Midlatitude Cyclones Lecture 5 PDF

Midlatitude Cyclones Lecture 5 EESA09 Wind House Keeping Midterm will take place on Thursday October 17th between 3 to 5 pm Midterm format – will be discussed at the end of the lecture  Outline Midlatitude Cyclones Midlatitude Cyclones What are Midlatitude Cyclones Cy...

Midlatitude Cyclones Lecture 5 EESA09 Wind House Keeping Midterm will take place on Thursday October 17th between 3 to 5 pm Midterm format – will be discussed at the end of the lecture  Outline Midlatitude Cyclones Midlatitude Cyclones What are Midlatitude Cyclones Cyclones and Anticyclones Fronts Polar front theory (Cyclogenesis) Midlatitude cyclones and associated weather events Great Lake Storms Perfect Storm Strom of the century, 1993 1998 Ice Storm 1999 blizzard of Toronto Freezing Rain  Freezing Rain 2013 https://www.google.com/search?q=Videos+of+freezing+rain+2013&oq=Vid eos+of+freezing+rain+2013&gs_lcrp=EgZjaHJvbWUyBggAEEUYOTIHCAEQIR igATIHCAIQIRigAdIBCDc2NTJqMGo0qAIAsAIA&sourceid=chrome&ie=UTF- 8#fpstate=ive&vld=cid:27b68bf9,vid:_eMBpyEn93E,st:0 https://www.youtube.com/watch?v=mFjt0elh5AY  Midlatitude Cyclones What are they? Commonly referred to as a “low” or “low pressure” or “frontal system” Major weather maker in the midlatitudes (35o – 60o) Most storms in Southern Ontario in the fall, winter, spring are midlatitude cyclones Occur approximately every 4 to 7 days  Midlatitude Cyclones 100s to 1000s km in extent (larger than hurricanes) Less intense winds Can have thunderstorms and tornadoes associated with them (cold front) Midlatitude Cylones Cyclones and Anticyclones Fronts Polar Front theory Cyclones and Anti-cyclones -recall Cyclones are associated with clouds, precipitations, and winds Exhibit a characteristic pattern as they move from west to east The first sign of a cyclone approaching from the west is the cirrus clouds that appear roughly 12 to 24 hours in advance of the warm front Anticyclonic weather is characterized by clear skies and light winds Clear skies are also caused by sinking air that can cause very high temperature in summer Climatology of the Midlatitudes -recall Polar front region between Polar and Ferrel cells Three cell theory (recall from Lecture 2)  Air Masses revisited Air Masses Midlatitudes - battle ground between cP (continental polar) and mT (maritime tropical) Midlatitude Cyclones Cyclones and Anti-cyclones Fronts Polar Front theory  Fronts Division between air masses Stationary Front Cold Front Warm Front Occluded Front  Stationary Front Stable Low pressure trough Horizontal wind shear Alternating blue triangles and red semi- circles Stable – lack of latent heat to fuel storm Cold Front Cold air pushing into a warm air mass Designated by blue line with triangles facing warm air Frontal slope 1:50 15-25 knots (7 - 13 m/s) Heavy precipitation along the front where mT air is forced up  Cold Front Criteria for identification Strong temperature gradient Change in moisture (dew point) Shift in wind direction Pressure change Clouds and precipitation patterns Warm Front Warm air pushing into a cold air mass Designated by red line with semi-circles pointing toward cold air Slope 1:150 - 1:300 Gentle precipitation (drizzle) Occluded Front Cold front catches up with warm front Warm air forced above surface Warm front-style precipitation Alternating blue triangles and red semi-circles Warm Occluded Front Midlatitude Cylones Large Scale flow – reviewed Fronts Polar Front theory Polar Front Theory Polar front is a semi-continuous boundary separating cold polar air from more moderate mid- latitude air. Mid-latitude cyclone (wave cyclone) forms and moves along polar front in wavelike manner. Frontal wave, warm sector, mature cyclone, triple point, secondary low, family of cyclones. Polar Front Theory Low pressure or cyclone is the principal weather maker at midlatitudes Development of a low pressure begins with a small perturbation or disturbance along the polar front (division between polar and Ferrel cells) Polar Front Theory Step One Stationary front with a strong horizontal wind shear (Wind shear is horizontal gradient of wind direction and can be unstable.) Rising air at the center of the low favors the development of clouds Polar Front Theory Step Two Under certain conditions a kink or small disturbance forms along the polar front A "cold front" of cold air pushes to the south and warm