ETA-BASED MOS GUIDANCE - THE 0000/1200 UTC ALPHANUMERIC MESSAGES

by

J. Paul Dallavalle and Mary C. Erickson

1. INTRODUCTION

This Technical Procedures Bulletin (TPB) describes the format and contents of the Eta MOS alphanumeric messages generated during the 0000 and 1200 UTC forecast cycles. These messages contain forecasts of the max/min temperature; time-specific surface temperature and dew point; total sky cover; surface wind direction and wind speed; probability of precipitation (PoP) for 6- and 12-h periods; categories of quantitative precipitation for 6- and 12-h periods; and probability of thunderstorms and conditional probability of severe thunderstorms for 6- and 12-h periods. Guidance is provided for projections of 6 to 60 hours for most weather elements. Note that a particular element line (see Sections 3 - 13) is not included in the message when all of the forecasts in that line are unavailable. The messages will become operational during spring of 2002.

2. MESSAGE HEADING

The message heading shown above (see Figs. 1 and 2 also) identifies the station for which the guidance is valid, the forecast cycle, and the day and hour for which the forecasts are valid. In this example, the message is valid for Albany, NY (KALB). All stations are identified by the ICAO four-character identifier.

The "ETA MOS GUIDANCE" appearing on the same line as the station call letters identifies the message contents. The date of the forecast cycle during which the message is issued follows this information. The form of mm/dd/yyyy where mm is the month (1 through 12), dd is the day (1 through 31), and yyyy is the four-digit year is used. The forecast cycle is identified by the standard 0000 or 1200 UTC. In this example, the MOS guidance for KALB was issued from the 0000 UTC forecast cycle of the Eta model on October 24, 2000.

The DT and HR lines denote the date and hour at which the forecasts are valid. The DT line indicates the day of the month. Note that the month is denoted by the standard three or four letter abbreviation. For temperature, dew point, sky cover, wind direction, and wind speed, the date and hour denote the specific time that the forecasts are valid. These forecasts are valid every 3 hours from 6 to 60 hours after initial time. For PoP, quantitative precipitation, thunderstorms, and severe weather, the time indicates the end of the period over which the forecasts are valid. For the max/min temperature, the date group gives only the approximate ending time of the daytime and nighttime periods for which the max and min temperature guidance, respectively, are valid.


3. X/N - MAXIMUM/MINIMUM TEMPERATURE

The max/min surface temperature forecasts are displayed for projections of 24, 36, 48, and 60 hours after the initial data time (0000 or 1200 UTC). Although the forecasts are presented at consecutive 12-h intervals, each forecast is actually valid for a daytime or nighttime period. For the Eta-based MOS guidance, daytime is defined as 7 a.m. to 7 p.m. Local Standard Time (LST). Nighttime is defined as 7 p.m. to 8 a.m. LST. Thus, the valid date in the appropriate column of the DT and HR lines must be converted by the forecaster to his/her local date. This local date then denotes the appropriate daytime or nighttime for the max or min temperature forecast, respectively. For the 0000 UTC forecast cycle, the temperatures are shown in max/min (X/N) order and are valid for today's max, tonight's min, tomorrow's max, and tomorrow night's min. For the 1200 UTC cycle, the temperatures are shown in min/max (N/X) order and are valid for tonight's min, tomorrow's max, tomorrow night's min, and the day after tomorrow's max. Each temperature forecast is presented to the nearest whole degree Fahrenheit, and three characters are allowed. A missing forecast is indicated by a 999.


4. TMP - SURFACE TEMPERATURE

Time-specific 2-m temperature forecasts are valid every 3 hours from 6 to 60 hours after 0000 and 1200 UTC. These forecasts are valid at 0600, 0900,..., 2100, 0000 UTC, and so forth. Each temperature forecast is presented to the nearest whole degree Fahrenheit; a missing forecast is indicated by a 999. Only three characters are available for the temperature forecasts. Thus, two consecutive forecasts of 100 degrees or more or of -10 degrees or less appear with no spaces between them.


5. DPT - SURFACE DEW POINT

Time-specific 2-m dew point forecasts are valid every 3 hours from 6 to 60 hours after 0000 and 1200 UTC. These forecasts are valid at 0600, 0900,..., 2100, 0000 UTC, and so forth. Each dew point forecast is presented to the nearest whole degree Fahrenheit; a missing forecast is indicated by a 999. Three characters are available for the dew point forecasts so that two consecutive forecasts of -10 degrees or less appear with no spaces between them.


6. CLD - TOTAL SKY COVER CATEGORIES

Forecast categories of total sky cover (see the following table) are available in plain language for projections at 3-h intervals from 6 to 60 hours after the initial data times (0000 and 1200 UTC). All forecasts are valid for specific times (i.e., 0600, 0900, 1200, and so forth). Two characters identify the category (CL - clear; SC - scattered; BK - broken; OV - overcast); a missing forecast is denoted by XX.

