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Weather conditions on bar directly above are near Lakefront. Weather conditions with Moon are O'Hare (official).

Thursday, November 11, 2021

SPC Nov 12, 2021 0100 UTC Day 1 Convective Outlook

SPC 0100Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0657 PM CST Thu Nov 11 2021 Valid 120100Z - 121200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN PENNSYLVANIA INTO THE DELMARVA... ...SUMMARY... A couple strong to severe thunderstorms may occur across the Mid Atlantic by early morning, towards the end of the period. ...Synopsis... A strong mid-level cyclone will continue to deepen while progressing eastward across the Upper Mississippi Valley through 12Z (the end of the forecast period). While the associated mid/upper level longwave trough deepens, a belt of 60-90 kt 500 mb flow will pivot around the trough and overspread a 50-70 kt southerly 850 mb jet centered over the Hudson Valley in the 07-12Z period. At the surface, strong convergence along a lee-trough axis/cold front will promote the development and organization of low-topped convection capable of producing strong wind gusts. ...Mid Atlantic... As the surface cold front crosses the Appalachians and approaches the lee trough, low-level convergence is expected to increase as the 50-70 kt low-level jet materializes and modest theta-e advection ensues. The 00Z GSO and WAL observed soundings depict upper 50s F surface dewpoints, but overall shallow moisture in the surface-850 mb layer. As such, buoyancy is expected to remain quite marginal when warm-air advection occurs, with MLCAPE likely remaining under 500 J/kg on a widespread basis. Nonetheless, a narrow, low-topped squall line is expected to develop along the immediate lee of the surface trough axis around 07-09Z. Point forecast soundings across portions of eastern PA southward towards Delmarva suggest that 50 kt southerly winds may occur as low as 400-500 m AGL. Despite the lack of buoyancy, any mechanically driven downward momentum transport within the line may support a couple strong wind gusts, with an instance or two of tree/power-line damage possible with the stronger gusts, hence the introduction of Category 1/MRGL probabilities. The damaging-gust threat is expected to persist past 12Z into the Day 2 period east of the current MRGL risk area. ..Squitieri.. 11/12/2021 Read more LIVE: spc.noaa.gov
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