Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Oct 19 2023 08:08:22 FOUS30 KWBC 190808 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 407 AM EDT Thu Oct 19 2023 Day 1 Valid 12Z Thu Oct 19 2023 - 12Z Fri Oct 20 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Kleebauer Day 2 Valid 12Z Fri Oct 20 2023 - 12Z Sat Oct 21 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Kleebauer Day 3 Valid 12Z Sat Oct 21 2023 - 12Z Sun Oct 22 2023 .....A MARGINAL RISK OF EXCESSIVE RAINFALL IS EXPECTED ACROSS PORTIONS OF NEW ENGLAND... A prominent upper trough located east of the Mississippi will dig and tilt neutral to negative across the northeastern U.S on Saturday, eventually closing off across southern New England the latter half of the forecast period. Surface cyclogenesis along the eastern seaboard will move steadily to the north before being captured by the 5H trough leading to the surface reflection maturing and being tugged back to the northwest once around the latitude of Long Island. Moisture advection regime will reach peak by Saturday afternoon and evening as the surface low begins its occlusion phase. PWATs between 1-1.5 deviations above normal will be positioned over central and northern New England within the axis of deformation leading to enhanced rainfall across a zone extending from North Country in NY state, through VT/NH into western ME. Avg precip totals mark 1-2" across the aforementioned zones with local maximum up to 2.5" possible considering the dynamical component of the precip field within an upslope regime across the higher terrain. Deterministic QPF fields are consistent with totals around 2" within the heaviest rainfall during the period, a lot coming within the 6-12 hr window when the axis of deformation is at its peak. With the surface low occluding and drifting to the north, rainfall footprint will be well-defined and meander before finally ending after the current forecast cycle. In the probabilistic realm, NBM 75th and 90th percentiles would approach the forecast 3 and 6 hr FFGs within the terrain focused zone, which is the main area of concern. NASA SPoRT soil moisture is sitting around the 50-55th percentile with local areas up closer to 60-70th percentile along the NY/VT border, so the setup isn't a slam dunk by any means, but the dynamic nature of the system coupled with terrain issues and longevity could lead to isolated flash flooding concerns within the lower threshold of the forecast risk area. A Marginal Risk was maintained from the D4 outlook to keep continuity, but did trim some of the previous forecast back as guidance begins to lock in on the potential within central and northern New England. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-1t-uMvINo9DPkrPWmRFcPzFIPOXfMWgaM4OBuJlGHW1= IWMzv3fLpGydS8rS2DTmkO-jzx9RrcgS8Gi29M2nwAe44Io$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-1t-uMvINo9DPkrPWmRFcPzFIPOXfMWgaM4OBuJlGHW1= IWMzv3fLpGydS8rS2DTmkO-jzx9RrcgS8Gi29M2nY1o-M3s$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-1t-uMvINo9DPkrPWmRFcPzFIPOXfMWgaM4OBuJlGHW1= IWMzv3fLpGydS8rS2DTmkO-jzx9RrcgS8Gi29M2nqLTkhTs$=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) .