Abnormal Weather II October 24, 2007

Heat Waves Can occur anywhere in the tropics and temperate zones Common in urban areas, steppes, prairies, and deserts Caused by a persistent ridge in the jet stream – high pressure encourages stable, clear weather Frontal systems are blocked – storm systems pass around the polar edge of the high following the jet stream

Heat Waves Air under the High becomes increasingly hot and dry Eventually energy radiated into space equals that received from the sun producing higher than normal temperatures

Mugginess Even though there is no rain, heat waves can have high relative humidity levels along the east coast Moist air enters the area from the Gulf of Mexico and Atlantic Ocean producing muggy heat waves Meteorologists define heat waves as days when the maximum expected temperature is over 98.6ºF

Heat Wave: Human Comfort Heatstroke – when the body loses the ability to control its core temperature. Sweating stops and skin appears pale and gray How does mugginess impact human comfort? What about dry heat? Which is more dangerous, dry heat or mugginess?

Cold Spells Jet Stream can bring polar air masses deep into the US producing extremely low temperatures and often above-average precipitation This is common when the North Pacific high-pressure cell intensifies and pumps arctic air into the continent

Flood-Producing Weather Two types of weather produce river floods –Excessive rainfall – stationary fronts –Rapid snowmelt

Wildfire Weather Low humidity, low precipitation, plus strong winds

Fire Weather Forecast FIRE WEATHER PLANNING FORECAST FOR NORTH AND CENTRAL GEORGIA NATIONAL WEATHER SERVICE PEACHTREE CITY GA 359 PM EDT TUE OCT DISCUSSION... COLD FRONT PUSHING THROUGH THE STATE THIS AFTERNOON SHOULD BRING SOME MUCH NEEDED RAINS TO THE AREA. AIR BEHIND IT IS DRIER...HOWEVER IT WILL NOT BE ENOUGH TO FOR ANY THREAT OF RED FLAG CRITERIA BEING MET. BEST RAIN CHANCES THROUGH THE PERIOD WILL BE ACROSS NORTH GEORGIA WITH WRAP AROUND PRECIPITATION AND EAST GEORGIA OUT AHEAD OF THE FRONT.

INVERSIONS - A layer in the atmosphere where the temperature increases with altitude. The smoke and warm gases generated by a fire will rise only until the temperature equals that of the surrounding air; then, the smoke flattens out and spreads horizontally because it has lost its lift. Warm A i r over Cold Air = STABLE conditions Cold Air over Warm Air = UNSTABLE conditions

Temperature Inversions Mixing heights represent the top of the layer through which relatively vigorous mixing will take place. It is the height at which smoke will lose its buoyancy and stop rising.

Fire Predictions Western US – thunderstorms that produce fire Eastern US – extended droughts Fire Meteorologists –10-minute average winds –24-hour rainfall totals –Temperature –Relative humidity –Dew-point temperature –Plus soil moisture, mixing height