Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Nov 03 2025 01:04:09 FOUS30 KWBC 030104 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 804 PM EST Sun Nov 2 2025 Day 1 Valid 01Z Mon Nov 03 2025 - 12Z Mon Nov 03 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE NORTH CAROLINA OUTER BANKS... Opted to introduce a Marginal risk for portions of the NC Outer Banks for the overnight period. A developing low pressure may bring periods of heavier convection into these coastal areas resulting in=20 a localized flash flood risk. The last several HRRR runs have all=20 indicated localized rainfall amounts over 5", with some runs=20 depicting isolated max rainfall in excess of 7". The big question=20 will be whether these higher totals remain offshore, or are able to get into the Outer Banks. Recent obs show easterly winds at=20 Hatteras, NC and northerly flow just west of Pamlico=20 Sound...suggesting an axis of convergence and possibly allowing for an advection of instability into the Outer Banks from the=20 Atlantic. Thus the HRRR depiction of heavier convection getting=20 onshore seems plausible, and while the magnitudes may not be as=20 extreme...the pattern would favor slow moving convection and there=20 is a reasonable threat of rainfall exceeding 5". So while confidence in the heavier convection getting onshore is only=20 average...we think there is enough of a conditional threat to=20 justify introducing a Marginal risk with localized flash flooding a possibility. Chenard=20 Day 2 Valid 12Z Mon Nov 03 2025 - 12Z Tue Nov 04 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Orrison Day 3 Valid 12Z Tue Nov 04 2025 - 12Z Wed Nov 05 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF NORTHWESTERN CALIFORNIA AND FAR SOUTHWESTERN OREGON... 2030Z Update... The latest multi-model consensus continues to advertise arrival of strong atmospheric river activity late Tuesday and into early Wednesday morning across portions of especially southwest OR and northwest CA. This will be driving by strong jet energy rounding the base of a deep layer trough amplifying offshore of the West Coast. Enhanced deep layer Pacific moisture transport and orographic ascent along the coastal ranges will yield heavy rainfall. Generally 2 to 4 inch rainfall totals are still anticipated by early Wednesday morning across the southwest-facing slopes of far southwest OR and northwest CA, but some spotty 5+ inch totals will be possible given the level of elevated IVT magnitudes which may peak Tuesday night around 1000 kg/ms. Given the consistent meteorological setup compared to continuity, only very minor tweaks were made to the Marginal Risk for excessive rainfall for this update. Orrison Previous discussion... The next strong landfalling atmospheric river (IVT > 750 kg/ms) looks to impact coastal portions of northern CA/far southwestern OR come Tuesday afternoon, likely peaking in strength in the evening to overnight period. Initial low-level flow earlier in the day looks more ideally directed perpendicular to the coast/mountains, but by the time higher IVT sets in veering to the SW-SSW may mitigate the effectiveness of the topographic lift (with otherwise limited instability as MUCAPE of less than 250 J/kg is forecast). Even still, this is a relatively warm system (with the cold core staying offshore until beyond Day 3) and PWATs of 1.2-1.4" are in the vicinity of the 90th percentile climatologically. Rainfall totals of 2-4" are generally expected (and may locally exceed 4"), and much of that could occur in a 6-12 hour period. The inherited Marginal Risk is sufficient (in-line with the latest GEFS-driven machine learning first guess field) and has been maintained (with only minor adjustments based on the latest models QPF footprint). Any flash flood impacts are most likely where relatively high rainfall rates (0.25"+/hr) coincide with sensitive burn scars. Churchill Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!63kJliZHfLBHXu_HmYM8QwSxCJ2ZlQd1ki92EgWjN-D9= i-DcTbeb-arSAn3b2rOZmsCN0qC3kaDuORsWbfFSir2dmEg$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!63kJliZHfLBHXu_HmYM8QwSxCJ2ZlQd1ki92EgWjN-D9= i-DcTbeb-arSAn3b2rOZmsCN0qC3kaDuORsWbfFSxDGRWBA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!63kJliZHfLBHXu_HmYM8QwSxCJ2ZlQd1ki92EgWjN-D9= i-DcTbeb-arSAn3b2rOZmsCN0qC3kaDuORsWbfFS7Mx5VSM$=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .