Severe Storm Risk - Arnold AFB, TN

There is a Marginal Severe Storm Risk for your location. Continue reading for today's outlook from the National Weather Service's Storm Prediction Center. -------------------- National Severe Storm Outlook THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF THE OHIO VALLEY INTO THE SOUTHERN MID-ATLANTIC AND CAROLINAS SUMMARY Severe thunderstorms capable of mainly damaging gusts are possible across portions of the Ohio Valley into southern Mid-Atlantic and Carolinas on Saturday afternoon and evening. Isolated occurrences of large hail and severe wind gusts also appear possible over parts of the northern and central Plains Saturday into Saturday night. Synopsis A prominent mid-level ridge will persist over the central CONUS between upper lows over the Pacific Northwest and the Gulf of St. Lawrence into NB/NS. Several weak disturbances (some of convective origin) will progress through the periphery of the ridge, serving as foci for thunderstorm development. At the surface, an area of low pressure is forecast over the western Dakotas with an associated boundary --the location of which may be modified by convective outflow-- extending into the OH Valley and southern Mid-Atlantic. The eastern extension of the boundary will begin to push south as a cold front Saturday afternoon into night as high pressure builds into the Great Lakes. Ohio Valley into the Carolinas A mature to decaying MCS is expected to be ongoing 12Z Saturday over portions of the middle to upper OH Valley, aided by a subtle mid-level disturbance/possible MCV. There is considerable variability across the 00Z convection-allowing models in the longevity and extent of the convective system over the central Appalachians into southern Mid-Atlantic through the remainder of the morning. Should the MCS remain intact, isolated occurrences of damaging wind are possible. Renewed thunderstorm development is likely by afternoon along the residual MCS cold pool and/or synoptic front as temperatures in the 90s to around 100 combine with boundary-layer dewpoints in the low to mid 70s to yield MLCAPE up to 2000-3000+ J/kg with steepening low-level lapse rates. Additionally, the models indicate some enhancement of mid-level winds in association with the disturbance/MCV moving through the southern Mid-Atlantic during the afternoon, which may yield more organized multicells and line segments with the predominant hazard being damaging wind gusts into the evening. Farther to the west, additional strong to severe storms appear possible along and ahead of the composite boundary from the vicinity of the OH River south into the Cumberland Plateau where widely scattered damaging wind gusts also appear possible. Northern and Central Plains A band of elevated thunderstorms is expected to be ongoing 12Z Saturday, centered over eastern SD. That activity is expected to diminish through the morning with the cessation of the nocturnal low-level jet; however, isolated occurrences of large hail and severe wind gusts appear possible prior to dissipation. In the wake of the early-day storms, the presence of steep low/mid-level lapse rates and richer boundary-layer moisture with eastward extent will contribute to a moderately to strongly unstable air mass by afternoon with MLCAPE of 2000-3500+ J/kg. Nebulous forcing for ascent and capping relating to the proximity of the mid-level ridge axis lead to uncertainty in the specific details regarding the location and extent of surface-based thunderstorm development during the afternoon into evening. However, the presence of the surface low, outflow-modified surface front, and a lee trough over the High Plains will be candidates for storm development. The strongest deep-layer shear (30-40 kt) is forecast to the north of the surface low and composite boundary over ND and northern SD into western MN where a conditional risk of supercells capable of large hail and severe wind gusts exists. Elsewhere, high-based pulse and multicell storm modes appear possible with the primary hazard being widely-spaced severe wind gusts. The isolated severe threat may persist into the overnight hours in the vicinity of a nocturnally strengthening low-level jet. Western Montana A belt of enhanced mid/upper-level flow will exist across the region, to the east of the upper low over the Pacific Northwest. Heating along the high terrain coupled with the possible influence of a weak mid-level disturbance is expected to support an increase in high-based showers and a few thunderstorms during the afternoon and evening. While lapse rates will be steep with strong deep-layer shear, the absence of appreciable moisture will limit MLCAPE to generally less than 250 J/kg. As such the potential for severe wind gusts is currently too low to warrant 5% wind probabilities.