Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Nov 09 2022 08:47:37 FOUS30 KWBC 090847 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 346 AM EST Wed Nov 09 2022 Day 1 Valid 12Z Wed Nov 09 2022 - 12Z Thu Nov 10 2022 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS MUCH OF THE FLORIDA PENINSULA... ....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... In coordination with all of the impacted offices, the Slight Risk area was expanded westward with this forecast update to include the eastern half of the Florida Panhandle, and the southern half of Georgia up to the Alabama border. The forecast track of Nicole continues to shift westward with a faster forward speed. Forecast rainfall across this area will be generally in the 2 to 4 inch range, with the highest values in the eastern Panhandle up to the southeast corner of Georgia. The chances of flooding are being mitigated somewhat by the antecedent dry conditions over much of the area, with the exception of any rivers that were swollen by Ian a few weeks back, particularly in the Jacksonville area. The north and westward shift also means more rainfall spreading further north into the Carolinas and the Blue Ridge of southwestern VA. Here the broad easterly flow will upslope along the mountains, which will locally enhance rainfall rates. Again in these areas this will be offset by recent dry conditions, especially across northern GA and eastern TN. Rainfall will only begin in areas north of the Marginal into KY and WV, and the very dry conditions in these areas will preclude any flooding threat through 12Z Fri. ....Upper Midwest... Very few changes to the inherited Marginal Risk area, other than a very small expansion over the Arrowhead of MN, where the latest guidance suggests a maximum of rainfall over this area during the day Thursday before colder air moves in Thursday night and changes any remaining moisture over to snow. 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. Wegman 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... 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!-Wdq7dpH5GqbT_KF4J9A7mEYRqW-riM85De1_Ku4LmdC= t4uLLISLInWLtBiWhc2AHyBPtwaT73ggtuOrXaJDgNQPuB4$=20=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-Wdq7dpH5GqbT_KF4J9A7mEYRqW-riM85De1_Ku4LmdC= t4uLLISLInWLtBiWhc2AHyBPtwaT73ggtuOrXaJD_fAvKIA$=20=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-Wdq7dpH5GqbT_KF4J9A7mEYRqW-riM85De1_Ku4LmdC= t4uLLISLInWLtBiWhc2AHyBPtwaT73ggtuOrXaJDIS29iSg$=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) .