####018010326#### FXUS62 KGSP 161840 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 240 PM EDT Fri May 16 2025 .SYNOPSIS... Very warm and humid conditions remain in place through tonight as a cold front sends a line of showers and thunderstorms across the area late tonight into Saturday morning. The front stalls in the vicinity of the area Saturday through early next week, keeping a relatively active pattern in place. && .NEAR TERM /THROUGH SATURDAY/... Key Messages: 1) Severe Thunderstorm Watch remains in effect for the NW corner of the CWA through 22Z/6 PM. 2) A line of strong-to-severe thunderstorms is expected to impact the mountains late tonight, with the threat decreasing eastward. 3) Temps around 10 degrees above normal. As of 145 pm EDT Friday: Latest regional mesoanalysis depicts a moderate-to-strongly unstable, but capped air mass across our forecast area this afternoon. Meanwhile, extensive cirrus shield associated with upstream convection has also hindered heating somewhat and acted to suppress cumulus development across our area. The cap does weaken a bit toward the NW, and a Severe Thunderstorm Watch remains in effect for the northwest corner of the CWA. Having said that, regional radar imagery is probably depicting the location of the cap quite well, as cold pool associated with ongoing strong/ severe convection that has been moving E/NE across southern/ eastern Kentucky has struggled to initiate new cells into northeast TN. As such, this convection is forecast to pass comfortably north of our area through mid- afternoon. We will continue to advertise small PoPs north of I-40 late this afternoon into the evening, but the latest convection-allowing models have trended toward the idea of the cap holding through this evening...even across the northern areas. IF any deep convection is able to initiate in our area, shear parameters are more than adequate for supercells and attendant threats of very large hail, damaging downbursts, and possibly an isolated tornado. The next round of strong-to-severe convection is expected to begin organize ahead of a cold front within a very unstable and strongly sheared environment across the western Ohio and Tennessee Valleys late this afternoon and evening. All guidance sources generally agree that convection will congeal along a larger scale cold pool across TN/KY by late evening and accelerate toward the southern Appalachians, likely reaching western NC between midnight and 3 AM, bringing the potential for widespread strong-to-damaging wind gusts...especially the counties bordering TN. However, convection will likely weaken/become less organized as the complex terrain disrupts the cold pool/shear balance. The big question then becomes whether convection can reorganize along the cold pool as it moves off the high terrain into the foothills and Piedmont during the pre-dawn hours. The environment east of the mountains is expected to remain largely capped...arguing against the potential for reorganization. Additionally, shear parameters are strong...and studies have shown that strong shear cam actually be detrimental for regeneration along a terrain-crossing cold pool. Nevertheless, there's more than enough uncertainty to advertise chance PoPs east of the mountains. While the main severe wx threat overnight will be from damaging wind gusts...low level shear will be adequate for brief spin-ups, mainly across the TN border counties. The cold pool will effectively push a frontal boundary through the CWA Saturday morning, leaving behind lower theta-E air (mainly manifest as lower surface dewpoints). As such, forecast soundings during the daylight hours feature much weaker instability, and CAMs develop little in the way of diurnal convection. Therefore, after some lingering token small morning PoPs, chances drop to less than 20% across most of the area during the afternoon. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... As of 130 PM EDT Friday: Most of the model guidance are in agreement with the synoptic frontal boundary completing a full fropa across the CFWA and stalling south of the I-20 corridor by Saturday evening as the vertically stacked parent low sets up shop over the northeastern CONUS. The frontal boundary will be draped from the Southern Plains through the Lower MS Valley and Deep South Saturday night as the cold front becomes reactivated when convection initiates over the Southern Plains and Ozarks Saturday evening before becoming clustered and translating east. The flow aloft becomes more progressive Sunday into Monday as a digging upper low over the western CONUS carves out a ridge over the central CONUS, while orientating the flow from the northwest to southeast across the CFWA. Early Sunday morning, the flow aloft won't be fully established, but a potential decaying MCS could make a run at the southwest mountains and Savannah River Valley. Model guidance differ with the overall evolution, with the ECMWF/CMC indicating very little SBCAPE, while the NAM/GFS show a couple hundred J/kg of SBCAPE as it slips towards the area. Kept some mentionable PoPs in this region