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Thursday, September 23, 2021

SPC Sep 23, 2021 0100 UTC Day 1 Convective Outlook

SPC 0100Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0734 PM CDT Wed Sep 22 2021 Valid 230100Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF CENTRAL APPALACHIANS...MID-ATLANTIC AND CAROLINAS... ...SUMMARY... Thunderstorms associated with a marginal tornado and wind-damage threat will be possible this evening into tonight from the central Appalachians into the Mid-Atlantic. A few strong wind gusts may also occur in the Carolinas this evening. ...Central Appalachians/Mid-Atlantic... The latest water vapor imagery shows a high-amplitude upper-level trough located over the Great Lakes and Ohio Valley with south-southwesterly mid-level flow over much of the Northeast. At the surface, a 1003 mb low is located in far northwestern Pennsylvania. A pre-frontal trough extends southeastward from the surface low into west-central Pennsylvania and then southward into central Virginia. Thunderstorms are ongoing along and near the pre-frontal trough. Ahead of the storms, surface dewpoints are in the 65 to 70 F range and weak instability is present. The strongest instability is located from southeast Pennsylvania southward into far eastern Virginia where the RAP is estimating MLCAPE to be in the 500 to 750 J/kg range. In addition, the WSR-88D VWP near Washington D.C. has strong speed shear and veering winds with height in the lowest 1 km. This is resulting in 0-1 km shear in the 35 to 40 kt range suggesting that a marginal tornado threat could develop as the thunderstorms along the pre-frontal trough move eastward. The marginal tornado threat could affect much of Pennsylvania, Maryland and central Virginia along and near the axis of a 40 to 55 knot low-level jet. Any storm that rotates may also produce strong wind gusts. ...Carolinas... The latest surface analysis shows a pre-frontal trough located across the central Carolinas. Thunderstorms are ongoing near the pre-frontal trough along and near interstate-74 and then extending southwestward to near Sumter. Ahead of the storms, surface dewpoints are in the mid 70s F and MLCAPE is estimated to be in the 1000 to 1500 J/kg range. This combined with steep low-level lapse rates may be enough for a marginal wind-damage threat for a few more hours this evening. ..Broyles.. 09/23/2021 Read more LIVE: spc.noaa.gov