Significant Wind Levels
Significant levels are also selected for wind
changes. When a sounding is evaluated manually,
winds are plotted on either the Winds Aloft Graphing
Board or the Winds Aloft Plotting Chart. Wind
directions are plotted on a direction scale, and wind
speeds are plotted on a speed scale. The MRS
automatically evaluates winds and selects the proper
significant levels. Some stations report Fixed Regional
Levels for winds in place of significant wind levels.
FIXED REGIONAL LEVELS (WIND). Winds
for the Fixed Regional Levels (table 1-5) must be
reported by all designated Synoptic Stations in WMO
Region IV, North America and Hawaii. This is a
regional code convention. Current software in the MRS
does not evaluate fixed regional levels, so they must be
manually selected and encoded. This may be done by
manually plotting the observed wind directions, wind
speeds, and pressure for each minute of flight on a
Winds Aloft Graphing Board or Winds Aloft Plotting
Chart at the appropriate altitude. The pressure level,
wind direction, and speed may then be determined for
each fixed regional level. After the surface level, the
first fixed regional level that is reported is the next
higher level above the surface. When fixed regional
levels are reported, additional significant levels may
also need to be considered. In these cases, the MRS-
selected significant wind levels are not used.
UP THROUGH
ABOVE 100-hPa
100-hPa
FEET
METERS
FEET
METERS
s u r f a c e
0
60,000
18,000
1,000
300
70,000
21,000
2,000
600
80,000
24,000
3,000
900
90,000
27,000
4,000
1,200
100,000
30,000
6,000
1,800
110,000
33,000
7,000
2,100
140,000
42,000
8,000
2,400
150,000
45,000
9,000
2,700
160,000
48,000
12,000
3,600
170,000
51,000
14,000
4,200
180,000
54,000
16,000
4,800
190,000
57,000
20,000
6,000
200,000
60,000
25,000
7,500
etc.
etc.
30,000
9,000
35,000
10,500
50,000
15,000
SELECTING SIGNIFICANT WIND LEVELS.
Significant level winds are used by ships and MRS-
equipped stations that are not required to report fixed
regional level winds. The MRS uses the following
WMO requirements when selecting significant wind
levels:
The surface and last level of the sounding
The maximum wind(s)
Any level of abrupt change in wind speed
(greater than 10 knots) or direction
The terminating wind (last wind speed of the
sounding is greater than 60 knots and is the highest wind
speed observed)
Supplemental levels so that plotted wind
directions at selected significant levels may be
connected with straight lines and no direction (except in
layers of winds less than 10 knots) will deviate by more
than 10 degrees
Table l-5.—Fixed Regional Level Altitudes for Reporting
Winds in WMO Region IV
Supplemental levels so that plotted wind speeds
at selected significant levels may be connected with
straight lines and no wind speeds will deviate by more
than 10 knots
Stations that report only fixed regional level winds
must also select significant level winds based on the
criteria above, when applicable.
Supplemental Information
In addition to time, altitude, pressure, temperature,
humidity, dew-point depression, and winds, the level
printouts include RI, the refractive index in N units; and
MRI, the refractive index in modified or M units. The
Tactical Environmental Support System (TESS) uses
M-units as the primary input for refractive effects
analysis and forecasts.
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