of the CFWA as a result, while any convective debris could alter afternoon highs on Sunday, but warm thicknesses and slightly lower dewpoints (upper 50s-lower 60s) will help afternoon highs top out ~5 degrees above normal. Deep layer northwesterly flow becomes better established later Sunday as the upper ridge axis gradually shifts over the MS Valley, while an upper low churns over the western CONUS and the other upper low meanders over New England, creating an Omega-like blocking pattern. In this case, drier air will filter into the area, but convective initiation on the leeside of the western upper low and dryline across the Plains will create an assembly line for the activity to grow upscale and make a couple of MCS runs towards the CFWA during the early part of next week with the first MCS possibly tracking towards the area sometime on Monday. Confidence is low on the exact timing and placement of the MCS, but the synoptic setup is favorable and will likely throw a monkey wrench into the temperature and PoP forecast with the associated QPF response and convective debris. However, higher heights build into the area by early next week and should keep temperatures on track to rise a category or so above normal outside of the monkey wrench. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... As of 230 PM EDT Friday: The upper ridge gradually shifts further east towards the eastern-third of the CONUS, while breaking down as the upper low over the western CONUS gets pushed from behind as a Pacific Northwest jet punches in. This will disorientate the northwesterly regime, but guidance try to send one more MCS towards the region late Monday into Tuesday, but will likely hit the northern tier of the CFWA this time around or miss to the north altogether. Diffluent flow aloft becomes better establish later Tuesday into Wednesday as the ridge continues to slide eastward and the upper low deepens into a closed low, which eventually becomes established across the Great Lakes region. Expect an increase in deep layer shear as a result, which will coincide with daily diurnal instability to help instigate strong to severe storms ahead of an encroaching frontal boundary. Model guidance also show a potent shortwave rounding the base of the closed low Wednesday into early Thursday to help the frontal boundary advance eastward and complete a fropa sometime during the first half of Thursday. Drier air is expected behind the front as broad cyclonic flow aloft remains in place and low-level CAA filters in with weak high pressure, setting the stage for a post-frontal regime by the latter half of the forecast period. Northwesterly flow will commence and could produce a few orographically enhanced showers along the TN border. Continued northwesterly flow pattern remains in place through the end of the forecast period and could make the area vulnerable to another favorable MCS pattern, but likely to become more set and stone after D7. Temperatures will be at or slightly above normal Tuesday and Wednesday, before the post-frontal regime allows temperatures to fall a category or so below normal Thursday and Friday. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... At KCLT and elsewhere: VFR is forecast through the period. Isolated thunderstorms are possible late this afternoon near KHKY, but the probability of a storm in the vicinity is around 20%, and therefore not worthy of a TAF mention. A line of thunderstorms organizing over the TN/OH Valleys later this afternoon/evening is expected to begin weakening as it moves E/SE across east TN and western NC late this evening into the early part of the overnight. At this time, it is not clear whether this convection will hold together long enough to reach any of the TAF sites. Nevertheless, Prob30s for TSRA are warranted at most sites at some point between 06-12Z Saturday. Gusty winds are likely if the convection holds together. (Even if the convection doesn't hold together, remnant outflow boundary may still be capable of gusty winds.) Otherwise, S/SW winds are expected to increase to around 10 kts by this evening...generally persisting through tonight before increasing to 10-15 kts with higher gusts by early afternoon Sat. Outlook: The potential for mainly diurnal convection increases again Sunday, with chances continuing through the middle of next week. Early morning fog/low stratus will be possible, especially in the mountain valleys and in locations where appreciable rain fell the previous afternoon/evening. