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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.


Saturday, November 13, 2021

SPC Nov 13, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0148 PM CST Sat Nov 13 2021 Valid 132000Z - 141200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTHERN NEW ENGLAND... ...SUMMARY... Isolated to scattered damaging winds, a brief tornado, and small to marginally severe hail remain possible across the southern New England until around 6 PM EST. ...Southern New England... The primary changes at 20Z are to clear probabilities in the wake of ongoing convection, and expand the Slight Risk slightly southward to cover the remainder of Long Island. Low-topped but strongly sheared convection will move across southern New England for the remainder of the afternoon into the early evening. Marginally severe hail has already been noted with these storms, and the locally damaging wind threat will likely increase from 20-22Z as low-level flow increases, before convection encounters increasingly stable conditions and weakens this evening. See MCD 1946 for more details. ..Dean.. 11/13/2021 .PREV DISCUSSION... /ISSUED 1018 AM CST Sat Nov 13 2021/ ...NYC to southern New England... Water vapor imagery and model guidance show an intense mid-level speed max exceeding 95kt at 500mb rotating across the Mid-Atlantic region today. This feature is sampled by the LWX VAD, and is forecast to track off the NJ/Long Island coast by mid afternoon. The left-exit region of this jet will result in strong large scale forcing for ascent and cyclogenesis over Long Island/CT today, with southerly low-level winds strengthening in the warm sector of the low. Surface dewpoints will struggle to climb beyond 55F, but very cold mid-level temperatures (at-or-below -20C at 500mb) and full sunshine over region will result in steep lapse rates and a brief period of sufficient MLCAPE for vigorous convection. Current indications from CAM ensembles suggest that storms will form around 18z over northern NJ/southeast NY and track east-northeastward into parts of CT/MA/RI. Strengthening winds just above the surface, coupled with steep low-level lapse rates support a risk of damaging wind gusts as the main threat with the strongest cores. There will also be some risk of hail and an isolated brief tornado or two. The size of the area of concern, coupled with limited low-level moisture, result in considerable uncertainty whether storms will have time to organize to severe limits before they move out of the most favorable environment. The activity should move off the coast of eastern MA by 00z, ending the threat. Read more LIVE:
SUNRISE AND SUNSET TIMES IN UTC (if you're not logged in to Google)
CHICAGO UTC-6 during CST (Central Standard Time, e.g., winter)
CHICAGO UTC-5 during CDT (Daylight Savings Time, e.g., summer)