288 FXUS63 KIND 032250 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 650 PM EDT Mon May 3 2021 .Mesoscale Update... Issued at 650 PM EDT Mon May 3 2021 Convective allowing models and radar trends support thunderstorms moving into northwestern parts of central Indiana after 02z. This upstream activity is currently moving east and approaching Rockford, Peoria and the northern St. Louis suburbs and has recently produced large hail and a tornado. Along and ahead of the convection, moderate instability with a surface base CAPE axis extended from south central Missouri to northeastern Illinois, and a 50 knot mid level jet streak was just north of St. Louis. This combo of instability, shear and moisture will keep these storms going through the late night as they move towards the Wabash River. && .Short Term...(This evening through Tuesday night) Issued at 328 PM EDT Mon May 3 2021 ...HIGHLY CONDITIONAL SEVERE WEATHER THREAT OVERNIGHT... Surface analysis this afternoon shows an area of low pressure to our northwest over NE Iowa/SE Wisconsin/NW Illinois, with a quasistationary front extending eastward through the Great Lakes, and a cold front extending south/southwestward into western Missouri to a second developing low over southern Oklahoma. These lows and baroclinic zone will be the focus for a conditional severe weather threat overnight that remains uncertain. Latest synoptic guidance has coalesced somewhat around the slower solution advocated by the Euro in recent days with the development of the aforementioned secondary low as the more substantial upper level trough swings through the Four Corners region this afternoon. It continues to appear that regional severe weather potential, if it occurs, will be in separate waves late this evening into the overnight, and then late tonight to just after daybreak Tuesday. Supporting factors for severe weather are as follows: 1) Ample deep layer shear, instability, and moisture. 2) Support of an upstream MCV for the first wave, and support of the broader frontal zone/secondary low for the second. 3) Steep midlevel lapse rates. 4) Presence of a 30KT southwesterly low level jet feeding into the region later tonight. Inhibiting factors for severe weather are as follows: 1) Widespread cloud cover has suppressed insolation throughout the day, although some clearing may be able to sneak into our west/southwest late this afternoon. 2) Timing is diurnally poor, particularly for the second wave which now looks most likely to arrive around daybreak Tuesday, and stabilizing boundary layer will limit surface-based instability and may result in elevated storms with perhaps a marginal hail threat at best. 3) Presence, albeit transient in some forecast soundings, of an elevated warm layer/cap between roughly 850-700mb. 4) Potential for first wave of convection to move a bit further south through the area and fully exhaust available instability prior to arrival of second wave. Many, but not all, of the 12Z CAMs coalesced around a solution whereby convection, currently developing over western Iowa and northeast Missouri ahead of the aforementioned MCV, consolidates into a QLCS and pushes southeastward along the instability gradient, perhaps brushing our west/southwest late this evening into the early overnight, with a lengthy gap afterwards before consolidated showers and storms ahead of the secondary low over the southern Plains into the Mississippi Valley arrive late in the night/around daybreak Tuesday. The HRRR continues to suggest, albeit not as robustly as earlier runs, that the first wave of convection will push more east/southeastward into the forecast area, perhaps posing a severe threat as it weakens with eastward extent, with the second wave again arriving on a more west/northwesterly course from the central Mississippi Valley around daybreak. Cannot totally discount this with the potential for the MCV to continue to push eastward along the broader baroclinic zone, but the tendency should be for convection to move more east/southeastward in the open warm sector, such as it is. The preponderance of the evidence, along with current orientation of the developing instability axis, although it should translate eastward with time (but erode later in typical diurnal fashion), suggests that the non-HRRR solutions are a bit more likely, although given the competing factors, confidence remains a bit lower than would ordinarily be the case this close to the potential events. Agree with the rescission of the enhanced risk from the area and the pullback of the slight further to the west in the most recent SWO day 1 update. One final complicating factor is speed of the front moving through the area. A thunderstorm threat and at least a very marginal severe threat, will likely linger into Tuesday ahead of the front, particularly south/southeast, depending on the evolution of features overnight. As far as Tuesday night is concerned, guidance suggests a secondary vort lobe in the overall cyclonic flow will allow showers to linger, but the thunder threat, and particularly the severe threat, will likely be long over by then. Preferred Consshort max/min temps to NBM given the continued slowing trend of the overall synoptic setup. && .Long Term...(Wednesday through Monday) Issued at 328 PM EDT Mon May 3 2021 Continued...changeable spring weather will continue to be the theme for Wednesday through Monday. The lingering cold front is expected to exit the area on Wednesday...allowing dry high pressure to build through the Ohio Valley on Wednesday. Thus will trend toward a dry forecast at that time. Aloft through Friday...strong ridging looks to remain in place over the Rockies while a deep cyclone over Hudson Bay provides broad cyclonic flow aloft for Indiana...the Great Lakes and the Northeast. A few embedded short waves are depicted to push across Indiana on Thursday and Friday afternoon...but deep moisture remains unavailable and lower levels are not organized. Thus will trend toward low chc pops on each afternoon as these wave pass as forecast soundings show attainable convective temperatures but shallow instability. On Saturday through Monday a more zonal flow appears in place aloft as a surface low pressure system develops over the Plains. An associated surface warm front looks to be parked over southern Indiana on Saturday and lingers across the area through Monday. Models then suggest a few low pressure systems pushing along the front and across Central Indiana through the weekend. Thus chances for showers and storms through the weekend look reasonable. && .Aviation...(00Z TAF Issuance) Issued at 627 PM EDT Mon May 3 2021 IMPACTS: * MVFR or VFR ceilings through 04z-06z. * Showers and thunderstorms and MVFR and worse flying conditions, potentially strong to severe, after 04z. * Winds 210-240 10 knots or less shifting to the northwest after 08z as a cold front drops southeast over the terminals. Higher wind gusts in thunderstorms. DISCUSSION: A cold front will drop southeast across central Indiana overnight. The front will interact with a moderately unstable airmass and veering wind with height and trigger scattered to numerous thunderstorms late tonight into Tuesday morning. The first concern will be the strong to severe storms moving in from Illinois. The most likely impact window for the terminals with this batch would be from 04z-09z. Then, more convection will likely be moving in from the southwest. This activity may be more widespread. Modest southwest winds will shift to the northwest and north on Tuesday in the wake of the cold front. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ Mesoscale...MK Short Term...Nield Long Term...Puma Aviation...MK