Wednesday, May 8

NorthGeorgiaWX · May 8

Good Wednesday morning!
We are going to have a very active day today and tomorrow weather-wise, so everyone will need to have a method of receiving severe weather alerts. Our severe weather threat will be conditional and complex, so we'll need to watch the evolution as the day progresses.

The southeast is in the warm sector this morning, with dew points in the upper 60's across north Georgia, and in the 70's to our west. Those dew points are just fuel for the fire. Combine that with very steep lapse rates, and you end up with severe weather conditions later this evening and into tomorrow, with all modes of severe weather possible. Due to the very cold upper levels, very large hail is possible, as well as high winds, tornadoes and heavy rain.

The forecast for today and tomorrow is conditional on what happens to our west today, so let's take a look at our setup. Since the Storm Prediction Center takes the lead with events like these, here is their description of what is going on.
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A very moist and unstable warm sector will already be in place this morning across parts of OK/TX, and eastward along/south of a warm front into the mid Mississippi, lower Ohio, and Tennessee Valleys. Strong to extreme instability (aided by a plume of midlevel lapse rates spreading eastward from the Plains) and moderate to strong deep-layer shear will support a potentially volatile severe thunderstorm environment through the day into the evening.

Initial storm development is expected near/north of the warm front from southeast KS into southwest MO, which may already be underway at 12Z (8am) with a threat of hail and localized severe gusts. The early convection will play a major role in the evolution of downstream severe potential through the day, with some potential for a MCS to develop and move east-southeastward. Should this occur, a swath of damaging wind could spread toward the TN and lower OH Valleys, along with a threat for line-embedded tornadoes and some hail. If morning convection does not evolve into an MCS, then there may be a somewhat greater potential for supercell development during the afternoon, though an eventual evolution into multiple intense storm clusters is expected with time, with an attendant threat of large to very large hail and damaging winds (with at least isolated gusts in excess of 75 mph possible).

Within a seasonably deep upper-level trough, one embedded mid/upper low is forecast to move eastward from the north-central Plains into the upper MS Valley, while another mid/upper-level low is forecast to develop within the trailing portion of the upper trough across the Great Basin. To the south of the Great Plains mid level low, an embedded shortwave trough and attendant jet maximum will move from the central Plains toward the mid Mississippi Valley. Farther northeast, a shortwave trough and attendant surface low will move from the upper Great Lakes region into the Northeast. A complex but potentially significant severe weather episode still appears possible over a broad region from the ArkLaTex vicinity into parts of the mid MS/OH/TN Valleys. All severe hazards will be possible, with some threat for strong tornadoes, very large to giant hail, and swaths of damaging wind.
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"Challenging" is the word that the Atlanta NWS office uses to describe the severe forecast for today. Our severe weather potential is at the mercy of what happens to our west and north today.
Let's look at what the NWS thinks for us:
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TODAY through THURSDAY
"Since most of the convection during the short term period is dependent upon upstream activity and any development of an MCS, the forecast will be very challenging. The models have been fairly consistent from run to run showing an MCS dropping southeast from the TN Valley late Wednesday/early Thursday morning. However, not quite sure the hi-res models have a great handle on the evolution of this system. The HRRR has a couple of distinct waves of convection, with one of them the MCS in question. The waves of convection are fairly close together and an earlier system could definitely impact the evolution of a later system. The first system could move SE across northern portions of the state Wednesday evening and into the overnight hours. A secondary wave of convection is progged to approach northern portions of the state early Thursday morning, near 12Z (8am)...potentially the main MCS. This system moves southeast across much of the CWA during the day. The evolution of this system is VERY dependent upon any earlier convection.

If the evening/overnight tonight wave holds together and does impact portions of north/northeast GA, this area could get worked over fairly well before the main MCS moves through. However, if the wave doesn't hold together, northeast portions of the CWA will have the same potential for severe weather that the remainder of the CWA will have when the main MCS is forecast to move through. Do think the potential for hazardous weather will be greater with the main MCS that begins to move through early Thursday morning and continues southward through the day.

All of the parameters will be there for severe thunderstorms with any waves/MCS that impact the CWA overnight and early Thursday. There will be plenty of moisture, forcing, shear and instability. Mid level lapse rates are impressively steep. The primary hazards for severe thunderstorms haven't changed from previous days, but timing will be somewhat difficult to nail down until these systems actually develop and are able to sustain themselves.

Generally, I think the best chances for more widespread storms/severe will be with the main MCS push. Any activity that develops ahead of the main MCS will also have the potential to become severe, but maybe not have the potential to be as widespread. Damaging wind gusts and large hail will be the primary hazards. There will also be potential for tornadoes. Locally heavy rainfall is a given."

THURSDAY NIGHT/FRIDAY
"A cold front will be situated across north Georgia at the start of the period Thursday night. There may be some ongoing convection within the area during this time, dependent on how development trends evolve Thursday afternoon. The focus for later Thursday night into Friday morning will then turn to the potential for an MCS that could approach from the west. A shortwave will initiate convection across east Texas into Louisiana which may congeal into a convective complex and race eastward Thursday evening through early Friday morning as supported by much model guidance. Still, uncertainty remains regarding this scenario as well as the track of said convective complex if it occurs; however, SBCAPE and bulk shear parameters would be supportive of a damaging wind threat if this scenario manifests. The areas most likely to experience impacts in this case would likely be our Middle Georgia counties and points southward to the Gulf Coast."