SPC Mar 4, 2018 0600 UTC Day 1 Convective Outlook

By Newsroom America Feeds at 4 Mar 2018

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1148 PM CST Sat Mar 03 2018 Valid 041200Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS A PORTION OF NORTHEAST TX...EASTERN OK...WESTERN AR...AND NORTHWEST LA... ...SUMMARY... Isolated to widely scattered storms may impact a portion of the central and southern Plains today into this evening. A few storms could produce marginally severe hail across eastern Oklahoma into the Ark-La-Tex region. More numerous storms are probable tonight over the lower Missouri and middle Mississippi Valleys, but other than small hail, no severe weather is expected with this activity. ...Synopsis... Basal portion of western states mid-upper level trough and accompanying 90+ kt 500-mb jet will progress east this forecast period, reaching the Four Corners region and central Rockies this afternoon and then into the central Plains tonight to early Monday, as it becomes negatively tilted. Strong height falls spreading across the central High Plains will support a deepening area of lower pressure across western KS/southwest NE region through the afternoon, with this low tracking toward eastern NE/southeast SD tonight. A trailing cold front will advance east/southeast through the central and southern Plains where it will intercept a dryline this evening through tonight. A warm front will advance north through the lower and middle MS Valleys. Easterly trajectories will persist into this afternoon across much of the Gulf of Mexico, emanating from a large area of continental-polar high pressure in the eastern states. This will limit greater moisture return and subsequent boundary-layer modification poleward through the southern and central Plains ahead of the progressive mid-upper level trough. Widespread stratus beneath the eastward expansion of an elevated mixed-layer plume should contribute to substantial surface-based convective inhibition in most of the warm sector. ...Eastern OK into the Ark-La-Tex region... A couple of transient low-amplitude southern-stream impulses are expected to track across north TX to the lower Mississippi Valley this forecast period. Forcing for ascent with one of these impulses this morning and a second this afternoon to early evening could aid in thunderstorm development. This upward vertical motion will be further enhanced by low-level warm air advection with storms being elevated. Midlevel lapse rates and CAPE could support small to marginally severe hail with some of this activity. ...Dry line in the southern Plains... In addition to the lack of better quality in moisture return and the presence of a stable boundary layer beneath a cap east of the dry line, the lack of a deeper dry line circulation suggests the potential for storm initiation should remain quite low. This is further confirmed with the lack of any of the hi-res cams showing convective initiation along the dry line this afternoon. Although strong effective bulk shear is forecast along the dry line with the potential for a very narrow corridor of marginal instability from northwest TX into far western OK, the aforementioned negative factors for sustained updrafts precludes the reintroduction of a marginal severe risk area. ...Lower Missouri and Middle Mississippi Valleys... Widespread showers and thunderstorms are expected to develop in this region overnight with isentropic ascent and modest destabilization along low-level jet and north of warm front. However, the thermodynamic environment appears too marginal to support more than possibly some small hail. ..Peters/Elliott.. 03/04/2018 Read more



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