.Short Term...(Today through Sunday) Issued at 305 AM EST Sat Nov 13 2021 Many locations across central Indiana have seen their first snowflakes of the season over the last several hours. Early this morning...pockets of flurries continue to drift across the northeast half of the forecast area in tandem with an upper trough axis. 08Z temperatures were in the 30s with continued brisk westerly winds making it feel even colder. The warm pleasant weather enjoyed through much of the first ten days of the month now feel like a distant memory and will feel even further away as the weekend progresses. The first true winter-like weekend of the season is upon us with cold gray weather expected through Sunday with the added potential for a dusting of snow late tonight into Sunday morning as a surface wave tracks through the lower Great Lakes. A deep upper level low was centered over James Bay this morning with a sharp trough axis currently swinging through the region. This will be replaced by subtle ridging aloft later today before another piece of energy on the back side of the upper low pivots across the upper Midwest and into the Ohio Valley for Sunday. At the surface... ridging will follow in tandem for later today with the upper ridge ahead of the aforementioned surface wave dropping out of the northern Plains late today and across the lower Great Lakes for Sunday. The combination of these features will be a continued unsettled weather pattern for much of the weekend. Scattered flurries continue early this morning but have generally decreased in coverage as drier air aloft begins to advect into the region. Despite the drier air expanding with the ridging as the day progresses...model soundings and RH progs show a stout low level inversion that will persist all day and into this evening. With moisture trapped beneath the inversion...a low stratus deck will remain through this evening and while the moisture remains shallow with little to no forcing aloft...cannot rule out a few flurries or sprinkles lingering into the afternoon. Steepening lapse rates beneath the inversion also support this potential which should mainly focus over the northern half of the forecast area. Brisk W/SW winds will continue today as well though not be anywhere near as gusty as on Friday. The approach of the surface wave from the northwest later tonight will bring the first measurable snowfall to much of central Indiana focused predominantly during the predawn hours through Sunday morning before warming through the boundary layer gradually transitions snow back to rain. Nice mid and upper level diffluence will develop ahead of the approaching surface low and upper trough late tonight which in tandem with a surge of isentropic lift aided by strengthening 850mb flow will spread precip into the region from the west after 05-06Z. Critical thicknesses support the precip type to be snow for much of the forecast area through daybreak Sunday with any mixing with rain likely confined to the lower Wabash Valley where the boundary layer will be slightly warmer. Precip type will gradually switch to rain through midday Sunday from southwest to northeast before snow mixes back in late day with renewed cold advection behind a cold frontal passage. As mentioned above...confidence continues to grow in seeing the first measurable snowfall for much of the forecast area early Sunday with a dusting up to perhaps around an inch with the highest amounts across northern counties. With road temperatures still quite warm...expect most accums will be confined to grassy and elevated surfaces with little to no impacts to travelers. This will likely melt as temperatures warm on Sunday. Precip will be coming to an end by sunset Sunday as the low pulls away and high pressure begins to build in from the west. Temps...well below normal temperatures are expected through the weekend. Low level thermals support undercutting guidance with highs later today likely to struggle to 40 degrees. Sunday will end up only subtly warmer by a couple degrees. Brisk conditions today with the potential for higher gusts Sunday will bring a raw chilly feel to the air. Lows tonight will drop into the upper 20s and lower 30s. && .Long Term...(Sunday Night through Friday) Issued at 305 AM EST Sat Nov 13 2021 The beginning of the long term period will be dry but chilly after a trough exits the area and ridging takes its place. Tight pressure gradients will continue winds gusting to around 25 kts for Sunday night, but as the axis of the surface high settles in, winds will drop back down to 5 to 10 kts for the start of the work week. The airmass origin will change quickly during the first half of the week from a chilly, westerly airmass to a warm, southerly one. This shift in the flow comes ahead of another trough, allowing for strong warm air advection as temperatures Tuesday and Wednesday are expected to briefly return to the 60s. A surface cold front associated with the trough will allow lift for the moisture also being advected into the area. A line of rain showers is expected to track from NW to SE through the day Wednesday and possibly into the day Thursday. The exact timing of this system has yet to be ironed out, but models are trending more towards Wednesday to Wednesday night than Thursday at this time. There is agreement on a lack of instability so will keep out any mention of thunder for now. Behind the front, a northwesterly airmass will return temperatures back into the 40s and 30s, with lows possibly dipping into the 20s, for the remainder of the period. Friday looks dry due to subsidence passing through, but central Indiana could see additional rain and mixed precipitation over the weekend. && .Aviation...(12Z TAF Issuance) Issued at 539 AM EST Sat Nov 13 2021 IMPACTS: - MVFR ceilings through early evening...then returning towards daybreak Sunday - Periodic westerly wind gusts approaching 20kt through early afternoon - Snow showers impacting the terminals predawn hours Sunday DISCUSSION: A few flurries continue to drift across central Indiana early this morning underneath a thick MVFR stratus deck. As drier air aloft expands into the region...the flurries should gradually diminish through the day. However...a stout inversion will keep the stratus deck over central Indiana all day with only modest improvement towards sunset. Westerly winds will be in excess of 10kts into the afternoon with periodic gusts to near 20kts before falling back by late afternoon. Model soundings show the inversion relaxing this evening which should enable a return to VFR ceilings into the early overnight. Clouds will remain though as low pressure approaches from the northwest. Precipitation will expand across central Indiana after 06Z with low level thermals supporting the precip type as snow. Could see visibility restrictions within the light snow through daybreak Sunday with ceilings once again returning to MVFR and perhaps dropping to IFR or lower Sunday morning. Winds will back to southerly towards daybreak Sunday.
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