July 5, 2009 in Idaho Voices

Wildfire danger accompanies our great summer weather

Michelle Boss

A string of sunny and 80-degree days is perfect for a lot of things. It is great for boaters on area lakes, for kids at the local pools, and for meteorologists who like to take a break from the rigors of complex forecasting patterns.

As always, however, there is a price to pay. Every hot and dry day contributes to the drying out of surrounding vegetation. It is this time of year, under conditions like these, in which we are only one windstorm or lightning bolt away from devastating wildfires.

Meteorologists deal with weather as it relates to wildfire potential, but also are responsible for providing critical spot forecasts to aid in the fight of existing fires. Even in the absence of fires, forecast conditions such as wind, humidity and the chance for thunderstorms are closely monitored.

Strong winds, besides being a general nuisance, greatly contribute to the drying out of vegetation by speeding up the evaporation process. Long periods of low relative humidity do likewise. Though thunderstorms during this time of year bring the chance of precipitation, these storms are often more of a liability. Widespread wetting rains, of 1/10 of an inch or more, rarely occur with these storms. One bolt of lightning can initiate a wildfire, which can grow due to the turbulent and gusty winds of passing thunderstorms, while feeling little effect from any scant rain that may accompany them.

While just about any time during the Inland Northwest’s typically hot and dry summers poses a risk for wildfires, certain weather patterns increase that risk. The National Weather Service will issue what’s called a red flag warning when conditions are especially dangerous due to the potential for wildfire starts from lightning, or due to the effects of low relative humidity (20 percent or less) and sustained winds (15-plus mph) on the growth of fires once they start.

Providing spot forecasts during a wildfire is a challenging task. Many times, fires are in rugged and varied terrain where surface weather observations are not available. The meteorologist must take into account the fact that wildfires are not only affected by the weather, but affect the weather as well.

The heat from a wildfire creates an area of low pressure, which not only can alter the surrounding wind speed and direction, but can result in the formation of a thunderstorm directly over the fire. On rare occasions, the intense heat and associated updrafts from a fire can create what is called a fire whirl or fire tornado. These can grow to be 300 to 400 feet tall and 20 to 50 feet wide and move at speeds of 5 to 7 mph or more.

Michelle Boss can be reached at weatherboss@comcast.net.

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