MD 0519 CONCERNING SEVERE POTENTIAL…WATCH LIKELY FOR PARTS OF SERN NE…SWRN IA…NWRN MO…N CNTRL/NERN KS
Mesoscale Discussion 0519 NWS Storm Prediction Center Norman OK 0229 PM CDT Wed Apr 19 2017 Areas affected...Parts of sern NE...swrn IA...nwrn MO...n cntrl/nern KS Concerning...Severe potential...Watch likely Valid 191929Z - 192200Z Probability of Watch Issuance...95 percent SUMMARY...Thunderstorm development with increasing severe weather potential is expected by late afternoon. At least a couple of severe weather watches are likely to be issued across the region by 21Z. DISCUSSION...A cyclonic mid/upper jet streak (including 50+ kt at 500 mb) is in the process of nosing through the central Plains and mid Missouri Valley region. Strongest forcing for ascent in the exit region of this feature likely will remain focused well to the cool side of a fairly sharp surface frontal zone, along which a modest surface cyclone is now beginning to migrate east northeast of the central Nebraska/Kansas border area. At the same time, the nose of a plume of warm and capping elevated mixed layer air is wrapping into the mid Missouri Valley region, across much of the warm/moist sector of the surface low, and northward to the cool side of the front ahead of the low. However, latest model output, including the Rapid Refresh, suggests that the leading edge of lower/mid tropospheric cooling is now roughly near/east of the Grand Island NE through Russell KS. As this continues to spread east northeastward this afternoon, guidance indicates that it may provide the focus for increasing thunderstorm development by 21-23Z, from near the surface low southward along the dryline (as it is overtaken by the southward advancing cold front) into parts of central Kansas. In the presence of thermodynamic profiles characterized by very steep mid-level lapse rates and mixed layer CAPE on the order of 1500-2000 J/kg, deep layer shear appears more than sufficient for supercells. Near a 40 kt southerly 850 mb jet, sizable clockwise curved low-level hodographs will contribute to a risk for tornadoes. The extent of the tornado threat remains a bit uncertain due to an expected tendency for fairly deep boundary layer mixing and some drying within the warm sector, and rather cool/stable air to the north of the front. Any tornadic potential may tend to be maximized within a rather narrow corridor along and to the north of the warm front, just ahead of the surface low, across parts of southeastern Nebraska into southwestern Iowa. ..Kerr/Thompson.. 04/19/2017 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...DMX...EAX...FSD...OAX...TOP...ICT...GID... LAT...LON 40649785 41199747 41869727 42439643 42439552 42159522 40939509 39139671 38679899 39309897 39779839 40649785
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