air ("warm front") pushes to the north The pivot point is the lowest local pressure and is the low pressure centre. Precipitation begins. Polar Front Theory Step 3 Fully developed wave The wave moves east or northeast. It takes 12 to 24 hours to reach this stage of development The centre pressure continues to drop. Large bands of precipitation have formed. A "warm sector" has formed in the region between fronts. Polar Front Theory Step 4 The faster moving cold front catches up with the warm front, reducing the size of the warm sector. Step 5 Occlusion occurs as cold front catches up with warm front. This is the most intense part of the storm. There is widespread precipitation.  Polar Front Theory Step 6 Storm dissipates after occlusion. The source of the energy (mT air) has been cutoff (i.e. no more latent heating). Storm gradually weakens and dissipates.  Polar Front Theory Succession of highs and lows  Outline Midlatitude Cyclones Midlatitude Cyclones What are Midlatitude Cyclones Cyclones and Anticyclones Fonts Polar front theory (Cyclogenesis) Midlatitude cyclones and associated weather events Great Lake Storms Perfect Storm Strom of the century, 1993 1998 Ice Storm 1999 blizzard of Toronto Freezing Rain Midlatitude Cyclones in the Great Lakes Region Great Lakes storms major precipitation events - lake levels major cause of erosion, sediment transport ship and property damage Great Lakes storm climatology References: Angel & Isard (1998); Isard et al. (2000) Storm Climatology: Frequency and Intensity Angel & Isard (1998) cyclone track data since 1900 seasonal distribution of storms  Great Lake Climatology Where do the storms come from? Isard et al. (2000) studied this issue Table 1 : Frequency of storm types over the Great Lakes Basin* Storm Origin July October January April Number of storms per month 4 6 8 7 Alberta 40% 42% 34% 24% Gulf of Mexico 0% 3% 3% 4% Central Rocky Mtns. 21% 19% 18% 29% Northern Canada 3% 3% 6% 0% Northern Pacific 3% 3% 9% 4% Great Lakes 20% 19% 18% 20% other 13% 11% 12% 19% *Adapted from Phillips and McCulloch, 1972 About 20% Midlatitude cyclones have their origins at the Great Lakes  Outline Midlatitude Cyclones Midlatitude Cyclones What are Midlatitude Cyclones Cyclones and Anticyclones Fonts Polar front theory (Cyclogenesis) Midlatitude cyclones and associated weather events Great Lake Storms Perfect Storm Strom of the century, 1993 1998 Ice Storm 1999 blizzard of Toronto Freezing Rain The Perfect Storm October, 1991 Hallowe’en Storm Cold air from US West meet with warmer air mass from Atlantic Formed Nor’easter or Sebastian Junger Hatteras Low Perfect Storm Hurricane Grace 25-29 October Hurricane #8 Oct 28-Nov2 Midlatitude storm formed from remnants of Hurricane Grace Later transformed to Hurricane #8 – the “unnamed hurricane” Perfect Storm Perfect Storm Hundreds of millions of dollars damage along east coast of US Loss of life Andrea Gail – 6 Others – 4 1997 Sebastian Junger book, “Perfect Storm” 2000 Movie  Outline Midlatitude Cyclones Midlatitude Cyclones What are Midlatitude Cyclones Cyclones and Anticyclones Fronts Polar front theory (Cyclogenesis) Midlatitude cyclones and associated weather events Great Lake Storms Perfect Storm Strom of the century, 1993 1998 Ice Storm 1999 blizzard of Toronto Freezing Rain  Storm of the century Storm began on March 12, 1993 as a frontal wave off the Texas coast The storm then intensified into a deep open wave cyclone over Florida The storm moves northeastward and becomes occluded over Virginia As it moves northward, it crossed a few states in USA and finally reached Cape Breton Island, Nova Scotia It caused a deep snow blanket from Alabama to eastern Canada The storm damaged hundreds of homes, produced 11 tornadoes in Florida, caused an estimated damage of #3 billion and claimed 250 lives  Outline Midlatitude Cyclones Midlatitude Cyclones What are Midlatitude Cyclones Cyclones and Anticyclones Fronts Polar front theory (Cyclogenesis) Midlatitude cyclones and associated weather events Great Lake Storms Perfect Storm Strom of the century, 1993 1998 Ice Storm 1999 blizzard of Toronto Freezing Rain Ice Storm 1998 January 3 - 10, 1998 80 mm of freezing rain worst natural catastrophe in Canadian history 28 lives lost 3 million without electricity 15,857 troops deployed $4.2 billion in economic loss $1.5 billion in insurance claims Midlatitude cyclone