ATMO 10/16 - 500mb Height Patterns

Wind Direction and Speed at 500mb:
- Direction is parallel to height iso bars
- The arrow should have lower heights on the left and higher heights on the right
- Speeds are relatively higher where the height contours are closer together and relatively slower where the height contours are farther apart
- Surface lows are "steered" by 500mb winds
- Hurricane systems are moved around by the 500mb winds
- Individual thunderstorms are mostly influenced by the 500mb winds

Precipitation:
- Likely on the down wind side of the trough axis
- Air rises as it comes out of the trough
- Unlikely on the down wind side of the ridge axis
- Air sinks as it comes out of the ridge

Long Wave:
- Wavelength: distance between trough to trough (typically a few thousand kilometers)
- Northern Hemisphere typical has between 3 and 7 waves if you look around the north pole

Why Precipitation/Clear Skies:
- Divergent force above 500mb after troughs (upper tropospheric divergence)
- Faster wind speeds produce stronger divergence (stronger weather producer)
- Convergent force above 500mb after ridges (upper tropospheric convergence)

Types of trough/ridge combinations:
- Zonal/Flat: little precipitation (weaker weather conditions close to average)
- Meridional/Amplified: possible precipitation (stronger weather conditions, well above or below average)
- Retrograding: when the trough or ridge moves westward instead of eastward
- Stationary/Blocked patterns: similar weather day to day

Curvature of Trough:
- The sharper the curvature, the stronger the divergence, the stronger the weather that is produced

Short waves: (No test questions on short waves)
- Much smaller than long waves
- Mini-troughs or ridges within the long wave
- Produce smaller areas of weather
- Typically move through the long wave pattern faster than the long wave itself moves
- "Pieces of energy", "little disturbances in the flow", "Pocket of cold air aloft"

Closed and Cut off low:
- Cut off low: a closed low detached from the mainstream 500mb winds and can remain stationary for a long period of time (few days to a week)

Extra Credit Assignment:
- Available online on the course website
- Analyzing 500mb maps

Part 1a:
- Play a TV weather man's role and make a very general forecast of the united states

Part 1b:
- Make sure you give the estimated 500mb height for Tucson!
- Give a little more precise forecast of Tucson and give above/below average temperature forecasts
- Is Tucson in a favorable place for precipitation?

Part 2a:
- Compare forecasted and real/true 500mb maps
- For each forecast, tell whether or not you're forecast would have been good or not

Part 2b:
- Compare forecasted and real/true 500mb maps for Tucson
- Make sure you give the estimated real 500mb height for Tucson!
- For your Tucson forecast, tell whether or not it was a good forecast or not

Extra credit goes towards your homework grade. Counted as half as much as the 2nd and 3rd homework assignments.