Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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014 FXUS63 KIND 241056 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 656 AM EDT Fri May 24 2024 .KEY MESSAGES... - Isolated thunderstorms possible this afternoon with more widespread coverage this evening/overnight. A few storms may be severe with strong gusty winds. - Showers and thunderstorms likely on Sunday. Severe thunderstorms are possible. - Temperatures will return to near normal next week && .SHORT TERM (Today and tonight)... Issued at 305 AM EDT Fri May 24 2024 Mostly quiet weather conditions are expected for much of the day with ridging centered over the Ohio Valley. At the surface, weak high pressure is aiding in optimal conditions for fog development with mostly clear skies and light winds. Look for any patchy fog to quickly mix out after sunrise. Increasing southerly flow ahead of an approaching system will lead to warmer temperatures in the mid 80s. While much of the day should remain quiet, increasing moisture could support isolated diurnal thunderstorms across W/SW portions of central IN. Forecast soundings show weak deep-layer shear in the afternoon, thus severe weather is not expected. More widespread convection is likely during the evening/overnight hours as most CAMs show an MCS across eastern Nebraska propagating towards the Great Lakes Region. The main portion of this MCS may stay to the north of the area, but low-level convergence along the front will be sufficient to allow for scattered thunderstorm development in a very unstable airmass across IL. New convective development should then grow upscale as it progresses eastward. CAMs are still not in great agreement regarding timing of the storm complex moving into the area. In addition, there remains uncertainty in convective organization. The main reason for this being that effective bulk shear will be relatively weak as the line of storms outpaces the stronger mid-level flow over IL/WI. However, the favorable thermodynamic environment combined with weak but sufficient deep-layer shear for loosely organized storms supports an isolated damaging wind gust threat. Locally heavy rainfall is also possible. The convective evolution of this system across IL will be monitored closely later today as there is still a chance for a more organized MCS to develop. Given the latest trends in CAMs having a weaker MCS/cold pool, the timing of best rain chances appears to be this late this evening into tonight. A stronger cold pool would lead to a sooner arrival of precipitation so this may need to be updated in future updates. Expect temperatures generally in the upper 50s to low 60s overnight. && .LONG TERM (Saturday through Thursday)... Issued at 305 AM EDT Fri May 24 2024 The main concern for the long term will be the potential for a severe weather outbreak including all severe weather types and heavy rain and localized flooding Sunday and Sunday night. Saturday through Sunday night... The long term will start off less ominous with a cold front sweeping east into eastern Indiana by daybreak Saturday. Behind this front, ridging will build in late in the day and night which will bring a brief respite to the convection over western sections and all of central Indiana Saturday afternoon and into the night. However, a Northern Plains trough will dig southeast and spin up a surface low that will lift northeast across the Missouri Valley Sunday and into the western Great Lakes Sunday night. An associated warm front will lift northeast across central Indiana Sunday morning and a cold front will then sweep east across the area Sunday night. Upstream storms, potentially in the form of an MCS will likely move through Sunday morning near the warm front and then re-development will likely occur Sunday afternoon and night in the warm sector, along and ahead of the quickly advancing cold front. Exact timing is still too difficult to pinpoint all the way out to Sunday but what is known is the combination of a potent mid to late Spring System, potentially very unstable atmosphere along with strong 0-3km shear present a clear severe weather outbreak possibility Sunday and Sunday night. Model soundings are suggesting sfc based CAPEs in excess of 2000 J/kg and 0-3km Bulk Shear of 40-50 knots along with long curved hodographs and 0-3km SRH in excess of 500 m2/s2 by Sunday afternoon. Any discrete storm, either early near the warm front or later in the warm sector, ahead of the cold front, could potentially develop rapidly and rotate. Upper level winds will also steer these storms along rather quickly to near 40 mph. In addition to severe weather, heavy rain and localized flooding will also be a concern as PWATs could be as high as 1.8 inches, which is the max moving average for late May for the nearby ILN upper air site. Went with 30 to 50 percent morning PoPs reflecting the possibility some of the slower end models verify and also with uncertainty if an MCS will in fact be fully in tact and then 70 to 90 percent PoPs for the afternoon and night when instability will be increasing and later the cold front will be getting closer. The southerly low level flow will also result in temperatures some 5 to 10 degrees above normal with highs in the lower to middle 80s looking reasonable. Memorial Day through Tuesday... A pair of upper waves will drop down from the northwest Memorial Day and Tuesday. Both of these will have enough moisture and instability to work with to be able to generate at least scattered convection, especially during the peak heating afternoon hours. Temperatures will likely be closer to normal in the wake of the Sunday night cold frontal passage which translates to afternoon highs mostly in the 70s. Tuesday night through Thursday night... Look for mostly dry and seasonable weather the remainder of the long term as ridging builds in overhead. && .AVIATION (12Z TAF Issuance)... Issued at 653 AM EDT Fri May 24 2024 Impacts: - Predominately VFR conditions through 00Z this evening, isolated thunderstorms possible during the afternoon - More widespread coverage of thunderstorms with brief MVFR or worse flying conditions possible after 00z this evening - MVFR ceilings expected to develop at some TAF sites after 06Z tonight Discussion: Patchy fog has developed this morning with minor visibility reductions at a few TAF sites. Expect any fog to quickly mix out over the next hour or two. Ridging will result in predominately VFR flying conditions through 00Z this evening. An approaching line of storms is then expected to push across central Indiana during the evening and overnight hours. Some of these storms may be strong or severe with localized gusts to 50 knots possible and frequent lightning, especially towards LAF where better instability/wind shear should align. Winds will increase to around 10 knots today. Expect wind direction to be out of the south. Once the storms move out, MVFR ceilings may develop late overnight. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Melo LONG TERM...MK AVIATION...Melo