872 FXUS63 KIND 300957 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 557 AM EDT Thu Sep 30 2021 ...Updated Aviation Discussion... .Short Term...(Today through Friday) Issued at 257 AM EDT Thu Sep 30 2021 Surface analysis once again depicts a weak boundary across the region, mostly dignified through a moisture boundary and wind shift, as clouds are keeping temperatures fairly warm exclusive from the boundary's location. Some fog is possible along the boundary where winds are calm and elevated moisture values are co-located with slight decreases in temperature. However, cloud cover will inhibit diurnal cooling, limiting any fog growth to low lying areas and near streams/rivers. Through tomorrow, the upper level pattern over central Indiana will remain stagnant as an omega block forces any weak disturbances well north into Canada. This will keep the sharp ridge over the Midwest and Ohio Valley over the next several days. The surface layer will provide some alterations as a thermal boundary remains draped across the region. With enhanced CAA over the Mid-Atlantic, this boundary has shifted its orientation to N/S leaving a W/E temperature gradient across central Indiana. This boundary will provide some lift within the easterly flow, but with weak low level winds and strong pressure induced subsidence, no precipitation is expected throughout the period despite the frontal boundary. As mentioned previously, temperatures will vary west to east across central Indiana due to the boundary. As high pressure builds in the low levels, the frontogenetical forcings will weaken, lessening the temperature gradient from day's past. Current expectations are for highs to range from mid 80s to the west and upper 70s to the east. This trend will continue overnight, with a gradual 8-10 degree gradient. Clouds will also play a factor in the temperature gradient as, some mid level moisture return will promote cloud growth over the western half of the region. Very little change is expected tomorrow as surface high pressure keeps the elevated moisture west of the region and maintains the overall air mass over the region; Expect similar temperatures and sky cover. && .Long Term...(Friday night through Wednesday) Issued at 257 AM EDT Thu Sep 30 2021 Saturday through Sunday night... Models suggest southwest flow will be in place aloft providing moisture advection along with warm air advection. Lift will be expected across the area as an upper trough and associated cold front over the Mississippi Valley will be advancing toward the Ohio Valley. THus will continue to trend toward cloudy skies along with pops on Saturday through Sunday night. Given the expected clouds and rain will trend highs at or below the NBM and lows warmer. Monday and Tuesday... ECMWF suggests ridging building across the upper midwest as Sunday's Trough and cold front begin to exit east. Subsidence is depicted to build across the area by Monday night and Tuesday. However on Monday...cyclonic lower level flow will remain and forecast soundings suggest diurnal convective rain showers will possible. Thus will continue some pops on Monday...but trend toward a dry forecast on Tuesday as Dry air and subsidence become more predominate. Wednesday... An odd weather pattern is suggested by the ECMWF by Wednesday as an upper low is projected to retrograde from Michigan toward Western KY within an Omega type flow aloft. The GFS meanwhile suggests a more typical pattern of an upper low pushing south from the northern plains to Arkansas/KY. Meanwhile at the surface an inverted trough is suggested through Tennessee and KY. For now...some pops seem reasonable given the the pattern...but uncertainty remains high. && .Aviation...(06Z TAF Issuance) Issued at 556 AM EDT Thu Sep 30 2021 IMPACTS: -MVFR/IFR fog possible at KHUF and KBMG, until 14Z. -VFR Conditions are expected otherwise. DISCUSSION: Outside of some MVFR/IFR conditions in ground fog at KBMG and KHUF, VFR conditions are expected to continue. MVFR fog has already developed at BMG and HUF as dew point depressions are 2-3F. Diurnal cooling may lead to brief periods of IFR. As heating and mixing resumes by 14Z...all TAF sites will return to VFR and P6SM. High pressure over the eastern Great Lakes will provide light easterly surface flow through the period. Forecast soundings and Time heights show a dry column. Thus only a few passing CI will be expected within the flow aloft. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ Short Term...Updike Long Term...Puma Aviation...JP