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FXUS62 KFFC 181440 AAB AFDFFC

Area Forecast Discussion...UPDATED National Weather Service Peachtree City GA 1040 AM EDT Sat May 18 2024

Morning Update

UPDATE
Issued at 1015 AM EDT Sat May 18 2024

The forecast is on track thus far this morning, so minimal edits have been made.

Water vapor satellite imagery and radar imagery depict a fetch of moisture and embedded convection stretching from south-central GA through the FL Panhandle to the northern Gulf. Strong to severe storms have generally remained south of the CWA thus far this morning, where MLCAPE is greatest, although a strong storm cannot be ruled out across our southern counties. Gusty winds and small hail would be the primary threats. Otherwise, moderate to heavy rainfall will persist across our southern counties for the next several hours as the moisture axis shifts to the south and east.

The shortwave/concentrated area of vorticity currently over the shared borders of AR/MS/TN will track eastward through the day, acting as an impetus for scattered to widespread convection across north GA and portions of central GA. The progression of scattering/clearing cloud cover will have a major influence on when/where convection initiates as the day goes on. See the below short term forecast discussion for information on the anticipated storm hazards today.

Martin



SHORT TERM
(Today through Sunday)
Issued at 411 AM EDT Sat May 18 2024

Much of the Southeast CONUS remains under enhanced southwesterly upper level flow ahead of a shortwave trough advancing into the Lower Mississippi River Valley region. Meanwhile, a strong upper level jet streak is present within the southwesterly flow aloft, which extends from the central Gulf Coast into the Appalachians.
Showers and thunderstorms have developed across portions of central and south Alabama and underneath the right-rear quadrant of this upper jet. These storms will advance eastward, and more convection will fire near remnant outflow from the MCS that decayed over south Georgia last night. As such, rain chances will steadily from southwest to northeast through the early morning hours, with likely PoPs forecast in portions of west-central Georgia and chance PoPs elsewhere across the forecast area this morning and into the early afternoon.

Low cloud ceilings and patchy are in place across much of the forecast area as the morning begins. Low temperatures and dewpoints will start the morning primarily in the mid 60s. With ample moisture the boundary layer, thunderstorms this morning will have MLCAPE values of as high as 1000-1500 J/kg to work with in portions of central Georgia. Furthermore, the influence of the jet streak will contribute to deep layer bulk shear values of 40-60 kts. 0-1 km shear values are also anticipated to range from 20-25 kts. These environmental parameters, along with the orientation of the aforementioned shear in association with the jet streak, will allow some thunderstorms to become organized into linear clusters capable of producing damaging wind gusts. This is anticipated to become more likely after sunrise, with diurnal heating leading to increasing surface-based instability.

Speaking of afternoon heating, broken to overcast cloud coverage is forecast to persist across the majority of the forecast area today. As such, high temperatures are expected to remain confined to the mid to upper 70s across the majority of the area. Still, with dewpoints increasing into the upper 60s by this afternoon, SBCAPE values are forecast to increase to 1500-2500 J/kg during the peak heating hours this afternoon. Later this afternoon, the axis of the shortwave will approach north Georgia, which will provide forcing for another round of showers and thunderstorms starting in the far northern tier. With similar shear profiles from this morning, and also mid-level lapse rates of 6.5-7 C/km, a few of these storms will also have the potential to become strong to severe, capable of producing damaging wind gusts and hail.
These storms are forecast to advance southward during the late afternoon and into the evening, at which point they will begin to diminish in coverage after sunset with the loss of diurnal heating.

