Area Forecast Discussion
Issued by NWS Huntsville, AL
Issued by NWS Huntsville, AL
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855 FXUS64 KHUN 270752 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 252 AM CDT Fri Sep 27 2024 ...New NEAR TERM, SHORT TERM, LONG TERM... .NEAR TERM... (Today and Tonight) Issued at 249 AM CDT Fri Sep 27 2024 The outer rain bands from Hurricane Helene have begun to move into the region early this morning as the remnants of the system push into east central Georgia. As Helene moves further inland, it is forecast to interact with a deepening trough of low pressure over the Mid South region. This interaction will pivot Helene back to the NNW and into the Southern Appalachians of NC/TN by Friday morning -- and eventually further to the west into Middle Tennessee by the afternoon as the two systems merge. It should be noted that the current track of Helene is further to the east than originally thought and this may slightly impact projection on rainfall/QPF. Deep tropical moisture will continue to advect into the region early this morning as evidenced by PWATs creeping into the 1.5" to 2.0" range over much of the area by 09-12z and potentially over 2" across portions of northeast Alabama. As Helene pivots to the north and eventually NNW, greater forcing along a convergence boundary along the AL/GA border may focus tropical rain bands across portions of northeast/north central Alabama into southern middle Tennessee from roughly a 4 AM to 1 PM window. This could produce rainfall amounts in the 2 to 4" range (with locally higher amounts) over this 6-9 hour period. Should this materialize, a localized flash flooding threat would evolve where the heaviest bands setup, especially in poor drainage areas. Rises on rivers, creeks, and streams would also occur late in the day and into the overnight and evening hours. Our highest confidence in this evolving would be in areas east of I-65, especially in locations along the AL/GA border. HREF Grand Ensemble show probabilities of 70-100% of total rainfall exceeding 3" (thru 1 AM Saturday) northeast of a line from Ft Payne to Scottsboro to Winchester, with much lower probs south and west of that line. Thus, a lower confidence in a flash flood threat exists in our northwest Alabama counties, where QPF is forecasted to be close to 1". Still, these areas received very heavy rainfall from TC Francine a couple weeks ago and we`ll have to watch closely the location of these rainbands to see if they do setup a little further to the west. A Flood Watch is in effect for the entire area through 1 AM Saturday morning. Due to the strong pressure gradient from Helene and its eventual merger with the aforementioned trough later today, strong gradient winds will also be a concern (especially across our eastern areas along the Cumberland Plateau). Wet soils in these areas (combined with gusty winds up to 30-40 MPH) could knock down trees and a few power outages are a distinct possibility. A Wind Advisory is in effect to highlight this threat through 1 AM Saturday morning. One more note about today: the dense cloud cover and rain chances will keep high temperatures much lower and in the upper 60s to mid 70s. && .SHORT TERM... (Saturday through Monday) Issued at 249 AM CDT Fri Sep 27 2024 The remnant center of Helene will stall over TN/KY later tonight, and although QPF amounts will be much lighter, medium to high rain chances (30-80%) remain in the forecast Friday night into Saturday due to light shower activity. Rises on rivers, creeks, and streams may still be ongoing and persist into the weekend, mainly in locations that receive the heaviest rainfall. Ridging to the west will amplify and eventually help to nudge the remnant low to the east into the central Appalachians by Monday. Rain chances will continue to drop to 20-50% on Sunday and 10-20% by Monday as the system pulls away. A gradual warming trend will take place as high temperatures finally return to the upper 70s to lower 80s by Monday. && .LONG TERM... (Monday night through Thursday) Issued at 249 AM CDT Fri Sep 27 2024 High pressure will build into the Deep South and Tennessee Valley during the middle to later part of the work week as we finally begin to dry out. Highs will return to the low to mid 80s with ample sunshine each day. In this drier, more comfortable air mass, we`ll finally get a decent taste of autumn heading into the first week of October with Min RH values drop to around 40-50% percent during the afternoon hours. && .AVIATION... (06Z TAFS) Issued at 1238 AM CDT Fri Sep 27 2024 Ceilings will lower quickly overnight to MVFR/IFR conditions as rainbands associated from the remnants of Helene push into the region. Visibilities will drop into the 3-5 SM range from the early morning hours through much of the afternoon due to SHRA and/or mist as the rainbands move through the TN Valley. Strong, gusty winds will increase throughout the morning hours into the afternoon and evening into the 25-30 kt range due to the strong pressure gradient from Helene passing to the east. Amendments may be needed during this timeframe due to the potential for strong gusty winds and reduced visibilities from SHRA. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...Flood Watch through late tonight for ALZ001>010-016. Wind Advisory until 1 AM CDT Saturday for ALZ001>010-016. TN...Flood Watch through late tonight for TNZ076-096-097. Wind Advisory until 1 AM CDT Saturday for TNZ076-096-097. && $$ NEAR TERM...AMP.24 SHORT TERM....AMP.24 LONG TERM....AMP.24 AVIATION...HC