Area Forecast Discussion
Issued by NWS Atlanta, GA
Issued by NWS Atlanta, GA
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776 FXUS62 KFFC 171515 AAB AFDFFC Area Forecast Discussion...UPDATED National Weather Service Peachtree City GA 1115 AM EDT Fri May 17 2024 ...Morning Update... .UPDATE... Issued at 1033 AM EDT Fri May 17 2024 West-to-east oriented convective banding has set up across south- central AL this morning and has not shown much sign of northward advancement. Moderate to heavy rain and embedded, elevated thunderstorms associated with this activity have begun to move into the southwestern portion of the CWA, where WPC has a Slight Risk for excessive rainfall and localized flash flooding. Will need to monitor trends in the upstream convection as it continues to shift into west-central GA over the next several hours. In addition, SPC has made an eastward expansion to the Slight Risk area over portions of central Georgia, now including Warner Robins and Cordele. Dense cloud cover will likely prevent much diurnal destabilization, so any strong to severe storms across said area will depend on upscale growth of the MCS over south- central AL and its continued general eastward movement. Damaging wind gusts and hail remain the primary hazards with any severe storms. The tornado threat is low, but not zero. Martin && .SHORT TERM... (Today through Saturday) Issued at 504 AM EDT Fri May 17 2024 As the morning begins, the upper level ridge responsible for yesterday`s dry and sunny conditions is moving eastward towards the Atlantic coast. Meanwhile, positively-tilted troughing is positioned over Texas. Southwesterly flow aloft will set up between these two features, which will allow for steady advection of deep moisture into the forecast area. A shortwave disturbance traversing this southwesterly flow, has triggered an MCS, which is currently centered to the south of Mobile Bay and will continue to move eastward over the northern Gulf of Mexico. High clouds on the northeast side of this complex have been spreading over the forecast area in the early morning hours, which will be followed by showers moving from west to east into the area this morning. The axis of the aforementioned trough and an upper level speed max will advance towards the area over the course of the day. With increasing deep moisture, dewpoints are forecast to increase into the mod to upper 60s across north and central Georgia. Furthermore, precipitable water values will rise to between 1.6 and 1.9 inches by this afternoon. After the coverage of showers increases through the morning, scattered convective activity is expected to become more likely by mid afternoon and into the evening hours. As warm air works its way northward from the Gulf, temperatures in south-central Georgia will warm into the low to mid 80s, while only rising into the 70s elsewhere across the area under persistent cloud cover and showers. The influence of the aforementioned speed max will contribute to 0-1 km shear values of 20-25 kts and deep layer bulk shear values of 40-50 kts this afternoon and evening. The warmest, most humid areas in south- central Georgia will also see the greatest surface-based instability, with SBCAPE values progged to range from 1000-1500 J/kg. This environment will be supportive of severe thunderstorm development in south-central Georgia, while thunderstorms are expected to remain elevated in north Georgia. The SPC has diagnosed a Slight Risk (level 2 out of 5) of severe thunderstorms in west-central Georgia, including Columbus, and a Marginal Risk (1 out of 5) elsewhere across central Georgia. To begin in the early afternoon and early evening, thunderstorms are anticipated to be discrete and potentially supercellular, and severe storms that occur will be capable of producing large hail, damaging wind gusts, and possibly a couple of tornadoes. In the late evening into the overnight hours, the upscale growth of storms will become outflow driven, potentially evolving into an MCS. In this phase, damaging wind gusts will be the primary hazard with any severe storms that develop. It is worth noting that the severe weather threat will be conditional. It will ultimately be contingent upon how far north warm air from the Gulf is able to advance and the behavior of outflow boundaries from upstream convection. Considering the high PWATs and deep atmospheric moisture, stronger storms could produce locally heavy rain, particularly in the mid afternoon to early evening where the potential for deep convection and training motion look most likely. With soils across much of the area being saturated from recent rainfall, if storms move in a training motion over common locations, it could lead to increased runoff and localized flooding concerns. As the trough axis moves into the Lower Mississippi River Valley region, the warm front is expected to continue to work its way northward into Georgia through Saturday morning. At this time, dewpoints will increase into the upper 60s in north Georgia and low to mid 70s in central Georgia. At this time, low temperatures are forecast to start off in the low to mid 60s in north Georgia, and upper 60s to low 70s in central Georgia (south of the