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...CAC NEAR TERM...JDL SHORT TERM...CAC LONG TERM...CAC AVIATION...JDL ####018011449#### FXUS63 KLMK 161843 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 243 PM EDT Fri May 16 2025 .KEY MESSAGES... * SIGNIFICANT SEVERE WEATHER OUTBREAK POSSIBLE LATE THIS AFTERNOON INTO THIS EVENING. * All severe weather hazards are on the table, including damaging winds, large hail, tornadoes, and torrential rainfall. A few strong tornadoes and instances of very large hail are possible. * Strong to severe thunderstorms are also possible this morning west of Interstate 65, with large hail as the main hazard. && .MESOSCALE... Issued at 243 PM EDT Fri May 16 2025 Cloud cover has quickly abated the LMK forecast area. With partly to mostly sunny skies, we have quickly warmed into the lower-middle 70s over in our east with mid-upper 70s in the I-65 corridor and points west. Lower 80s were noted generally west of I-165. GOES 19 meso imagery clearly shows a boundary from northern TN northwestward into western KY. The boundary is easy to see in the dewpoint data as south of the boundary dewpoints were in the lower 70s and to the north dewpoints were still in the middle 60s. In addition, the ample shear shows up nicely with horizontal convective roll clouds across much of western KY. For the next several hours, we'll continue to watch to see if storms will form along the aforementioned boundary. 18Z WoFS is rolling in and this run has ingested real-time radar/sat imagery for initialization purposes. Some early data from that suggests at least some isolated-scattered storms developing along the aforementioned boundary across southern KY in the next few hours. We're already seeing some showers down across Simpson/Allen/Barren counties at this time. && .UPDATE... Issued at 1123 AM EDT Fri May 16 2025 A large area of convection continues to push through central and eastern Kentucky this morning. This rainfall is being forced by strong warm advection along with lift associated with a southwest low-level jet axis. While the surface layer is pretty stable from nocturnal cooling, we do have an EML aloft with fairly steep low-mid level lapse rates. There was capping overnight until the cap mixed out due to nocturnal cooling and convection has taken off. Storms have been on/off severe this morning with mainly marginally severe hail being reported in the storms. Given the near surface stability, gusty winds have been observed on occasion, but nothing near severe levels. With PWATs well above 1.50 inches, we're seeing torrential rainfall with these storms as well. Going forward, main area of severe convection will be from roughly south of a line from Butler County northeast to Harrison County. In this area storms capable of torrential rainfall, and hail up to 1 inch in diameter in the strongest cores will be possible. A more concentrated wind threat may emerge with a small scale bow/MCS that is trying to take shape near Hopkinsville. This activity will surge eastward along the KY/TN border this morning. Have done a local extension of WW259 through noon EDT. We did cut off the northern area of that watch where additional severe weather is not anticipated. Rainfall amounts have been impressive with an inch to an inch and three quarters falling along a line from Mayfield northeast through the Elizabethtown area. We expect portions of the Bluegrass and southern KY to pickup on similar rainfall through the morning, most likely an inch to an inch and a half. Given recent rains from this morning and expected additional rainfall this afternoon/evening, have coordinated with JKL and hoisted a Flood Watch for the southern half/two-thirds of the LMK forecast area. As for the afternoon hours...Somewhat of a complicated forecast here as ongoing clouds and convection is likely to linger over central and eastern KY into the afternoon. Recent satellite imagery does show back edge of the clouds clearing the Paducah area and working eastward. The overall theme that we have been messaging seems to OK at the moment. That is, we expected additional thunderstorms to fire out across eastern MO/NE AR/W KY/S IL in the next few hours. Parameter space out that way will support discrete supercells with very large hail, damaging winds, and strong tornadoes (some long track possible). This activity will move eastward toward central KY while growing up scale into a large or a couple of MCS/QLCS's resulting in widespread damaging winds and spinup tornadoes within the line. The actual evolution of this afternoon/evening's activity remains the most challenging. It appears that a two pronged scenario could develop across the region. First, ongoing convection across southern KY may end up stalling out and leaving some sort of baroclinic boundary in place. As skies clear out, this boundary will become the focus for convective development this afternoon. It is possible that we could see isolated-scattered supercells develop along this boundary from roughly Paducah eastward to Bowling Green and toward Somerset. This boundary could then lift north/northeast into the evening hours. Parameter space across KY would support all modes of severe weather. However, given ongoing cloud cover and shorter time of insolation, not overly confident how unstable we could become. Meanwhile back to the west, expected supercell development should be ongoing while developing upscale into 1 or more lines. These QLCSs should then plow eastward resulting in damaging winds, spin up tornadoes within the line, along with some isolated-scattered large hail. This scenario has support from many of the 12Z CAMs though though the question is how far north could the baroclinic