####018006344#### FXUS63 KLMK 160807 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 407 AM 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 336 AM EDT Fri May 16 2025 Boundary has lit up from the Shawnee National Forest in southern Illinois ENE to near Henderson, and storms tapped into strong elevated instability to produce vigorous cores aloft. Given the very unstable and strongly sheared environment, as storms continue to develop through early morning they will carry mainly a SVR hail threat from the Pennyrile into the Hoosier National Forest and sections of Kentucky west of Interstate 65. Damaging winds and even a tornado or two can't be ruled out completely, but storms will have a really difficult time becoming sfc based. Confidence is also slightly diminished south of the WK Parkway but we could see convection down toward BWG later in the morning. && .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 /06Z TAFS THROUGH 12Z SATURDAY/... Issued at 137 AM EDT Fri May 16 2025 Main challenge in this TAF set is timing and impacts of two different potential waves of convection. Low-confidence forecast overnight as hi-res models show new development after ~08Z. Consensus timing on a morning wave would be starting 10-12Z for the terminals but could easily be focused just in the north on SDF and LEX or just south in BWG. Will carry a period of SHRA for now without any significant restrictions in cig/vis. Gusty SSW winds through the afternoon, and then another wave of storms comes in starting around 00Z, mainly for SDF and LEX. Handled those with TEMPO for IFR vis and gusty winds in the stronger storms. The evening storms could produce significant severe wind gusts, but this will be modulated by the behavior of morning storms, so will not hit that too hard just yet. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ MESOSCALE...RAS SHORT TERM...RAS LONG TERM...CG AVIATION...RAS ####018006520#### FXUS61 KBTV 160807 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 407 AM EDT Fri May 16 2025 .SYNOPSIS... Warm and humid conditions will continue to support chances of showers and thunderstorms over the next several days. The greatest potential for precipitation will be late Friday and again on Saturday afternoon, with cooler conditions arriving on Sunday that will linger into the first half of next week. && .NEAR TERM /THROUGH SATURDAY/... As of 407 AM EDT Friday...An upper level low centered over the Great Lakes will continue to meander eastward, with several associated frontal boundaries and shortwaves moving through the region, bringing daily chances for showers and thunderstorms both today and Saturday. Patchy fog has developed across parts of the region this morning, but should quickly dissipate after sunrise. Daytime highs will continue to be warm, with another day of upper 70s and low 80s expected across the region. By the afternoon, conditions look to become more favorable for convective development, with CAPE values in excess of 500 J/kg across most of the region. Looking at model soundings, heavy rainfall and some slower-moving storms look to be the main concern this afternoon. Shower activity will wane Friday night, although a few lingering showers may be possible. Overnight lows will continue to be on the mild and muggy side, only dropping into the mid 50s and 60s. The showery and active pattern continues into Saturday with several rounds of showers and possible thunderstorms expected, with the first round of showers moving through in the early morning and then additional convection in the afternoon. There is still some uncertainty in regards to how Saturday plays out, especially given the multiple rounds of precipitation. The latest HREF guidance suggests that cloud cover may linger throughout much of the day Saturday, which may limit any convection for Saturday afternoon. If enough clearing is able to take place by the early afternoon, there could be enough instability for a few stronger to locally severe thunderstorms to develop, with SPC maintaining a Marginal Risk across the region for Saturday. With plenty of moisture available, any storms that do develop will likely feature heavy rainfall. Between both Friday and Saturday, rainfall amounts between 0.50 and 1.0 inches can be expected, with locally higher amounts possible within thunderstorms. WPC does have a Marginal Risk for excessive rainfall across the region for both Friday and Saturday given the potential for heavy rainfall and slower storm motions, but there are no flood concerns at this time. Temperatures during the Saturday will continue to be on the warm side, generally in the 70s to near 80 degrees. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... As of 407 AM EDT Friday...The second half of the weekend will feature a drastic shift as an upper low pivots directly over our forecast area. Remnants of Saturday's showers and thunderstorms will quickly exit to the east Saturday night, but any break in the precipitation will be fairly short lived. The upper low will swing down along or just south of the international border late Saturday night through Sunday, and expect a resurgence of showers in response. Winds will turn to the west and eventually northwest as the low moves to our east, ushering in a much colder airmass. Highs on Sunday will likely only be in the mid 50s to low 60s, with perhaps some places locations in the southern Champlain Valley/CT River Valley nudging into the mid 60s. Showers will become focused in the northern mountains by Sunday afternoon. Winds will be a touch gusty, but not overly so with gusts generally topping out around 25 mph. Showers will wane Sunday night as we lose daytime heating, though still expect at least scattered precipitation overnight. Lows will mainly be in the 40s, though the Adirondacks could dip into the upper 30s by early Monday. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 407 AM EDT Friday...The cool and showery weather will persist through at least Monday as we remain on the western periphery of the upper low. Highs on both Monday and Tuesday will be in the 50s, though some of the colder spots in the Adirondacks and east of the Green Mountains could well struggle to get out of the 40s, especially on Monday. The pattern becomes more uncertain thereafter, with guidance indicating a complex interplay between an upper shortwave digging into the Great Lakes/near Hudson Bay while another upper trough moving into the Midwest, perhaps phasing into a cutoff low somewhere over the eastern CONUS. The main theme is that shower chances will continue through much of the week, and temperatures will remain below normal. