864 FXUS63 KIND 291039 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 539 AM EST Fri Dec 29 2023 .Key Messages... - Chances for a mix of rain and snow will persist through tonight - Little or no additional accumulation is expected during the day today or tonight - Seasonable temperatures persist through the next week && .Mesoscale Update... Issued at 539 AM EST Fri Dec 29 2023 Radar shows some areas of relatively intense snow this morning, with echoes of nearly 40 dBZ noted in the heaviest areas. INDOT cameras show some snow on the roads under the stronger echoes, so have issued a Special Weather Statement for slick spots in the western forecast area. The snow will continue to rotate south across the area through sunrise, depositing less than an inch of snow. Temperatures will remain above freezing for the most areas. && .Short Term...(Today and tonight) Issued at 301 AM EST Fri Dec 29 2023 Early this morning, an upper level low continued to slowly sink south across central Indiana. A mix of rain and snow is falling across parts of the western and southern forecast area. Temperatures were in the lower to middle 30s, with dewpoints in the lower 30s. Before Sunrise Today... As the upper low continues its slow trek south, forcing will continue across the area, focused on the western and southern portions of central Indiana. Will go with high chance to likely category PoPs there with lower PoPs to the east and north. Soundings are below freezing except right near the surface, with both rain and snow observed across the area. Relatively heavier precipitation is resulting in snow with a mix or rain in lighter areas. Also, farther east, there are some areas where drier air aloft may be preventing ice forming in the cloud, resulting in drizzle. Thus, isolated locations in the west and southwest might see up to an inch of snow on grass, but most areas will see a dusting or less. Today... The upper low will continue to drift south, taking the forcing with it. Initially, will keep some slight chance to chance category PoPs going most areas with the low still nearby. The far southwest may still be under enough forcing for likely PoPs early. PoPs will then gradually diminish them from north to south into early afternoon. Precipitation type will initially be light snow or a mix with continued marginal thermal profiles near the surface, but then warming should change precipitation to a mix with mostly rain. Some additional light snow accumulation on grass may occur in the far southwest before temperatures warm up. During the latter part of the afternoon, a cold front will work its way into the area from the north. Enough moisture will linger for the front to work with to produce chance PoPs across the north by the end of the today period. Clouds will keep temperatures from rising too much, but highs in the upper 30s to perhaps around 40 can be expected. Tonight... The cold front will continue to move southeast through central Indiana tonight. As noted above, enough moisture will linger for some chance PoPs most areas as the front moves by. Marginal thermal profiles will again result in a mix of rain and snow, but no snow accumulation is expected. Low temperatures will be in the lower and middle 30s. && .Long Term...(Saturday through Thursday) Issued at 301 AM EST Fri Dec 29 2023 The long range period features numerous weak systems passing through the region bringing a few chances for light precipitation and temperatures at to slightly above normal for this time of year. .Saturday through Monday... Mainly dry and cool conditions expected for the first half of the weekend on Saturday as a generally northerly flow pattern remains across the Great Lakes region and Midwest. On Saturday, Central Indiana will be in between the departing upper low to the east and another weak system diving south out of Canada into the Upper Great Lakes. BUFKIT soundings show much drier air pushing in aloft associated with brief ridging building in on Saturday. However, cyclonic flow at the surface around larger scale low level troughing over the Great Lakes may make it difficult to dry out the boundary layer. BUFKIT profiles on shorter range models indicate the potential for moisture trapped in the boundary layer under a subsidence inversion leading to increased low level clouds. For this reason, keeping skies partly to mostly cloudy for Saturday. Weak "warm" air advection ahead of the next system will allow for surface temperatures to rise above freezing into the mid 30s to low 40s despite increased cloud cover. Potential for light precipitation Sunday into Monday as the aforementioned system drops southward from Canada into Michigan. This fairly weak, stacked area of low pressure will bring another shot of cooler air to the region, increasing clouds, and the chance for light rain/snow. Surface "cold" front moves in the first half of the day Sunday with cold air advection on the backside. ECMWF forecast soundings show deeper moisture with this system reaching into the DGZ, whereas the GFS is drier and shallower with its moisture profile for Sunday into Monday. These differences could mean the difference between scattered snow showers and just areas of light drizzle and rain. For now, best chance at any precipitation is along and north of the I-70 corridor. For now will have rain/snow mix in the forecast for North Central Indiana. Temperatures will be closer to normal on Sunday as cold air advection keeps highs in the 30s for most of the region. Coolest areas will be North Central Indiana with more cloud cover, slightly colder low level temperatures, and higher chances for precipitation. Overall, not expecting a very impactful system, mainly light nuisance showers. The upper trough hangs back over the Ohio Valley into Monday while high pressure slides by to the southwest. Potential is there with this set up for left over moisture to become trapped in the boundary layer resulting in low clouds and maybe fog the first half of Monday. Increased clouds in addition to a cooler airmass overhead, expect highs closer to normal in the 30s. .Tuesday through Friday... Surface high pressure becomes centered over the Southeast CONUS middle of next week while upper ridging builds ahead of the next system organizing in the Plains. Uncertainty still exists in the overall evolution of the midweek system. A few areas in question are how much influence the southern and north stream branches of the jet will have on the area and where/if will they phase. Latest ECMWF and GFS ensemble runs disagree on potential phasing with this system, which will impact the rest of the week's forecast. A more phased system could mean better moisture advection northward and better chances for precipitation, but also colder air on the backside for late week. Weaker, separate systems may leave Indiana right in the middle with an overall more mild and dry forecast. For now, keeping PoPs quite low and temperatures closer to normal or just above in the mid 30s to low 40s. Higher confidence exists in Tuesday;s forecast with dry conditions and above normal temperatures. Uncertainty increases Wednesday into Thursday. .Beyond day 7... Some hints in ensemble guidance of a trend towards a more active pattern. Longer range guidance has been hinting at a sudden stratospheric warming event occurring in the Arctic come early to mid January. This correlates nicely with the Arctic Oscillation going negative as shown by many ensembles. Will be watching this closely as this could lead to a period of winter-like weather and colder temperatures come mid January into February. && .Aviation...(06Z TAF Issuance) Issued at 1155 PM EST Thu Dec 28 2023 Impacts: - Poor flying conditions, IFR to LIFR, are expected - A mix of rain and snow will occur at times, mainly western sites Discussion: As low pressure slowly moves south across the sites Friday, IFR to LIFR ceilings are expected. Visibility may dip into IFR category in precipitation. Ceilings may briefly try to improve to MVFR Friday afternoon, but they would retreat back to IFR Friday night. Confidence is not high enough to include. With temperatures near to a little above freezing, precipitation type will likely vary from rain to snow at times. Greatest concentration of snow will likely be at KLAF/KHUF. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ Mesoscale...50 Short Term...50 Long Term...CM Aviation...50