Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Apr 30 2023 22:43:48 AWUS01 KWNH 302243 FFGMPD MEZ000-MAZ000-NHZ000-VTZ000-010442- Mesoscale Precipitation Discussion 0220 NWS Weather Prediction Center College Park MD 642 PM EDT Sun Apr 30 2023 Areas affected...portions of Central New England Concerning...Heavy rainfall...Flash flooding possible Valid 302242Z - 010442Z Summary...Instability appears to be increasing near and offshore southern New England as an atmospheric river takes aim at the region. Hourly rain totals to 1.5" and local amounts to 3" are expected, which could lead to both short and long duration flood concerns. Discussion...SPC mesoanalyses show increasing instability not far offshore the coast of southern New England, with a bubble of 500+ J/kg MU CAPE presented. Radar returns have shown increasingly showery and less stratiform rainfall, with some hints at warm topped convection on recent imagery. Precipitable water values are 1-1.3" per recent GPS data, which given 1000-500 hPa thickness values of 5520-5550 meters implies a saturated atmosphere. Inflow at 850 hPa is south-southeast at 45 kts per VAD wind profiles. A coastal front has been evident near the ME coast stretching across southern New England, which is likely aiding shower development to some degree. Divergence aloft is increasing to the east of an upper low near Lake Michigan and ahead of a negatively tilted upper trough approaching from the southwest/the Mid-Atlantic States. With time, as a complex low pressure system near the southern and central Mid-Atlantic states deepens and moves up the Delaware into Hudson River Valleys, inflow off the Atlantic/an atmospheric river aimed at the region should strengthen further, with 850 hPa winds increasing to roughly 70 kts, dragging the coastal front inland.=20 It should also lure precipitable water values up near 1.5", which is quite anomalous for this time of year. Even without any instability, this would yield hourly rain totals above 0.5". The available instability should allow hourly totals to reach 1.5" at times, which if they persist for an hour or two would broach the 3 hour flash flood guidance and potentially lead to flash flooding rather than longer duration flooding. Flash flood guidance is rather low as rainfall across southernmost ME and much of New Hampshire has been above to well above average this past week -- soils are partially saturated. Occurrences of rapid onset flooding are expected to be isolated to widely scattered. Roth ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5boRdNl6LrfE7r_DKXBO6ZWlwTg9KOB5Fr1lOZiDlZky558Z3-DIsHfsrKWZrVd58rAX= 46BaArdZWPjHGmXoFxj5Tes$ for graphic product... ATTN...WFO...BOX...BTV...CAR...GYX... ATTN...RFC...NERFC...NWC... LAT...LON 45406961 44786852 44156828 44016865 43786952=20 43407024 42977070 42767128 42807193 43787215=20 44827132=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) .