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... Through 06Z SATURDAY...VFR conditions are currently prevailing across the region at this hour, with calm or light terrain- driven winds. Despite the VFR conditions, patchy mist and fog developing across the region will bring some reduced visibilities, which continue through about 12Z with conditions rapidly improving after sunrise. Given the patchiness of the fog and uncertainty in persistence, TEMPO groups were utilized in the forecast. Once the fog dissipates towards 12Z, VFR conditions should prevail once again. Shower activity will increase throughout the afternoon, with some possible embedded thunderstorms, with some heavier showers possibly bringing reduced flight conditions at times. Winds will generally be southerly between 5 and 10 knots. Outlook... Saturday: Mainly VFR, with local MVFR possible. Definite SHRA, Slight chance TSRA. Saturday Night: Mainly VFR, with areas MVFR possible. Likely SHRA, Slight chance TSRA. Sunday: Mainly MVFR, with local IFR possible. Likely SHRA. Sunday Night: Mainly MVFR, with areas IFR possible. Chance SHRA. Monday: Mainly MVFR, with local IFR possible. Chance SHRA. Monday Night: Mainly MVFR, with local VFR possible. Slight chance SHRA. Tuesday: Mainly MVFR, with local VFR possible. Slight chance SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Kremer NEAR TERM...Kremer SHORT TERM...Hastings LONG TERM...Hastings AVIATION...Kremer ####018006002#### FXUS63 KDTX 160809 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 409 AM EDT Fri May 16 2025 .KEY MESSAGES... - Warm today with another round of showers and thunderstorms likely late this evening. Isolated storms may be strong to severe, mainly between 8 PM and 1 AM. Damaging winds and large hail are the main threats. - Cooler conditions this weekend, with westerly wind gusts 30 to 40 mph on Saturday. && .DISCUSSION... The cutoff upper low responsible for the early morning MCS continues to meander over the upper Midwest today. Sunny conditions are expected through the daylight hours as mid-level subsidence dominates in the wake of the morning convection. Deep southwesterly flow brings in a secondary warm sector with highs reaching the mid 80s. Strong daytime mixing will cause dew points to fall to the lower to mid 50s - offering a less humid feel compared to yesterday. Southerly wind becomes breezy to around 20 to 25 mph, eventually advecting in dew points back into the mid to upper 50s by the evening. Meanwhile, mid-level cooling commences late in the day as the upper trough begins to pivot into the central Great Lakes, allowing instability to build as 700-500mb lapse rates increase to around 8 C/km. Forcing is disorganized through the early evening hours suggesting little potential to overcome the resident cap near 700mb. After 00z, upper flow becomes increasingly unbalanced at the nose of a 90 kt jet streak as the trough takes on a negative tilt - providing better support for synoptic lift and convective initiation as a pre-frontal surface trough lifts northeast across the area. Given the timing near and after sunset, there remains uncertainty regarding whether the cap will erode and instability (~750 to 1000 J/kg MLCAPE) will become realized at the surface before storms move through. Bulk 0-6km wind shear of 40 to 50 kt is supportive of a broken line of strong to severe storms with damaging wind and large hail the main threats. Severe potential is highest between 8pm and 1am before the trough sweeps through, then lingering showers and sub- severe storms may persist into the morning hours as the cold front trails behind. Most areas will receive around or less than 0.25" of rain tonight, but localized areas may see up to around 1". The stacked low pressure system slowly advances into northern Lake Huron on Saturday with a much cooler air mass working in through the day. Highs reach the 60s as a tight pressure gradient produces gusty westerly winds to 30 to 40 mph. Moisture wrapping around the low and weak instability will bring a continued chance for light showers at times through the day. Mid-level ridging then begins to settle into the area Sunday into the early work week to favor surface high pressure with dry and cool conditions. The next period to watch will be Tuesday night into Thursday as a closed low tracks from the Midwest toward the Great Lakes and Ohio Valley. This will provide the next opportunity for showers and storms. && .MARINE... Southerly 15-20kt winds develop today following the passage of last night's warm front as the surface low tracks over Lake Superior. Stubborn areas of fog likely linger through at least the morning though with dewpoints falling, expectation is the decreasing humidity should allow for a gradual diminishing trend for the latter half of the day. Respectable cold front is set to sweep across the region late tonight supporting another round of showers and thunderstorms in advance. Set up is not as favorable compared to Thursday night with coverage likely limited to a broken line with any strong to severe embedded storms being more isolated in nature. Moderate west-southwest winds follow Saturday with the strongest winds (20-30kts) expected over the southern half of the region where the gradient is strongest. Small craft advisories are warranted for most if not all nearshore waters as a result. Low fully departs Sunday shifting winds to the northwest. Gusts peak near 20kts during the day before weakening overnight as weak high pressure slides overhead. && .PREV DISCUSSION... Issued at 1232 AM EDT Fri May 16 2025 AVIATION... Squall line producing very strong winds, large hail, isolated tornados, and persist downpours continues to work from west to east across the terminals tonight. Gusts in excess of 60 knots and at least one confirmed tornado have been reported upstream with this system. Trends continue to favor MVFR visibility reductions in the main rain band, with brief IFR reductions noted at MBS and FNT. Timing the exit is the main forecast concern for the next TAF cycle as the lingering back-edge will be slower to depart from DTW and DET near the very beginning of the TAF window. The line should fully clear east of all sites by 07Z. Post-frontal VFR conditions move in early Friday and throughout the day. Surface flow weakens, backing from southwest to southeast during the afternoon. Additional showers and storms possible late Friday evening. For DTW/D21 Convection... A decaying line of strong to severe thunderstorms crosses DTW during the 05-06Z time window. THRESHOLD PROBABILITIES... * Medium for ceiling 5000 feet or less toward midnight through sunrise the low through Friday. * High for thunderstorms tonight, mainly 05-06Z Friday, then low confidence after 00Z Saturday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...TF MARINE.......KDK AVIATION.....KGK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.