October 11, 2018
SPC Oct 11, 2018 2000 UTC Day 1 Convective Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0237 PM CDT Thu Oct 11 2018 Valid 112000Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF NORTH CAROLINA...VIRGINIA INTO THE MID ATLANTIC... ...SUMMARY... A few tornadoes are possible through about 11 PM EDT from northern/eastern North Carolina across southern Virginia into the Delmarva region. The most probable corridor is across northeast North Carolina and southeast Virginia this afternoon. ...DISCUSSION... A couple changes have been made to the outlook for this issuance. The first change is to downgrade the categorical outlook to just slight risk. So far, Tropical Storm Michael has not been an efficient tornado producer. Although low-level shear will be favorable for tornadoes this afternoon into this evening, coverage is expected to be less than was previously forecast. The second change to the outlook is to trim the southern part of the slight risk and thunder areas due to the northeastward progression of Michael. ..Broyles.. 10/11/2018 .PREV DISCUSSION... /ISSUED 1126 AM CDT Thu Oct 11 2018/ ...Mid-Atlantic States... Primary expansion change is to adjust the Slight Risk slightly farther north across parts of DE/MD. Considered further increasing tornado probabilities across northeast NC and southeast VA, but deferred. The center of TC Michael continues to track quickly northeast, just northeast of Charlotte as of 16Z, and will reach southeast VA this evening. Arcing band of showers and sporadic thunder is ongoing from just north/east of Raleigh-Durham to coastal NC. Breaks in the cloud cover downstream of this band have resulted in surface temperatures warming into the lower to middle 80s already, which is supporting a moderately buoyant air mass with MLCAPE from 1000-1500 J/kg. As this convective arc spreads northeast through the afternoon, intensification of embedded updrafts is expected along the northeast periphery of the strong low-level wind field. This will favor a swath of effective SRH from 200-500 m2/s2, supporting several rotating cells into early evening. Increasing baroclinicity downstream of the track of Michael in the Delmarva region suggests that favorable low-level southeasterlies will generally remain close to the coastal regions near the southern portion of Chesapeake Bay. This should limit the northern/western extent of any lingering tornado threat this evening.