I have always been fascinated by the behavior of our atmosphere and oceans. The more I learned about them the more I realized how critical "thresholds" are in our science. I know I can hear you saying it again, what is he talking about? It will become clear pretty fast, read on.

We either have clouds with some coverage of the sky or we have none. Cloud formation is controlled by saturation of moisture in the atmosphere and if relative humidity reaches 100% or very close to it clouds form, if humidity stays at 99% no clouds form. That magic 100% humidity threshold controls clear or cloud! You and I know it either rains or it doesn't.

A cloud has to reach a critical water loading point before cloud drops coalesce and begin to fall in the cloud gathering size as they capture other tiny drops along their fall and eventually produce rain.

If water loading is not high enough, we keep a threatening looking cloud but get no rain! So there is a water loading threshold in every cloud if surpassed transitions from no rain to rain!

If it precipitates it will be rain, snow, sleet, or hail. The form of precipitation we get depends on critical atmospheric thresholds mostly centered near the freezing or melting point of water.

If temperatures in cloud and at ground are just a hair too warm, we get rain or in some rarer cases hail or sleet.

If temperatures in cloud and at ground are just a hair below freezing (32F/0C) we get snow. That magic 32F threshold makes a big difference to precipitation impacts in our neighborhood as rain runs off, while snow can stay an entire winter!

It turns out that on any day the ability for air to rise and form a tall cloud, we call a cumulonimbus, depends on how temperature changes with height. If air warms with increasing elevation above ground or a puff of air that is lifted cools to a temperature colder than its surroundings it will stop rising and may actually descend. If that air puff remains warmer than its surrounds it will continue to rise and that rise could result in a 50,000 foot cumulonimbus cloud with lightning and thunder!

There is a vertical temperature change threshold everywhere, every day that tells us if we get little or no rising air or we get a cumulonimbus cloud. Of yes, thresholds are everywhere in weather. Dew or no dew on the grass, on leaves and on our cars depends solely on the air reaching a threshold temperature which results in saturation. So we either get dew or we don't depending upon whether the air saturation temperature threshold is reached or not!

Along our coasts or lake shores we often sea a daytime sea breeze form; air blows from water to land. Formation of the sea breeze is control by the temperature difference between land and water.

If land becomes warmer than water we get a sea breeze, if it remains cooler we do not. So there is a critical land water temperature threshold that dictates onset of sea breeze or not! Fog formation is controlled by a critical threshold too. It is basically a very shallow cloud perched on the ground.

Fog formation is controlled by whether air near the ground reaches saturation, condenses and forms a cloud or it doesn't. This threshold can be very delicate and met more often in very shallow form over the cool grass in a graveyard than over the warmer asphalt street. But no matter it is a humidity threshold that dictates whether we get fog or clear air!

We find thresholds in our oceans too. If winds are light the sea surface becomes mirror like. If winds are very light we may see some very small "capillary waves" on the water surface but it mostly remains pretty smooth. But when wind reaches a critical speed and/or has gusts with it that do, we begin to see capillary waves break, and that forms whitecaps.

You have seen whitecaps many times on lakes, at the beach, on a ship and in movies. There is a critical threshold of wind and its gustiness that when met causes whitecaps; if it is not met we see no whitecaps. These are important because waves grow much faster when whitecaps form; they transfer energy from the very tiny wave scales to much larger ones.

At some coastal beaches waves are blocked by land on many days and that coast is void of waves. But if those waves reach a critical wave period (time between successive wave crests) threshold, then wave energy is bent enough to direct waves around land that typically acts as a block and we get waves on beaches we usually do not see. This all depends on a threshold of wave period being met or not!

I could go on and on with examples of atmosphere and ocean thresholds, but I think you get the point. My fascination with weather and oceans lies in these thresholds and trying to determine when many of them are going to be met or not. Being wrong by one degree in air temperature or wrong by one second in wave period can lead to huge errors in our forecasts of clouds, rain, precipitation type, wind, fog, dew and coastal waves. It turns out these are the very elements of most interest to you; and they are all controlled by thresholds! Thresholds move and change from one day to the next which really makes forecasting them tricky.

So I guess what I am saying to you is next time you blame the weather person for a "bad forecast" just remember it may have been that the forecast was "almost" perfect, but unfortunately a critical threshold was barely missed possibly by a fraction of a degree! Such is the nature of weather and marine forecasting, it's all about accurately forecasting thresholds, not just forecasting the simple absolute numbers.