Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Wed May 10 2017 Valid 102000Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF SOUTHWEST OKLAHOMA AND NORTHWEST TEXAS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS EXTENDING FROM PARTS OF INDIANA/ILLINOIS WEST-SOUTHWEST TO SOUTHEAST COLORADO...AND SOUTHWARD INTO TEXAS... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT RISK AREA... ...SUMMARY... Scattered severe thunderstorms are expected along a corridor from the southern Plains to the middle Mississippi Valley. The strongest activity should focus across parts of northwest Texas into southwest Oklahoma where very large hail and a few tornadoes are possible. ...Discussion... Forecast reasoning from prior outlooks remains on track, with current convective evolution generally in line with expectations. As such, changes with respect to the current outlook are limited to line tweaks -- particularly with the ENH risk area which is being shifted slightly southward. With convective outflow currently aligned from roughly El Reno, OK southwest through Childress, TX to a dryline/outflow intersection point in Motley County TX, the centroid of greatest severe risk appears to be focused a tad farther south. Along with risk for large hail -- including with a developing storm near the dryline/outflow intersection, greatest tornado risk appears likely within this southwest-to-northeast corridor in the vicinity of the outflow. Otherwise, no major changes to the outlook appear necessary at this time. ..Goss.. 05/10/2017 .PREV DISCUSSION... /ISSUED 1135 AM CDT Wed May 10 2017/ ...Northwest TX/western OK... A persistent MCS continues to generally weaken as it spreads northeastward across south-central/southeast KS at late morning. A trailing outflow boundary extends southwestward and continues to exhibit some southward movement across west-central/southwest OK into parts of the northwest TX low rolling Plains and Caprock vicinity. A closed mid/upper trough over eastern AZ/western NM this morning will gradually accelerate east-northeastward, reaching the south-central High Plains late tonight. 12Z upper-air analysis featured a belt of a strong southwesterly winds (50+ kt at 500mb and 100 kt 250mb) over northern Mexico into the southern High Plains. The strong mid/high-level winds will continue to spread east-northeastward through afternoon and evening atop an eastward-mixing dryline across much of west/northwest TX. An northeast-advecting elevated mixed layer atop middle 60s F surface dewpoints will contribute to 2000-2750 J/kg MLCAPE in west TX and western OK areas to the east of the dryline and south of the remnant outflow boundary. Severe thunderstorm development is most likely by mid/late afternoon near the dryline and modifying outflow-related triple point across the southern TX Panhandle/TX low rolling Plains and western parts of north TX into southwest OK. Effective shear in excess of 50 kt will support supercells capable of very large hail. While low-level shear will initially be weak, the influence of the outflow boundary and an evening-time increase in a southerly low-level jet will support the potential for tornadoes. ...IA/MO/IL/IN... A warm front will continue to slowly spread northward across southeast IA and north-central portions of IL/IN and southern OH, while a weak surface wave develops east-southeastward across the region through tonight. Surface dewpoints in the low/middle 60s F near and south of the front will contribute to MLCAPE values of 1000-2000 J/kg with weak inhibition by mid-afternoon. Aided by an MCV/weak mid-level disturbance, initial strong to severe thunderstorm development should occur this afternoon across southern IA and northern MO into IL. Deep-layer shear will be favorable for initial supercells, while low-level shear will be adequate for some tornado risk, particularly just east of the surface wave. Storms are likely to cluster over time and move east-southeastward into IL/IN from late afternoon into evening, potentially with an increased risk for damaging winds. ...TX Edwards Plateau/Big Country late tonight... The dryline will likely stall this afternoon and then retreat some to the west late this evening. Thunderstorm development will be possible along this boundary overnight, when lingering moderate-strong buoyancy and substantial deep-layer shear will support a risk of storm clusters capable of producing large hail and damaging winds.Read more
from SPC Forecast Products http://ift.tt/u32qoI
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