SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0149 PM CST Thu Feb 18 2021 Valid 182000Z - 191200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE EASTERN FLORIDA PANHANDLE TO THE GEORGIA AND FAR SOUTHERN SOUTH CAROLINA COASTS... ...SUMMARY... A strong-to-severe storm or two are possible through this evening from the eastern Florida Panhandle to the Georgia and far southern South Carolina coasts. The main hazards with this activity are gusty winds and perhaps a brief tornado. ...20z Update - FL Panhandle to south GA... The Slight risk has been removed with this update. Convection has struggled to maintain and/or increase in intensity this afternoon. Much of the shower and isolated thunderstorm activity across the region is elevated, on the cool side of the front, which now extends from just south of Savannah GA to very near Tallahassee FL. Surface heating into the mid 70s to mid 80s has occurred ahead of the front, and dewpoints in the mid 60s to near 70 F are aiding in MLCAPE values around 250-500 J/kg. Poor midlevel lapse rates will limit further destabilization. Surface winds ahead of the front have veered to the southwest, decreasing convergence along the boundary. Nevertheless, moderate low level shear overlies the area and could aid in brief upticks in intensity/organization of cells track northeast over the next few hours. The overall severe threat however appears marginal and limited in space and time, with any tornado threat being quite conditional on a stronger storm actually developing. As a result, the Slight risk has been removed, though a Marginal risk remains from the eastern FL Panhandle to the GA and far southern SC coasts. ..Leitman.. 02/18/2021 .PREV DISCUSSION... /ISSUED 1030 AM CST Thu Feb 18 2021/ ...FL Panhandle to south GA... Categorical risk areas have been mainly adjusted to decrease the western and northern extent with a persistent, low probability tornado environment expected to continue into this evening. Overall lightning trends have decreased somewhat through late morning within a swath of scattered convection that is elevated from the eastern Carolinas to surface-based over the northeast Gulf. The surface warm sector characterized by mid to upper 60s surface dew points resides across the central to eastern Panhandle and north FL into a portion of south-central to southeast GA. A lack of stratus in north FL to southeast GA will result in more robust boundary-layer heating and the front reaching the Savannah to southwest GA vicinity before oscillating back south later today. This heating will likely be necessary to aid in sustaining surface-based thunderstorm redevelopment given the weak mid-level lapse rates evident in 12Z observed soundings across FL. Low-level southwesterlies should be strongest at present and slowly subside into this evening, but at least 40 kt flow will likely persist through late afternoon. With a lack of cyclogenesis, low-level hodographs, while adequate for supercell development, are unlikely to broadly improve. This suggests the severe threat may remain conditional, and require convection to develop/spread towards the warmer boundary layer farther east. A weakening trend should ensue after sunset as the boundary layer cools and low-level hodographs become increasingly marginal.
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