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| That band of blue in Southern IL and IA tells a fascinating story. |
So tonight, things are relatively mediocre throughout the state, as high pressure has moved in and pushed away any winds with it. Though light migration is occurring right now in response to the lack of headwind, this isn't what steals the show. What steals the show is a tiny and weak low pressure system in Southern IL and IA, which is bringing a fascinating migratory response (see below).
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On this surface analysis, you can see a southward-facing cold front in Southern IL right next to a northward-facing warm front in Indiana. In between these front lines is a tiny low pressure center (remember winds revolve counterclockwise around Low Pressure systems). Its winds extend about as far from its center as these two specific warm and cold front lines extend. Its winds are almost indistinguishable from the high pressure over NE IL they are so weak, but they're just barely strong enough that the southward facing cold front is followed by northerly winds favorable for migration. So, as a result, a narrow band of heavy migration is occurring just north of the given cold front--restricted entirely to the narrow area of favorable conditions. A few other patches of migration are occurring around this band; these are likely birds responding to the combination of weak winds from the high pressure and the northerly winds to the west of the low pressure system, but these areas of migration are a bit more mysterious. Isn't this all friggin' awesome! I love this stuff.
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Looking in what has repeatedly been a depressing wind forecast, it looks like the theme will be retained until Tuesday evening. At that point, it appears that another front will be passing in Illinois from northwest of us. Until then, expect migration to be occurring in light increments until southerly headwinds take over some time tomorrow afternoon.
Good stuff. That low pressure system was pretty exciting.
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