Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Nov 27 2022 12:46:55 ACUS01 KWNS 271246 SWODY1 SPC AC 271245 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0645 AM CST Sun Nov 27 2022 Valid 271300Z - 281200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE MID-ATLANTIC REGION... ....SUMMARY... Isolated severe thunderstorms are possible over parts of the Mid-Atlantic region this afternoon. ....Synopsis... The mid/upper-tropospheric pattern is characterized by broadly cyclonic, somewhat split flow over the central/western CONUS. A leading trough/cyclone -- with circulation center apparent in moisture-channel imagery over southeastern MO -- will eject east-northeastward today and devolve into an open shortwave trough. By 00Z, the trough should be located over the Lower Great Lakes, PA, and northern MD. The still-weakening trough will move rapidly offshore from the New England Coast by 09Z. That will occur as an upstream shortwave trough -- now located over portions of CO/NM -- pivots across the southern Plains, to the lower Mississippi Valley through 12Z tomorrow. An upstream cyclone -- now over much of central/northern BC/AB -- will expand and shift southeastward to southern SK by the end of the period, with an intense speed max digging southeastward over the northeastern Pacific toward the Pacific Northwest. This process will lead to supportive troughing over the central CONUS for severe potential discussed in the day-3 outlook. The 11Z surface analysis showed a low over south-central IL, with occluded front arching southeastward over southwestern IN, central KY, to near CHA. The triple point was drawn near CSG, with cold front southward over the west-central FL Panhandle, then southwestward over the central/southwestern Gulf. The warm front was drawn over southern GA, then along coastal SC to near CHS, bending eastward across the Atlantic. By 00Z, the low should be near the southern shore of Lake Ontario in NY, with occluded front across eastern PA to eastern MD, cold front from there over eastern NC and northern FL, and warm front extending eastward offshore from the Delmarva Peninsula. By 12Z, the low should be east of ME under the mid/upper trough, with cold front offshore all the Atlantic Coast except central FL. ....Eastern NC to lower Chesapeake Bay region... Scattered to numerous showers, and isolated to scattered thunderstorms, are expected to move quickly northeastward across the region through afternoon. The deepest, longest-lived cells may pose a damaging wind and/or tornado threat, but each hazard remains too uncertain to upgrade the unconditional outlook level at this time. Time series of forecast soundings show very large low-level hodographs across the outlook area through midday and perhaps into early afternoon. This is related to relatively backed near-surface winds beneath an intense (60-70-kt) LLJ, but with surface trajectories emanating from relatively stable theta-e profiles that keep effective-inflow parcels rooted predominantly in an elevated inflow layer. Veering of flow to a major southerly component will lead to substantial hour-by-hour decrease of hodograph size/ curvature at any given locale this afternoon, through they still will remain long and supercell-favorable overall during the prefrontal interval. The decreasing hodographs will coincide with strengthening boundary-layer theta-e -- related mainly to warm and moist advection from Gulf Stream trajectories, since cloud cover and precip will limit diabatic heating from insolation. Modified RAOBs and forecast soundings suggest that surface dewpoints around 67-68 deg F and higher should correspond to unambiguously surface-based inflow. A brief time window -- shifting northeastward across the outlook area through afternoon -- may exist when shrinking, but still supercell-supporting hodographs overlap with at least marginally favorable surface-based buoyancy. If a thunderstorm can get rooted in this narrow, northeast-translating corridor and stay in it, conditional tornado potential exists. However, the greatest buoyancy (peak MLCAPE in the 500-1000 J/kg range) still is expected to lag the most-favorable low-level shear, before frontal passage unfavorably reduces both. ....Central Appalachians/Allegheny Plateau... A brief window may develop for strong gusts with a narrow, frontal band of thunderstorms, for a couple hours during early/mid afternoon. The most probable area for this conditional potential appears to be from northern WV across western PA, before convection outruns any already meager surface-based instability it encounters. The regime will be characterized by increasing large-scale ascent through midday into early afternoon, as the mid/upper trough approaches, as well as frontal lift. Deep shear will be favorable, with effective-shear magnitudes reaching 50-60 kt in a nearly unidirectional wind profile. Some progs (that extend a relative midlevel dry slot far enough north into the prefrontal sector) indicate around 200-600 J/kg MLCAPE developing, from a combination of theta-e advection and weak diabatic heating. At this time, the potential for severe gusts appears too isolated and uncertain for an outlook area, but may need one in a future update, should parameters become just slightly more unconditionally favorable. ...Edwards/Mosier.. 11/27/2022 $$ = = = 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) .