Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Feb 12 2025 00:57:13 FOUS30 KWBC 120056 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 756 PM EST Tue Feb 11 2025 Day 1 Valid 01Z Wed Feb 12 2025 - 12Z Wed Feb 12 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF EASTERN TEXAS INTO THE LOWER MISSISSIPPI VALLEY... A Slight risk remains for portions of eastern TX into central/northern LA, far southern AR and western MS. A shortwave=20 and upper jet moving into TX will support increased ascent and the=20 development of another round of convection tonight into Wednesday.=20 A strengthening low level jet is also anticipated, which will=20 result in increased moisture and instability being drawn northward, along with an uptick in moisture convergence. The ingredients are=20 in place for organized convective development with heavy rainfall=20 rates. Activity will likely initiate over central TX this evening=20 and should be quick moving off to the east. This quick movement=20 will be a limiting factor for flash flooding, but hourly rainfall=20 could still locally approach 2", which could drive at least an=20 isolated flash flood threat...especially over areas that have seen=20 lowered FFG from rainfall earlier today and/or more sensitive urban areas.=20 By later tonight into Wednesday morning we may begin to see more=20 convective development along the warm front downstream of the area=20 of organized convection. This could allow for some west to east=20 training to occur, locally increasing the flash flood risk over=20 portions of far east TX into LA. The system as a whole remains=20 progressive, which will put a cap on the magnitude/coverage of the=20 flood risk. However the strong dynamics combined with a=20 strengthening west to east oriented axis of lower level moisture=20 convergence supports some training potential by later tonight and=20 an isolated to scattered flash flood risk. To the east, locally heavy convection may drop a quick 1-2" of=20 rain over portions of central AL and GA, but this should not pose=20 more than a localized flash flood risk. Lighter rain rates will=20 continue across portions of northern AL/GA and into portions of TN=20 and the western Carolinas. Not expecting much of a flash flood risk here, but the prolonged moderate rainfall may result in some minor areal flood concerns. Chenard Day 2 Valid 12Z Wed Feb 12 2025 - 12Z Thu Feb 13 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE TENNESSEE VALLEY INTO THE MID-SOUTH... ....Tennessee Valley into the Mid-South... Another wave of low pressure will move through the area Wednesday into Wednesday night, bringing additional widespread precipitation to the region. Increasing low level moisture combined with the favorable upper level support should result in robust rainfall with embedded convection. An axis of 2 to 3 inches is expected during the 24-hour period from portions of Louisiana through southwest North Carolina. Embedded within that will be the possibility of higher amounts, most likely over portions of Alabama and Georgia where the overlap of available instability and potential for training/repeating rounds of rainfall appear most likely. Combined with the preceding day rainfall, 48-hour totals exceeding 3-5" will be possible and this will likely lead to excessive runoff and increasing soil saturation. As a result, a higher end Slight Risk in the ERO is maintained, with the greatest risk for flash flooding over portions AL/GA. ....California Coast... The beginning of the active/wet period for the West Coast begins late in the period as the initial surge of atmospheric moisture arrives after 00Z Thursday across coastal central California. This will bring the initial threat of flooding, though the bulk/peak of it will be in the Day 3 /Thursday/ period. Taylor Day 3 Valid 12Z Thu Feb 13 2025 - 12Z Fri Feb 14 2025 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL PARTS OF THE SOUTHERN CALIFORNIA COAST... ....California... The peak of the atmospheric river is expected during this period with the initial focus on coastal central California at the start of the period, then the best IVT shifts southward through the period, reaching southern California by the end of the period Thursday night. IVT values from the GFS peak at around 600-700 kg/m/s initially along the central coast then settle around 400-500 kg/m/s as the AR reaches SoCal. The greatest QPF amounts will be confined to the coastal terrain areas as well as for the Sierra. Total amounts for the 24-hour period look to be between 1-3" with the favored terrain areas and peaks topping out between 4-5". The primary concern is the potential for damaging and potentially life-threatening burn scar flash flooding and debris flows, particularly for southern California where the Moderate Risk (Level 3/4) is in place. Even outside the burn scar regions, the intense rain rates and rainfall totals over the highly urbanized area could bring scattered to numerous instances of flash flooding. Elsewhere, a broad Slight Risk (Level 2/4) exists for much of the coastal ranges as well as the Central Valley and lower elevations of the Sierra Nevada. There is a Moderate Risk of excessive rainfall over portions of the Southern California coast embedded within a broader Slight risk of excessive rainfall covering much of the central and southern California coast. An atmospheric river is expected to skirt the coast as it makes its way south and east. The primary concern is for damaging flooding and debris flow from the numerous fresh burn scars in the region given the 24-hour QPF in the 1.5 to 3.5 inch range...with potentially localized higher amounts. In addition...the area is highly urbanized and an environment in which much of the rainfall will turn immediately to runoff. Farther north...the Slight risk was extended into portions of the Sacramento Valley and San Joaquin Valley...where QPF is not expected to be as great but the conditions have been wetter and soils are more saturated than soils farther south. ....Florida Panhandle and Southern Georgia... Lingering heavy rainfall will continue Thursday across portions of the Florida Panhandle and southern Georgia, ahead of the approaching cold front. Rainfall amounts look to be generally in the 1-3" range, with some potential for localized rain rates sufficiently high enough to cause some urban/localized flooding concerns. Taylor Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5mPBbwXDTu9S_Os7z2R78zojVwY0UBQLGREeQ4mag062= VtOHaobYGlHN06TQD4v27vhnTKSbdRMtpsug72mdDFk9NjI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5mPBbwXDTu9S_Os7z2R78zojVwY0UBQLGREeQ4mag062= VtOHaobYGlHN06TQD4v27vhnTKSbdRMtpsug72mdxv5Ykxc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5mPBbwXDTu9S_Os7z2R78zojVwY0UBQLGREeQ4mag062= VtOHaobYGlHN06TQD4v27vhnTKSbdRMtpsug72mdjm6QWjQ$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .