Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0158 PM CST Sun Dec 25 2016 Valid 252000Z - 261200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF SOUTHEAST NEBRASKA AND NORTHEAST KANSAS THROUGH LATE THIS AFTERNOON... ...SUMMARY... Strong to isolated severe wind gusts remain possible through this afternoon across mainly a portion of southeast Nebraska and northeast Kansas. ...NE/KS/OK... Strongest forcing for ascent and sufficient destabilization has continued to trend to the northern extent (closer to the track of the potent shortwave trough) of the east-northeastward advancing narrow convective line/cold front. As this shortwave trough deepens, tracking northeast from the central High Plains into the Upper Midwest tonight, midlevel winds across Kansas to Missouri will continue to become southwesterly. This will result in warming 700-500 mb temperatures, and a further reduction in thunderstorm potential with southward extent this afternoon. This has been illustrated in the convective outlook with the removal of general thunderstorm and/or severe weather probabilities from parts of KS to northwest TX. Mosaic radar showed a 5-10 mile wide arcing band of convection (with lightning along its northern extent) extending from central SD through central NE, and into central KS to central OK. The recent southern extent of lightning data resides north of the warm sector now located across southeast NE and northeast KS (surface dew points in the upper 50s and temperatures around 60 F). This suggests the primary convective regime is further outpacing the east/northeastward spread of higher theta-e and surface-based inflow parcels. These trends suggest a Slight risk is no longer warranted as thunderstorms continue to become elevated, moving away from the available warm sector. However, this outlook will maintain a smaller marginal risk area for locally strong wind gusts, possibly becoming severe, across northeast KS and southeast NE, given the presence of very strong winds located just off the surface per wind profile at WSR-88D TWX. ...Northeast CO to western SD... This outlook has expanded the general thunderstorm area to include this region as thunderstorms will continue to develop within a regime of strong upward vertical motion and steep midlevel lapse rates for elevated destabilization. ..Peters.. 12/25/2016 .PREV DISCUSSION... /ISSUED 1024 AM CST Sun Dec 25 2016/ ...NE/KS/OK... Around a 10-mile wide arcing band of thunderstorms is ongoing across western KS to the western OK/TX Panhandle border. This narrow convective swath is coincident with the passing of an occluding Pacific cold front that will continue to sweep eastward, likely reaching the Lower Missouri Valley to Ozark Plateau region this evening. Strong surface wind gusts have been common with passage of this band across southwest KS into the OK/TX Panhandles, with a recent severe wind gust measured at Dodge City. Minor intensification of this band remains possible into early afternoon, mainly centered on central KS where the strongest forcing for ascent impinges on the northern portion of the modifying warm sector. While deep-layer shear is quite strong owing to an intense mid-level jet (100-120 kt at 500 mb and 65-75 kt at 700 mb) ejecting ahead of the vigorous shortwave trough over CO, the nearly meridional deep-layer flow regime should continue to foster convection generally paralleling the front. From mid/late afternoon onward, the northeastward translation of the primary convective regime will outpace the eastward spread of sufficiently high-theta-e and surface-based inflow parcels, effectively pinching off the warm sector from north to south. While a marginal/conditional severe threat may persist as far east as the Lower Missouri Valley, a gradual decrease in overall wind potential is expected, given the progressively more elevated nature of the convection with time. Farther south across southeast Kansas and northern Oklahoma, the strongest large-scale ascent and winds aloft, as well as surface isallobaric forcing, will be ejecting away from the region. This, in turn, will lead to weakening trends in deep shear, convergence, and mid-level lapse rates, serving to marginalize the overall threat.Read more
from SPC Forecast Products http://ift.tt/u32qoI
No comments:
Post a Comment