Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1241 AM CDT Sun Apr 30 2017 Valid 301200Z - 011200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TODAY AND TONIGHT NEAR/EAST OF THE MISSISSIPPI VALLEY THROUGH PORTIONS OF THE SOUTHERN GREAT LAKES...LOWER OHIO VALLEY AND CENTRAL GULF STATES... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS AREAS SURROUNDING THE SLIGHT RISK... ...SUMMARY... Severe thunderstorms are possible today into tonight, from the vicinity of the Mississippi River eastward through portions of the the southern Great Lakes region, lower Ohio Valley and central Gulf states. This includes a risk for storms capable of producing tornadoes, a couple of which could be strong. ...Synopsis... Models indicate that a belt of westerlies emanating from the mid-latitude Pacific will remain amplified through this forecast period, with large-scale ridging across the eastern Pacific into the Pacific coast, and across the Atlantic Seaboard into the western Atlantic, and large-scale troughing over much of the interior United States. The large-scale troughing appears likely to take on an increasing negative tilt orientation, as a significant embedded short wave perturbation pivots northeast out of the central and southern Plains through the Mississippi Valley by late tonight. Substantive further deepening of a lower/mid tropospheric cyclone is forecast as it tracks northeast of the southern Plains. At the surface, the low may occlude early in the period across and northeast of the lower Missouri Valley, with secondary low development likely migrating across northeastern Missouri through northern Illinois this afternoon and evening. Within the potentially broad warm sector of the cyclone, models indicate 50-70 kt southerly 850 mb will develop near/east of the Mississippi Valley today. The core of a 100+ kt south/southwesterly 500 mb jet may lag to the west of the warm sector, but mid/upper flow fields above the warm sector should still be more than sufficient to support potential for organized severe storm development, including supercells. Uncertainties abound concerning the extent to which thermodynamic profiles within the warm sector will become conducive to severe weather potential. It appears that the northeastward advection of elevated mixed layer air will become disrupted or cut-off from much of the warm sector, and with the mid-level cold core lagging to the west of the surface cold front, mid-level lapse rates are not expected to become particularly steep. Furthermore, considerable remnant pre-frontal convective development/cloud cover may be present early in the period, and drying associated with ridging centered off the Atlantic coast appears likely to slow boundary layer moistening across much of the Southeast into portions of the Ohio and Tennessee Valleys. ...Mississippi Valley to western slopes of the Appalachians... Taking into account the preceding discussion, uncertainties seem too large to allow for more than an outlook of a categorical slight risk at the present time. But given the strength of the synoptic system and associated wind fields, and at least a corridor of pre-frontal boundary layer moisture characterized by surface dew points in the mid 60s to near 70F, it may not be out of the question that a window of opportunity for considerable severe weather potential could develop this afternoon and evening. This seems mostly likely to be focused near or just east of the Mississippi Valley, and mostly in the wake of an initial north/south oriented band or two of thunderstorms spreading east of the Mississippi Valley, where guidance appears suggestive that breaks in the overcast could allow insolation to contribute to at least pockets of mixed layer CAPE on the order of 1000-2000 J/kg. Of particular concern is that the environment could become conducive to at least isolated to widely scattered long lived discrete supercell development, initially anywhere from portions of eastern Missouri into Illinois, southward through portions of western Kentucky and Tennessee into northern Mississippi. In the presence of clockwise curved low-level hodographs characterized by strong to extreme shear, some of these could become capable of producing strong tornadoes. It is possible thunderstorm activity could eventually consolidate into one or two organized eastward advancing lines, into portions of the southern Great Lakes region, and across the central Gulf states by late this evening. ..Kerr/Gleason.. 04/30/2017Read more
from SPC Forecast Products http://ift.tt/s7Jkvo
No comments:
Post a Comment