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Description of the NAM MOS Alphanumeric Message


The NAM-Based MOS guidance is generated from 0000 UTC and 1200 UTC model output from the Environmental Modeling Center's NAM Model. This guidance is valid for stations in the Continental United States, Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands. Forecast elements are valid from 6 to 72 hours in advance.



Sample Message

KDCA   NAM MOS GUIDANCE    1/24/2008  1200 UTC 
DT /JAN  24/JAN  25                /JAN  26                /JAN  27
HR   18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 06 12
N/X                    15          24          20          30    28
TMP  36 35 30 24 21 18 16 21 23 22 23 21 20 21 22 24 27 29 29 29 30
DPT  14  9  3  0 -2 -4 -3 -3 -2  2  8 12 15 17 19 22 24 25 25 24 21
CLD  CL CL FW FW SC SC BK OV OV OV OV OV OV OV OV OV OV OV OV BK FW
WDR  34 33 34 35 34 36 36 06 14 08 05 04 02 02 03 05 05 06 03 35 34
WSP  07 14 14 11 10 10 08 03 02 05 07 11 11 12 10 07 04 04 07 11 10
P06         0     0     0     0    55    76    60    34    36 13  9
P12                     0          58          86          48    25
Q06         0     0     0     0     1     1     1     0     1     0
Q12                     0           1           2           1     0
T06      0/ 0  0/ 9  0/ 1  1/ 0  3/ 0  0/ 0  0/ 1  0/ 0  3/ 0  0/ 0
T12            1/ 9        1/ 1        3/ 0        1/ 1     1/ 0
SNW                     0                       6                 0
CIG   6  8  8  8  8  7  7  7  7  4  4  3  2  3  3  2  2  1  1  2  8
VIS   7  7  4  5  5  5  6  7  7  7  7  7  7  7  7  7  7  7  7  6  5
OBV   N  N BR BR BR BR  N  N  N  N  N  N  N  N  N  N  N  N  N HZ BR


  • DT = The day of the month, denoted by the standard three or four letter abbreviation
  • HR = Hour of the day in UTC time. This is the hour at which the forecast is valid, or if the forecast is valid for a period, the end of the forecast period.
  • N/X = nighttime minimum/daytime maximum surface temperatures.
  • TMP = surface temperature valid at that hour.
  • DPT = surface dewpoint valid at that hour.
  • CLD = forecast categories of total sky cover valid at that hour.
  • WDR = forecasts of the 10-meter wind direction at the hour, given in tens of degrees.
  • WSP = forecasts of the 10-meter wind speed at the hour, given in knots.
  • P06 = probability of precipitation (PoP) during a 6-h period ending at that time.
  • P12 = PoP during a 12-h period ending at that time.
  • Q06 = quantitative precipitation forecast (QPF) category for liquid equivalent precipitation amount during a 6-h period ending at that time.
  • Q12 = QPF category for liquid equivalent precipitation amount during a 12-h period ending at the indicated time.
  • T06 = probability of thunderstorms/conditional probability of severe thunderstorms during the 6-hr peri od ending at the indicated time.
  • T12 = probability of thunderstorms/conditional probability of severe thunderstorms during the 12-hr per iod ending at the indicated time.
  • SNW = snow fall categorical forecasts during a 24-h period ending at the indicated time.
  • CIG = ceiling height categorical forecasts at the hour.
  • VIS = visibility categorical forecasts at the hour.
  • OBV = obstruction to vision categorical forecasts at the hour.

Definitions of Categorical Elements

QPF Categories
0 no precipitation
1 0.01 to 0.09 inches
2 0.10 to 0.24 inches
3 0.25 to 0.49 inches
4 0.50 to 0.99 inches
5 1.00 to 1.99 inches
6 2.00 inches or greater


Snow Fall Amount Categories
0 no snow or a trace expected
1 > a trace to < 2 inches
2 2 to < 4 inches
4 4 to < 6 inches
6 6 to < 8 inches
8 >= 8 inches


Visibility (VIS) Categories
1 < 1/2 miles
2 1/2 - < 1 miles
3 1 - < 2 miles
4 2 - < 3 miles
5 3 - 5 miles
6 6 miles
7 > 6 miles
Ceiling Height (CIG) Categories
1 < 200 feet
2 200 - 400 feet
3 500 - 900 feet
4 1000 - 1900 feet
5 2000 - 3000 feet
6 3100 - 6500 feet
7 6600 - 12,000 feet
8 > 12,000 feet

Cloud (CLD) Categories
CL clear
FW > 0 to 2 octas of total sky cover
SC > 2 to 4 octas of total sky cover
BK > 4 to < 8 octas of total sky cover
OV 8 octas of total sky cover or totally obscured



MAV Obstruction to Vision (OBV) Categories
N none of the following
HZ haze, smoke, dust
BR mist (fog with visibility >= 5/8 mile)
FG fog or ground fog (visibility < 5/8 mile)
BL blowing dust, sand, snow

National Weather Service
Office Of Science and Technology
Meteorological Development Laboratory
Statistical Modeling Branch
1325 East West Highway
Silver Spring, MD 20910
Page Author: MOS Web Team
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Page last Modified: Thursday, 01 July 2010 14:10 UTC