boundary lift prior to the QLCS coming in from the west. The HRRR is most aggressive with its northward movement taking it as far north as I- 64. On the other hand the WRF ARW/NSSL WRF and the RRFS all keep the boundary more over southern KY while plowing the QLCS out to the west eastward rather quickly. MPAS runs are not in yet, but will evaluate them early this afternoon. && .SHORT TERM /THROUGH TONIGHT/... Issued at 407 AM EDT Fri May 16 2025 A significant severe weather outbreak is possible later this afternoon and this evening across the Ohio Valley. Storms developing ahead of an incoming cold front will quickly become severe in a very unstable and strongly sheared environment. All severe weather hazards, including widespread damaging winds, very large hail, and strong tornadoes are possible, as well as localized flash flooding. Main bust potential hinges on the evolution of storms this morning, which have developed over western Kentucky. These storms will have a large hail threat of their own, especially west of Interstate 65. While they will at least temporarily stabilize the atmosphere, strong warm advection is likely to win out, allowing a fairly quick recovery this afternoon. With around 3000 J/kg of mixed-layer CAPE, 1000 J/kg of downdraft CAPE, and 60 kt of effective shear, initially discrete storms will organize into at least bowing segments. A few of the discrete cells could produce very large hail and/or strong tornadoes, and line segments could produce hurricane-force wind gusts. Spin-up tornadoes will also be in play with any of the bowing structures as well. The peak severe threat could be slightly delayed depending on how quickly the atmosphere can reload after morning convection, but the threat will mainly be focused on the evening hours. Initial discrete cells could develop in the late afternoon. It's also worth noting that in the late evening, the line will become more east-west oriented, opening the door for excessive rainfall especially over south-central Kentucky. Confidence in the exact placement is low at this time, but it bears watching as the event unfolds. Bottom line, significant severe weather is possible late this afternoon and this evening. Make sure you have multiple ways to receive warnings and a plan in place should a warning be issued! && .LONG TERM /SATURDAY THROUGH THURSDAY/... Issued at 352 PM EDT Thu May 15 2025 By Saturday morning, the actual cold front will be pushing through the area with most of the showers and storms exiting to our east. The associated upper low will be over the Great Lakes with the longwave trough axis extending south over the OH and TN Valleys before flattening out against the subtropical ridge over the Gulf. Weak CAA behind the front will result in climatological normal temperatures for the weekend with highs in the mid to upper 70s to lower 80s accompanied by breezy WSW winds on Saturday. Overall, most will experience a fair weather weekend. Southern KY will see a slight chance of showers on Sunday as the southern edge of the new airmass begins to lift northward due to the next low pressure system strengthening over the Central Plains. This will begin another period of unsettled weather as we enter the beginning of the new work week. By Monday, a warm front will begin lifting across the region resulting in warm and moist air advection, as PWATs surge into the upper percentiles of SPC's sounding climatology. Models tend to agree on convection from our west moving into our area by Monday morning with another round Monday evening. The warm front appears to stall over the region, prolonging our shower and storm chances into Tuesday and Wednesday before the occluded low pushes through on Wednesday. With model soundings advertising sufficient instability and ML guidance also showing enhanced severe probabilities, severe weather can not be ruled out. Details remain hazy this far out, but will continue to monitor closely with subsequent forecast packages. Stay tuned. && .AVIATION /18Z TAFS THROUGH 00Z SUNDAY/... Issued at 109 PM EDT Fri May 16 2025 Early morning convection is finally pushing to the east of the region. VFR conditions are expected this afternoon with a period of sun/clouds with gusty southwest winds. Next wave of vigorous storms is expected to arrive this evening. The overall convective evolution remains challenging as scattered supercells will be possible across central KY while a large squall line moving in from the west. For now, have largely updated the previous TAF to keep storms in the region beginning around 23Z with the bulk of it occurring between 16/23Z-17/05Z. Given the extensive squall line and expected wind field, have opted to use VRB25G50 in the TAF as the squall line passes through. Most convection should be east of the terminals by 17/06Z, with light SW winds and high cigs for Saturday morning. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...Flood Watch through late tonight for KYZ026>028-039>041- 045>049-053>057-061>067-070>078-081-082. IN...None. && $$ MESOSCALE....MJ UPDATE.......MJ SHORT TERM...RAS LONG TERM....CG AVIATION.....MJ