Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Sep 18 2023 18:00:36 AWUS01 KWNH 181800 FFGMPD MEZ000-MAZ000-NHZ000-RIZ000-CTZ000-NYZ000-182355- Mesoscale Precipitation Discussion 1082 NWS Weather Prediction Center College Park MD 159 PM EDT Mon Sep 18 2023 Areas affected...southeastern New England Concerning...Heavy rainfall...Flash flooding likely Valid 181756Z - 182355Z SUMMARY...Heavy rainfall with rainfall rates locally over 1 in/hr can be expected for southeastern New England through the remainder of the afternoon into early evening. Localized flash flooding will be likely along with expected 3-hr totals of 2-3 inches. DISCUSSION...Regional radar imagery across the Northeast at 1745Z showed a broad shield of moderate to locally heavy rain, located ahead of a large mid/upper level trough over the eastern U.S. with multiple embedded shortwaves contained within. One such shortwave was located over the northern Mid-Atlantic region, translating northeastward while acquiring a slightly negative tilt. In the lower levels, a mesoscale low was identified with local radar imagery, located ~40 miles SSW of Westhampton, NY with a motion toward the NNE near 25 kt over the past 3 hours. GPS data showed precipitable water values ranging between 1.3 (southern ME) and 1.7 inches (southern CT) with 20-30 kt of southerly 850 mb winds place. Winds below 850 mb were backed toward the southeast while deeper-layer mean winds were from the SSW at 30-40 kt. Extrapolation and short term forecasts from the RAP suggest that the mesolow will continue toward the NNE into eastern MA by 22/23Z. At the same time, the RAP is forecasting the development of a 130 kt upper level jet streak over southern to central New England, placing southeastern New England within the favorable right entrance region. Low level upslope flow is also expected to contribute to locally high rainfall rates. While poor 700-500 mb lapse rates of only 5-6 C/km and extensive cloud cover should cap instability below 500 J/kg for much of the day, limiting rainfall rates, strong dynamics should act to compensate. Areas of heavy rain, training from south to north, are expected at times, especially for southeastern New England along and east of the mesolow track. Pockets of rainfall in the 4-8 inch range have fallen over portions of southern to central New England over the past week, increasing susceptibility to runoff. While perhaps not widespread, localized areas of flash flooding are considered likely through 00Z, especially given overlap with recent heavy rainfall and urban locations with poor drainage. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9DEqTDcu83wNNyEGICjjAxHpM_qLJNpLUv14hl_Y4XL7k8OCiq3duiquEIN533M7eMD6= Ihcl7xB40VbhlzjWSf7rflk$ for graphic product... ATTN...WFO...ALY...BOX...GYX...OKX... ATTN...RFC...NERFC...NWC... LAT...LON 43977077 43827027 43107021 42537038 42137053=20 41547079 41287117 41257204 41307300 41547333=20 41977315 42827216 43677124=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) .