gph 212 – air masses, fronts, cyclones newman notes …

GPH 212 – AIR MASSES, FRONTS, CYCLONES Newman Notes #10

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AIR MASSES Air Mass: large body of air with similar properties of ______________ and _____________ in any ___________________________________________________. Source Region: Ideal Source Regions a) b) Major source regions are found in the: a) __________________________ and b) __________________________ 1. TEMPERATURE a) b) c) d) 2. MOISTURE a) b) There are five types of air masses associated with North America 1. Maritime Tropical (_____) 4. Continental Polar (_____) 2. Continental Tropical (______) 5. Continental Arctic (______) 3. Maritime Polar (_____) 3. STABILITY INDICATORS a) Stable (w) - air mass is _______________ than the __________________ 'w' air masses: b) Unstable (k) - air mass is ___________ than the ______________.e.g., mPk 'k' air masses:


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AIR MASS MODIFICATION

Air masses move out of their source regions • Properties are ________________ by the ________________________________ • Modification occurs because of:

o Exchange of ___________________________ with the surface o ________________________________________________________ o ___________________________________ associated with large-scale

vertical motions e.g., cP air mass modifies as it moves SE into the southern U.S. e.g., cP air mass crosses the east coast and moves over the western Atlantic. Evaporation from the sea leads to large areas of low clouds/fog. Example of heating and destabilization. e.g., cP traveling over snow-covered ground is NOT modified as much (due to albedo of surface)

Five Air Masses affecting North America 1. cA (Continental Arctic) - _________________________________________ a. Source: Rarely reaches U.S., but when it does, ________________________________ 2. cP (Continental Polar) - ____________________________________________ a. Source:

Moves into _____________________________ resulting in _______________ down to Gulf of Mexico

3. mP (Maritime Polar) - ___________________ a. ___________________________________________ for this air mass ___________________________ and ______________________________ b. ______________ air masses affect U.S. more than the _____________________ c. Pacific: originally ______________ air - moved over ______________________ 4. cT (Continental Tropical) - _______________________ a. Source: _________________________________. ________ important air mass

to the United States - __________________________________ and… b. Only influences the U.S. in the __________________________ 5. mT (Maritime Tropical) - _______________________________

a. __________________________ for this air mass ___________________________ and ___________________________

b. Gulf of Mexico/Subtropical Atlantic Ocean Winter: 1. lower layer of air is _________________:


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2. meet ____________ air; Summer: 1. 2. c. Pacific 1. 2. More __________________________________ 3. Contributes to ________________________ in California 4. Brings _________________________ precipitation in winter

WEATHER IMPACTS FROM AIR MASSES LAKE-EFFECT SNOW * _______________________________________ moves across the Great Lakes * Air __________________ through ____________________ from the warm water. * The warm air starts to _________________ producing ___________________. * Once the air reaches the _____________________, the clouds deposit large quantities of ____ SIBERIAN EXPRESS * A large _________________, _________________ air mass moves from _________________

____________________________________________________________________ * A _____________________ ____________________________ dominates the region

(central U.S.) * Combination of ________________ and __________________ cause ________________ temperatures. NOR’EASTER * Usually occur during ____________________________________________________ * Slow moving ___________ moves to the north of ___________________ with a

____________ moving up the ______________________. * Causes ___________________ wind of ______ air to the south

(____________________________________)


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* Colder air from north may come in contact with warm air from the south causing

____________________ * Situation can cause strong _________ winds, heavy ________________, coastal _________,

______________________________________

FRONTS Front: A sloping boundary between air masses with different properties of: A front is also associated with a _______________ in the pressure pattern. The slope of the front influences the __________________________________ that form. Types of Fronts and Symbols The type of front is determined by ___________________________________________: e.g., cold front = Stationary Front a.

b. surface winds blow _________________________________, but in _________________________________ on either side of the front

c. slopes from surface toward _________________ d. weather: e. precipitation: f. location: colder air usually on the ___________________________


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Cold Front Usually occurs where Slope is ______________ than that with a warm front (or stationary front) If warm air is _________________, thunderstorms may form and a _____________ can develop. If warm air is ________________, nimbostratus and altostratus may form. Typical Weather Conditions Associated with a Cold Front Weather Element Before Passing While Passing After Passing Winds south-southwest gusty, shifting west-northwest Temperature warm sudden drop steadily

dropping Dew Point high; remains steady sharp drop lowering Clouds incr. Ci, Cs, then either

Tcu* or Cb Tcu or Cb often Cu

Pressure falling steadily minimum, then sharp rise

rising steadily

Precipitation short period of showers

heavy showers of rain or snow, sometimes with hail, thunder, and lightning

decreasing intensity of showers, then clearing

Visibility fair to poor in haze poor, followed by improving

good except in showers

* Tcu stands for towering cumulus, such as cumulus congestus; whereas Cb stands for cumulonimbus.


