Moisture, Clouds & Precipitation
Explain the difference between the dry adiabatic lapse rate and the moist adiabatic lapse rate.
Dry adiabatic lapse rate (DALR) ≈ 10°C/km (unsaturated air).
Moist adiabatic lapse rate (MALR) ≈ 6°C/km (saturated air, latent heat release slows cooling).
What surface wind belt exists between 30° and 60° latitude in each hemisphere?
Westerlies
Why: Air flows poleward from subtropical highs and is deflected eastward.
Identify the most likely source region for a cA air mass affecting the continental United States.
Arctic Basin/Northern Canada/Greenland interior.
Why: Very high latitudes yield very cold, very dry air.
What symbol represents a stationary front on a surface weather map?
Alternating red semicircles and blue triangles on opposite sides of a line.
Explanation: Indicates boundary where air masses are not moving significantly.
List the four main lifting mechanisms that can produce clouds.
Orographic lifting, frontal lifting, convergence, convection.
What is the name for the boundary between the Polar Cell and the Ferrel Cell?
Polar front
Why: Boundary between cold polar air and warmer mid-latitude air.
What sequence of cloud types is typically seen ahead of a warm front in the correct order of appearance?
Ci → Cs → As → Ns → St (sometimes fog).
Why: Gentle overrunning produces layered clouds that thicken/lower.
What does “SLP” mean in a METAR, and in what units is it reported?
Sea Level Pressure, in tenths of mb.
Explanation: SLP 120 = 1012.0 mb.
Explain why condensation releases latent heat and how this affects rising air parcels.
Condensation releases latent heat, warming the rising air parcel and helping it rise further.
Define “scale height” and give its approximate value in the atmosphere.
Scale height ≈ 8 km
Why: It’s the height over which atmospheric pressure decreases by a factor of eee in an isothermal atmosphere.
Describe the wind shift typically observed with the passage of a cold front in the Northern Hemisphere.
Commonly S/SW → W/NW after passage.
Why: Frontal passage veers wind as colder, denser air advances.
On a station model, the number “047” in the upper right corner for pressure means what in millibars?
004.7 mb.
Explanation: If the first digit ≤ 5, prefix with “10” → 1004.7.
A weather balloon measures a temperature of 5°C and a dew point of -1°C at the surface. Will clouds form immediately if the air rises, and why or why not?
No — clouds won’t form immediately. The air must cool to its dew point; with T = 5°C and Td = -1°C, it must rise and cool 6°C before saturation.
Write the hydrostatic equation and explain what it represents.
dP/dz=−ρg
Why: The hydrostatic equation expresses the balance between downward gravity and the upward pressure gradient.
List four key indicators on a surface weather map that help identify a frontal boundary.
Sharp temperature gradient; dew point jump; wind shift; pressure trough (and cloud/precip band).
Why: Classic diagnostics where air masses meet.
If the 700 mb chart shows high relative humidity and upward motion, what type of weather might you expect?
Cloudiness and possible precipitation.
Explanation: High RH + upward motion = rising moist air → clouds/precip.
Why do high dew points often signal the potential for severe thunderstorms?
High dew points = more water vapor available for condensation → stronger updrafts and heavier precipitation in storms.
Explain how the seasonal shift of the ITCZ produces a monsoon circulation.
Seasonal ITCZ shift changes wind direction
Why: Land warms/cools faster than ocean, reversing pressure gradients.
On a surface analysis map, you observe a sharp dew point gradient but little temperature difference — what type of boundary might this indicate?
Dry line.
Why: Moisture boundary (mT vs. cT), not primarily a temperature front.
Explain what a “trough axis” line indicates on an upper-air chart.
Line of lowest heights along a trough.
Explanation: Indicates axis of cyclonic curvature aloft.