Area Forecast Discussion
Issued by NWS Atlanta, GA
Issued by NWS Atlanta, GA
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122 FXUS62 KFFC 021854 AFDFFC Area Forecast Discussion National Weather Service Peachtree City GA 254 PM EDT Tue Jul 2 2024 ...Afternoon Area Forecast Discussion... .SHORT TERM... (This afternoon through Wednesday) Issued at 252 PM EDT Tue Jul 2 2024 Upper level high pressure remains centered over Mississippi/Alabama, which is expected to continue expanding eastward into an E-W oriented ridge over the short term period. An associated surface high pressure is positioned near the New England coast. Surface ridging associated with the high has developed along the lee side of the Appalachians and has spread across much of north Georgia from the northeast. The airmass under this wedge of high pressure is noticeably milder and drier than observed the last several days. High temperatures will range from the mid 80s to near 90 this afternoon. Dewpoints have also dropped into the 50s to low 60s in the Atlanta metro area and to the north and east. The frontal boundary that traversed through the forecast area yesterday has become stationary across south Georgia, with scattered showers and thunderstorms ongoing in the vicinity of the front. Some of this precipitation will continue across portions of south-central Georgia through the afternoon, but a stable airmass within the wedge will keep PoPs to a minimum across the northern 2/3 of the forecast area. After a cloudy start the morning across the majority of the forecast area on Wednesday, the wedge will begin to break down as the high pressure center moves offshore into the Atlantic. At this time, the frontal boundary will slowly lift back to the northeast, with dewpoints in the upper 60s and 70s creeping back to the north in kind. With increasing dewpoints and highs rising into the low 90s across the majority of north and central Georgia (with the exception of the higher elevations of the far northeast), MUCAPE values are forecast to increase to 1000-1500 J/kg in portions of central and west Georgia, south and west of the frontal boundary. These instability values will be sufficient for scattered diurnally-driven thunderstorms, with the highest coverage in south-central Georgia where there will be the greatest low level moisture and precipitable water values approaching 2 inches. With vertical profiles indicating tall but thin CAPE profiles and very limited shear, the threat for severe weather on Wednesday is shaping up to be quite low. King && .LONG TERM... (Thursday morning through next Monday) Issued at 252 PM EDT Tue Jul 2 2024 Key Messages: - A Heat Advisory may be needed (40% chance) for portions of east central Georgia between Friday and Sunday. - Afternoon and evening thunderstorms should become more numerous Friday, Saturday and Sunday. Heat Concerns to End the Week: The core of an upper level ridge will drift gradually eastward over the course of this week. Overall, 500 mb heights should peak in Georgia on Thursday or Friday, but 850 mb temperatures may continue to inch upwards over the weekend. These trends should allow temperatures to climb back towards the mid and upper 90s to conclude the week. The warmer temperatures should be accompanied by surface dewpoints in the 69-74 degree range, and this may push afternoon heat indices back into the triple digits. Our current forecast suggests heat indices above 105 in parts of Georgia Thursday, Friday, Saturday and Sunday. If these values hold (a 1-2 degree decrease in surface dewpoints or temperatures would prevent values over 105) then a Heat Advisory (40% chance) may be warranted for some locations south and east of Atlanta. Peak heat indices in the Atlanta Metro are currently forecast to be in the 100 to 104 degree range. Thunderstorms Chances Trending Upwards: An upper level trough tracking through the Great Lakes should push a weak frontal boundary towards Georgia late in the week. While the strength of this boundary may be fading, it should still provide sufficient lift to serve as a focal point for storm activity. Guidance from the EPS and GEFS suggests increasing instability (Mean SBCAPE values > 1000 j/kg) and moisture (PW values near 2 inches) along and ahead of the frontal boundary. Combine these factors with diurnal heating and the lift/surface convergence along the frontal boundary, and an uptick in the coverage of afternoon and evening thunderstorms is anticipated. Our forecast rain chances currently peak near 60% on Saturday. The potential for strong or severe thunderstorms remains low due to limited shear (surface to 500 mb bulk shear generally less than 15 kt) and modest mid level lapse rates (700-500 mb values near 5.5 C/km). If stronger storms do occur, they would be most probable near the GA/TN border where bulk shear values my be closer to 20 kt Friday and Saturday. Rainfall rates may be local heavy with any storms that occur (1-2 inches per hour) due to the potential for climatologically high PW values (in the 90th percentile). Albright && .AVIATION... (18Z TAFS) Issued at 128 PM EDT Tue Jul 2 2024 At the time of this writing, ceilings have scattered out across north Georgia as drier air filters into the area. MVFR ceilings remain at MCN/CSG, although they are expected to improve to VFR by 20-21Z. SHRA/TSRA is forecast to remain to the south of all TAF sites through the remainder of the afternoon. Winds will be E to SE through the period, starting at 10-14 kts with gusts of 20-25 kts. Wind speeds will progressively diminish this afternoon and evening, dropping to 4-8 kts by 02Z and into Wednesday. Low ceilings are anticipated once again during the morning on Wednesday, dropping to MVFR after 09Z. Some periods of IFR ceilings will furthermore be possible from 12-15Z. //ATL Confidence...18Z Update... Medium confidence on low ceilings on Wednesday morning. High confidence on all other elements. King && .PRELIMINARY POINT TEMPS/POPS... Athens 69 92 73 95 / 10 20 10 30 Atlanta 73 91 75 94 / 10 30 20 40 Blairsville 65 86 68 89 / 10 20 10 60 Cartersville 72 93 74 95 / 10 20 10 40 Columbus 76 93 75 94 / 20 50 30 50 Gainesville 70 90 74 94 / 10 20 10 40 Macon 73 93 73 95 / 10 40 20 30 Rome 73 94 75 96 / 0 20 10 50 Peachtree City 72 91 73 94 / 10 30 20 40 Vidalia 74 91 75 94 / 30 60 30 30 && .FFC WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...King LONG TERM....Albright AVIATION...King