1. Hurricanes and Winter Storms

2. Hurricane Formation Required factors 1. warm tropical oceans, 26.5 o C (80 o F) min. surface temperature 2. Area of converging winds a. Mid-latitude weather systems intrude the tropics b. Low pressure area along ITCZ. c. Ripples from instability in Easterly trade winds (Easterly waves), most Atlantic hurricanes form this way

3. Hurricane Formation ITCZ Easterly wave trough convergence (reduced wind speed) rising air / storm divergence (increased wind speed) sinking air

4. Hurricane Formation The Fujita Scale is used to rate the intensity of a tornado by examining the damage caused by the tornado after it has passed over a man-made structure. The "Percentage of All Tornadoes 1950-1994" pie chart reveals that the vast majority of tornadoes are either weak or do damage that can only be attributed to a weak tornado. Only a small percentage of tornadoes can be correctly classed as violent. Such a chart became possible only after the acceptance of the Fujita Scale as the official classification system for tornado damage. It is quite possible that an even higher percentage of all tornadoes are weak. Each year the National Weather Service documents about 1000 tornado touchdowns in the United States. There is evidence that 1000 or more additional weak tornadoes may occur each year and go completely undocumented.Fujita Scale The "Percentage of Tornado-Related Deaths 1950-1994" pie chart shows that while violent tornadoes are few in number, they cause a very high percentage of tornado-related deaths. The Tornado Project has analyzed data prior to 1950, and found that the percentage of deaths from violent tornadoes was even greater in the past. This is because the death tolls prior to the introduction of the forecasting/awareness programs were enormous: 695 dead(Missouri-Illinois-Indiana, March 18, 1925); 317 dead(Natchez, Mississippi, May 7, 1840);.255 dead(St. Louis, Missouri and East St. Louis, Illinois, May 27, 1896); 216 dead(Tupelo, Mississippi, April 5, 1936); 203 dead(Gainesville, GA, April 6, 1936). In more recent times, no single tornado has killed more than 50 people since 1971. The Fujita Scale(also known as the Fujita-Pearson Scale) may not be a perfect system for linking damage to wind speed, but it had distinct advantages over what had gone on before its inception. And it was simple enough to use in daily practice without involving much additional expenditure of time or money. From a practical point of view, it is doubtful that any other system would have found its way into widespread accepted use, even to this day. The entire premise of estimating wind speeds from damage to non-engineered structures is very subjective and is difficult to defend from various meteorological perspectives. Nothing less than the combined influence and and prestige of the late Professor Fujita and Allen Pearson, director of NSSFC(National Severe Storm Forecast Center) in 1971 could have brought this much needed system into widespread use. The FPP scale rates the intensity of the tornado, and measured both the path length and the path width. The Fujita part of the scale is as follows:Professor Fujita and Allen Pearson The Fujita Scale F-Scale NumberIntensity PhraseWind SpeedType of Damage Done F0Gale tornado40-72 mph Some damage to chimneys; breaks branches off trees; pushes over shallow-rooted trees; damages sign boards. F1Moderate tornado73-112 mph The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads; attached garages may be destroyed. F2Significant tornado113-157 mph Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light object missiles generated. F3Severe tornado158-206 mph Roof and some walls torn off well constructed houses; trains overturned; most trees in fores uprooted F4Devastating tornado207-260 mph Well-constructed houses leveled; structures with weak foundations blown off some distance; cars thrown and large missiles generated. F5Incredible tornado261-318 mph Strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles fly through the air in excess of 100 meters; trees debarked; steel re-inforced concrete structures badly damaged. F6Inconceivable tornado319-379 mph These winds are very unlikely. The small area of damage they might produce would probably not be recognizable along with the mess produced by F4 and F5 wind that would surround the F6 winds. Missiles, such as cars and refrigerators would do serious secondary damage that could not be directly identified as F6 damage. If this level is ever achieved, evidence for it might only be found in some manner of ground swirl pattern, for it may never be identifiable through engineering studies Hurricanes intensify when condensation of water vapor in rising air releases heat energy into storm, setting off a chain reaction. The heat makes the surrounding air more buoyant, causing it to rise further. To compensate for the rising air, surrounding air sinks. The sinking air is compressed by the weight of the air above it, and it warms. The pressure rises at the top of the layer of warmed air, pushing air outward. As the air spreads outward, the total air pressure at the surface drops. The more the pressure drops, the more the winds intensify, drawing more heat and moisture from the ocean surface. (Graphic by Robert Simmon, NASA GSFC.)

5. El Nino and La Nina Ocean Surface temperatures Normal: Moderate Easterly trade winds El Nino: Weak Easterlies Warm waters move east Pacific Stronger westerly upper winds in Atlantic prevent hurricanes More storms in Pacific La Nina: Strong Easterlies Warm waters in west Pacific Weak westerly upper winds in Atlantic More hurricanes in Atlantic on Easterly waves

6. Winter Storms Blizzard = 35 mph winds, 300 ft. visibility, 3 hour duration 1:10 rain: snow Danger = low temperatures, high winds, white out effect, power outage, road closure The Great White Hurricane of March, 1888 with 50 in. of snow, 45 mph winds, 4-50 foot snowdrifts, 36 hours, 400 deaths The Great Midwest Blizzard of Jan., 1967 Blizzard of Feb, 1978 The Superstorm of March 1993 with 6 in. of snow in N. Fla. 3.5 feet and 35 foot snowdrifts in NE, thundersnow, storm surge, tornadoes, power outage, 300 deaths, 12.9cu. Miles of snow weighing between 5.5 and 25 billion tons The Blizzard of Jan. 1996

7. Blizzard Formation A south-dipping jet stream A strong low pressure center receiving humid maritime air A strong high pressure arctic air mass High PGF and very strong winds