Subj : MESO: Mesoscale Discussion 2120 To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Sep 09 2023 18:09:25 ACUS11 KWNS 091809 SWOMCD SPC MCD 091808=20 NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-DCZ000-VAZ000-WVZ000-092045- Mesoscale Discussion 2120 NWS Storm Prediction Center Norman OK 0108 PM CDT Sat Sep 09 2023 Areas affected...Portions of the Mid-Atlantic Concerning...Severe potential...Watch possible=20 Valid 091808Z - 092045Z Probability of Watch Issuance...60 percent SUMMARY...A gradual increase in the threat for scattered wind damage may prompt Severe Thunderstorm Watch issuance at some point this afternoon. DISCUSSION...Recent visible satellite and radar imagery show a well defined MCV present over northwestern PA and far southwestern NY, moving slowly northeastward. A diffuse surface boundary is present to the east of the MCV across parts of southern NY into central PA and MD. Persistent cloud cover along/north of this boundary has hampered daytime heating to some extent, and a zone of differential heating exists from roughly the higher terrain of the Appalachians in central PA into far southern NY. Aided by modest ascent attendant to the MCV, thunderstorms have already developed across parts of central PA. Separate areas of convection are also ongoing across parts of northern VA/southern MD, and over eastern NJ in association with a sea breeze. The 12Z IAD observed sounding showed generally modest lapse rates aloft, but latest surface observations indicate that a fairly moist low-level airmass exists across much of the Mid-Atlantic along/east of the weak surface boundary. Where area of clearing have occurred, MLCAPE has already increased to around 1500-2500 J/kg. Additional heating through the rest of the afternoon may support modest additional increases in boundary-layer instability. Away from the mid-level MCV circulation, flow remains modest through much of the troposphere. Closer to the circulation, namely central PA into south-central NY, around 30-35 kt of southwesterly mid-level flow is fostering similar values of deep-layer shear. A mix of multicells and occasional supercells may develop and spread northeastward across these areas through the afternoon/evening. Scattered damaging winds should be the main threat, especially where low-level lapse rates have been steepened by greater diurnal heating. But, isolated large hail may also occur with the more cellular convection. Thunderstorms across VA/MD/DE/NJ will probably tend to be less organized given weaker deep-layer shear, but isolated damaging winds still appear possible with downbursts given a favorable thermodynamic environment with ample DCAPE (900-1000 J/kg or greater). At some point this afternoon, a Severe Thunderstorm Watch may be needed for parts of the Mid-Atlantic, especially if convection near the MCV begins to show signs of clustering or supercellular characteristics. ...Gleason/Guyer.. 09/09/2023 ....Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!6tkBb9nZEUhcnxGpLE_Ms8goj9zCF6trikQpE07MWlde9Q48ql1qHrtdPgNxBxuKY-KQyR187= YDhS9un7gGJsVQJvjc$ for graphic product... ATTN...WFO...OKX...ALY...PHI...BGM...CTP...LWX... LAT...LON 40097897 41107834 41677785 42157684 42417546 42187445 41867403 41277396 39977421 39467457 38567662 38607712 39257909 40097897=20 =3D =3D =3D 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) .