Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1255 AM CDT Tue May 02 2017 Valid 021200Z - 031200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS EVENING INTO THE OVERNIGHT HOURS ACROSS PARTS OF THE SOUTH CENTRAL PLAINS... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE TONIGHT ACROSS PARTS OF SOUTHEAST TEXAS... ...SUMMARY... Strong thunderstorms may impact portions of the south central Plains this evening into the overnight hours, and perhaps portions of southeast Texas late tonight, accompanied by some risk for severe weather. ...Synopsis... Models indicate that a weakening lower/mid-level cyclone and associated mid-level short wave trough will accelerate northeast of the Great Lakes, through Quebec and the Canadian Maritimes during this period. In its wake, mid-latitude westerlies will remain broadly cyclonic east of the Mississippi Valley through the western Atlantic, to the south of a broad vortex centered northeast of Hudson Bay. However, upstream, it appears that the westerlies will undergo considerable amplification across the mid-latitude Pacific into western North America, including large-scale ridging building across the Pacific Coast, Canadian Rockies and U.S. intermountain region. As at least a couple of strengthening short wave perturbations dig downstream of the ridging, larger-scale troughing is forecast to begin evolving by late tonight, from the lee of the U.S. Rockies into the central Plains. This latter development probably will remain out of phase with mid-level troughing in a weaker belt of subtropical westerlies, across the northern Mexican Plateau into Baja, but at least one perturbation emerging from this feature is forecast to accelerate across the Rio Grande Valley through the northwestern Gulf coast by 12Z Wednesday. In lower levels, a weakening, shallow surge of cooler air (associated with the eastern Canadian cyclone), may progress off the south Atlantic coast, and through portions of the Florida peninsula, but the leading edge of the deeper cool/cold surge may stall across portions of the Mid Atlantic coast into the south central high Plains. Strong heating within a developing lee surface trough across the southern high Plains may contribute to considerable strengthening of the frontal zone across the Texas/Oklahoma Panhandle region into western Oklahoma. However, a substantive return flow of moisture from the western Gulf of Mexico may not advance much north of the lower Rio Grande Valley and deep south Texas until after sunset this evening. ...Panhandle region through northern Oklahoma/southern Kansas... Evapotranspiration may contribute to boundary layer moistening within easterly upslope flow developing within the frontal zone across the south central Plains. The models may be too aggressive with the moistening, but in the presence of steepening lower/mid tropospheric lapse rates, weak to modest boundary layer destabilization still appears possible across western Oklahoma into the Panhandle region by late this afternoon. Aided by forcing for ascent and strengthening vertical shear associated with an initial digging short wave impulse, it appears that convection initially developing across parts of southeast Colorado and the Raton Mesa area could intensify while spreading southeastward through early evening. This may be accompanied by gusty winds and some hail, before primary convective development tends to become rooted in strengthening lower/mid tropospheric warm advection after dark. Models suggest that the elevated leading edge of the return flow from the Gulf of Mexico could contribute to the maintenance or intensification of storms later this evening into the overnight hours across parts of northern Oklahoma and adjacent southern Kansas, accompanied by at least some risk for severe hail. ...Southeast Texas/upper Texas Gulf coast area... Models continue to indicate a return of seasonably high boundary layer moisture content by late tonight, in the presence of lower/mid-level warm advection and sufficiently strong shear for supercells. However, it is still at least somewhat unclear whether inhibition associated with the warming aloft will suppress deep convective development, even with the approach of the mid/upper impulse. Given at least some continuing signal within the model output that convective development may occur prior to 12Z Wednesday, low severe weather probabilities will be maintained based on this possibility. ...South Florida... Models suggest that some cooling and weakening of inhibition will allow for scattered thunderstorm development across the interior southern peninsula and Atlantic coastal areas, in the presence of a moist, potentially unstable boundary layer. Lower/mid tropospheric wind fields are expected to remain weak, but some strengthening of high level (250 mb) flow to around 50 kt is forecast during the day. It may not be out of the question that this could enhance storm development, mainly near the Atlantic sea-breeze this afternoon. However, severe storm development still seems too conditional for even 5 percent severe probabilities at the present time. ..Kerr/Cohen.. 05/02/2017Read more
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