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Low-pressure systems form under areas of wind divergence that occur in the upper levels of the atmosphere (aloft). The formation process of a low-pressure area is known as cyclogenesis. In meteorology, atmospheric divergence aloft occurs in two kinds of places:
A surface low can have a variety of causes for forming. Topography can force a surface low to form when an existing baroclinic wave moves over a mountain barrier; this is known as "lee cyclogenesis" since the low forms on the leeward side of the mountains. [17] [18] Mesoscale convective systems can spawn surface lows which are initially warm ...
Depth of 26 °C isotherm on October 1, 2006. There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to sustain a low-pressure center, a preexisting low-level focus or disturbance, and low vertical wind shear. [3]
The NWS also issued a red-flag warning for the Chicago area on Tuesday, saying in an advisory, "Critical fire weather conditions are either occurring now or will shortly."
A banner indicating a red flag warning, flown at a CAL Fire station in 2022. A red flag warning is a forecast warning issued by the National Weather Service (NWS) in the United States to inform the public, firefighters, and land management agencies that conditions are ideal for wildfire combustion, and rapid spread. [1]
A "red flag warning" will be in effect Monday afternoon across the Southern High Plains into western Oklahoma, according to the National Weather Center Norman, and a "fire weather watch" is in ...
The PDS red flag warning below was issued by the National Weather Service in Reno, Nevada, on December 19, 2017. [7] On August 3, 2018, the National Weather Service in Reno, Nevada, issued another PDS red flag warning to communicate the threat of life-threatening fire danger due to strong gusty winds and low humidity.
Parts of the Chicago area could see severe thunderstorms Tuesday evening, with hail, strong winds and tornadoes possible, according to the National Weather Service. Northwestern Illinois and the ...