Area Forecast Discussion
Issued by NWS Huntsville, AL
Issued by NWS Huntsville, AL
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858 FXUS64 KHUN 270538 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1238 AM CDT Fri Sep 27 2024 ...New AVIATION... .NEAR TERM... (Tonight) Issued at 838 PM CDT Thu Sep 26 2024 Hurricane Helene has strengthened to a Category 4 hurricane and is forecast to make landfall tonight in the Big Bend area of the Florida coastline. Just northwest of this, a stationary front resides along the Florida panhandle northeastward through the Appalachians. This has been the driver for the predecessor rain event (PRE) throughout the southeast ahead of Helene and has resulted in 0.5-2" throughout the I-65 corridor and northeastern AL as well as portions of southern middle TN. This frontal boundary is set to continue to provide forcing for shower development ahead tropical banding from Helene overnight during which higher chances of showers move into the area (especially east of I-65). Training of showers will cause a medium-high flood concern along and east of I-65 as 2-4" is forecast to move over the area overnight. A Flood Watch is in effect through 1 AM Saturday throughout all of northern AL and southern middle TN to account for the period of prolonged rainfall we are about to experience. This initial wave of rainfall and subsequent flooding threat will be particularly hazardous due to it occurring overnight when flooding is harder to see. Never drive through flooded roadways and report any flooded roadways to law enforcement. In addition to the flooding threat, gusty winds also begin to increase overnight as Helene moves inland. Sustained winds around 15-20 mph with gusts up to 25-35 mph (potentially higher in areas of higher elevation) will likely be realized by daybreak and will increase throughout the day Friday. A Wind Advisory will be in effect beginning at 1 AM to account for this. Due to saturated soils, downed trees and power lines are likely to occur which will result in power outages. Be prepared for power outages by making sure your devices are charged, using flashlights instead of candles to avoid fires, and practicing generator safety to avoid carbon monoxide poisoning. As far as a severe threat goes, we are not forecasting severe weather at this time. Lapse rates are weak and will result in a very low chance of thunder/lightning along our eastern edge of the CWA. Instability is very low as well, resulting in no tornado threat at this time. Small changes in Helene`s track will affect the forecast, so we encourage everyone to stay up to date on the latest information. If Helene shifts westward, we could have locally higher rainfall totals as well as higher wind gusts. && .SHORT TERM... (Friday through Sunday) Issued at 312 PM CDT Thu Sep 26 2024 Helene will continue to impact the area through Friday and additional flash flooding and river flooding though could occur. Thus, a flood watch remains in effect from 1 am CDT on Friday through 1 AM CDT on Saturday. Guidance is showing the energy from the remnant of Helene being absorbed into a upper low along/just behind the front. Some additional moderate to heavy rainfall could linger flash flooding and areal flooding to 1 AM CDT on Saturday. Thus, the flood watch was extended through that time. There should be a good gradient in rainfall totals in a transition zone from NW Alabama further NE across the remainder of the area. One to three inches looks more likely in NW Alabama, with the higher amounts more likely further northeast between 3 and 5 inches with some isolated higher amounts around 7 inches possible through Saturday morning. Flash and areal flooding concerns should ease Saturday afternoon into Saturday night. && .LONG TERM... (Sunday night through Thursday) Issued at 312 PM CDT Thu Sep 26 2024 Global models suggest that the deep-layer cyclone to our north will continue to lift slowly northeastward on Sunday night, with SW flow to the east of a trailing trough axis maintaining a moist airmass across the TN Valley. It appears as if the drying trend aloft will be complemented by a drying trend in the low-levels by the middle of next week, as a cold front tracks southeastward through the TN Valley. Although the cold front may indeed advect a drier continental airmass into the region, highs will warm back into the l-m 80s by Tuesday/Wednesday due to abundant sunshine each afternoon. A dry forecast may return by next week. && .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...HC SHORT TERM....KTW LONG TERM....KTW AVIATION...HC