518 FXUS62 KFFC 051730 AFDFFC Area Forecast Discussion National Weather Service Peachtree City GA 1230 PM EST Fri Jan 5 2024 ...New 18Z Aviation Discussion... .SHORT TERM... (Today through Saturday) Issued at 438 AM EST Fri Jan 5 2024 The short term period (and into next week) will be characterized by a progressive flow pattern at the upper levels. As the morning begins, much of the eastern CONUS is positioned underneath an upper ridge extending from the northeast Gulf Coast to the Great Lakes region. Surface high pressure associated with the ridge is moving across the Appalachians and eastward towards the mid-Atlantic coast. As this occurs, surface winds have shifted to easterly as a CAD wedge develops along the lee side of the Appalachians and into northeast Georgia. A cutoff upper low over the southern Great Plains will meanwhile lift northeastward over the course of the day today, at which time a shortwave on the southwestern side of the low will develop a surface low just off the southeast Texas coast. This low will move eastward across the northern Gulf of Mexico this afternoon and into tonight. With a dry airmass and clear skies to start the morning, lows will start the morning the mid to upper 20s across the majority of the forecast area. With the wedge building in across north Georgia, temperatures to the north of I-20 will struggle to get above 50 this afternoon (and even struggle to get to 40 in the higher elevations of far northeast Georgia). High temperatures will range from the mid 50s to low 60s to the south of the wedge. Upper level cloud cover will begin to increase in coverage starting mid-morning and continue through much of the day. Tonight, the surface low will move onshore near the LA/MS coast and continue northeastward inland. Precipitation chances will quickly increase from west to east across the area, becoming widespread after midnight. Continued cool easterly flow within the wedge will have temperatures in the low to mid 30s across portions of northeast Georgia during the overnight hours. As a result, a wintry mix will be likely in the higher elevations of far northeast Georgia as precipitation overspreads the wedge. Model soundings still indicate a fairly deep warm nose around the 850 mb level at about 5 degrees. With temperatures expected to hover around freezing for much of the overnight hours and ample moisture in place, the most likely mode of wintry precipitation appears to be freezing rain. At the onset of precipitation just after midnight, it is possible that some of the light freezing rain could mix with sleet and/or rain. Temperatures will gradually warm through the overnight, rising into the mid 30s by sunrise, with freezing rain coming to an end shortly after. A Winter Weather Advisory has been issued for portions of far northeast Georgia from 11 PM tonight until 8 AM on Saturday morning. Total ice accumulations of around one-tenth to two-tenths of an inch are possible in the highest elevations, with light icing possible elsewhere in the Advisory. Will need to continue to monitor the observations as the wedge sets up, as cooler temperatures spreading further south than forecast could warrant an expansion of the Winter Weather Advisory. Winds at the highest elevations could moreover gust to as high as 30 mph. Aside from far northeast Georgia, widespread rain is likely overnight and Saturday morning. Isolated thunderstorms will be possible in central Georgia (mainly south of Columbus and Macon) where marginal instability will be present. The axis of the aforementioned shortwave will move quickly northeastward towards the Carolinas by Saturday afternoon, at which point the low pressure system will move out of the forecast area. Some trailing light rain will continue into the early afternoon on the back side of the low, with chances diminishing going into the evening. Overall, rainfall amounts are forecast to range from 1/2 to 1 inch, with some locally higher amounts possible. Similar to this afternoon, the presence of the wedge in north Georgia will be reflected by the high temperatures on Saturday afternoon, with highs in the upper 40s to low 50s within and reaching into the 60s to the south. King && .LONG TERM... (Saturday night through Thursday) Issued at 438 AM EST Fri Jan 5 2024 Key Messages: - Potent storm system will approach the area on Monday, bringing the potential for locally heavy rainfall and severe thunderstorms late Monday night into Tuesday. An upper low pressure trough is forecast to rapidly dig over the Rocky Mountains on Sunday, with a low in the base of the trough. This low will start out with a 500 mb height of around 536 dam over the Four Corners region Sunday evening before moving ESE across the S Plains by Monday evening. The low will then lift ENE and deepen as it sweeps across the OH Valley by Tuesday evening. Global models remain in very good agreement with respect to the progression of this feature, with most models similar regarding timing of the trough and within about 6 dam height-wise by day 5. At the surface, low pressure and an attendant frontal system will rapidly develop and move E from near Las Vegas on 12Z Sunday to near Little Rock by 12Z Tuesday. Warm, moist air is expected to surge northward on increasing southerly winds late Monday night into Tuesday morning, with dew points reaching 55+ degrees near and S of the Atlanta metro area. MUCAPE values will increase in kind, with values approaching 500 J/kg in the aforementioned areas. Effective wind shear during this time frame will be around 40 knots. Due to the very progressive nature of this storm system, the best chance of severe weather will be on Tuesday from early morning in the SW CWA through about mid-afternoon in the SE. SPC is currently outlooking a 15% chance of severe thunderstorms across our southernmost counties during this period. There is still the potential for the severe threat, however brief, to extend even farther to the N. Residents should continue to monitor the latest forecast updates in the coming days. Another feature of this storm system will be the rapid transport of deep moisture into the area. Precipitable water values are forecast to surge from around half an inch Monday afternoon to over 1.5 inches by early Tuesday morning, then drop back to a half inch by Tuesday evening. Although the period of heavy rainfall won't be particularly long-lived, there is the potential for locally heavy amounts in a fairly short period of time. The latest storm total QPF amounts with this system range from just over 2" over portions of NW GA to over 3" across the SE portion of the area wrapping back into the Atlanta metro area. Local amounts over 4" are also possible on the SE slopes of the mountains of NE GA due to orographic effects. Area rainfall amounts will bring the potential for at least localized flooding. As this storm system rapidly departs, wrap-around moisture and colder air will lead to some light snow showers or a rain/snow mix Tuesday night across portions of N GA, but accumulating snow is not expected at this time. /SEC && .AVIATION... (18Z TAFS) Issued at 1224 PM EST Fri Jan 5 2024 The remainder of the afternoon should be VFR with MVFR cigs moving in after 00Z with some very light precip. Cigs and vsbys will deteriorate as widespread rainfall moves into the area around 05-06Z. Winds will also be out of the east with sustained speeds between 10-15kt. Some gusts in the low 20kt are possible. Cigs look to remain IFR/LIFR through the late morning/early afternoon. //ATL Confidence...18Z Update... Med confidence all elements. NListemaa && .PRELIMINARY POINT TEMPS/POPS... Athens 35 49 40 54 / 90 90 10 0 Atlanta 38 51 42 52 / 90 70 10 0 Blairsville 31 47 35 45 / 90 80 20 0 Cartersville 36 50 38 51 / 90 80 10 0 Columbus 48 61 43 57 / 90 40 0 0 Gainesville 34 47 40 50 / 90 80 10 0 Macon 45 62 42 58 / 100 50 10 0 Rome 36 50 37 53 / 90 70 20 0 Peachtree City 39 54 40 53 / 90 60 10 0 Vidalia 49 70 45 60 / 100 60 10 0 && .FFC WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 11 PM this evening to 8 AM EST Saturday for GAZ006>009-014>016. && $$ SHORT TERM...NListemaa LONG TERM....SEC AVIATION...NListemaa