Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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360 FXUS63 KIWX 171633 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 1233 PM EDT Fri May 17 2024 .KEY MESSAGES... - Some localized dense fog possible this morning, particularly across northwest Indiana. Patchy dense fog possible again tonight. - Isolated to scattered showers and thunderstorms possible this afternoon with some locally heavy downpours possible. - Warm conditions for this weekend into Tuesday. Highs Sunday through Tuesday into the lower to middle 80s. - A potential of more organized storms with some strong/severe potential late Tuesday, but still low confidence on timing and extent of severe threat. && .DISCUSSION... Issued at 352 AM EDT Fri May 17 2024 A couple of distinct areas of stronger forcing have materialized this morning. One mid level trough continues to lift northeast across east central Indiana and is associated with some weak isentropic upglide and weak convergence in 925-850 mb layer. These showers, with perhaps an isolated thunderstorm, should continue to overspread areas mainly along and south of the US 24 corridor across far NE Indiana/NW Ohio with this morning. Inspection of water vapor imagery this morning also depicts a sharper vort max progressing eastward across northwest Illinois which could play some factor in promoting additional isolated/scattered showers and storms this afternoon. In the meantime, other forecast challenge this morning deals with fog potential. Vertical moisture gradients do not appear to be extremely supportive of widespread dense fog scenario, with indications of more of a fog/stratus combination setup this morning. Some pockets of locally dense fog are possible across northwest Indiana in closer proximity to approaching weak sfc trough axis. Fog should dissipate after 12-13Z. This weak sfc trough and approaching short wave could provide a focus for isolated-scattered showers and thunderstorms again this afternoon, although exactly where this weak convergent axis sets up by this afternoon is of low confidence. Some weak onshore flow off Lake Michigan could sharpen this trough up enough for isolated late morning/afternoon shower/thunderstorm development. A secondary area of focus could be across southeast third of the area as large scale 925-850 mb flow is confluent in nature with large scale modest low level moisture convergence. Steering flow will be quite weak today, so any showers that do form will exhibit some slow storm motions and could produce some highly localized heavier rain amounts where they do occur. Isolated showers may hold on into this evening, but should exhibit a downward diurnal trend heading into the mid-late evening hours. Breaks in clouds in wake of departing NW IL wave this evening and high crossover temps should support some patchy fog development across most of the area tonight, with at least a potential of some pockets of dense fog early Saturday morning. For Saturday, precip chances somewhat difficult to resolve as weak upper level ridge should have some weak positive height tendencies across the Great Lakes. However, at the same time, a weak upper level short wave will be rippling through this ridge from the Mid MS Valley. Some residual weak convergent axis may also persist across southeast half of the area which could provide a focus for diurnally enhanced isolated shower/storm. Once again, weak steering flow will result in weak movements of any cells Saturday. Saturday will feature the beginning of a warming trend that will continue into early next week with highs in the low-mid 80s. For Sunday, a primarily dry day is expected, but recent trends may suggest a non-zero chance for an isolated afternoon shower. Warmer conditions Sunday should drive a weak lake breeze that may provide just enough low level convergence and pooled moisture along any lake breeze boundary for an isolated shower. Confidence is too low to include mentionable PoPs at this time, but perhaps something to look at going forward. Pattern should become more active heading into the Monday-Wednesday timeframe. A lead short wave is expected to eject out of the Central Plains Monday morning, reaching the western Great Lakes Monday evening. Guidance is struggling in agreement on the strength of this disturbance as it lifts northeast with some suspicion that GFS may be overdone on the strength due to some convective feedback issues. Some warm advection wing elevated convection appears to be a possibility Monday night, but shear profiles at this point will not be impressive with not much organization to any convection. It still appears as though the Tuesday into possibly Wednesday period will need to be watched for the greatest strong-severe potential, but confidence remains low. Some subtle dProg/dT trends noted in various guidance of slightly more disjointed mid/upper level forcing evolution and a bit more prolonged maintenance of stronger upper ridging across the Great Lakes into Tuesday. This could keep greatest convective coverage on Tuesday across far north, or into lower central Lower Michigan with warm frontal progression, with more widespread precip chances possibly holding off until late Tuesday night in this slightly slower trend. Given these trends are recent, would like to see a little more run to run consistency before major changes to blended PoPs. However, it is possible PoPs may need to tempered for portions of the area Tuesday afternoon into Tuesday evening. Strong/severe potential will hinge largely on timing of this forcing with perhaps greater potential just upstream of the local area. Shower and storm chances persist Wednesday as lagging upper forcing is expected to track across the Ohio Valley. A trend to slightly cooler and drier conditions is expected for end of this period, but overall pattern heading into next weekend may remain active as medium range models continue to hint at progressive eastern Pacific waves affecting central CONUS. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1233 PM EDT Fri May 17 2024 Lingering MVFR to low VFR stratocu should mix out to all VFR by or shortly after issuance. CU may become agitated enough to generate isolated convection mid afternoon through early evening given growing buoyancy near a lake breeze and washed out frontal boundary. Point chances are low (20%), so opted not to include a vicinity shower mention in the TAFS. Fog/stratus then once again becomes a concern early Saturday morning given ample near sfc moisture, light/variable winds, and temps falling below xover values. Opted to hold with a IFR mention in the 08-13z window to account for this potential. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...None. OH...None. MI...None. MARINE...None. && $$ DISCUSSION...Marsili AVIATION...Steinwedel