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Warm Front Usually occurs where Characteristics similar to a _____________________ front. Initial cirrus may be more than ______________________________________________ Typical Weather Conditions Associated with a Warm Front Weather Element Before Passing While Passing After Passing Winds South-southeast-east variable south-southwest Temperature Cool-cold, slow

warming steady rise warmer, then

steady Dew Point Steady rise steady rise, then steady Clouds In this order: Ci, Cs,

As, Ns, St, and fog; occasionally Cb in summer

stratus-type clearing with scattered Sc; occasionally Cb in summer

Pressure usually falling leveling off slight rise, followed by fall

Precipitation light-to-moderate rain, snow, sleet, or drizzle

drizzle or none usually none, sometimes light rain or showers

Visibility poor poor, but improving fair in haze


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Cold Front vs. Warm Front Precipitation Cold Front: Precipitation location: Intensity: Duration: Warm Front: Precipitation location: Intensity: Duration: Occluded Front


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Occurs when a _______________________________________ and _________________ a warm front. Typically form __________ in a cyclone’s life cycle. 3 types of occlusions: determined by ________________________________ between the air behind the cold front and ahead of the warm front.

• ________________________________ (most common east of Rockies) o air behind cold front is __________ than air ahead of warm front o weather is like a _________________ during frontal passage

• ________________________________ ( most common in the Pacific NW) o air behind the cold front is _________________as air ahead of warm front o weather is like a ________________ during frontal passage

• ________________________________ o _______________________ between air masses, marked by ___________

____________________________________________________________ Typical Weather Conditions Associated with a Cold-Type Occluded Front Weather Element Before Passing While Passing After Passing Winds southeast-south variable west to northwest Temperature Cold Type Warm Type

cold-cool cold

dropping rising

colder milder

Dew Point steady usually slight drop, especially if cold-occluded

slight drop, although may rise a bit if warm-occluded

Clouds in this order: Ci, Cs, As, Ns

Ns, sometimes Tcu or Cb

Ns, As, or scattered Cu

Pressure usually falling low point usually rising Precipitation light, moderate, or

heavy precipitation light, moderate, or heavy continuous precipitation or showers

light-to-moderate precipitation followed by general clearing

Visibility poor in precip. poor in precipitation improving Criteria used to locate a front on a surface weather map


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1. ____________________________________________ over a relatively short distance 2. changes in the air’s __________________ content (change in ________________) 3. shifts in the wind ___________________________ 4. ________________________ and _____________________________ 5. ________________________ and __________________________________ patterns

EXTRA-TROPICAL (MID-LATITUDE) CYCLONES

The extra-tropical cyclone (mid-latitude cyclone, low pressure, or low), is a major weather maker in the mid and high latitudes. Surface winds blow _____________________________________ Surface winds ________________________________________________________ Life Cycle of Extra-Tropical Cyclones (Norwegian Cyclone Model) Cyclogenesis (birth of a cyclone)

• starts along the _____________________ as a _________________________ • sets up __________________________________ (_______________________) • location is directly under an area of ___________________________________ • __________________ develops with ___________________________________

as shown in the figure • _______________________________ as cyclonic circulation develops • westerlies aloft ____________________________________________ as it grows

Wave Cyclone

• central pressure continues to __________ and winds strengthen due to increased _______________________

• upper level trough ________________ and is located ______________________ ________ center

• warm sector is better defined • fronts form a pronounced ________________________ and _________________

_____________________ in satellite images • extensive _____________________ cloudiness is _________________________ • cyclone moves ____________________ at 25-35 mph

Beginning of Occlusion


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• warm sector _________________________ and occluded front ___________ _________________________

• upper level pattern shows _____________________________ and is _______ _______________________________________________________________

• ____________________________ the cold front cloud band from the comma cloud

• cyclone moves _____________ at ~ 20 mph

Bend-Back Occlusion

• surface low may become _______________ from the westerly steering flow and the occluded front is ______________________________________ of the low

• warm sector is __________________ from the cyclone center • ___________________ favors development of a secondary cyclone • eventually the cyclone weakens (_____________________________________)

Entire cycle can occur over __________________________________________ if upper level conditions are ideal. ____________________________ will result in poorly defined systems.

Extra-Tropical (mid-latitude) Cyclone Weather Figure 10. 12 in your text represents an intensifying cyclone in the Upper Midwest. Extra-Tropical Cyclones: cold side or warm side Storm track determines weather at points on the ground

• Track A puts Chicago on the _____________________ with passage of fronts • Track B puts Chicago on the ____________________ with no frontal passages • Study this idea…you’ll do this in lab and on a test.

