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    For the 18Z TAFs...
    Under a ridge of high pressure, the main concern for the terminals
    for the remainder of the afternoon and into the evening will be
    winds. Latest radar imagery indicates that a lake breeze boundary
    has formed, but is making little inland progress. some of the high
    res model guidance is suggesting that the lake breeze could push
    inland through ORD by 21-23z, but with a speed of less than 10kt.
    Other guidance would suggest that the boundary could stall before
    reaching ORD/MDW but pushing through GYY. Have included the wind
    shift to ely at 7kt at 23z. Diurnal cu development across the
    region should remain sct through the afternoon and then dissipate
    with sunset while winds go lgt/vrbl as well.
    The next concern will be pcpn trends for the late night hours and
    into tomorrow. Latest guidance remains consistent on pcpn
    spreading from southwest to northeast, with some potential for at
    least some sct shra toward daybreak and then increasing in
    coverage and intensity as a low pressure system tracks newd
    through the Middle Mississippi Valley. High levels of deep layer
    moisture are expected to be in place, so local pcpn rates should
    be relatively high at times. With at least some modest
    instability with the system, expect that tsra would be more
    embedded within a larger shield of shra, so, have maintained the
    prob30 group for tsra, but with higher confidence in pcpn chances,
    have gone with prevailing shra by late morning. Cigs/vis will
    likely drop to mvfr with the heavier shra/tsra and there is a
    chance for short periods of ifr conditions.