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Forecast Discussion for Indianapolis, IN
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363 FXUS63 KIND 190523 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 123 AM EDT Thu Jun 19 2025 .KEY MESSAGES... - Hot and humid this weekend with near Heat Advisory conditions by Sunday && .FORECAST UPDATE... Issued at 955 PM EDT Wed Jun 18 2025 Adjustments were made to the latest forecast, mainly to POPs and winds overnight. Convection has mostly subsided across central Indiana as stronger forcing shifts east. Latest KIND radar imagery and surface observations show a few storms lingering across the far southeast. These storms will move push east shortly with the potential for additional redevelopment later tonight. Overall forcing is relatively weak, but lingering moisture and weak forcing may promote scattered showers or a few storms at times. The best chance would be near or south of I-70 where slightly stronger forcing and deeper moisture will align. Look for temperatures to bottom out near dewpoints in the mid-upper 60s tonight. Winds are already diminishing across northwest portions of central Indiana. Due to this, the Wind Advisory in effect will be allowed to expire at 10PM EDT. && .MESOSCALE UPDATE... Issued at 354 PM EDT Wed Jun 18 2025 Buoyant low levels, low LCLs, and sufficient low level shear continues to support a tornado threat late this afternoon. The greatest threat will be associated with surges/RIJs within the QLCS, and with discrete or quasi-discrete shallow supercells over southern Indiana. Midlevel speed maxima enhanced by the upstream MVC will enhance shear further over the next couple of hours. One potential negative to a more robust tornado threat may be weakness in hodograph aloft and poor venting. && .SHORT TERM (This evening through Thursday)... Issued at 1218 PM EDT Wed Jun 18 2025 ...SEVERE WEATHER EXPECTED THIS AFTERNOON... ...BEST CHANCE OF SEVERE BETWEEN 1PM AND 9PM... THIS MORNING INTO EARLY AFTERNOON A strong MCV (mesoscale convective vortex) has developed overnight from yesterday`s convection and is currently located over east central Missouri. This feature will be enhanced by a shortwave trough aloft, strengthen further, and track northeast through the afternoon. Latest ACARS soundings out of IND show a fairly stable boundary layer with only modest lapse rates aloft. However, instability will increase as the near-surface layer continues to warm. The hodograph is long and slightly curved in the 0-3km layer and quite messy above that. Going forward, as mentioned above, continued surface warming will lead to a very unstable air mass by this afternoon ahead of the approaching MCV. Guidance is generally within the 2000-3000 J/Kg MLCAPE range, with a few members even higher. Of particular note is the abundance of near-surface instability due to a very moist boundary layer. Guidance shows 3CAPE values between 100-200 J/Kg across the majority of our area by 18z. STORM MODE AND HAZARD TYPE With a stronger MCV materializing, greater mesoscale forcing for convection will likely be present in addition synoptic-scale forcing from the shortwave aloft. Additionally, greater backing within the surface wind field is expected as one heads northwest (closer to the low center). This backing may act to locally enhance curvature within the low-level hodographs, leading to an increased tornado threat. In the low to mid-levels, the strong MCV is acting to enhance the low-level jet which may reach 45-55kt as low as 925mb. With steep boundary layer lapse rates anticipated, it would not take much to mix these winds to the surface. Should any cold pools form and help convection organize into lines or line segments, then RIJ enhancement may lead to a more widespread / significant wind threat. As for large hail potential, given weakness within the 500-250mb flow this may not be that widespread. Still, given the amount of CAPE present and fairly high ELs (10-12km), some isolated instances of severe hail are certainly possible. Our primary severe hazard today will depend on storm mode. Shear vectors are oblique to a wind shift that extends southwest from the MCV/low center. Combined with relatively weak flow aloft, a linear to quasi-linear mode is preferred with the potential for some discrete storms in the open warm sector. With abundant low-level shear and moisture, a tornado threat is present especially as one nears the MCV center and along a pseudo warm front extending to its northeast. The tornado threat may occur in discrete storms as well as within linear elements...especially if low-level flow can align in such a way that promotes mesoscale circulations. Strong to severe wind gusts are likely to be the primary hazard today given the steep low-level lapse rates and intense LLJ, combined with enhancement from potential cold pool dynamics. In addition to the above hazards, flash flooding will be possible should any storm training occur. Recent rainfall has lead to quicker flash flood response times. A broad non-convective wind threat may evolve on the southwest and south side of the departing MCV. Some members of guidance show wind gusts between 40-50kt across our northwestern counties later this afternoon. A wind advisory may be needed across these areas later on. TIMING With the low/MCV now apparent, CAMs have come into better agreement regarding timing. Activity may reach the Indiana/Illinois line as early as 1pm, traversing Indiana during the afternoon hours before exiting into Ohio around 9pm. Storms may linger a bit longer across our south as the MCV lifts northeastward and the trailing boundary slows. && .LONG TERM (Thursday through Tuesday)... Issued at 356 AM EDT Wed Jun 18 2025 Thursday will see an exiting upper wave and seasonable temperatures. Some lingering showers and storms could still be around in the morning, or even a few isolated pop ups in the afternoon, but largely expecting most of the rain to have come to an end by daybreak Thursday. The end of the week and into the weekend high pressure both aloft and near the surface will be building, tracking from Texas and then centering over the Ohio Valley by Sunday. Heat and humidity will dominate the long term as highs Saturday through mid next week will be around 90 to 93 degrees and dewpoints persistently in the 70s. With heat indices likely getting to above 100 for several days, it is probably that heat advisories will be needed. A few models are showing that isolated afternoon storms could be possible given the heat and humidity, but would expect the high pressure in place would be enough to suppress any showers or storms. Chances for rain are looking better towards mid-next week when the high pressure shifts further east, weakening over central Indiana. Looking beyond the long term, hot, humid conditions are expected to continue. && .AVIATION (06Z TAF Issuance)... Issued at 123 AM EDT Thu Jun 19 2025 Impacts: - MVFR ceilings (IFR at LAF) expected later tonight into Thursday late morning/midday - A few showers or storms early in the period at a few sites - Wind gusts in the 15-20KT range Thursday afternoon from 280-300 degrees Discussion: As an upper trough passes through the region overnight, a few lingering showers or storms may impact some of the sites early in the period, followed by widespread MVFR ceilings (IFR likely at LAF). The ceiling restrictions will last through late morning/midday before VFR returns at all sites. During the afternoon hours Thursday, west/northwesterly wind gusts can be expected at times in the 15-20KT range. These gusts will subside in the late afternoon/evening in typical diurnal fashion. Light winds and mostly clear skies are expected tomorrow night across the area. This may allow for some patchy fog formation given good radiational cooling conditions, though this is far too uncertain for inclusion at this time. && .IND WATCHES/WARNINGS/ADVISORIES...None. && $$ UPDATE...Melo SHORT TERM...Eckhoff LONG TERM...KF AVIATION...Nield |
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