WEATHER FORECASTING & ANALYSIS
EVERYDAY WE NEED TO STUDY
- Practice identifying cloud types, interpreting their significance, their direction, movement, sequence.
- Make systematic observations.
- Observe surface wind speed and direction.
- Make a daily forecast each day, and check it.
- Keep your eye on the sky. Feel the changes in temp, wind, humidity.
Haze - dust > 1 mile
Mist - water vapour < 1 mile
Fog < 1/2 mile
- What is the present weather?
- Can you rely on the forecast?
- When was it updated?
- What is the forecast trend: worse, same, better?
- What marine warnings are in effect or forecast?
- What is the weather summary?
- What forecast areas are important to you? Note the differences and importance of knowing the land, coastal, and offshore forecasts and conditions.
- Where is the weather coming from, and at what rate?
Perhaps you want to use more technical science.
- "When dew is on the grass, rain will never come to pass. But when grass is dry before morning light, look for rain before the night.”
- "Red sky in morning sailors take warning, red sky at night, sailors delight."
- Clover leaves close when wind is greater than 20 mph.
- Dandelions close when temperature is less than 51 degrees F.
- You can see your breath around 45 degrees F.
- Crickets’ chirp temperature gauge: (# times/min minus 40 divided by 4) plus 50 = Temperature F.
- Frogs croak when it’s muggy.
- Notice the animals: birds nervous and twittering; sandflies feeding frenzy,;mosquitos after a storm; frogs; crickets; porpoises leaping and slapping.
78% nitrogen, 21% oxygen, <1%argon, trace of helium, ozone, neon & krypton. In troposphere these are always in same proportion. Water vapor can vary from 0-7%.
- Heap Clouds – Cumulus
- Layered Clouds - Stratus
- Heaps and Layers
- Rain Clouds - Nimbus
FRONTS and THEIR MOVEMENT
- Advisory: 36 hrs+
- Watch: 24-36hrs
- Warning : <24 hrs
HIGH: clockwise w/o fronts
Anticyclone. Established over land masses, slow to move, depressions often diverted around.
LOW: counterclockwise w/ fronts
Cyclone. Normally have an associated warm sector or front with moist air condensing into clouds followed by a cooler, polar air front. The cold front swings in behind the depression and carries a shorter period of heavy rain, often have sudden increase in wind speed and change of wind direction.
Differences in pressure are isobars. Can be viewed as contour lines. When isobars are close together, the wind is stronger.
Vast bodies of air with uniform temperature and moisture characteristics:
Cold Front: unstable
- WIND: gusty
- VISIBILITY: good
- CLOUDS: cumulus
- PRECIP: showers
Warm Front: stable
- WIND: steady
- VISIBILITY: poor
- CLOUDS: stratus
- PRECIP: drizzle
Weather Masses are named for where they are formed in on of these six main regions:
Arctic; Continental Polar; Maritime Polar; Continental Tropical; Maritime Tropical; Equatorial.
- Cold air pushes under warm air. Fast moving: 20-35 kt. Moves E-SE following warm front.
- Weather deteriorates fast. Clouds seen 50-150 miles away.
- Warm air slides over cold air. Moves slowly: 10-15 kt. Occurs on E side of Low. Weather deteriorates slowly. Clouds seen 1000+ miles away.
- “Buys Ballot’s Law”
- Stand with your back to the wind; turn 15 deg to your right. Low on your left; High on your right.
Pressure Changes and Barometer
Average sea level pressure is 29.92 inches of mercury and 1013 millibars.
950-1035 mb. Steady, F/RR >6mb/3hr, F/RM = 3-6mb/3hr, F/RS <3mb/3hr
A reading of 980 will allow the tide levels to rise a foot, while a reading of 1030 will depress levels about a foot.
Combined with the movement of water due to a deep low, can create "storm surges" of several to 20 feet.
- When do they happen? What are they like on surface? Wind, sea state.
- What is your plan? Where are you and what are you going to do?
- Thunder follows lightning by 5 sec / mile.
- The storm cell is not precisely localized, so one could be 10 miles, then 4 miles, then 8 miles - all from the same general compass direction.
POLICY: 30/30 rule.
If it takes less than 30 seconds to hear thunder after seeing the flash, lightning is near enough to pose a threat; after the storm ends, wait 30 minutes before resuming outdoor activities.
Minute water droplets near earth's surface
Radiation Fog: Forms over land early morning, may drift a short ways to sea. Usually with clear skies and light winds.
Sea Fog: When warm air moves over colder sea water, moisture condenses into fog. Sea surface temp must be less than the dewpoint of the air mass. Marine (advection) most persistent; lasts several days. Clears when wind increases >15k (becomes low stratus), or wind shifts bringing colder air.
Precipitation Fog: When warm precipitation from aloft falls down through cooler layer near the ground. Also called Frontal. Can be extensive; depends on warm front size. Forms with warm front, nimbostratus, and rain. Clears when wind shifts with warm front.
Arctic Sea Smoke: When very cold arctic air moves over warmer sea water, moisture evaporates from the sea and saturates the air.
Be attentive to different signs of what is going on around you. Kayak by sound. Be quiet; be relaxed. Notice:
- lighter colored water
- sound of surf, land, buildings
- buoyage and bottom shape
- wave directional changes
Equipment at your ready:
- fully prepared chart
- fog horn
- flare gun
- strobe light
- bright paddles
- bright lights
Study the chart, then Study the chart, then Study the chart. And remember, most power boaters head toward the buoys; should you, too?