Weather forecasting has become so technologically
advanced that computer models can predict the time when rain
will fall over your house, or when a tornado will cross your
street. Even then, Mother Nature can fool the smartest computer
program at anytime, making weather predicting still somewhat of
a guessing game.
Sensible anglers watch the weather forecast
for two reasons. First, they study forecasts to equate
prevailing conditions into their fishing patterns and tournament
game plans. The second reason is to see how wind, rain or worse
might affect their boating plans.
In both cases, basic knowledge of how weather
systems form and function can pay off with a safe, productive
day on the water. And in some cases, watching weather unfold
before your very eyes can help you make quick adjustments to a
fishing pattern.
Following is a primer in “Weather 101” that
you can apply while on the water to plan and predict how weather
might affect your day.
Clouds
Clouds form when air is cooled to its dewpoint
or when the air reaches saturation. There are four basic cloud
categories observed in our atmosphere.
Cirro: High-level clouds which form
above 20,000 feet and are usually composed of ice crystals.
Cirrus generally occurs in fair
weather and point in the direction of air movement at their
elevation.
Nimbus: Typically form between 7,000
and 15,000 feet and bring steady precipitation. As the clouds
thicken and precipitation begins to fall, the bases of the
clouds tend to lower toward the ground.
Cumulo: Look like white fluffy
cotton balls and show the vertical motion or thermal uplift of
air taking place in the atmosphere. The level at which
condensation and cloud formation begins is indicated by a flat
cloud base, and its height will depend upon the humidity of
the rising air. These clouds can reach 60,000 feet.
Strato: Consist of a feature-less
low layer that can cover the entire sky like a blanket,
bringing generally gray and dull weather. The cloud bases are
usually only a few hundred feet above the ground. Over hills
and mountains they can reach ground level when they may be
called fog.
Precipitation
The vertical distribution of temperature will
often determine the type of precipitation (rain vs. snow vs.
sleet vs. freezing rain) that occurs at the surface during the
wintertime. More often than not, the temperature does not
decrease with height but increases, many times by several
degrees, before decreasing. This increase, then decrease is
called and inversion. In winter, an inversion can be critical in
determining the type or types of weather.
Air Mass
An air mass is a large body of air with
generally uniform temperature and humidity. Air masses can
control the weather for a relatively long time period: from a
period of days, to months. Most weather occurs along the
periphery of these air masses at boundaries called fronts.
Fronts are the boundaries between two air masses. Fronts are
classified as to which type of air mass (cold or warm) is
replacing the other. For example, a cold front demarcates the
leading edge of a cold air mass displacing a warmer air mass. A
warm front is the leading edge of a warmer air mass replacing a
colder air mass. If the front is essentially not moving it is
called a stationary front.
Fronts don’t just exist at the surface of the
earth, they have a vertical structure or slope as well. Warm
fronts typically have a gentle slope so the air rising along the
frontal surface is gradual. This usually favors the development
of widespread layered or stratiform cloudiness and precipitation
along and to the north of the front. The slopes of cold fronts
are steeper and air is forced upward more abruptly. This usually
leads to a narrow band of showers and thunderstorms along or
just ahead of the front, especially if the rising air is
unstable.
Cold fronts typically move faster than warm
fronts, so in time they “catch up” to warm fronts. As the two
fronts merge, an occluded front forms. In the occluded front,
the cold air undercuts the cooler air mass associated with the
warm front, further lifting the already rising warm air.
Fronts are usually detectable at the surface in a number of
ways. Winds usually “converge” or come together at the fronts.
Also, temperature differences can be quite noticeable from one
side of the front to another.
Finally, the pressure on either side of a
front can vary significantly.
Here is an example of a location that experiences typical warm
frontal
passage followed by a cold frontal passage: Clouds lower and
thicken as the warm front approaches with several hours of light
to moderate rain. Temperatures are in the 50s with winds from
the east. As the warm front passes, the rain ends, skies become
partly cloudy and temperatures warm into the mid 70s. Winds
become gusty from the south. A few hours later, a line of
thunderstorms sweeps across the area just ahead of the cold
front. After the rain ends and the front passes, winds shift to
the northwest and temperatures fall into the 40s and skies
clear.
Wind
Wind is simply the air in motion. Usually when
forecasters talk about the wind it is the horizontal motion they
are concerned about. If you hear a forecast of west winds of 10
to 20 mph that means the horizontal winds will be 10 to 20 mph
from the west.
The vertical component of the wind is
typically very small (except in thunderstorm updrafts) compared
to the horizontal component, but is very important for
determining the day to day weather. Rising air will cool, often
to saturation, and can lead to clouds and precipitation. Sinking
air warms causing evaporation of clouds and thus fair weather.
You have probably seen a surface map marked
with H’s and L’s which indicate high and low pressure centers.
Surrounding these “highs” and “lows” are lines called “isobars.
“Iso’ means “equal” and a “bar” is a unit of pressure so an
isobar means equal pressure. Forecasters connect these areas or
equal pressure with a line. Everywhere along each line is
constant pressure. The closer the isobars are packed together
the stronger the pressure gradient is.
Pressure gradient is the difference in
pressure between high and low pressure areas. Wind speed is
directly proportional to the pressure gradient. This means the
strongest winds are in the areas where the pressure gradient is
the greatest.
technologically
advanced that computer models can predict the time when rain
will fall over your house, or when a tornado will cross your
street. Even then, Mother Nature can fool the smartest computer
program at anytime, making weather predicting still somewhat of
a guessing game. 
weather and point in the direction of air movement at their
elevation.
passage followed by a cold frontal passage: Clouds lower and
thicken as the warm front approaches with several hours of light
to moderate rain. Temperatures are in the 50s with winds from
the east. As the warm front passes, the rain ends, skies become
partly cloudy and temperatures warm into the mid 70s. Winds
become gusty from the south. A few hours later, a line of
thunderstorms sweeps across the area just ahead of the cold
front. After the rain ends and the front passes, winds shift to
the northwest and temperatures fall into the 40s and skies
clear.