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Weather- Exam 3

Terms in this set (70)

Air Mass
Large body of air with homogenous T and Td characteristics
*Influenced by surface over which they form (source region: extensive regions with physically uniform surface characteristics)
Cold Air Masses
High latitudes over cold surfaces
*Arctic, Polar
Warm Air Masses
Low latitudes over warm surfaces
*Tropical
Humid Air Masses
Over wet surfaces
*Maritime
Polar
North Atlantic, Pacific
Tropical
Atlantic/Pacific, Gulf of Mexico
Stability depends on...
Circulation
*Polar- unstable (k) in winter, stable (w) in summer
*Tropical- unstable (k) from Gulf of Mex., stable (w) for Pacific
Continental Air Masses
*Arctic (A): Arctic ocean (in winter), always stable (w)
*Polar (P): Interior Canada, always stable (w)
*Tropical (T): Desert SW-US or Central Mex., usually stable (w), unstable (k) under convection/convergence
Moisture (dew point) classified by...
Maritime (m): wet
Continental (c): dry
Temperature...
Arctic: bitter cold, winter
Polar: cold, cool
Tropical: warm, hot
Stability...
w: stable
k: unstable
cA
Cold, dry air from Arctic (winter only)
cP
Cold/cool, dry stable air from interior Canada
mP
Cool, humid air from N.Pacific/Atlantic Oceans
mT
Warm/hot, humid air from S.Pacific/Atlantic Oceans, Gulf of Mex.
cT
Hot, dry air from Central Mex. & Desert SW (summer only)
Front
Boundary b/t unlike air masses
Blocking highs
Strong anticyclonic circulation redirects movement of cyclones
Lake Effect Snow
Enhanced snowfall over land areas leeward of the Great Lakes
Polar front moves...
North in Summer, South in Winter
Fronts form...
ahead of advancing air masses
Cold Front
Boundary b/t a cold/cool air mass (cP or mP) advancing on a warm air mass (mT)
*S to NW wind shift, T & Td decrease, T-storms, brief & heavy rain
*Blue upwards triangles
Warm Front
Boundary b/t a warm air mass (mT) advancing on a cold/cool air mass (cP or mP)
*E to S wind shift, T & Td increase, widespread nimbostratus, light-moderate precip.
*Red upwards circles
Dryline
Boundary b/t a warm, dry air mass (cT) and a warm, humid air mass (mT) that forms in late Spring through Summer
*Acts like a cold front, forms severe T-storms & tornadoes
*Orange
Fronts are identified by a sharp change in...
Wind direction, temperature, dew point
Stationary Front
Air mass boundary in which neither advances (cP or mP onto mT)
*Winds parallel at front, scattered showers
*Blue triangles point down, red circles point up
Occluded Front
Surface cold front lifts a warm front
*Purple
Frontal wedging of warm air...
forms clouds and precipitation
Overrunning
Warm air rises gently (forms Nimbostratus)
Vertical Develop
Warm air rises sharply (forms Cumulus, Cumulonimbus)
Midlatitude Cyclone (MLC)
Low P storm system formed w/in midlatitudes
*Comma shaped cloud cover pattern
Polar Front Theory
Describes surface movement of air masses around an MLC
Conveyor Belt Theory
Describes both surface and upper-level air flow around an MLC
*transport polar and tropical, continental and maritime masses
*warm conveyor belt= most unstable
Cold air is....than warm air
more dense
MLC's develop...
along the polar front where polar and tropical air masses converge
*move W to E
Alberta Clipper
Fast moving storms (winter blizzards)
Panhandle Hook
Extreme changes in T, produce ice storms (form in transition seasons)
Colorado Low
Produce heavy precipitation and severe weather (form in transition seasons)
Nor'Easter
Coastal storms, produce snow, ice, rain, and T-storms
4 main stages of development (originate in Pacific mP and mT)
1. Cyclogenesis
2. Open
3. Occluded
4. Dissolving
Cyclogenesis
Wave develops, low P center, draws in cP
Open
cP advances, cold front, cyclone draws in mTk, mT advances/strengthens leading to warm front
*cold & warm= well developed
Occluded
Cold front occludes warm front forming occluded front, increases stability
*strongest stage
Dissolving
Storm weakens, increasing P, no significant P center (generally this stage is not on weather maps)
Thunderstorms
Cyclone that generates lightning, forms w/in clouds of vertical development as warm, humid air rises (unstable ATM)
Air Mass Thunderstorms
"Pop-up t-storms", afternoon heating causes instability (k) in response to convection
Cumulus Stage
Convection initiated by warm surface, cumulus grows with updraft
Mature Stage
Heavy rain, downdraft of cold air
Dissipating Stage
Light rain, downdraft cools surface, only downdraft remains
Air Mass Thunderstorms tend to form....
within an mTk air mass, may form individual cells of cluster into groups called Mesoscale Convection Complexes
Thunderstorms become severe when...
warm updraft is separated from downdraft, mini cold front forms (Gust front)
Wind Shear
Change in wind speed and/or direction with height
*Upper level winds tend to be west winds aloft
*South surface wind (mTk)
* Separates updraft from downdraft
Severe t-storms can produce...
Heavy rain, localized flooding, strong winds, hail, tornadoes
NWS criteria to classify a t-storm as severe...
1. Winds > 58 mph
2. Hail > 3/4 in (penny)
3. Tornadoes
Mesocyclone
Vertical cylinder of rotating air within a supercell
Wall Cloud
Protrudes from cloud base below updraft, forms distinctive radar pattern (tend to move towards NE), hook echo
Supercell t-storm
A rotating cumulonimbus cloud, anvil head, shear cloud top
*Key features: overshooting top, mesocyclone, tornado, down draft
*May occur: individually, in groups w/in MCC, w/in elongated bands called squall lines
Hail
Frozen precip. formed w/in a t-storm updraft, starts off as ice crystals from Bergeron process, grow by added water w/ each pass
*Classified by diameter for size: direct measurement (uncommon), equivalence to common standard-sized object
Squall Line
Elongated band of supercells, tend to form in front of drylines and cold fronts
Downburst & Microburst
Strong, localized downdraft, mid-level cool, dry air aloft, dense air descends > 20 mph, spreads out at surface in all directions
Tornado
Narrow, rapidly rotating column of air, must form w/in a mesocyclone
Tornadoes are distinguished by...
1. Rotating funnel
2. From base of thunderstorm
3. Reaches the ground
Tornadoes have...
funnel cloud and a debris cloud
Tornado averages
150-600 m wide, travel at ~30mph, path at least ~16mi long, towards NE
Kinds of tornadoes
1. Rope tornado
2. Wedge tornado
3. Multi-vortex tornado
4. Water-spout tornado
Intensity classified by...
Ehanced Fujita Scale (EF-Scale)
*Wind speeds inferred from damage
*Accounts for structural integrity
Greatest air mass contrasts
W/in midlatitudes, Spring, early Summer, over land, wind shear
Outlook
Describes potential hazardous weather of concern in days 1-7
Watch
Issued when conditions are favorable for possible development
Warning
Issued when conditions are occurring/imminent, spotted by observer or indicated by radar- 5 to 20 mins
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