Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Nov 09 2022 20:21:45 FOUS30 KWBC 092021 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 320 PM EST Wed Nov 09 2022 Day 1 Valid 16Z Wed Nov 09 2022 - 12Z Thu Nov 10 2022 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS MUCH OF THE FLORIDA PENINSULA... 16Z Excessive Rainfall Outlook Discussion... Florida remains the prime focal point for excessive rainfall later today and through the overnight hours as Nicole approaches from the east. With WPC maintaining a 3 to 5 inch amounts...with isolated maximum of 8 inches...and a track from NHC that largely maintained continuity with the previous set of advisories...saw little reason to make changes. Maintained the Marginal in the Upper Midwest as models still advertise deep moisture working its way ahead of a dynamic northern stream system. Bann ....Florida Peninsula... Nicole, likely as a hurricane, will move into the Treasure Coast of the Florida Peninsula Wednesday night. Along and north of the track of the hurricane, deep tropical rains are expected over a large swatch of the Florida Peninsula. Unsurprisingly, Nicole brings PWATs well over 2 inches and over 3 standard deviations above normal to the state. The highest rainfall amounts will be in the area primarily between Cape Canaveral and Lake Okeechobee, which was an area pretty hard hit by Hurricane Ian. That said, what's reducing the flooding threat is the increasingly fast movement of Nicole, the track of which continues to shift north and west. While this will spread the heavier rain potential over a larger area (particularly on Thursday and Friday), it reduces the amounts any one area will see. Discussion was had with the impacted forecast offices overnight with upgrading to a Moderate risk over east central Florida, but for the reasons discussed above, it was decided the current Slight Risk remains the most appropriate flooding threat level. ....Upper Midwest... Very few changes made to the inherited Marginal Risk from northern MN over to the U.P. of Michigan. There continues to be a very slight northward shift in the model trends, but regardless, the dynamics remain unchanged. A stalled out front will draw anomalous moisture...up to 1.25" PWATs, which is as much as +4 standard deviations above normal for this time of year. CAPE values around 500 J/kg will support at least some convective elements which will all train northeastward along the front across the Marginal Risk area. Much of the area had been wet recently, especially along and just south of Lake Superior so soils are coming in with at least some antecedent moisture. Finally, convection ongoing at the time of this writing is continuing to saturate soils in that area.=20 Wegman Day 2 Valid 12Z Thu Nov 10 2022 - 12Z Fri Nov 11 2022 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST... ....Portions of the Southeast... Nicole will continue to be the focus for organized moderate to heavy rainfall as it moves from the central Florida peninsula towards the Big Bend region by Thursday evening and northward into portions of the Southeast U.S. by Friday morning. Some adjustments were made in response to QPF that varies from run-to-run and model-to-model and some consideration of dry advection on the west side of the system or due to shadowing by terrain. Overall, though, the changes tended to be pretty minor...with the northward shift in the track and some hints of dry air leading to an erosion of the QPF south of the track in the Florida peninsula. North of the track...QPF values of 3 to 5 inches with isolated maximum values of 8 inches are still forecast in Florida that tapers down to 2 to 4 inches farther north and west. Given dry antecedent conditions...several inches of rain will be more beneficial than destructive although flooding/flash flooding can not be entirely ruled out should the duration of heavy rainfall rates persist due to the storm making a pivot...or heavy rainfall occurs in an urban environment or region of poor drainage. Any rivers swollen by rainfall from Ian a few weeks ago may be more prone than surrounding areas as well.=20=20 ....Upper Midwest... No changes were needed to the inherited Marginal Risk area. Once again the strong low over the Plains and the stationary front over the Marginal Risk area will continue to wring out the 1.25" PWATs and highly anomalous moisture over the area. The Marginal Risk will primarily focus on the first half of the period, with much of the precipitation both over and changing over to snow by Thursday night. Bann Day 3 Valid 12Z Fri Nov 11 2022 - 12Z Sat Nov 12 2022 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR MUCH OF THE APPALACHIANS... ....20Z Update... Only minor edits were needed to the Marginal and Slight Risks from the overnight issuance. The 00Z/06Z and newer 12Z model cycles still indicated a westward trend in QPF compared to a day or two ago, given a slower upper trough movement and the timing of its interaction with Nicole and its moisture. This westward trend has slowed recently, allowing for continuity to look pretty good. The minor tweaks included shaving off the southeastern portion of the Marginal as rain may exit more quickly before the Day 3 period, a tiny expansion of the Slight west in Ohio accounting for the westward trend, and carving out portions of the Slight to account for terrain shadowing/downslope effects that seem to be coming more into focus. See the previous discussion below for additional meteorological information. Tate ....Previous Discussion... The forecast for Friday is the most changed with this forecast update compared with the inherited forecast. With Nicole/the remnants thereof continuing to track west in the guidance, the area subject to the interaction of the approaching upper level trough and Nicole also continues to shift west. Thus, the inherited Slight Risk has been shifted out of the I-95 corridor to favor much of the mountains from the southern Appalachians up to upstate New York. Much of this area has been very dry lately, which again cuts back the chances of flooding...however this is a very energetic system, with a very cold air mass driving southeastward supporting the right entrance region of a 110 kt jet. Then add the tropical moisture associated with Nicole and some heavy rainfall will likely overcome the antecedent dry conditions in the terrain of the Slight Risk area. Meanwhile because of the westward shift in the expected axis of heaviest rainfall, the entire I-95 corridor from VA north has been shifted out of the Slight Risk into a Marginal. The Marginal risk was also trimmed westward out of the eastern Carolinas and the Mid-Atlantic coast. Additional westward shifts in the forecast track of the moisture will likely result in additional trimmings of the Marginal Risk for coastal New England, with the expected rainfall for coastal New England down to around 1 inch...however the potential for severe weather on the east side of the Marginal Risk area and a possible reversal of the trend in the models, it was better to play it safe with this area until there is additional model guidance. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7pFb_-9BE9MvozA9LSaZs8oDHTYEMu2_tYGIM6DF0lBd= W4I2Gtd4wcl-NE8DCsux_FOvMoEi9sBjjLNnzH9nDmqVpio$=20=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7pFb_-9BE9MvozA9LSaZs8oDHTYEMu2_tYGIM6DF0lBd= W4I2Gtd4wcl-NE8DCsux_FOvMoEi9sBjjLNnzH9nvtbv8xY$=20=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7pFb_-9BE9MvozA9LSaZs8oDHTYEMu2_tYGIM6DF0lBd= W4I2Gtd4wcl-NE8DCsux_FOvMoEi9sBjjLNnzH9nhDxtiME$=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .