Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Sep 07 2023 20:00:12 ACUS01 KWNS 072000 SWODY1 SPC AC 071958 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Thu Sep 07 2023 Valid 072000Z - 081200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE NORTHEAST... ....SUMMARY... Thunderstorms -- some capable of producing locally damaging wind gusts and marginally severe hail -- will continue across portions of the Mid-Atlantic region and into New England into this evening. ....Discussion... Current expectations with regard to the convective scenario through tomorrow morning remain in line with prior reasoning. As such, aside from minor line adjustments, the overall forecast will remain unchanged with this outlook update. ...Goss.. 09/07/2023 ..PREV DISCUSSION... /ISSUED 1110 AM CDT Thu Sep 07 2023/ ....Synopsis... A mid-level high, centered over the southeastern New Mexico vicinity, appears likely to remain prominent through this period, with large-scale ridging building to its north, through much of the Rockies and adjacent Great Plains today through tonight. Downstream, several perturbations, comprising weak but amplifying larger-scale mid-level troughing east of the Mississippi Valley, are forecast to remain generally progressive, though mid-level ridging may continue to build near/east of the middle and northern Atlantic Seaboard, in the wake of a modest cyclone migrating eastward across portions of the Canadian Maritimes. The two more significant perturbations include a remnant mid-level trough forecast to slowly accelerate northeast of the lower Great Lakes region through southern Ontario and Quebec, and a weak developing mid-level low forecast to dig south-southeast of the lower Ohio Valley through Alabama/Georgia by 12Z Friday. East of these features, and ahead of a cold front which has already advanced into the Appalachians vicinity (while stalling across parts of the lower Mississippi Valley into southern Great Plains), deep-layer southerly mean flow and shear will likely remain mostly rather modest to weak (less than 20 kt). However, models do suggest that a more subtle perturbation migrating north-northeast of the Blue Ridge might contribute to a belt of modest south-southwesterly mid-level flow along the western periphery of the building ridge, with at least some signal that this could also become convectively augmented by tonight. ....Atlantic Seaboard... Seasonably moist air, beneath relatively steep lower/mid-tropospheric lapse rates, likely will contribute to sizable mixed-layer CAPE to the east of developing surface troughing to the lee of the Appalachians. This could become supportive of developing clusters of storms with potential to produce strong wind gusts, as convection initiates and slowly propagates off the higher terrain this afternoon. The most prominent and concentrated area of thunderstorm development still appears likely to be focused with the increasingly sheared short wave impulse and modestly strengthening southerly mid-level flow (30+ kt in the 700-500 mb layer) across eastern Pennsylvania and New York, and adjacent portions of the Mid Atlantic and New England, through early evening. This may include an upscale growing, and gradually organizing, thunderstorm cluster or two which may eventually pose a risk of producing a swath of strong to severe surface gusts. ....Lower Mississippi Valley/Gulf Coast vicinity... Destabilization associated with a corridor of strong pre-frontal daytime heating may become sufficient for thunderstorms capable of producing damaging wind gusts, perhaps aided by modest deep-layer shear near the leading edge of strengthening north-northwesterly mid/upper flow. ....Southern Great Plains... Potential for sustained convective development within a very warm and deeply mixed boundary across the Texas Panhandle into western Oklahoma late this afternoon remains uncertain. However, to the east of the lee surface trough, warm advection and lift associated with a nocturnal strengthening south-southwesterly low-level jet will pose better potential for thunderstorm development across northern/eastern Oklahoma tonight. It is possible that elevated instability and unsaturated sub-cloud air may be sufficient to contribute to potential for hail and gusty surface winds with some of this activity. ....Northern Great Plains... Models suggest that daytime heating may contribute to a deep mixed boundary layer with modest CAPE, along and south of a developing zone of stronger differential surface heating, southeast of the Black Hills into central Nebraska. Aided by forcing for ascent associated with a short wave digging around the northeastern periphery of the building larger-scale ridging, isolated strong thunderstorm development posing a risk for producing strong surface gusts is possible for a period late this afternoon and evening. $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .