| 21. | Pacific and modified polar air have jousted back and forth over the Plains this week.
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| 22. | The cold polar air mass met with humid subtropical air, leading to very low pressure.
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| 23. | But a new push of polar air into New England will retard the advancing sultry weather.
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| 24. | From September until February, frequent continental polar air masses coming from the East invade the area.
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| 25. | The boundary with polar air over Canada will be active from the Great Lakes to Montana.
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| 26. | Frequent surges of polar air have kept readings generally below seasonal levels for over two weeks.
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| 27. | A surge of polar air will reach from the Great Lakes to the lower Missouri Valley.
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| 28. | Behind this solar track, the sea and air grow warmer and the polar air currents retreat.
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| 29. | The boundary between polar air and Pacific air will be confined to the border ( sTetes.
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| 30. | The leading edge of a polar air mass will enter the Upper middle West on Wednesday.
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