Total Sky Cover Categories

7. WDR - SURFACE WIND DIRECTION / WSP - SURFACE WIND SPEED

Surface wind direction (WDR) and speed (WSP) forecasts are given at 3-h intervals for projections of 6 to 60 hours after the initial data times (0000 and 1200 UTC). These are forecasts of the 10-m winds (a 2-minute average) at specific times throughout each day (i.e., 0600, 0900, 1200 UTC, and so forth). The wind direction is given in tens of degrees and varies from 01 (10 degrees) to 36 (360 degrees). The normal meteorological convention for specifying wind direction is followed. The wind speed is given in knots; the maximum speed allowed in the message is 98 knots. For both direction and speed, missing forecasts are denoted by 99. A calm wind is indicated by a wind direction and speed of 00.


8. P06 - PROBABILITY OF PRECIPITATION IN A 6-H PERIOD

The P06 forecasts are for the probability of 0.01 inches or more of liquid-equivalent precipitation (PoP) occurring during a 6-h period. The 6-h PoP's 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 (0000 and 1200 UTC). In the message, the forecast values are displayed under the ending time of the 6-h period. The probability is given to the nearest percent. Values range from 0 to 100%. A missing forecast value is indicated by 999.


9. P12 - PROBABILITY OF PRECIPITATION IN A 12-H PERIOD

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The P12 forecasts are for the probability of 0.01 inches or more of liquid-equivalent precipitation (PoP) occurring during a 12-h period. For nearly all stations, the 12-h PoP's are valid for intervals of 12-24, 24-36, 36-48, and 48-60 hours after the initial data times (0000 and 1200 UTC). In the message, the forecast values are displayed under the ending time of the 12-h period. The probability is given to the nearest percent. Values range from 0 to 100%. A missing forecast value is indicated by 999.


10. Q06 - QUANTITATIVE PRECIPITATION AMOUNT IN A 6-H PERIOD

Guidance for liquid-equivalent precipitation amount (QPF) accumulated during a 6-h period is presented in categorical form on the line designated Q06. These forecasts are available for projections 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 time (0000 and 1200 UTC). The forecasts are displayed beneath the hour indicating the end of the 6-h period. The Q06 guidance is a categorical forecast of liquid-equivalent precipitation equaling or exceeding certain specified amounts in the 6-h periods. The categories are as follows:

Q06 Categories

Missing forecasts are denoted by 9.


11. Q12 - QUANTITATIVE PRECIPITATION AMOUNT IN A 12-H PERIOD

Guidance for liquid-equivalent precipitation amount (QPF) accumulated during a 12-h period is presented in categorical form on the line designated Q12. These forecasts are available for projections of 12-24, 24-36, 36-48, and 48-60 hours after the initial data time (0000 and 1200 UTC). The forecasts are displayed beneath the hour indicating the end of the 12-h period. The Q12 guidance is a categorical forecast of liquid-equivalent precipitation equaling or exceeding certain specified amounts in the 12-h periods. The categories are as follows:

Q12 Categories

Missing forecasts are denoted by 9.


12. T06 - PROBABILITY OF THUNDERSTORMS/CONDITIONAL PROBABILITY OF SEVERE THUNDERSTORMS IN A 6-H PERIOD

The T06 line represents forecasts for the probability of thunderstorms (to the left of the diagonal) and the conditional probability of severe thunderstorms (to the right of the diagonal) during a 6-h period. The 6-h probability forecasts 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 (0000 and 1200 UTC). In the message, the pair of forecast values is displayed under the ending time of the 6-h period. The thunderstorm probability is given to the nearest whole percent. Values range from 0 to 100%. A missing forecast value is indicated by 999. The conditional severe thunderstorm probability is given to the nearest whole percent. Values range from 0 to 98%. A missing forecast value is given by 99. Both the thunderstorm and conditional severe storm probabilities are available year-round for stations in the contiguous U.S. Note that these probabilities represent the likelihood of the event within a box approximately 47 km on a side and containing the station specified.


13. T12 - PROBABILITY OF THUNDERSTORMS/CONDITIONAL PROBABILITY OF SEVERE THUNDERSTORMS IN A 12-H PERIOD

The T12 line represents forecasts for the probability of thunderstorms (to the left of the diagonal) and the conditional probability of severe thunderstorms (to the right of the diagonal) occurring during a 12-h period. The 12-h probability forecasts are valid for intervals of 6-18, 18-30, 30-42, and 42-54 hours after the initial data times (0000 and 1200 UTC). In the message, the pair of forecast values is displayed under the ending time of the 12-h period. The thunderstorm probability is given to the nearest whole percent. Values range from 0 to 100%. A missing forecast value is indicated by 999. The conditional severe thunderstorm probability is given to the nearest whole percent. Values range from 0 to 98%. A missing forecast value is given by 99. Both the thunderstorm and conditional severe storm probabilities are available year-round for stations in the contiguous U.S. These probabilities represent the likelihood of the event within a box approximately 47 km on a side and containing the station specified.


14. AVAILABILITY

The 0000 and 1200 UTC Eta MOS guidance will be available at approximately 0230 and 1430 UTC, respectively, in 6 alphanumeric messages transmitted to NWS AWIPS and Family of Services (FOS) circuits and containing guidance for stations in the contiguous United States (CONUS). Guidance is not available for stations outside of the CONUS. The following two-line WMO headers will be used:

WMO Header - Region


15. STATION LIST

The Eta MOS guidance will be available for approximately 1258 stations in the CONUS The guidance is transmiteed in the six bulletins described in Section 14.

The user may check the following home pages for the station lists and corresponding WMO headers:

http://www.nws.noaa.gov/tdl/synop/