Ice Storm Ice Storm Ice Storm Ice Storm  Outline Midlatitude Cyclones Midlatitude Cyclones What are Midlatitude Cyclones Cyclones and Anticyclones Fonts Polar front theory (Cyclogenesis) Midlatitude cyclones and associated weather events Great Lake Storms Perfect Storm Strom of the century, 1993 1998 Ice Storm 1999 blizzard of Toronto Freezing Rain  Regional Topography Toronto cradled by local topography including Niagara Escarpment, Oak Ridges Moraine  Blizzard of 1999 How did it happen? Series of 4 storms passed to the south of Toronto in early January, 1999 Storm centre to the south of Toronto, allows for east to southeast winds Winds sweep across Lake Ontario gathering moisture and energy Leads to larger than normal snowfall Midlatitude cyclone with enhancement from Lake Effect Jan. 2, 1999 00Z Sfc Jan. 2, 1999 12Z Sfc Jan. 3, 1999 00Z Sfc Jan. 3, 1999 12Z Sfc Jan. 4, 1999 0Z Sfc Blizzard of 1999 (Gough 2000) Asked the question how unusual was the blizzard of 1999? Unusual event – does not appear to be part of a trend for such events Excessive snow due to 4 successive storms which had pathways that led to enhanced snowfall due to passage of wind over Lake Ontario  Outline Midlatitude Cyclones Midlatitude Cyclones What are Midlatitude Cyclones Cyclones and Anticyclones Fonts Polar front theory (Cyclogenesis) Midlatitude cyclones and associated weather events Great Lake Storms Perfect Storm Strom of the century, 1993 1998 Ice Storm 1999 blizzard of Toronto Freezing Rain  Freezing Rain 2013 The city of Toronto, Canada’s largest urban center, was among the hardest hit by the freezing rain of December 2013 that extended from Northeastern United States to Southern Ontario to Quebec to Maritimes in Canada https://www.youtube.com/watch?v=p9N67TRsm2I Extent of the freezing rain 2013  Freezing Rain - mechanism Warm air forms a wedge between two layers of cold air – one high up in the atmosphere and one at the surface. Precipitation that begins as snow quickly turns to rain as it falls through the warm air. Then, as the raindrops re-enter the cold, they become supercooled, dipping below the freezing point even though they remain liquid. In such a state, droplets of water freeze on contact when they touch a surface, forming an icy glaze on roads, sidewalks and everything else.  Freezing rain vs. ice storm When the ice accumulation is more than 6mm, the freezing rain is called ice storm. The freezing rain of 2013 accumulated between 30 mm to 40 mm of ice.  Sequence of events -2013 Severe weather warnings of freezing rain were forecasted on the eve of Thursday December 19 for the next day. The freezing rain started late on Friday December 20 and left a significant coat of ice over the city. On December 21st, a second wave of freezing rain hits even harder. The total freezing rain over this period amounted close to 40 mm causing ice mass of up to 30 mm. Considering that 1 linear meter of ice with 30 mm width and thickness, respectively, weighs about 0.8 kg, the combination of accumulated ice and strong winds snapped tree branches bringing down power lines, poles, and other structures of the distribution system in unprecedented proportions. The damage suffered by urban forestry was unprecedented as the ice accretion caused major damages and losses to the trees. Trees snapped as they were dormant and fragile during winter weather. The ice storm hits the power distribution system predominately servicing urban communities and cities in southern Ontario. About 500 wires were down leaving more than 300,000 customers without power Affected areas in the GTA  Discussion Questions What are midlatitude cyclones? What is the importance of midlatitude cyclones for the weather of Toronto? Describe the theory that explains the formation of a midlatitude cyclones? Are freezing rains midlatitude cyclones? Discuss the freezing rain of 2013 by focusing on the sequences of events and impacts. What are some differences between hurricanes and midlatitude cyclones? Midterm Format and Review Covers lectures from 1 to 5 up to today’s lecture Format of the midterm: Two sections: 1st section: 30 multiple choice questions 2nd section: 4 short answer questions I will hold a review session for the midterm during reading week virtually. The date and time will be announced at Quercus.  Next week Thunderstorm and Tornadoes The following week- Midterm on October 17th