Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jan 13 2024 00:22:11 FOUS30 KWBC 130022 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 721 PM EST Fri Jan 12 2024 Day 1 Valid 01Z Sat Jan 13 2024 - 12Z Sat Jan 13 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID-ATLANTIC AND NORTHEAST... 0100 UTC Update -- Just minor modifications made to the previous Day 1 ERO, most notably based on the current observational trends (now post-frontal) to remove the Marginal Risk area that was across portions of the Mid Mississippi Valley and western Ohio Valley. Hurley Previous discussion below.. ....Mid-Atlantic and Northeast U.S.... Surface low pressure is expected to form over the Mid-Atlantic region later today along a boundary associated with deepening low pressure over portions of the Ohio Valley. The resulting inflow of low level moisture is maximized at about the same time that upper level divergence increases through a deep layer due to the approach of an upper level jet especially during the afternoon/evening over the Mid-Atlantic region and moreso into parts of the Northeast U.S. from this evening into the overnight hours. QPF amounts are not blockbuster values...due to the relatively short window of opportunity given the progressive nature of the system. However...models are beginning to pick up on a period of elevated convection and associated increase in rainfall rates which may prove to be problematic in areas still draining off water from the heavy rainfall earlier in the week.=20 Amounts alone are such that a Slight Risk area in parts of the Mid-Atlantic would probably not have been entertained had it not come on the heels of the heavy rainfall earlier in the week across an area that has been wet for at least 4 weeks. Confidence is higher for impacts farther north into parts of the Northeast U.S. where higher amounts from this event will overlap areas soaked a few days ago...in part given the higher magnitude afforded by strengthening low level flow and increasingly deep moisture.=20 ....Pacific Northwest... The Marginal remains largely the same, but in following with the latest guidance shifting a bit southward in response to the latest guidance. Locally enhanced rainfall rates are expected from later today into early Saturday morning with several bouts of heavy rainfall within the coastal plain extending from northwest CA up through central OR given steepening low- and mid-level lapse rates. There could be some localized flooding with the urbanized corridors along the coast, but nothing too extraordinary in the grand scheme. Bann Day 2 Valid 12Z Sat Jan 13 2024 - 12Z Sun Jan 14 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR COASTAL NORTHWEST CALIFORNIA AND A VERY SMALL PORTION OF SOUTHWEST OREGON... ....2030Z Update... No changes were made to the inherited ERO risk areas, both those in Maine and CA/OR look on track as far as placement goes. In CA/OR amounts have come up a bit (about 1/4 to 1/2 inch) from inherited, though the area along the coastal ranges are very capable of handling even the 3-5 inches forecast, so while the Slight is low-confidence since amounts have come up have opted to keep the Slight unchanged with this update. Wegman ....Previous Discussion... ....Northwest Corner of California and Southwest Oregon... On-shore flow of deep moisture is expected to continue from the Day 1 period into the weekend with an additional 2-4" of rainfall...and isolated maximum amounts around 5 inches in the higher terrain along the coast of coastal northwest California and clipping the extreme southwest corner of Oregon. Latest guidance shows enough elevated instability where the combined effects of the moisture plume interacting with the terrain could result in isolated amounts approaching 5 inches. NBM probabilities for at least 3" are remained in the 50-60% range within the King Range for the Day 2 time frame with 2" having a large 50+% area encompassing northwest CA. As a result...an upgrade to a Slight Risk was introduced given the compounding effect of multiple days worth of rainfall. The Marginal Risk surrounding the Slight Risk areas was mostly maintained elsewhere with few changes needed from yesterday's Day 3 ERO. ....New England... Remnant moisture on the eastern flank of the broad cyclonic circulation over the Great Lakes will continue through coastal New England before exiting into Canada the latter half of Saturday. Consistent timing in the models of the area of low pressure resulted in similar QPF amounts over New England compared with previous forecast cycles...resulting in little need for more than a few cosmetic changes to the outlook. All the rainfall and snowmelt within the past series of events will culminate in some localized flood potential. Bann Day 3 Valid 12Z Sun Jan 14 2024 - 12Z Mon Jan 15 2024 ....2030Z Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman/Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7dArjlP3gUY31CHEmOhyuH7EGjgv-RDo0oCgzmh8Jdqm= hlnHYpGPwhI1JXI2uz5qe1MxLaXL0UQOp4rRt8WAiBwqo-k$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7dArjlP3gUY31CHEmOhyuH7EGjgv-RDo0oCgzmh8Jdqm= hlnHYpGPwhI1JXI2uz5qe1MxLaXL0UQOp4rRt8WAUZROcoU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7dArjlP3gUY31CHEmOhyuH7EGjgv-RDo0oCgzmh8Jdqm= hlnHYpGPwhI1JXI2uz5qe1MxLaXL0UQOp4rRt8WAEXtTpkw$=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) .