959 FXUS63 KIND 160628 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 228 AM EDT Thu May 16 2024 .KEY MESSAGES... - Patchy to areas of fog through daybreak again and possibly again tonight. - Rain and storm chances return at times late today through Saturday. - Above normal temperatures this weekend through the middle of next week. - Increasing threat for strong to severe storms by Tuesday and Wednesday next week. && .MESOSCALE UPDATE... Issued at 228 AM EDT Thu May 16 2024 Latest observations show RH values nearing 100 percent across much of central Indiana with pockets of non-dense fog forming across the northeastern portions of the forecast area where clouds cleared earlier this evening. Cloud cover over the last hour has cleared further to the southwest with the expectation that patchy to areas of fog will spread across much if not all of central Indiana towards daybreak. The main question will be whether fog can become dense with only a weak near surface inversion and lack of subsidence limiting the threat for widespread dense fog. Will continue to monitor the observational trends and may need to introduce a brief Dense Fog Advisory in the coming hours if the visibility drop becomes more widespread and intense compared to current expectations. && .SHORT TERM (Today and tonight)... Issued at 228 AM EDT Thu May 16 2024 Today. Any morning fog will quickly begin to dissipate as daytime heating increases the dewpoint depression and erodes the fog. Conditions then look dry and quiet through much of the day before the next broad trough brings a return to rain late this evening into the early overnight hours. Models are struggling to get a handle on the mesoscale forcing of the system with a fairly wide spread on areas of heavier precipitation leading to a lower confidence in location for showers and a few rumbles of thunder after 22Z. A front will push towards the area but is expected to become gradually more diffuse as it pushes through Illinois and races out ahead of the better forcing associated with the parent low pressure system in the Dakotas. This will further help to limit shower coverage into the evening along with keeping the thunder potential to a minimum. Temperatures will be a bit warmer today with the periods of clear skies through the early afternoon which will allow for highs to climb into the mid to upper 70s. Tonight. Clouds and scattered showers will likely stick around for much of the night tonight with model soundings showing persistent saturation at the top of the boundary layer, but will have to keep an eye out for any locations that do begin to clear as the recent rains will help to supersaturate the low levels and may allow for some fog formation, especially across northwest Indiana where rain to be less in coverage. Further to the southeast, clouds and occasional rain should help to limit the fog formation with less efficient radiational cooling even as winds drop to near calm. These thoughts are backed up by the HREF probabilities for MVFR to IFR fog generally remaining under 10 percent outside of the Lafayette area and closer to Chicago where probabilities are closer to 50 percent. Lows tonight will only drop into the low 60s with the higher expected dewpoints tonight compared to the previous night. && .LONG TERM (Friday through Wednesday)... Issued at 228 AM EDT Thu May 16 2024 Progressive pattern aloft will continue into the weekend with the potential for another round of rain and storms Friday into early Saturday as a weak upper wave passes through the Ohio and Tennessee Valleys. Ridging develops over the Ohio Valley by Sunday as a split level upper level flow develops in response to an expanding trough over the western states. This will transition into a more amplified regime for next week with multiple waves kicking out of the upper trough and across the Midwest...increasing the risks for more robust convection and severe weather by Tuesday and Wednesday next week. Friday through Sunday Night The focus will be on the positively tilted upper wave tracking from the southern Plains Friday morning into the upper Ohio Valley by late Saturday. Trends have started to shift the focus of the most widespread rainfall south closer to the Ohio River and points south. The main reason for this shift is the expected development and track of a convective cluster through the lower Mississippi Valley late tonight into Friday which is likely to mitigate some of the deeper moisture transport as far north as central Indiana. The strong low level jet dynamics that had been showing up as well the last few days by late Friday have also been displaced to the south. The catalyst in the secondary wave of rainfall for late Friday into Saturday morning is a weak surface wave tracking through the Tennessee Valley. The greatest coverage to rain and convection will now focus across the southern half of the forecast area with the bullseye of deepest forcing aloft and moisture suggesting heaviest rainfall will set up across Kentucky. Locally heavy rainfall and higher rates within convective cells remain a possibility but should be more scattered in nature across southern Indiana. These trends have lowered the overall flood concerns for Friday afternoon into Saturday locally at this time...but any fluctuation back north would bring the swath of heaviest rainfall north of the Ohio River and could potentially bring concerns back into play for southern counties. The remnant upper wave will be drifting across the lower Ohio and Tennessee Valleys Saturday...with enough moisture and instability available across the region to produce scattered convection on Saturday...peaking during peak heating in the afternoon. The upper wave will move east of the area Saturday night with ridging aloft quickly expanding into the region. With the addition of surface high pressure by Sunday...expect warm and dry conditions across central Indiana to wrap up the weekend. Temperatures will remain seasonable through Saturday with highs mainly in the 70s. By Sunday with the influx of warm advection and ridging aloft...highs into the lower and mid 80s look reasonable. Monday through Wednesday With the transition to a more amplified upper level pattern across the country...ridging will remain the prominent feature over much of the eastern states to begin next week. An influx of moist...humid southerly flow on the back side of the surface ridge will maintain warmer temperatures across the region with mid and possibly upper 80s in play by Tuesday. The shift in the upper level pattern will also introduce a greater threat for more significant convection and severe weather across the region by Tuesday and perhaps extending out further into next week. As the western trough begins to shift east...waves will eject from the parent trough and move into the Plains...upper Midwest and eventually further east into the Great Lakes and Ohio Valley. Those waves aloft will interact with an increasingly moist and unstable airmass to generate increasing risks for convective clusters and a heightened potential for severe weather...with Tuesday highlighted as a cold front approaches the region. The active and stormy pattern may extend into Wednesday as the front pushes through the area...with potential for more storms by later next week as the front returns north into the region. Highs will dip back into the mid and upper 70s midweek as the front passes through. && .AVIATION (06Z TAF Issuance)... Issued at 1254 AM EDT Thu May 16 2024 Impacts: - IFR vsbys due to FG from 10Z to 13Z. - RA returns after 20Z, MVFR cigs towards 06Z. Discussion: MVFR to IFR vsbys are expected towards daybreak with current observations showing some lowered vsbys already across outlying areas. Fog may be brief, but confidence is too low to go lower than 1SM at this time. Daytime heating will bring a quick end to the fog with quiet weather and VFR conditions through much of the day. Rain is likely to return this evening into tonight with highest coverage after 06Z so will keep just a VCSH mention for now before that point. Winds will generally remain less than 10kts with a general southerly direction through the TAF period. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ MESOSCALE...White SHORT TERM...White LONG TERM...Ryan AVIATION...White