Subj : MESO: Heavy rain - floodi To : All From : Mike Powell Date : Sun Jul 16 2023 09:25:00 AWUS01 KWNH 161344 FFGMPD MEZ000-MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-161943- Mesoscale Precipitation Discussion 0745 NWS Weather Prediction Center College Park MD 944 AM EDT Sun Jul 16 2023 Areas affected...New England Concerning...Heavy rainfall...Flash flooding likely Valid 161343Z - 161943Z SUMMARY...Areas of significant and locally life-threatening flash flooding are expected going through the early to mid-afternoon hours from extremely heavy showers and thunderstorms. DISCUSSION...The latest GOES-16 IR satellite imagery in conjunction with dual-pol radar shows an expansive area of extremely heavy shower and thunderstorm activity lifting north up across central and southern New England as shortwave energy pivots across the region ahead of a stronger upper trough gradually dropping southeast into the Great Lakes region. This energy is interacting with a plume of deep tropical moisture and instability surging up along the East Coast and inland across the Northeast. In fact, the latest 12Z RAOB data and VWP data shows the nose of confluent 40+ kt low-level jet nosing in off the western Atlantic Ocean and up across Long Island and much of the interior of New England which is helping to drive a 2.25+ inch PW axis up across CT/MA and nosing into southern NH and southwest ME. These PWs are near or at record levels relative to climatology for this time of the year. Coinciding this corridor of strong moisture transport is an axis of moderately unstable air with MLCAPE values of as much as 1000 to 1500 J/kg. Vertical shear parameters are relatively steep as well with as much as 30 to 40 kts of effective bulk shear in place which is facilitating some notably strong and linear bands of convection with some transient supercell type structures. Going through midday and the early to mid-afternoon time frame, the heaviest rainfall focus is expected to be over CT/MA and a large portion of NH and southwest ME where the stronger convective cells will be capable of producing rainfall rates of 2 to 4 inches/hour, with additional rainfall totals of as much as 5 to 7 inches possible given notable concerns for cell-training. The stronger orographic ascent/upslope flow into higher terrain of the Worcester Hills of central MA and up into the White Mountains of NH will be areas most likely to see the heaviest totals. Given the combination of extreme rainfall rates, cell-training, locally wet antecedent conditions and areas of rugged terrain, there is an elevated threat of significant and life-threatening flash flooding over the next several hours. Orrison ATTN...WFO...ALY...BOX...BTV...CAR...GYX...OKX... ATTN...RFC...NERFC...NWC... LAT...LON 45687070 45636982 45166939 44256964 43387020 42177090 40847223 40497303 40727382 41567368 42527302 44147211 45177139 = = = --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .