Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 04 2023 09:49:58 AWUS01 KWNH 040949 FFGMPD MEZ000-MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-NJZ000-PAZ000-041545- Mesoscale Precipitation Discussion 0634 NWS Weather Prediction Center College Park MD 549 AM EDT Tue Jul 04 2023 Areas affected...southern NY/Long Island into central/southern New England Concerning...Heavy rainfall...Flash flooding likely Valid 040946Z - 041545Z SUMMARY...A very isolated flash flood threat across southern NY into New England is expected to increase in probability and coverage after 12Z. Slow moving cells will be capable of producing rainfall rates of 1-3 in/hr. While the coverage of these higher rates may be somewhat limited, recent heavy rainfall across New England makes the probability of at least localized flash flooding likely through 16Z. DISCUSSION...Regional radar imagery at 09Z showed a small area of thunderstorms just north of I-84 along the PA/NY border. A second area of showers, with recent weakening, was noted along the southern NH/ME border. Both areas have had observed rainfall rates of ~0.5-1.0 inches in 15 minutes, a testament to the efficiency of rainfall generation within the environment. According to the 09Z SPC mesoanalysis, precipitable water values ranged from 1.7 to 2.0 inches from the northern Mid-Atlantic region into central New England, along with weak MLCAPE of ~500-1000 J/kg. However, high surface dewpoints in the upper 60s to lower 70s has supported limited to negligible low level convective inhibition across most locations across the region. A shear axis extending from central New England into east-central PA with Weak mid-level vorticity maxima along and ahead of the shear axis was observed on 6.9 micron water vapor imagery, with forecast movement toward the east over the next 6 hours. Forcing ahead of this mid-level feature along with daytime heating (despite cloud cover) should be enough to generate an increasing coverage of thunderstorms after 12Z, and especially by 15Z, over southern New England. Weak steering flow from the Lower Hudson Valley into southern VT/NH/ME will support slow moving cells with high rainfall rates. Farther south, while deeper-layer mean winds are a bit stronger at 10-15 kt, 850 mb winds increase with southward extent...increasing the potential for training of cells. Rainfall of 0.5 to 1.0 inches in 15 minutes and peak hourly rainfall of 2-3 inches will be possible, some of which could fall on top of saturated soils from recent heavy rain over the past few days. At least localized areas of flash flooding are considered likely. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_F6eIY-Ssyj68JqN_FONOkrqoH0EcnRlk3E-m_bKyr8Fd9OyT_hcANE226jG7_ZfcZ9r= 4N3xHQpHwj86nn1xtAEwMKg$ for graphic product... ATTN...WFO...ALY...BGM...BOX...BTV...GYX...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 44006973 43536951 42857013 41677057 40797223=20 40517356 40717447 41357508 42227464 43117294=20 43937126=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) .