding to the specific forecast times starting with 6 hours and concluding 60 hours after 0000 and 1200 UTC. The QPF code for a 12 hour period is to the right of the diagonal appearing at 12 hour intervals commencing with 24 hours after 0000 or 1200 UTC and ending at 60 hours.

QPF CATEGORIES

0                            no precipitation expected;                         
1                            0.01 - 0.09 inches;                                
2                            0.10 - 0.24 inches;                                
3                            0.25 - 0.49 inches;                                
4                            0.50 - 0.99 inches;                                
5                            greater than 1.00 inches for 6 hour QPF;           
6                            1.00 - 1.99 for 12 hour QPF;                       
                             unavailable for 6 hour QPF;                        
9                            Greater than 2.00 for 12 hour QPF;                 
                             no forecast available.                             

THUNDERSTORM AND SEVERE STORM PROBABILITIES:
TSV06 and TSV12

• The forecast of the probability of a thunderstorm occurring during a 6 hour period (TSV06) are displayed to the left of the diagonal for each 6 hour interval commencing with 6 hours and ending with 60 hours following 0000 or 1200 UTC. A conditional probability of severe thunderstorms during the same 6 hour interval appears to the right of these diagonals.
• Likewise, the thunderstorm probability forecasts for a 12 hour period (TSV12), together with the 12 hour conditional severe thunderstorm probabilities, are given on a separate line, using the same format as noted above for TSV06. The 12 hour intervals commence with 6 hours following 0000 or 1200 UTC and end with 54 hours.
• All thunderstorm and severe thunderstorm probabilities are coded to the nearest whole percent. The thunderstorm probabilities range from 0 to 100%, and a missing value is "999". The range for the conditional severe thunderstorm probabilities is from 0 to 98%, with a missing value of "99".

PRECIPITATION TYPE FORECASTS: PTYPE

• The forecast of precipitation type (PTYPE), provided that precipitation will occur, appears in the FOUS 14 message for each specific time. This set of statistics is generated for the cold season only. The forecast code utilizes a single letter, as found in the following table, and is found under each forecast time between 6 and 60 hours after 0000 and 1200 UTC.

PRECIPITATION TYPE CATEGORIES

R              Liquid              Rain, drizzle or a mixture of rain and snow   
Z              Freezing            Freezing rain, freezing drizzle, ice pellets  
                                   or a combination of any of these with other   
S              Solid               types                                         
X              Missing             Snow, snow grains, snow pellets or snow       
                                   showers                                       
                                   Missing                                       

PROBABILITY OF FREEZING PRECIPITATION FORECASTS: POZP

• The conditional probability of freezing precipitation (POZP) forecasts are included in the FOUS 14 message for the cold season only. This time specific probability is based upon the condition that precipitation occurs at that time. In this context, freezing precipitation is defined as the occurrence of freezing rain or drizzle, ice pellets, or any mixture of these elements with other precipitation types. The probabilities are listed to the nearest whole percent (with a range from 0 to 100%) for each specific 3 hour time from 6 to 60 hours after 0000 and 1200 UTC. A missing forecast is identified by "999".

PROBABILITY OF SNOW FORECASTS: POSN

• The conditional probability of snow (POSN) forecasts, based upon the condition that precipitation occurs, are included in the FOUS 14 message for the cold season only. In this context, snow is limited to the occurrence of a pure snow event, to include snow, snow showers, snow grains, snow pellets or any combination of these elements. Snow mixed with rain is considered a liquid precipitation event. The probabilities are listed to the nearest whole percent (with a range from 0 to 100%) for each specific 3 hour time from 6 to 60 hours after 0000 and 1200 UTC. A missing forecast is identified by "999".
• Note: While the conditional probability of liquid precipitation is not provided in this message, the three conditional probabilities for freezing, frozen (snow) and liquid must add to 100%.

SNOW AMOUNT CATEGORICAL FORECASTS: SNOW

• Forecasts of the amount of snow accumulated for both 6 hour and 12 hour periods (SNOW) are included in the FOUS 14 message for the cold season only. A set of five categories is used and the numeric codes are listed below; these categories depend upon the length of the period. These categorical forecasts of snow amount for a 6 hour period appear to the left of the diagonal, under the times commencing with 12 hours and ending with 60 hours after 0000 or 1200 UTC. The forecasts of snow for the 12 hour periods are found to the right of the diagonal, under the times commencing with 24 hours and ending with 60 hours after 0000 or 1200 UTC.

SNOW AMOUNT CATEGORIES

0                        no snow expected;                                      
1                        a trace to less than 2 inches;                         
2                        2 inches or more for 6 hour forecast;                  
4                        2 to less than 4 inches for 12 hour forecast;          
                         unavailable for 6 hour forecast;                       
5                        4 to less than 6 inches for 12 hour forecast;          
                         unavailable for 6 hour forecast;                       
9                        6 inches or more for 12 hour forecast;                 
                         no forecast available.                                 

CEILING HEIGHT CATEGORICAL FORECASTS: CIG

• Ceiling height forecasts (CIG) for each specific 3 hour forecast time from 6 to 48 hours are made using seven categories of ceiling height. The digital code for each forecast ceiling height category appears in the accompanying table. These single digit forecast codes are found under the appropriate valid time.

CEILING HEIGHT CATEGORIES

1                                       less than 200 feet;                     
2                                       200 to 400 feet;                        
3                                       500 to 900 feet;                        
4                                       1000 to 3000 feet;                      
5                                       3100 to 6500 feet;                      
6                                       6000 to 12,000 feet;                    
7                                       greater than 12,000 feet;               
9                                       no forecast available.                  

VISIBILITY CATEGORICAL FORECASTS: VIS

• Ceiling height forecasts for each specific 3 hour forecast time from 6 to 48 hours following 0000 or 1200 UTC are made using five categories of ceiling height. The digital code for each forecast ceiling height category appears in the accompanying table. These forecast codes are found under the appropriate forecast time header.

VISIBILITY CATEGORIES

1                               less than 1/2 mile;                 
2                               1/2 to 7/8 mile;                    
3                               1 to 2 3/4 mile;                    
4                               3 to 5 mile;                        
5                               greater than 5 mile;                
9                               no forecast available.              

OBSTRUCTION TO VISION CATEGORICAL FORECASTS: OBVIS

• Forecasts for those potential conditions causing obstructions to vision are made in terms of three categories for each specific 3 hour forecast time from 6 to 48 hours following 0000 or 1200 UTC. The single letter code for each category appears in the accompanying table. These forecast codes are found under the appropriate forecast time. Reduced visibilities caused exclusively by heavy precipitation events are not predicted.

OBSTRUCTION TO VISION CATEGORIES

F                        fog or ground fog expected;                            
H                        haze expected;                                         
N                        neither for nor haze are expected;                     
X                        no forecast available.                                 

Last revision 10 June 1996

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