UPPER AIR FLOW * Developing surface storm systems are ____________ that usually

_________________________. * What happens when an upper-level low is located ______________________ the surface low? It _______________ * Air flow aloft in the mid-latitudes usually consists of a series of _______________________ (______________________________________________) Convergence: Divergence:


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This type of convergence is also called _____________________ This type of divergence is also called _____________________ Convergence and divergence also result from _________________________________ Convergence Aloft: Divergence Aloft: For a surface low to develop or intensify, upper level __________________ of air must be ____________________ than surface ____________________________. PUTTING IT ALL TOGETHER . . . * Winds aloft _________________________________________ of surface storms. * Surface lows should move to the __________________________. * Surface highs should move to the _________________________. * Surface systems move at ~ __________________________ of the __________ winds. * If a surface low is under upper level ______________________, it will ______________________________. * If a surface high is under upper level _______________________, it will _______________________________.


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Principal Extra-tropical cyclone tracks • Tracks tend to converge toward the ________ (head to

the____________________) • Tracks appear to originate _________________________________, but actually

form over the _______________________________________. Just _______________ over the mountains, but then _______________.

• Cyclones that form in the ________________________________________________ (access mT)

500 mb map of Northern Hemisphere shows 5 longwaves (__________________________ or _____________________________) encircling the globe. Longwaves can remain _________________________, move east very slowly (__________________ ______________) or move west (____________________________________________________) Imbedded in longwaves are ________________________: small _____________________ or ________________________________________

The ___________________________ the wavelength, the ________________ it moves downstream. Shortwaves move east at a speed close to the ____________________________________________ ______________________________________________________________________ Shortwaves tend to ______________________ when they approach a ___________________________ (1 and 3), and ________________ when they approach a ___________________________ (2). Contour lines _____________ to isotherms = _______________________________ and windflow is ____________________________________________________ Contour lines ________________ isotherms = ____________________________ and temperature ________________________ occurs. Near _______________________________. Distinct air mass regions exist. Always baroclinic near mid-latitude cyclones.


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Advection Examples: 1. no advection 2. Stronger __________________________, greater ___________________________________ 3. closer____________________ implies ______________________ transport temperature __________________efficiently The greater the angle (up to 90 degrees) between winds and isotherms, the ___________________ will take place. The isobars and isotherms form parallelograms or boxes (sometimes called solenoids); the size of the boxes is ______________________________________ to the intensity of advection.

In the diagram above: more ____________advection taking place than ___________ advection. Smaller boxes imply _________________________. Larger boxes imply _________________________. So… __________________________ = wind must blow across the isotherms from colder to warmer regions. See blue arrows in diagram on previous page. __________________________ = wind must blow across the isotherms from warmer to colder regions. See red arrows in diagram on previous page. (a) Longwave 500 mb trough over stationary front. Currently ___________________


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(b) Shortwave _________________ and creates ___________________ in the flow = baroclinic instability This causes horizontal and vertical motions that ______________________________________. Convergence at 1 (creates “___”) and divergence at 2 (creates “____”) Cold air advection is occurring at position _____, cold air brought into the ___________. Cold air is dense and ________________________ of the 500 mb surface. _________________= lower ____________. So trough ________________. Cold, heavy air also sinks here. At position _____, warm air advection _______________________ and builds the ridge. Warm air rises here and condensation releases latent heat to fuel storm. (c) Storm ___________________ and storm should start to weaken now. Warm moist air is ________________ from storm with cold dry air drawn into the center of surface low. Upper low has been ______________. Upper and surface low are now ____________________. Winds slacken, pressure _____________ and low is said to be _________________. Jet Streaks… Strongest winds in the core of the jet = _______________________________ or ______________ Tend to form in ____________________________ where pressure gradients are _____________ If curved jet streak, then div at point 3 and con at point 1 _________________________________ (“D”) of jet streak will draw ________________________ upwards which will enhance the cyclone causing further pressure drops This storm has proper _____________________________________________________________ Vorticity, Divergence, and Developing Storm Systems Anything spinning has ___________________________ Faster spinning = _________________________________ When viewed from above…


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• air that spins ______________________________ has _____________________________ • air that spins __________________________________ has _________________________

Two types: _________________________________ and _________________________________ Northern Hemisphere: earth’s vorticity (_________________________________) is always _______ Because earth spins ____________________________________________. Vorticity depends on ______________: _______________________________________________ Moving air will usually have additional vorticity relative to the earth’s surface = __________ vorticity Two causes of _______________________: 1. 2. Absolute vorticity = * Earth’s vorticity at any latitude = When upper-level divergence moves over a weak cyclonic circulation, ________________________ ____________________________________________ (more positive) and ____________________

gph 212 – air masses, fronts, cyclones newman notes …

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