Here's an update from the WGN
Weather Center on the latest thinking on the threat for severe
weather in the Chicago
Though clearly outside the period of peak solar heating, an influx of warmer, more humid air predicted to be ongoing by then will have the atmospheric moisture content (the "precipitable water" values) surging to 1.84" of evaporated water at the same time a pocket of especially strong jet stream winds approaches from the west. Air sinks immediately below the front quadrant of such band of strong upper winds commonly referred to by meteorologists as a "jet streak". But, this large scale sinking of air actually enhances the upward motion of the air just ahead of such a feature--which is where theChicago
The 4 to 8 a.m. window would be the period in which the ascension of air would be at its peak and, therefore, potentially the most supportive of thunderstorm formation in the increasingly moist air expected to be pouring into the area. In addition, the faster than usual vertical temperature decline--in other words the instability of the atmosphere-- projected by computer models as well as energy calculations (so-called "CAPE" values--an acronym for "Convective Available Potential Energy") 2500 joules per kilogram--1000 is widely viewed as the severe thunderstorm threshold--appear likely to be supportive too. Many of the critical values we examine for severe weather generation are fairly comparable to early this past Saturday when predawn thunderstorms roared across part of theChicago
An impressive line of thunderstorms developing fromSouth
Dakota into Minnesota as we post
this at 3pm Tuesday appears to be the first stage of the thunderstorm cluster
expected to reach at least sections of the Chicago Wyoming and South Dakota
Tom Skilling
Though clearly outside the period of peak solar heating, an influx of warmer, more humid air predicted to be ongoing by then will have the atmospheric moisture content (the "precipitable water" values) surging to 1.84" of evaporated water at the same time a pocket of especially strong jet stream winds approaches from the west. Air sinks immediately below the front quadrant of such band of strong upper winds commonly referred to by meteorologists as a "jet streak". But, this large scale sinking of air actually enhances the upward motion of the air just ahead of such a feature--which is where the
The 4 to 8 a.m. window would be the period in which the ascension of air would be at its peak and, therefore, potentially the most supportive of thunderstorm formation in the increasingly moist air expected to be pouring into the area. In addition, the faster than usual vertical temperature decline--in other words the instability of the atmosphere-- projected by computer models as well as energy calculations (so-called "CAPE" values--an acronym for "Convective Available Potential Energy") 2500 joules per kilogram--1000 is widely viewed as the severe thunderstorm threshold--appear likely to be supportive too. Many of the critical values we examine for severe weather generation are fairly comparable to early this past Saturday when predawn thunderstorms roared across part of the
An impressive line of thunderstorms developing from
Tom Skilling
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