21.   Meanwhile, colder air will surge south along the western flank of the low pressure zone bringing a period of ice to central Missouri and northern Arkansas.

22.   Most winter high pressure zones are essentially mounds of cold air.

23.   One low pressure zone will promote inclement weather from the southern Plains to the Ohio Valley on Thursday while a new disturbance sweeps into the West Coast states.

24.   Scattered showers and thunder are also expected across the Great Lakes states as moist air interacts with a broad low pressure zone in Illinois.

25.   Sinking currents of air in a strong high pressure zone will keep the Gulf Coast sunny.

26.   Slowly, a pattern emerged linking years with unusual cloudiness to changes in high pressure zones near Hawaii and in the North Atlantic.

27.   Sunny and mild weather will stretch from Texas to the Southwest as air sinks around a large high pressure zone.

28.   The catalyst for the late season freeze, an Arctic high pressure zone, will retreat toward the Southeast Coast Friday.

29.   The catalyst for the wintry weather was a vigorous jet stream disturbance, coupled with a strong surface low pressure zone.

30.   The associated high pressure zone will slide slowly eastward across New England through Saturday, with drought conditions continuing.