warm front). Temperatures are then expected to warm into the upper 70s to low 80s ahead of an cold front moving eastward from Alabama. During the peak heating hours, SBCAPE values could increase to as high as 2500 J/kg in portions of east-central Georgia. Enhanced southwesterly flow ahead of the shortwave will also contribute to deep layer bulk shear values of up to 40 kt. While conditions on Saturday will be heavily dependent on the evolution of the overnight and early morning MCS, convection is expected to develop in the afternoon ahead of the advancing cold front, and the environment and parameters mentioned above will be sufficient to support the development of some strong to severe thunderstorms. The primary hazards with any severe storms that form will be damaging winds, although hail and a brief tornado or two cannot be ruled out. King && .LONG TERM... (Saturday night through Thursday) Issued at 504 AM EDT Fri May 17 2024 The long term forecast picks up with the low pressure system and attendant cold front over the forecast area slowly progressing eastward as the upper level wave dives across the southeast. Ongoing showers and thunderstorms in the early evening hours Saturday will be in a favorable environment to become strong to severe. Undeterred by the appreciable loss of diurnal heating after sunset, thunderstorms are expected to persist through the early morning hours on Sunday as they are able to tap into an unstable (MUCAPE ranging from 500-1000+ J/kg) and dynamically supportive environment (bulk shear +/- 40kts). Despite the elevated nature of thunderstorms, a few could become strong to severe with the greatest hazard being damaging wind gusts. Hail up to 1 inch and a brief tornado (primarily across southeastern Georgia where 0-3km SRH is sufficient) will also be possible, though the probabilities are relatively low. SPC currently has a Slight Risk (level 2 out of 5) for severe weather progged for areas along and south of a line from roughly Columbus to Macon to Washington that is valid through the 12Z time frame on Sunday. As moisture wraps around the backside of the low as the system pushes eastward, another round of scattered to numerous showers is expected with locations across eastern Georgia Sunday forecast to see the best rain and thunderstorm chances. At this time, no severe weather is expected on Sunday with storm chances tapering off by Sunday night, but can`t rule out a strong storm. The other notable hazard through the weekend is the rainfall associated with the active weather in the short term and the weekend system. Some locations across central Georgia could receive around 2.0" of rain with a decreasing gradient to ~0.75" to the north. This forecast cycle has backed off a bit with respect to the rainfall totals through the weekend. Despite this, will need to keep an eye on any locations that see repeated instances of heavy rainfall in strong storms and/or training storms through the weekend where locally higher amounts may be possible. PWATs are running between 1.5-2.0+" across much of central Georgia, and while the sandier soils of the coastal Plain can handle more rainfall than their northern counterparts across the Piedmont, a few isolated instances of nuisance flooding will be possible. Beyond the busy start to the long term forecast period, high pressure aloft and at the surface returns to kick off the work week. A weak wedge will set up shop through the first half of the week bringing dry conditions to the area. PoPs return to the forecast with a chance of showers and thunderstorms for north Georgia Wednesday as a cold front approaches the area. As the frontal boundary sags south Thursday, chances for showers and thunderstorms will be on the table through the day Thursday. Temperatures in the upper 70s and low 80s at the start of the forecast period will begin a warming trend through the end of the extended with highs topping out in the upper 80s (with a few locations hitting the 90 degree mark across south central Georgia). KAL && .AVIATION... (12Z TAFS) Issued at 733 AM EDT Fri May 17 2024 Ceilings will lower to MVFR by 15z, in addition to showers becoming more widespread. Chances for thunderstorms appear to be greatest this afternoon with forcing from a disturbance aloft combined with diurnal instability. As such, TEMPOs have been introduced for TSRA at all sites for either 17z-21z or 18z-22z. Winds will be E to SE at 4-8 kts. Winds may briefly shift to SW this afternoon in portions of central Georgia. Ceilings are forecast to lower to IFR after 00z at the northern TAF sites. //ATL Confidence...12Z Update... Medium confidence on progression of ceilings and convection. High confidence on all other elements. Martin/King && .PRELIMINARY POINT TEMPS/POPS... Athens 64 80 63 80 / 80 60 50 60 Atlanta 66 79 65 81 / 70 70 50 50 Blairsville 60 75 59 76 / 80 70 50 60 Cartersville 63 80 62 81 / 70 70 50 50 Columbus 70 81 65 84 / 70 80 40 30 Gainesville 64 78 64 79 / 80 70 50 60 Macon 69 81 65 83 / 60 80 40 50 Rome 64 79 62 83 / 70 70 50 40 Peachtree City 66 80 63 82 / 70 70 40 40 Vidalia 72 84 68 83 / 40 80 60 60 && .FFC WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Martin LONG TERM....KAL AVIATION...Martin