Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jun 17 2023 15:37:35 AWUS01 KWNH 171537 FFGMPD MEZ000-MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-172135- Mesoscale Precipitation Discussion 0510 NWS Weather Prediction Center College Park MD 1136 AM EDT Sat Jun 17 2023 Areas affected...portions of New England Concerning...Heavy rainfall...Flash flooding possible Valid 171535Z - 172135Z SUMMARY...Slow moving and training of showers/thunderstorms across New England will pose a localized flash flood threat into the afternoon. Hourly totals of 1-2 inches and localized storm totals of 2-3 inches are expected. DISCUSSION...15Z water vapor imagery showed a closed mid to upper level low centered over Upstate New York with multiple vorticity maxima rotating nearby, around the low's center. Precipitable water values were near to slightly above average for mid-June with 1.1 to 1.3 inches in place from Long Island to Caribou, ME with saturated profiles as seen on GYX and CAR 12Z soundings. However, mid-level lapse rates were poor which should limit instability potential given the modest low level moisture. Fairly extensive cloud cover was noted on area visible satellite imagery, limiting MLCAPE so far to less than 500 J/kg (SPC mesoanalysis data) but some breaks in cloud cover were noted over northeastern VT and portions of southern New England. Continued breaks in cloud over and further heating into the afternoon are expected to yield pockets of 500+ J/kg MLCAPE over central/eastern MA/CT into RI. Despite the modest moisture/instability, cell motions are likely to be slow for a couple of reasons. First, 0-6 km mean layer winds are less than 5 kt from VT into southern NH and southeastern MA with forecasts for slower mean wind speeds to spread into southern ME later this afternoon. Second, given the weak mean-layer flow, 850 mb winds meeting or exceeding the mean layer flow will support the potential for slow movement and training cores of heavy rain. A relative max in 850 mb winds (20-30 kt) is likely to focus north of an offshore coastal low into central/southern ME into northern NH/VT, generating an upslope component to the winds along southeasterly and easterly facing terrain. The MPD threat area covers both threats of heavy rain, highlighting the greatest potential for slow moving cells from slow movement to training. While most of New England has been drier than average over the past couple of weeks, rainfall anomalies of 150+ percent of normal over the past week were noted for portions of western ME into NH and VT. Rainfall rates of 0.5 inches in 15 minutes and 1 to 2 inches in an hour (perhaps locally higher) are expected in a few areas over the next 3-6 hours. Localized to scattered areas of flash flooding will be possible through 21Z from central/southern ME into much of central/southern New England. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7yGEISwhfbQAPQFeEWPis_ddMOdztM0HX4Dz_oQGHI5Fd8EjqU7ENuSmp22iUDK_WoXb= z_Hvpp7gbsIiEmHdOO6Dzi4$ for graphic product... ATTN...WFO...ALY...BOX...BTV...CAR...GYX...OKX... ATTN...RFC...NERFC...NWC... LAT...LON 45397117 45347045 45026963 44826924 44406882=20 43956875 43176989 42527017 41777051 41417102=20 41267183 41547240 42177288 43167305 44577300=20 45027234=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) .