What are midlatitude cyclones?
Where to midlatitude CYCLONES OCCUR? Midlatitude cyclones occur within the moving boundary of the
Ferrel AND Polar cells referred to as the POLAR FRONT. IN THE POLAR FRONT
- Low and high pressures propogate along the polar front. These lows are called midlatitude
cyclones and largely characterize the weather conditions of the midlatitudes in the fall, winter
- Polar front often lies to the north of the Great lakes region.
Midlatitude cyclones which often occur as a result of surface heating
- Midlatitude cyclones are often called what? Low OR LOW PRESSURE
- Major weather maker in the midlatitudes (35-60)
- Most storms in Southern Ontario in the fall, winter and spring , are midlatitude cyclones
- Occur approximately every 4-7 days
- Less intense winds
- WHEN DO THEY OCCUR? They tend to occur between a cold polar air mass (cP) and a moist
tropical air mass (mT) , the warmth and latent heat (water vapour) provide energy for the storm
- WHERE DOES IT OCCUR IN NORTH AMERICA? Lee- side of the rocky mountains, producing
WHAT? Alberta Clippers and Colorado Lows
- Are typically 100s to 1000s of km in extent (larger than hurricanes) , but have less intense winds
- Where do they have thunderstorms and tornadoes associated with them? AT THE COLD FRONT
HOW ARE THEY FORMED? Unlike hurricanes, surface conditions are not the most dominant mechanism
for cyclone formation. UPPER LEVEL FLOW triggers storm formation, especially the jet stream
CLIMATOLOGY And the Midlatitudes
- Polar front is the region between the polar and Ferrel cells
- Midlatitudes is the battle ground between ? cP (CONTINENTAL POLAR) and mT (Maritime
- Divisions between air masses
- THE TYPES OF FRONTS ARE? Stationary , Cold front , warm front, Occluded Front
WHAT IS A STATIONARY FRONT?
- A stationary front is unstable- FALSE a stationary front is stable
- A stationary front has a high pressure trough- FALSE it has a low pressure trough - Horizontal wind shear
- WHAT DOES IT LOOK LIKE? Alternating blue triangles and red semi circles
- Stable- lack of latent heat to fuel storm
- What is a cold front? Cold air pushing into a warm air mass
- WHAT DOES IT LOOK LIKE? Blue line with triangles facing warm air
- cP and mT air although it can occur between mP and mT air. The mT air is forced above the
colder air mass , with a slope of 1:50, that is for every 50 km the air is forced up 1 km vertically
- STEEPEST OF ALL FRONTAL SLOPES
- What types of clouds form? Cumulus and cumulonimbus clouds form as a result of heavy
- What types of weather occurs along a cold front? The most violent weather
- What else can spawn from a cold front? Thunderstorms and tornadoes
- Where does heavy precipitation occur? along the front where the mT air is forced up
How to identify a cold front?
- Strong temperature gradient (differences between the two colliding air masses)
- Change in moisture (dew point) change occurs as a result of meeting wet and dry air masses
- Shift in wind direction
- Pressure change
- Clouds and precipitation patterns (cloud shaped)
Warm front- warm air pushing into a cold air mass
- Division between mT and mP air cP air , it is the leading edge of the midlatitude cyclone
- Leading edge of a midlatitude cyclone
- Designated by red line with semi- circles pointing towards the cold air
- Slope of 1:150- 1:300, and because the slope is smaller than a cold air mass the air is more
gently lifted above the surface
- Produces stratus and nimbostratus clouds, which produce light drizzle, etc
- Between the cold and warm front there is a region of air called what ? WARM SECTOR
- Its triangular with the
- apex at the low center where the warm and cold centers meet
OCCLUDED FRONT- cold front catches up with warm front, beginning at the apex of the storm
- Warm air forced above the surface
- Warm front style precipitation
- Alternating blue triangles and red semi-circles - An occluded front is the line linking the centre of the low pressure to the apex where the cold
and warm fronts are now meeting
Polar Front theory
- Low pressure or cyclone is the major weather maker at the midlatitudes
- Development occurs because of a small kink or disturbance along a polar front ( division
between polar and ferrel cells)
STEP 1: stationary front with a strong horizontal wind shear
STEP 2: Under certain conditions a kink or small disturbance forms along the polar front, which form s
clearly defined warm and cold fronts
What directions do the warm and cold front push ? 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.
STEP 3: BY THIS STAGE WHAT HAPPENS TO THE WAVE? Fully developed wave
- The warm front is the leading edge of the midlatitude cyclone
- The wave moves east or northeast. It takes 12 to 24 hours to reach this stage of
- The centre pressure continues to drop.
- Large bands of precipitation have formed.
- A "warm sector" has formed in the region between the fronts
Step 4: The faster moving cold front catches up with the warm front, reducing the size of the warm
Step 5: OCCLUSION OCCURS
- Occlusion occurs as cold front catches up with warm front.
- This is the most intense part of the storm.
- There is widespread precipitation