Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Thu Jun 22 2017 Valid 231200Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FRIDAY INTO FRIDAY EVENING ACROSS PARTS OF THE TENNESSEE VALLEY INTO THE CUMBERLAND MOUNTAINS AND SOUTHERN PORTIONS OF THE ALLEGHENY PLATEAU... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS SURROUNDING AREAS OF THE MID SOUTH INTO THE APPALACHIANS...UPPER OHIO VALLEY INTO WESTERN NEW ENGLAND... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE FRIDAY AFTERNOON AND EVENING ACROSS PARTS OF THE SOUTHERN PLAINS... ...SUMMARY... Thunderstorms may impact portions of the Mid South and Tennessee Valley eastward into the Cumberland Mountains and southern portions of the Allegheny Plateau Friday into Friday night, accompanied by a risk for potentially damaging wind gusts and perhaps a few tornadoes. Other strong to severe thunderstorm activity is possible near the southern Plains Red River Valley, and across the Texas Edwards Plateau/Pecos Valley region. ...Synopsis... Cyclonic flow within the mid-latitude westerlies appears likely to amplify southeastward into the middle Mississippi/Ohio Valleys and much of the Northeast during this period. Models suggest that this will be accompanied by significant low/mid-level cooling which may also nose southward to the lee of the Rockies, within at least a shallow near surface layer, through much of the southern high Plains by 12Z Saturday. As this occurs, the lower/mid tropospheric remnants of Tropical Storm Cindy are forecast to become increasingly sheared while merging into the westerlies and accelerating northeastward ahead of the evolving upper trough axis, generally across Kentucky/Tennessee and the central Appalachians, perhaps as far east as the northern Mid Atlantic Coast region by the end of the period. Across much of California and the Southwest, eastward across the Gulf states into the southwestern Atlantic, subtropical ridging is expected to remain fairly strong. ...Mississippi Valley into Atlantic Seaboard... Given the presence of the shearing remnants of the tropical system, the potential for strong/severe storm development along and ahead of the surface front advance southeastward into the middle Mississippi and lower Ohio Valley region during the day is becoming more unclear. Frontal/pre-frontal low-level convergence may be generally weak, and early day cloud cover/precipitation may reduce pre-frontal destabilization. As a result, severe probabilities have been lowered across this region. The primary focus for any appreciable severe weather potential Friday seems likely to become the belt of stronger southwesterly lower/mid tropospheric flow along and south of the shearing remnants of Cindy. Models suggest that this likely will be on the order of 40+ kt, across parts of the Mid South into the central Appalachians, and perhaps considerably stronger in closer proximity to the circulation center tracking across this region. Although lapse rates are likely to be weak, insolation beneath the mid-level dry slot ahead of the circulation may contribute to at least weak boundary layer instability. And this may be sufficient to support convective development accompanied by at least a risk for potentially damaging wind gusts. Depending on how fast the low/mid-level cyclonic circulation weakens, in relatively close proximity to the east/southeast of it, there may be potential for low-topped supercells accompanied by a risk for tornadoes, mainly during the afternoon and early evening hours. Across Pennsylvania and New York into western New England, any appreciable severe weather potential on Friday seems likely to largely hinge on pockets of stronger daytime heating. Mid-levels will be relatively warm with weak lower/mid tropospheric lapse rates, but the environment will be seasonably moist with modest southwesterly to westerly lower/mid tropospheric wind fields on the order of 30-40 kt. With sufficient boundary layer heating/destabilization, it may not be out of the question that forcing associated with a weak mid-level perturbation or two could enhance thunderstorm development across Pennsylvania, to the southeast of the Allegheny front. It is also possible that forcing downstream of a much more significant impulse within the mid-latitude westerlies could enhance thunderstorm development across the Adirondacks region of Upstate New York into portions of western New England Friday evening. ...Southern Plains... A corridor of strong pre-frontal boundary layer heating may become the focus vigorous storm development late Friday afternoon and evening. Activity may initiate where the stronger heating noses into higher boundary layer moisture content across portions of the Red River Valley (and supports large mixed layer CAPE on the order of 2000-3000+ J/kg), and along the axis of strongest pre-frontal heating/deep mixing across parts of the Edwards Plateau into the Pecos Valley. Both regimes may become conducive to the risk for severe hail and winds, despite generally weak prevailing deep layer mean flow/shear. ..Kerr.. 06/22/2017Read more
from SPC Forecast Products http://ift.tt/ws9HZn
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