Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Aug 09 2024 20:59:35 AWUS01 KWNH 092059 FFGMPD MEZ000-MAZ000-NHZ000-VTZ000-CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-10030= 0- Mesoscale Precipitation Discussion 0851 NWS Weather Prediction Center College Park MD 458 PM EDT Fri Aug 09 2024 Areas affected...Eastern New England...Northern & Eastern NY Incl. NYC...Eastern PA...NJ... Concerning...Heavy rainfall...Flash flooding likely Valid 092100Z - 100300Z SUMMARY...Post-Tropical Cyclone Debby lifting out of the Northeast with north-south line of broken thunderstorms capable of quick 1-3" and localized flash flooding risk. DISCUSSION...GOES-E WV suite shows a more classic extra-tropical cyclone signature with a well shaped comma-head and excellent anti-cyclonically curved outflow into the baroclinic shield across southeast Canada into the 110kt right entrance of the jet. A traditional north-south convergence axis exists across E NY into the Delaware Valley with a few newer convective cells as far south as N Delaware, this aligns more with the deep layer warm conveyor belt and highly anomalous moisture feed with 2-2.25" total PWats generally parallel to the 50-60kt 850mb LLJ. The cold front is well defined across central NY into central PA and W MD, but minus a bit of remaining boundary layer moisture and some solar insolation, activity is likely to be widely scattered, and fast moving to be much more than a nucense to ongoing flooding conditions in that area.=20 Strong moisture flux convergence/isentropical ascent into the deformation zone/comma head remains across a risk for training of 1.75-2.25"/hr rates across far northern NY for about an additional hour or two, the quick 2-4" total by 00z will likely induce flash flooding across St. Lawrance and Franklin, and perhaps clip northern Clinton county.=20 Along the warm conveyor belt, the pre-frontal convergence zone/trof intersects the LLJ obliquely, to result in a fractured line of thunderstorms across the Hudson Valley; but this broad southerly flow will be intersecting the mid to upper-slopes of the Greens, Whites and eventually Blue Ranges of the northern Appalachians providing moisture convergence for precursory ..25-.5"/hr rates. However, the deeper thunderstorms will support sub-hourly rates of 1.5" with spots of 2"/hr totals as they quickly progress east, with cells to the north moving faster but intersecting with those slopes that have be pre-soaked providing opportunity for rapid rises within sloped terrain likely leading to flash flooding though likely to be shorter in overall duration resulting in broken WSW to ENE streaks of 1-3". Further south the line into the Delaware River Valley, NJ and perhaps northern Delaware, mid-level steering flow will be weaker than further north at 20-30kts with a bit more southwest to northeast orientation as the next polar jet streak over the Great Lakes approaches the area and curves cyclonically through the lower Great Lakes. Slightly higher moisture will maintain similar strong moisture flux convergence in the low levels to support similar 2"/hr rates, but with slower forward progress and some potential for training, the further south cells have greater potential for higher rainfall totals in the 2-4" range particularly into southern NJ. Higher infiltration in sandier soils may limit some flash flooding potential but there remain some portions of the I-95 corridor from Wilmington, Philly to Trenton in proximity for urban flooding, though that should be in the nearer term before cells press into the Pine Barrens. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4TUmOWGikTBElFo0gjLtPV1LU_9hOdlA1vImcPF2Pg1-KlKdHgVfD6dgp7TPmPtk7_3F= drHkG3R8E_wiUe67P5QP_DU$ for graphic product... ATTN...WFO...ALY...BGM...BOX...BTV...BUF...GYX...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 45747050 45176993 44507006 43827081 42527175=20 41237272 40417355 39357445 38787528 39097594=20 39957562 41327489 42637428 43417411 43687462=20 43657532 44247587 44877543 45187391 45447142=20 =20=20=20=20=20=20=20=20=20=20=20=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .