SPC May 18, 2017 1730 UTC Day 2 Convective Outlook

By Newsroom America Feeds at 18 May 2017

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1222 PM CDT Thu May 18 2017 Valid 191200Z - 201200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FRIDAY INTO FRIDAY NIGHT ACROSS MUCH OF OKLAHOMA...NORTHWEST AND NORTH CENTRAL TEXAS...AND SOUTHERN KANSAS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SURROUNDING AREAS OF THE CENTRAL AND SOUTHERN PLAINS INTO THE MIDDLE MISSISSIPPI VALLEY... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS EASTWARD ACROSS THE LOWER OHIO VALLEY INTO THE MID ATLANTIC COAST REGION.... ...SUMMARY... Severe thunderstorms may impact a large portion of the southern and central Plains into the Middle Mississppi Valley Friday through Friday night, accompanied by the risk for large hail, potentially damaging wind gusts and a few tornadoes. Some risk for severe thunderstorm development also appears to exist across parts of the lower Ohio Valley into the Mid Atlantic Coast region. ...Synopsis... Large-scale troughing within a southern branch of split westerlies emanating from the mid-latitude Pacific appears likely to gradually shift east of the Rockies into the Plains during this period. This is expected to occur as a series of smaller-scale perturbations continue pivoting around the southern through eastern periphery of an embedded closed low centered near the Colorado Rockies by 12Z Friday. The mid-level low is forecast to redevelop northeastward through the central high Plains Friday through Friday night, but the manner and speed with which this occurs is a point of variability among the models and their respective ensemble output. However, guidance remains generally suggestive that cyclogenesis along a quasi-stationary frontal zone across the central Plains will remain rather modest through at least this period. Still, as a belt of 50-60+ kt cyclonic 500 mb flow overspreads the south central Plains warm sector, southerly 850 mb flow is forecast to strengthen to 30-40 kt, contributing to sufficient shear for organized severe storm development. Moderate to large boundary layer CAPE appears likely to develop by peak heating Friday across a broad area, southeast of the front/dryline across the Plains, east northeastward ahead of the front, through the Ohio Valley and Mid Atlantic Coast region into parts of the Northeast. This is expected to occur as low-level moisture return continues around the western periphery of low-level ridging centered off the south Atlantic coast. While the front, associated with a vigorous northern branch trough advancing across the Canadian Maritimes and New England, may advance south of New England and the northern Mid Atlantic Coast states by Friday night, it should stall or perhaps shift northward across the Ohio Valley, beneath building upper ridging downstream of the Plains trough. ...Central/southern Plains into middle Mississippi Valley... Uncertainties concerning the timing of larger-scale troughing and embedded small-scale perturbations emerging from the Intermountain West/Rockies are compounded by the potential for at least a couple of areas of ongoing thunderstorm activity within the warm sector at 12Z Friday. There remains a signal within the model output that considerable thunderstorm activity may be ongoing or rapidly develop across parts of northwest Texas through Oklahoma Friday morning into afternoon, in response to an area of enhanced lower/mid tropospheric warm advection associated with one short wave impulse progressing northeast of the southern Rockies. A severe hail/wind threat may not be out of the question with this activity, but it is also possible that this could have some impact on subsequent storm development across a sizable portion of the warm sector, from parts of northern Texas into Kansas. Depending on early period storm development, the dryline from parts of south central Kansas through western Oklahoma and northwest Texas may become the main focus for strong severe storm development late Friday afternoon. It still appears probable that the environment will be conducive to discrete supercell development, at least initially. And this threat may become maximized near the intersection of outflow, associated with prior storm development, and the dryline. At the present time it seems that this may be near the Red River area of southwestern Oklahoma, but uncertainty remains considerable. Into Friday evening and the overnight hours, models indicate the potential for one or two upscale growing thunderstorm clusters which may be accompanied by a severe wind/hail threat. This may occur southeastward ahead of the cold front/dryline through Oklahoma and parts of northern/central Texas, and along the warm front (ahead of the developing surface frontal low), across parts of the lower central Plains into lower Missouri/mid Mississippi Valleys. ...Ohio Valley into Mid Atlantic... The environment probably will become at least conditionally supportive of thunderstorms with at least some severe wind/hail potential, but this seems likely to occur largely in the presence of rising mid-level heights beneath building upper ridging. Although a belt of modest westerly mid-level flow initially over the middle Mississippi into lower Ohio Valley early in the period seems likely to weaken, it might not be out of the question that related perturbations provide support for renewed thunderstorm development Friday afternoon and evening. ..Kerr.. 05/18/2017 Read more



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