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WX0203 · Pressure & Wind

29 questions · 23 multiple choice · 6 written · ASA 109 Marine Weather — Pressure & Wind

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📈 Figure WX0203-1 — surface analysis map

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Q1
As the pressure gradient increases, the isobars will ...?
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Isobars are lines of constant surface pressure, shown at equal intervals, usually 4-mb apart.

Q2
Widely spaced isobars on a weather map indicate ...?
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Isobars are drawn at constant pressure intervals across the map.

Q3
Lines of constant pressure are called ...?
Q4
The “standard atmosphere” pressure at sea level is equal to ...?
Q5
Ship reports on surface analysis maps tell us the rate of pressure change (“pressure tendency”) over the past how many hours?
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This is an official definition used consistently.

Q6
Corrections which must be applied to an aneroid barometer reading at sea to get the proper sea level pressure include ...?
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Aneroid barometer is the typical kind used at sea.

Q7
The semidiurnal pressure variation is most noticeable where?
Q8
According to Buys Ballot’s law when an observer in the Northern Hemisphere experiences a northwest wind, the center of low pressure is located to the ...?
Q9
If an observer in the Northern Hemisphere faces the surface wind, the center of low pressure is ...?
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Draw a person standing in the circulation of wind around a low.

Q10
Atmospheric pressure can be expressed in several different units. Which are the best to use for marine weather applications?
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Standard atmospheric pressure: 14.696 psi, 760 mm, 29.922 in, 1013.25 mb.

Q11
What can be said about the role of a barometer in marine weather underway?
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Every vessel at sea has one, but are they really used.

Q12
We would consider a typical pressure to be high if it is above about ...?
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Question is about “typical,” not records.

Q13
What can be said about the monthly average sea level pressure at any specific US port?
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Climatic weather data is in the Coast Pilot.

Q14
Good weather is usually associated with a region of ...?
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Consider the vertical motion of air.

Q15
The needle of an aneroid barometer points to 30.05 on the dial. This indicates that the barometric pressure is ...?
Q16
What causes the pressure to drop on a barometer?
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A consistent pressure drop is a clear warning.

Q17
The greater the pressure difference between a high and a low pressure center, the ...?
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The pressure difference determines the pressure gradient.

Q18
To best check your barometer at the present pressure you would ...?
Q19
Which of the following indications afforded by the barometer are most meaningful in forecasting weather?
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Assume the barometer itself was all you had to go by.

Q20
Bad weather is usually associated with regions of ...?
Q21
Your boat speed is 7.0 kts. The apparent wind angle is 40° R. The apparent wind speed is 18.0 kts. Part A: What is the true wind speed in kts? Part B: What is the true wind angle relative to the bow?
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This must be solved by plotting or a calculator.

Q22
Your speed is 6.5 kts, your heading is 200 T. The apparent wind is 5.0 kts at an apparent wind angle of 150 R, on starboard gybe. What is (Part A) the true wind speed in kts and (Part B) the true wind direction?
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This must be solved by plotting or a calculator.

Q23
In normal sea conditions, the surface wind flows in what direction relative to the isobars?
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Sketch a high or low and draw in the winds.

Q24
Using Table 2.4-1, what is the surface wind speed and direction you would expect at 31.8° N, 147.0° W on the surface analysis map from figure WX0203-1? Answer should be speed in kts and direction 000-360.
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If needed, draw in a new isobar at the location of interest. We are looking for ±2 kts and ±10°.

Q25
List the names of two software programs that will display GRIB formatted weather maps and the links online to where you can download them. Plus add notes on where you can get the GRIB files to view.
Q26
Please confirm that you have watched one of the videos on downloading grib files (XyGrib or qtVlm). Your answer would be “Yes I watched,” and any comment you like to add.
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The new text encourages getting involved with model forecasts via GRIB files as soon as possible.

Q27
In the 12Z Aug 26 map of figure WX0203-1 there is a High at about 45 N, 135 W. What is the central value of that High pressure (the peak value at the center of the isobars)?
Q28
In the 12Z Aug 26 map of figure WX0203-1 there is a Low at about 53 N, 162 W. Is that Low getting deeper or filling over the next 24 hr?
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An X marks the location of a Low 24h later. Peak and minimum forecasted values are shown underlined.

Q29
When reading and recording the pressure from a typical aneroid barometer, we should...