Meteorology · Upper Air — 500 mb Pattern
On a 500-millibar chart, surface weather systems tend to move:
- AAlways due north
- BOpposite to the upper-level flow
- CIn the direction of the upper-level flow (steering winds)✓ Correct
- DRandomly, unrelated to the upper flow
Explanation
The 500-mb (roughly 18,000 ft) flow acts as the steering current for surface lows and fronts, which generally track with the mid-level winds. Forecasters use the 500-mb pattern of troughs and ridges to project where surface systems will go and how they will develop.
Authority: NWS; Bowditch (Pub. No. 9)
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