Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jun 29 2023 17:54:50 AWUS01 KWNH 291754 FFGMPD MEZ000-NHZ000-300000- Mesoscale Precipitation Discussion 0603 NWS Weather Prediction Center College Park MD 153 PM EDT Thu Jun 29 2023 Areas affected...Northern and Western Maine Concerning...Heavy rainfall...Flash flooding possible Valid 291800Z - 300000Z Summary...Showers and thunderstorms will expand in coverage and intensify through the afternoon. Rainfall rates at times may exceed 2"/hr, which through training could produce 2-3" of rain. Isolated flash flooding is possible. Discussion...The GOES-E visible satellite imagery this aftn depicts rapid Cu growth within clearing in the vicinity of a cold front. Beneath the deeper Cu, showers have rapidly developed across parts of northern and western ME during the past 1-2 hours. Forcing for ascent is being provided by modest height falls downstream of a mid-level trough axis and accompanying weak PVA as a subtle shortwave rounds its base. 850mb flow from the S/SW at 20 kts is impinging into a convergent axis to drive additional ascent, while also transporting robust thermodynamics characterized by PWs around 1.5 inches and SBCAPE of 1000-2000 J/kg. 850mb dewpoints across Maine are +10C, above the 90th percentile for the date, with the 12Z U/A sounding at CAR showing deep saturation and freezing levels above 11 kft indicating efficient rain processes will dominate today. During the next few hours, the high-res guidance is in good agreement that convection will expand and intensify along this convergent axis noted by elevated 6-hr HREF EAS probabilities. Rainfall rates may eclipse 2"/hr according to HREF neighborhood probabilities, with 15-min rainfall possibly reaching 1" in some areas as progged by the HRRR sub-hourly fields. Mean 0-6km winds are likely to remain progressive through the aftn at around 20 kts, but nearly unidirectional flow and aligned Corfidi vectors falling to 10 kts indicates an increased risk for training, as re-development occurs south into the higher instability and tracks north along the only slowly translating convergent axis. While most of the convection should generally be of the pulse variety, some organization is possible as 0-6km bulk shear climbs to 20-25 kts. This could result in some multi-cell development stretching into linear segments along any weak convergent boundaries within the otherwise unidirectional flow. This could briefly enhance intensity and duration of rainfall, and some areas could accumulate 2-3 inches of rain through this evening. Northern New England has generally seen 150-300% of normal rainfall during the past 14-days, with a relative maxima noted in AHPS across western ME. This is resulting in widespread streamflow anomalies above the 90th percentile, and 3-hr FFG of 1-1.5 inches for which the HREF indicates has a 30-50% chance of being exceeded. While overall coverage of convection may be somewhat modest, any of this heavy rain falling atop these sensitive soils could result in instances of flash flooding today. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8UulClGGaaDK6lnqYd_CQpA6geQSpgpt86bDF1t22C9cm_rJqfvDm3IGY9bwb0Jd0uPr= 4nxe47eWT4vSVnoFIAj_1j4$ for graphic product... ATTN...WFO...CAR...GYX... ATTN...RFC...NERFC...NWC... LAT...LON 47516926 47516850 47446811 47216783 47156782=20 46736777 46246808 45606857 44976924 44327015=20 44137067 44297111 44547119 45007102 45597067=20 46137033 46147032 46656995=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) .