Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Oct 20 2023 08:28:09 FOUS30 KWBC 200828 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 427 AM EDT Fri Oct 20 2023 Day 1 Valid 12Z Fri Oct 20 2023 - 12Z Sat Oct 21 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 2 Valid 12Z Sat Oct 21 2023 - 12Z Sun Oct 22 2023 .....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHEASTERN NEW YORK INTO NEW ENGLAND... Areas of moderate to heavy rain should be ongoing across the Northeast Saturday morning as mid-level shortwave energy moving through the middle of a longwave trough over the eastern U.S. and becomes negatively tilted by Saturday morning, with the axis extending from western New York to off of the northern Mid-Atlantic coast. While the main plume of moisture (2+ inch PWATs) will be well offshore ahead of the primary cold front associated with the primary area of low pressure, anomalous moisture (+1 to +2 standardized anomalies) with 1.0 to 1.3 inch PWATs should wrap back to the west into New England. The details of the evolution remain a bit unclear, but consolidation into a single surface low is expected to occur toward the Gulf of Maine with an inverted surface trough extending northwestward/westward into New England by early Saturday evening.=20 Limited instability should favor rainfall intensities that are below flash flood guidance in the area...although 24 hours may be in the 1 to 2.5 inch range given a prolonged duration of rainfall (especially over southern New England from 12-00Z where some slow movement of heavy rain will be possible near the surface low/inverted trough...just ahead of the negatively tilted upper trough axis swinging across the region). For the remainder of New England, 10 to 20 kt (locally higher) 850 mb winds from the southeast will focus into New England ahead of the developing surface low with some upslope component helping to enhance rainfall intensity. As the consolidated surface-850 mb low moves away from the region into the Canadian Maritimes through Saturday night into early Sunday morning, convergence along an attached low level inverted trough axis pivoting across portions of New England is expected to support slow moving areas of heavy rain. While a lack of instability should keep 1 hour rainfall rates within this regime low (no more than 0.5 in/hr is expected), the accumulation of rainfall over the 24 hour period could amount to localized 2 to 4 inch totals across northeastern New York into Vermont, New Hampshire, Maine and perhaps Massachusetts. The Marginal Risk area from continuity appears to be in good shape and remains the same for this update, especially given some of the lingering uncertainty in forecast details. Bann Day 3 Valid 12Z Sun Oct 22 2023 - 12Z Mon Oct 23 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5VnzS68AQrZTb7Z6LtaPwXNM7H1KPbL4pae41IHGVzGS= KeWmUoOHZ7OpWksFbxV9F8c64elGD8wNmOa1SESxHdxp8Js$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5VnzS68AQrZTb7Z6LtaPwXNM7H1KPbL4pae41IHGVzGS= KeWmUoOHZ7OpWksFbxV9F8c64elGD8wNmOa1SESxovOPP8A$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5VnzS68AQrZTb7Z6LtaPwXNM7H1KPbL4pae41IHGVzGS= KeWmUoOHZ7OpWksFbxV9F8c64elGD8wNmOa1SESxPUffUlc$=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) .