Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1229 PM CDT Thu Apr 27 2017 Valid 281200Z - 291200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM OKLAHOMA INTO THE OZARK PLATEAU AND LOWER OHIO VALLEY... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM A PORTION OF THE SOUTHERN PLAINS INTO THE OHIO VALLEY... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT RISK... ...SUMMARY... Numerous severe storms remain possible on Friday from a portion of the southern Plains into the lower to middle Mississippi, Ohio and Tennessee Valleys. ...Southern Plains through lower Mississippi and Ohio Valleys... Not much change from earlier thinking regarding the synoptic features for this outlook with some details concerning some threats still nebulous at this time. Embedded within a broad synoptic trough, a lead shortwave trough initially over the central Plains will deamplify and weaken as it moves into the Great Lakes area. Farther upstream an upper trough will amplify near the Four Corners region. At the surface a warm front will develop northward through north TX and OK eastward into the OH Valley, while a cold front advances south through the central Plains. A dryline will evolve across west-central into northwest TX or southwest OK during the afternoon where it will intersect the warm/quasi-stationary front. Height rises will occur from the southern Plains to the TN Valley in wake of the lead shortwave trough that will move toward the Great Lakes. Limited synoptic forcing for ascent and convective inhibition resulting from eastward expansion of the EML should limit thunderstorm initiation during the day over most of the warm sector. A convective signal is apparent in the last 4 runs of the ECMWF and more recently in the GFS for isolated to widely scattered thunderstorms during the late afternoon/evening near the OH-MS river confluence and lower OH Valley. Forecast soundings show a conditional environment very favorable for severe thunderstorms within the envelope of considerable 500-mb height rises. There is large uncertainty whether storms will develop, but if storms become sustained, a significant risk for hail/tornadoes may accompany the cellular activity. Farther west in the southern Plains, some chance for isolated thunderstorm initiation will exist at the intersection of dryline and front over northwest TX into southwest OK by late afternoon. Large CAPE and strong vertical shear will favor a conditional risk for supercells with very large hail and a few tornadoes should such initiation occur. Rich low-level moisture with large CAPE but strong convective inhibition will reside south of the warm/quasistationary front. The best chance for widespread thunderstorm initiation will occur during the evening and overnight from OK into northern AR, MO and into the TN and OH valleys as a strong, broad low-level jet enhances convergence and isentropic ascent within the strengthening baroclinic zone. Strong vertical shear profiles and instability will support organized storms including supercells with large to very large hail and damaging wind the main threats, though a few tornadoes may also occur with any surface-based storms developing closer to the warm front. ..Smith.. 04/27/2017Read more
from SPC Forecast Products http://ift.tt/ws9HZn
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