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FXUS62 KFFC 180814 AFDFFC

Area Forecast Discussion National Weather Service Peachtree City GA 414 AM EDT Sat May 18 2024


Morning Area Forecast Discussion

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
(06Z TAFS)
Issued at 144 AM EDT Sat May 18 2024

Ceilings are primarily MVFR across north and central Georgia, and gradually lowering. Ceilings are forecast to lower to mainly IFR in the next couple of hours, although a drop to LIFR is looking less likely than the previous forecast. Scattered -SHRA is spreading into west and central Georgia, and is expected to increase in coverage and spread north during the early morning hours. As a cold front 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 PROB30 for TSRA has been maintained for the northern TAF sites as a result. Winds will be S to SW at 5 kts through the early morning hours, becoming SW at 5-8 kts by 13Z and through the remainder of the day.

//ATL Confidence
06Z Update
Medium confidence on all elements.

King

PRELIMINARY POINT TEMPS/POPS
Athens 79 63 78 59 / 50 30 50 10 Atlanta 79 64 79 62 / 60 40 50 10 Blairsville 75 59 75 57 / 60 50 60 10 Cartersville 78 62 80 60 / 60 50 40 0 Columbus 79 65 83 64 / 60 30 40 10 Gainesville 77 63 78 61 / 60 40 50 10 Macon 79 65 80 62 / 60 30 50 10 Rome 79 61 83 61 / 70 50 30 0 Peachtree City 80 64 80 61 / 50 40 50 10 Vidalia 81 68 81 64 / 70 40 70 20

FFC WATCHES/WARNINGS/ADVISORIES
None.

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