Once you know the basics of onboard forecasting, you’ll be able to understand what your observations are telling you. Then you can use this information to modify and refine the official forecast. First, let’s look at the signs of weather stability and change:
|
Continuing good weather |
Indicators of a change |
Skies |
Clear, light to dark blue, bright moon; contrails dissipate |
Hazy; halo around the sun or moon; thick, lingering jet contrails |
Clouds |
Few puffy cumulus or high thin clouds, the higher the better |
Veil of clouds; clouds at multilayers and directions; cirrus |
Winds |
Generally steady, little change over the day |
Strong winds in early morning; wind shift to south |
Seas |
Sea swells same direction |
Seas confused; varying directions |
Temperatures |
Stable; heavy dew or frost at night |
Marked changes; increased humidity |
Dew Point |
Marked spread between dew point and temperature = no fog |
Close spread; probable fog if temperature drops |
Barometer |
Steady; rising slowly |
Falling slowly |
Sunrise |
Gray sky at dawn or sun rising from clear horizon |
Red sky; sun rises above horizon because of cloud cover |
Sunset |
Red sky; sun “ball of fire” or sets on a clear horizon |
Sun sets high above horizon, color purplish or pale yellow |
Approaching low
Clouds: high cirrus, gradually lowering and thickening
Wind: backing to southeast, possibly increasing
Barometer: begins to fall 2 to 10 millibars in three hours
Seas: Offshore swells increase, with decreasing period
What to expect: Rain within 15 to 24 hours. If low is west to northwest passing to your north, you will see fronts. If low is west to southwest passing to your south, you will not see distinct fronts.
Approaching warm front
Cirrus or mackerel clouds: Front is more than 24 hours away.
Lowering and thickening clouds (altostratus, nimbostratus): Front is less than 24 hours away.
Rain: begins lightly, becoming steady and persistent
Barometer: falls steadily; the faster it falls, the stronger the winds.
Winds: increase steadily, stay southeast
Visibility: deteriorates, especially in rain
Passing warm front
Sky: lightens toward western horizon
Rain: breaks
Wind: veers from south to southwest, may decrease
Barometer: stops falling
Temperature: rises
Within warm front
Wind: steady, typically southwest; will strengthen ahead of cold front Barometer: steady, may drop shortly ahead of cold front
Precipitation: mist, possible drizzle
Approaching cold front
Wind: southwest, increases; line squalls possible more than 100 miles ahead of front
Barometer: begins brief fall, could be rapid
Clouds: cumulonimbus builds to west
Temperature: steady
Rain: begins and intensifies, but duration short, one to two hours
Passing cold front
Wind: veers rapidly to northwest; gusty behind front
Barometer: begins to rise, often quickly
Clouds: cumulonimbus to nimbostratus and then clearing
Temperature: drops suddenly, followed by a slow decline
Rain: ends, gives way to rapidly clearing skies, possibly with leftover altocumulus clouds
To learn more about predicting the weather, take the Onboard Weather Forecasting seminar at a squadron near you.
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