Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat May 20 2023 22:54:13 AWUS01 KWNH 202254 FFGMPD MEZ000-MAZ000-NHZ000-RIZ000-CTZ000-NYZ000-210450- Mesoscale Precipitation Discussion 0319 NWS Weather Prediction Center College Park MD 653 PM EDT Sat May 20 2023 Areas affected...central/eastern Long Island into southern/eastern New England Concerning...Heavy rainfall...Flash flooding possible Valid 202251Z - 210450Z Summary...Localized low-end flash flooding will be possible across central/eastern Long Island into southern/eastern New England through 05Z. Rainfall rates of 0.5 to 1.0 in/hr (locally higher) and peak 6-hr totals of 2-3 inches can be expected. Discussion...GOES East water vapor imagery at 22Z showed an elongated shear axis extending southward from Long Island to just east of the Outer Banks. Deep-layered south to southwesterly flow was in place along the shear axis and ahead of a closed low crossing southern Ontario, supporting anomalous moisture transport into the Northeast. A combination of blended TPW imagery and GPS sensors indicated precipitable water values of 1.6 to near 2 inches from southern New England to just off of the northern Mid-Atlantic coast at 19Z. Roughly 1-2 inches of rain has been reported from southern CT into central/west-central Long Island through 22Z along with rainfall rates of 0.5 to 0.75 in/hr in Nassau County (Long Island) and southwestern/south-central CT. As the closed low over southern Canada tracks eastward into western NY early tonight, a 90 to 100+ jet streak at 250 mb ahead of the low will act to increase divergence aloft over the Northeast, while also aiding to increase 850 mb flow to 50+ kt by 03Z from near Providence, RI to southern ME. The strengthening low level flow is expected to increase precipitable water values into the 1.8 to 1.9 inch range for eastern Long Island into southeastern New England along with supporting weak MUCAPE up to ~750 J/kg. Low level convergence along the northern/western edge of the low level plume of moisture transport will align with mean steering flow, supporting repeating and training of heavy rain at times from central/eastern Long Island into southern/eastern New England. Rainfall rates are expected to peak in the 0.5 to 1 in/hr range, but the increase in instability and upper support could possibly support rates in excess of 1 in/hr at times. An additional 2-3 inches of rain is expected on a localized basis over the region through 05Z with the axis of heaviest rain shifting gradually from west to east with time. Rapid rises in water across urban locations and those prone to flooding will be at most risk from the expected rainfall, as well as possible overlap with the 1 to 2 inches of rain that has already fallen across portions of the region. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_IwvFKwuZKQT0Hr69ho2K__kk_uCrfmRlbCXWLUmxZi1wJs0CBduuhCym-ETfsWivInf= tDZzm0DKOEw6AvJuykp1INQ$ for graphic product... ATTN...WFO...BOX...GYX...OKX... ATTN...RFC...NERFC...NWC... LAT...LON 43367079 43287039 42677042 41587090 41007114=20 40767191 40527347 41527300 42657204=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) .