Area Forecast Discussion
Issued by NWS Atlanta, GA
Issued by NWS Atlanta, GA
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141 FXUS62 KFFC 241936 AFDFFC Area Forecast Discussion National Weather Service Peachtree City GA 336 PM EDT Tue Sep 24 2024 ...Afternoon Area Forecast Discussion... .SHORT TERM... (This evening through Wednesday) Issued at 334 PM EDT Tue Sep 24 2024 Highlights: -Increasing rain chances overnight into Wednesday, mainly across North and north-central GA as far south as metro ATL in response to an approaching frontal boundary -Locally heavy rainfall and potential for flooding concerns across northwest GA on Wednesday Isolated showers and storms will be possible through the afternoon today aided by a surface trough in Central GA and southwesterly flow aloft. Temperatures this afternoon are expected to remain the upper 80s to low 90s. The presence of clouds has tapered temperatures ever so slightly compared to the previous few days. Looking ahead to Wednesday -- a 500mb ridge currently of the northern Gulf will inch eastward as a midlevel trough swings through the Mid-MS Valley/Mid-South Region. At the sfc, this will bring a frontal boundary towards the northwestern portions of the forecast area. As a result, we can expect increasing clouds and increasing rain chances in our northern zones overnight into early Wednesday along and ahead of the frontal boundary. Per HREF and hi-res guidance, rain showers look to begin around sunrise, increasing in coverage especially through the afternoon. Additionally, thunderstorm chances increase through the afternoon persisting through the evening. The biggest thing to note compared to the previous forecast is increasing confidence on heavy rainfall leading to flash flooding across much of North GA including the ATL metro tomorrow (Wednesday) afternoon. Tropical moisture will be on the increase and will set up ahead of the frontal boundary moving in from the northwest. Thus, PWs will be upwards of 2+ inches per latest guidances. An upgrade (from WPC) will be forthcoming for northeast GA down south including Metro ATL for a Moderate Risk (3 out of 4) of Excessive Rainfall -- i.e. the greatest risk for rainfall intense enough to cause flash flooding. Latest forecast totals (for Wednesday only) ranges from 2 to 3 inches with locally higher amounts. Heavy rainfall and flash flooding potential will be the main concern for tomorrow (Wednesday) -- note: this is ahead of anything tropical related. As a result of increasing confidence in hydro related issues, we have opted to issue a Flood Watch for much of North and Central GA. This will encompass the threat for Wednesday and then the evolving threat for the Thursday-Friday timeframe in association with Tropical Storm Helene. For details about Tropical Storm Helene please see the long term discussion below. Temperatures through the short-term will trend slightly cooler especially across the north as clouds and rain increase. 07 && .LONG TERM... (Thursday morning through next Monday) Issued at 334 PM EDT Tue Sep 24 2024 Tropical Storm Helene is forecast to be a major hurricane by the time it is landfalling along the Big Bend region of Florida late Thursday. Significant impacts are also expected to be overspreading the local forecast area by this time as Helene rapidly moves northward through Thursday night. While model consensus remains quite good, at this juncture there is still some spread between ensemble members regarding the exact track of the center of Helene across our forecast area. A slightly more westerly track would expose the bulk of the area to more substantial impacts while a slightly more easterly track would shift the core of the strong wind and severe threat to eastern zones. Regardless, confidence continues to increase in substantial impacts for north and central Georgia as the storm is certain to push into the area in some capacity. Rainfall: Concern continues to mount for very significant rainfall totals that would lead to substantial flash flooding and flooding concerns. Given the expectation that a significant rainfall event is likely to occur in the short term on Wednesday in advance of the rainfall associated with Helene, conditions will be well primed for flooding concerns to become exacerbated on Thursday into Thursday night. Additional widespread forecast rainfall totals 3.5 to 5" with locally higher amounts occurring on top of potential 2-3+" rainfall amounts in some areas on Wednesday. A Moderate Risk for excessive rainfall is in effect for Thursday across the entire area with some potential for an upgrade for portions of the area if antecedent heavy rainfall verifies on Wednesday. A Flood Watch will be in effect for the entire area. Winds: The rapid inland progression of Helene will contribute to a substantial threat for strong winds within the local area. The strongest winds and gusts will be nearest and just to the east of the center of circulation, and thus this peak wind area will be dependent on the eventual track of the center. With that said, gusty winds will still affect the bulk of the forecast area well away from the storm`s center as this system will be broad and encompassing. The time frame within which the strongest winds and gusts are expected is from late Thursday evening into early Friday morning as the center of Helene quickly lifts northward. Widespread 35-50 mph gusts would be increasingly likely for much of the area with higher gusts anticipated near and east of the center. Higher 50+ mph gusts will be expected for areas closer to the center. Tornadoes: A Marginal Risk remains from the Storm Prediction Center for portions of central GA on Thursday within the eastern quadrant where tornadoes would be favored. This risk area will likely fluctuate based on the eventual track of Helene with areas east of the center favored for short-lived tropical tornadoes. Thanks to the very quick northward movement, Helene will fortunately depart the area quickly Friday morning with a drying trend from south to north. The remnants of Helene will then get absorbed into a broad closed low over the Mississippi and Ohio Valleys through the weekend. Isolated to scattered PoPs will hold into early next week. RW && .AVIATION... (18Z TAFS) Issued at 152 PM EDT Tue Sep 24 2024 Latest radar shows widely sct shra this aftn. Iso tsra cannot be ruled out with marginal instability in place. SCT to BKN cu field expected through 02z with high clouds increasing. Lower MVFR to FEw/SCT BKN deck starts to move in ahead of a frontal boundary in northwest GA after 06z settling in through the metro closer to 12z. Additionally, VCSH starts as early as 14z with onset of -SHRA between 16-18z. Did introduce a PROB30 for tsra at ATL tomorrow afternoon. Winds start off from the southwest, become light/vrb overnight <5kts, and then switch over to the SE side 08z-10z and stay on this side through 18z. //ATL Confidence...18Z Update... Medium confidence on all elements. 07 && .PRELIMINARY POINT TEMPS/POPS... Athens 68 83 67 75 / 30 60 70 90 Atlanta 70 81 68 73 / 40 80 80 90 Blairsville 63 73 62 70 / 60 80 80 90 Cartersville 68 79 65 74 / 60 90 80 90 Columbus 72 85 69 75 / 30 80 80 90 Gainesville 68 78 67 72 / 40 80 80 90 Macon 70 87 69 77 / 20 50 70 100 Rome 68 80 66 75 / 70 90 80 90 Peachtree City 68 82 66 73 / 40 80 80 90 Vidalia 70 89 72 80 / 10 20 60 90 && .FFC WATCHES/WARNINGS/ADVISORIES... Flood Watch from Wednesday afternoon through Friday afternoon for GAZ001>009-011>016-019>025-027-030>039-041>062-066>076- 078>086-089>098-102>113. && $$ SHORT TERM...07 LONG TERM....RW AVIATION...07