Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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634 FXUS63 KLMK 010606 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 206 AM EDT Sat Jun 1 2024 ...Updated Aviation Discussion... .KEY MESSAGES... * Rain and storm chances return for the weekend and continue into next week. Temperatures and dewpoints will also be on a steady increase into next week. && .UPDATE... Issued at 914 PM EDT Fri May 31 2024 Still on track for mostly dry conditions overnight even as high pressure retreats to the east. Cirrus shield is overspreading the Lower Ohio Valley at this time, but the precip shield associated with the approaching trof is well back in Missouri, extending SSE into the Lower Mississippi Valley. Expect rain showers to advance NE through the night, possibly spreading into south-central Kentucky just before daybreak. Think it may be a sharper and slower-moving leading edge than previously advertised, so it could take much of the day for precip to spread from Bowling Green to Lexington. Still expect it to happen eventually, so the main adjustments to this forecast are the hourly precip timing on Saturday. && .SHORT TERM /THROUGH THIS AFTERNOON/... Issued at 323 PM EDT Fri May 31 2024 High pressure over the central Appalachians will keep our weather generally quiet and dry for most tonight. A small area of weak low pressure moving eastward out of the Ozarks may introduce showers well after midnight west of I-65, but any showers would be scattered and very light. Low temperatures by sunrise will vary widely from the lower 50s in the Blue Grass closer to the high...to the lower 60s in southwestern portions of central Kentucky closer to the low and under thicker, more widespread cloud cover. On Saturday a 500mb shortwave trough will slowly move into the Ohio Valley from the west. Precipitable water values will be only slightly above normal, and afternoon dew points should only be from the mid 50s in eastern sections of central Kentucky to low 60s west. In addition, instability will be very weak. So, we`re expecting primarily showers with perhaps a few embedded rumbles of thunder. High temperatures should be in the middle to possibly upper 70s, depending on how widespread the clouds and showers are. && .LONG TERM /TONIGHT THROUGH FRIDAY/... Issued at 323 PM EDT Fri May 31 2024 Synopsis...The medium-range forecast will see a return of warmer and wetter conditions than the past several days. The period will start off with a weak, mid-level shortwave trough and attendant surface low moving across the Lower Ohio Valley while the formerly-placed upper ridge and surface high pressure weaken and relocate to the Eastern Seaboard. This will lead to scattered showers and isolated storms the second half of the weekend. For next week, attention turns to a powerful, northern-stream trough approaching from the Pacific Northwest accompanied by a large upper-level anticyclone on its southern flank. The anticyclone is eventually expected to stall and build from Texas to the Northern Rockies, allowing the trough to amplify and potentially close off over the Great Lakes vicinity with broad cyclonic circulation covering portions of the Eastern CONUS. At the surface, main low will occlude as it meanders over the Upper Midwest and southern Canada pushing a cold front to the Ohio Valley on Wednesday that will enhance regional storm chances. Model Evaluation/Confidence...Deterministic models agree fairly well on the large-scale pattern evolution through Monday with usual uncertainties regarding the mesoscale environment and its interaction with smaller wave energy. The latter will play a role defining onset and ending times of rain chances as well as best storm coverage. On the other hand, model confidence decreases on Tuesday and onwards regarding the progression and downstream amplification of the powerful, northern-stream trough while questions still remain with the strength of the blocking ridge to the west. Overall, the consulted deterministic guidance (GFS/ECMWF/CMC) show the amplifying wave over the Great Lakes but the Canadian remains on the faster and weaker end of the spectrum as it closes off and ejects the upper low quicker than the rest of the guidance. On the other hand, the GFS and ECWMF offer similar solutions with a slower and stronger trend during the last several runs. Last but not least, ML-based guidance is hinting at low chances of severe weather next Wednesday with the frontal passage; however, low confidence is placed in any severe weather based on current model variability. Sat Night - Sunday...Presence of weak, mid-level shortwave trough and attendant surface low will provide sufficient synoptic/mesoscale forcing to increase precipitation chances, especially Saturday night and Sunday morning when a modest 850-mb jet enhances moisture advection over the region and the profile saturates. Most of the shower activity appears to be stratiform with some embedded messy convective elements, judging by poor mid-level lapse rates, stable surface to 850-mb layer, and weak deep-layer shear. Severe weather is not anticipated at the moment. In addition, areal and river flooding concerns are low during the weekend as 48-hr rainfall is progged to be around an inch and soils have been able to dry during the past several days. That being said, some ponding and minor flooding issues could arise if convective training occurs. Best storm chances might be present Sunday midmorning and afternoon over south-central KY where potential instability and better mid-level lapse rates should promote stronger updrafts. Drier airmass will arrive Sunday evening. Monday - Wednesday...Still expecting warmer temperatures and increased humidity given theta-e advection amid southerly low-level winds. Brief and weak southern-stream vort waves will provide intermittent sources of lift during Monday and Tuesday to maintain daily rain chances in the forecast. As mentioned above, there is lower confidence in timing and coverage of precipitation and storm chances early in the week, even though the late afternoon and early evening periods are favored considering lack of strong lifting mechanisms and generally weak steering currents. Some of the diurnal convective activity could become strong Tuesday afternoon based on GFS forecast soundings showing strong moderately high SB-CAPE and steep mid-level lapse rates. As a result, if updrafts are able to overcome the low-level cap, the pulse convection cannot be ruled out. For Wednesday, strong to potentially severe storms appear possible as the cold front moves through the region, but there is still too much uncertainty to place sufficient confidence in this scenario. Thursday - Weekend...Very low confidence in weather elements during the period as model uncertainty increases substantially. All in all, forecast indicates slow lowering trend in rain chances towards the weekend with slightly cooler temperatures. && .AVIATION /06Z TAFS THROUGH 12Z SUNDAY/... Issued at 205 AM EDT Sat Jun 1 2024 Things are quiet across the TAF sites at this hour, with light right still off to the SW of BWG HNB. Seeing some high clouds and light ESE to SE winds early this morning, before lower ceilings and widespread rainfall move into our SW later this morning. Showers and a few thunderstorms then overspread the rest of the area through the day. Handled any Thunderstorm chances with Prob30 groups, but did prevail the rainfall as it is expected to be widespread. Surface winds veer to the S and strengthen around sunrise, and then gust up around 20-25 mph by late morning/midday through the afternoon. Ceilings are expected to lower to at least low MVFR with the widespread rainfall, and then linger around the low MVFR/IFR threshold toward the end of this TAF cycle. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ UPDATE...RAS SHORT TERM...13 LONG TERM...ALL AVIATION...BJS