A caveat to keep in mind is that the behavior and evolutions of this round of storms will depend on how the airmass recovers after storms earlier in the day. Furthermore, with precipitable water values expected to range from 1.5 to 1.8 inches, stronger storms that occur today are expected to be efficient rainmakers, which could cause localized flooding concerns where storms train over a common location. During the overnight hours, the trough axis itself will move southeastward through Georgia, with the best forcing and dynamics remaining ahead of the trough. By Sunday morning, the trough will begin to move offshore of the Georgia coast and into the Atlantic. The associated vorticity couplet will still be positioned over eastern Georgia. Combined with a weak moisture axis, this will result in showers once again on Sunday, with the highest coverage focused over the eastern portion of the forecast area. Lift in the vicinity of the trough axis, combined with diurnal instability, will be sufficient for the development of scattered thunderstorms among the showers on Sunday. At this time, severe weather is not expected on Sunday, although an isolated storm cannot be ruled out.

King



LONG TERM
(Sunday night through Friday)
Issued at 411 AM EDT Sat May 18 2024

Sunday evening, we should be seeing the end of our active and wet weather coming to an end as any remaining showers and thunderstorms should be tapering off. As the upper level trough and surface low push off the eastern seaboard, a ridge axis aloft will begin to orient itself along the spine of the Appalachians and a surface high will settle in along the lee of the mountains.
As the ridge axis shifts east to become established Monday, a few terrain induced afternoon showers and thunderstorms may fire across the northeast Georgia mountains. Otherwise, generally benign and dry weather conditions are expected outside of these location's. There's still model spread (~5 degrees) in the guidance over the maximum daytime temperature on Monday, particularly across eastern Georgia where temperatures will be moderated depending on how far southwest the extent of the wedge can become established and whether or not any afternoon storms can get going in the mountains. Temperatures Monday will be the coolest of the week with highs in the low to mid 80s for most locations outside of higher elevations. Temperatures will become more summer-like by Tuesday with highs in the mid 80s nearly areawide. A gradual warming trend will continue through the end of the forecast period into the upper 80s with some locations across southern central Georgia reaching the 90 degree mark. While the first half of the long term forecast will be largely dry, a low amplitude shortwave traversing the Plains will push a weak and diffuse boundary towards north Georgia, bringing the chance for rain back into the fold. Chance PoPs are introduced for north Georgia Wednesday where showers and a few thunderstorms will be possible. As the weak boundary sags south and becomes quasi- stationary, showers and thunderstorms will develop along the boundary across north and much of central Georgia as some weak disturbances in the quasi- zonal flow pass through. While no severe weather is expected at this time, instability around 500-1000 J/kg, steep midlevel lapse rates and modest shear could produce a few strong storms Thursday and Friday.

KAL



AVIATION
(12Z TAFS)
Issued at 730 AM EDT Sat May 18 2024

A round of showers and thunderstorms is ongoing roughly along and south of the I-85 corridor, warranting a TEMPO for TSRA from 12-14Z at MCN/CSG. Thunder is anticipated to stay mainly south of the northern TAF sites this morning. Ceilings as the morning begins have dropped to LIFR at the northern TAF sites, and is forecast to slowly lift to IFR by 13-14Z and to MVFR by 15-16Z. As an upper level disturbance advances towards north Georgia, it will send a broken line of organized SHRA/TSRA into north Georgia, which will work its way southward in the late afternoon and evening. A TEMPO for TSRA has been introduced at ATL from 21-01Z.
Winds are light to start the morning, primarily S to SW at 5 kts or less. Winds will increase to SW at 5-8 kts by 13-14Z and through much of the daytime today.

//ATL Confidence
12Z Update
Medium confidence on all elements.

King



PRELIMINARY POINT TEMPS/POPS
Athens 63 78 59 82 / 30 50 10 10 Atlanta 64 79 62 83 / 40 50 10 10 Blairsville 59 75 57 79 / 50 60 10 20 Cartersville 62 80 60 84 / 50 40 0 10 Columbus 65 83 64 84 / 30 40 10 10 Gainesville 63 78 61 81 / 40 50 10 10 Macon 65 80 62 83 / 30 50 10 10 Rome 61 83 61 85 / 50 30 0 10 Peachtree City 64 80 61 83 / 40 50 10 10 Vidalia 68 81 64 81 / 40 70 20 10

FFC WATCHES/WARNINGS/ADVISORIES
None.

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