008 FXUS63 KIND 150038 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 838 PM EDT Tue Sep 14 2021 .Mesoscale Update... Issued at 837 PM EDT Tue Sep 14 2021 A broken line of convection is currently passing through western and northern portions of central Indiana. This is expected to continue to pass through the region after sundown. Current analysis shows greatest surface based instability to the SW of Indianapolis where the impacts of diurnal cooling are less apparent. Still all of central Indiana remain above 2000 J/kg of CAPE, plenty for updraft development. Although surface based instability is greatest to the SW, lapse rates remain steeper over norther portions of the CWA. Even with instability, shear needs to be present to sustain updraft growth. With a broad trough aloft and a strong surface low over the Great Lakes, highest levels of shear is over northern central Indiana, collocated with steeper lapse rates, where thunderstorms should be able to sustain themselves even after sundown. Severe threat looks to decrease as the night progresses given the lack of deep layer shear present. Still north of I-70, 30-40 kts of effective bulk shear could be enough for an isolated organized thunderstorm to sustain itself for long enough to produce a severe wind gust. The greatest threat once again looks to be over northern portions of central Indiana. && .Short Term...(This evening through Wednesday night) Issued at 333 PM EDT Tue Sep 14 2021 ...A Few Strong To Severe Storms Possible This Evening... A cold front to the NW continues to approach central Indiana as of late this afternoon. A broad warm sector with temps in the mid 80s and sfc dewpts in the upper 60s/lower 70s has developed ahead of the front. Decent low and mid level lapse rates have resulted in CAPE values in the 2500-3000 j/kg range this afternoon. This moderate instability combined with effective bulk shear of 25-35 kts should result in strong to severe storms this evening. The best timing and location for the strongest storms will be along and north of a Terre Haute to Indy to Muncie line between 22z-3z. The main threats look to be strong to damaging winds and large hail. Storms should weaken as instability wanes by late evening and into the overnight hrs. Overnight expect showers/storms to continue to sink SE with the front with the best precipitation chances shifting from central to southern Indiana by the early morning hrs. For Wednesday, expect some showers/storms to linger in the morning across south central Indiana while drier/slightly cooler air filters in from the NW. Expect high temps in the mid 70s to lower 80s tomorrow. && .Long Term...(Thursday through Tuesday) Issued at 333 PM EDT Tue Sep 14 2021 The beginning of the long term will start out with the brief cooldown of near normal temperatures behind the front. The front is expected to stall south of the Ohio River through the latter half of the week. Aloft, ridging to the SE will help to keep a mostly dry forecast for the end of this week while heat and relatively humid conditions return this weekend. Temperatures will again climb above normal starting Friday and last into next week as southwesterly flow returns due to the placement of the ridging, advecting in the heat and moisture. Despite the SW flow, a bulk of the moisture will stay to the south of central Indiana for the end of the work week. A weak wave could provide enough lift to prompt some showers and storms Saturday into Saturday night. Upper ridging does look to become more dominant again Sunday into early next week but at this point central Indiana looks to sit more on the periphery of the high and not where the stronger subsidence would lie. So going to go with the suggested PoPs during the afternoon hours for the end of the long term. && .Aviation...(00Z TAF Issuance) Issued at 741 PM EDT Tue Sep 14 2021 IMPACTS: -Scattered thunderstorms, with main threat ending at from 1z at KLAF...to 6z at KBMG -Brief MVFR/IFR visibilities in/near storms, where isolated 50 kt gusts cannot be ruled out -Otherwise gusty SW winds diminishing tonight, veering to N by 12z DISCUSSION: Generally VFR conditions will continue tonight as a broken line of thunderstorms crosses the region from west to east this evening. Most convective cells this evening will contain thunder courtesy of ample instability...and brief MVFR/IFR visibility is possible in strongest storms. Isolated 50 kt wind gusts cannot be ruled out, especially through 4z. This main threat of thunderstorms should pass south/east of KLAF by 1z...and through KBMG by 6z. Following this threat VCSH and even a stray rumble of thunder are possible later tonight, although chances are generally too low to include either in TAFs more than a few hours after the main line passes. The supporting cold front will then cross the region from northwest to southeast through the middle of the night, with MVFR visibility possible for a few hours pre-dawn, especially at KIND/KBMG. Southwesterly winds at generally 7-13 kts early this evening...will veer to northerly at 4-7 kts following the frontal passage. VFR conditions are expected during the day Wednesday. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ Mesoscale...Updike Short Term...AMS Long Term...KH Aviation...AGM