SPC Oct 13, 2017 0600 UTC Day 1 Convective Outlook

By Newsroom America Feeds at 13 Oct 2017

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1245 AM CDT Fri Oct 13 2017 Valid 131200Z - 141200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS BY EARLY THIS EVENING...CONTINUING INTO THE OVERNIGHT HOURS ACROSS PARTS OF THE MIDDLE MISSISSIPPI VALLEY INTO THE CENTRAL PLAINS... ...SUMMARY... Widely scattered strong thunderstorms may impact portions of the middle Mississippi Valley into the central Plains, mainly tonight, accompanied by some risk for severe weather. ...Synopsis... Models suggest that subtropical ridging will remain prominent across much of the southeastern U.S. through this period, extending along an axis from the lower Rio Grande Valley into the southern Mid Atlantic Coast region. However, the westerlies may begin to trend more zonal. One initial short wave impulse, emerging from current larger-scale western Canadian/northwestern U.S. troughing, is forecast to continue accelerating east of the central Canadian provinces today through tonight. This appears likely to be accompanied by further deepening and occluding of a significant surface cyclone across the Hudson/James Bay region. A trailing cold front is expected to advance into the Great Lakes region/upper Mississippi Valley and central U.S. Plains, before stalling, in advance of another significant short wave trough forecast to dig through the northern Great Basin by late tonight. Moisture return is already underway on southerly low-level flow across the southern Plains, and this is expected to continue to advect north/northeastward into the frontal zone across the central Plains toward the Upper Midwest/Great Lakes region by tonight. Models suggest that, with colder air aloft lagging to the north/west of the front, mid-level lapse rates may not be particularly steep along the frontal zone. However, destabilization associated with the moistening is expected to be sufficient to support increasing thunderstorm activity. Additional widely scattered thunderstorm development is possible late this afternoon into this evening within a pre-frontal corridor of seasonably strong heating from the higher terrain of southeastern New Mexico northeastward into the Texas/Oklahoma Panhandle region, and perhaps again within lingering moist easterly low-level flow across the Florida Peninsula. Some risk for lightning may also accompany scattered diurnal convection beneath the mid-level cold pool associated with the digging impulse across the northern Intermountain West. ...Middle Mississippi Valley into the central Plains... Weak to moderate boundary layer destabilization appears possible near/northeast of an initial weak frontal wave expected to migrate across and northeast of the Kansas City, MO area by early this evening. Although mid/upper support for convective development remains unclear, models suggest that this may be accompanied by at least isolated thunderstorm development, in the presence of favorable vertical shear for supercells. A window of opportunity appears to exist for convection capable of producing severe hail and perhaps locally strong wind gusts as it initially tracks near/along the surface front, before tending to develop north/northeast of the front by late evening. Thereafter, warm advection, moistening and destabilization associated with a strengthening southwesterly 850 mb jet (30-40+ kt), above/to cool side of the surface front, is expected to contribute to increasing thunderstorm development overnight, from portions of the central Plains into upper portions of the middle Mississippi Valley. Within this regime, the environment may become conducive to widely scattered stronger storms accompanied by some risk for marginally severe hail. ..Kerr/Mosier.. 10/13/2017 Read more



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