404 FXUS63 KIND 120730 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 330 AM EDT Sat Sep 12 2020 .UPDATE... The SYNOPSIS, NEAR TERM and SHORT TERM sections have been updated below. && .SYNOPSIS... Issued at 330 AM EDT Sat Sep 12 2020 Powered by a weakening but still potent upper system that will move into the Great Lakes tonight and Sunday, a cold front will drop southeast across central Indiana overnight and into Sunday morning. This system will bring unsettled weather back to central Indiana late today and into early Sunday. High pressure will build in behind the cold front and mark a return of dry weather with seasonable or below temperatures through next Tuesday. More unsettled weather is possible starting next Wednesday as another cold front and upper system approach. && .NEAR TERM (Today and Tonight)... Issued at 330 AM EDT Sat Sep 12 2020 Tricky forecast for the today and tonight. Water vapor imagery clearing showing an upper low spinning over the Nebraska and South Dakota borders early this morning. Meanwhile, 11-3.9 micron satellite pictures and obs were indicating a stratus deck over the forecast area with occasional breaks that are tending to fill back in. This deck has been stubborn to leave and or dissipate the last couple of days. Model rh time sections keep plenty of moisture around today and cu development progs suggest plenty of diurnal cu potential, so despite GFS LAMP suggesting some dissipation of the stratus field after 12z today as a warm front moves through, look for any mid or late morning large breaks in the cloud cover to be temporary. Models in good agreement the upper low will open up tonight and move across the western Great Lakes. This will spin up a cold front that is expected to drop southeast across central Indiana after 06z Sunday. Convective allowing models suggest, convection will move into our northwestern counties after 18z. Model instability progs were showing some instability this afternoon and evening with surface base CAPEs mostly 1000 J/KG or below with the best instability, albeit waning, over areas east of Interstate 69 after 03z. Meanwhile, best shear will lag a bit behind the best instability and supports only having a Marginal Risk of severe weather per the Storm Prediction Center Day 1 Outlook. Believe the best chance of severe storms will be from 18z-03z in areas northwest of Indianapolis, where the better combination of deeper shear /1000-500 millibar bulk shear magnitude to 40 plus knots/ and instability /up to 1000 J/KG/ will be. Damaging winds continue to be the main severe threat with low level inflow unimpressive. Scattered to likely National Blend of Models PoPs look reasonable starting late today northwest and spreading southeast tonight. After coordination, decided to lower NBM temperatures a degree or two hear or there closer to the not as warm and lately better verifying CONSShort. .SHORT TERM /Sunday through Monday night/... Issued at 330 AM EDT Sat Sep 12 2020 With the cold front expected to be over southeastern Indiana 12z Sunday, left small morning PoPs in over southeastern counties. Otherwise, high pressre will build in and bring dry weather to the area Sunday afternoon and into the start of the long term. With clear skies and light to calm wind Sunday night, could see some more fog or low stratus. Low level thickness progs and limited cloud cover support the seasonable or slightly below blend with afternoon highs in the middle 70s to lower 80s. Good nighttime sleeping weather in store with overnight lows in the 50s. && .LONG TERM /Monday Night through Friday/... Issued at 349 PM EDT Fri Sep 11 2020 Central Indiana should expect typical mid-September weather for most of next week. Predominantly zonal mid-level flow will set-up over the region between a broad ridge along the southern states and an increasingly active series of waves across the Canada-US border. The period will start chilly as the first mass of surface high pressure slowly departs the area towards the northeastern US. Light surface winds will become southwesterly for Wednesday, promoting milder conditions. The next significant feature will be a second Canadian air mass that will reach Indiana later in the week...although lack of certainty surrounds its specific timing in the late Wednesday-early Friday time frame...as well as the potency of cooler air that will follow it. Therefore went with generally slight chances of showers and thunderstorms Wednesday-Friday, with greatest chances Thursday afternoon, and lower probabilities for our northern tier of counties. Partly to mostly clear skies will be common for the period. Afternoon highs should top out in the 75-80F realm, although late week could be potentially cooler if the frontal passage was faster and deeper. Morning lows will be in the 50's, excepting Wednesday night where 60-65F readings are expected. && .AVIATION (Discussion for the 120600Z TAF Issuance)... Issued at 1137 PM EDT Fri Sep 11 2020 MVFR conditions are expected during the overnight, with improvement to VFR in the daylight hours of Saturday morning. Confidence on timing is low. Area of MVFR clouds is trying to erode from multiple sides but is expanding on other sides. Thus confidence is low on its final evolution, so trended pessimistic and kept MVFR all through the night. These clouds should mix out leaving behind VFR conditions during much of the day Saturday. Convection is possible later in the afternoon west and spreading east into the evening. && .IND WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MK NEAR TERM...MK SHORT TERM...MK LONG TERM....AGM AVIATION...50