758 FXUS63 KLMK 061703 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 1203 PM EST Sat Feb 6 2021 Updated Aviation Discussion... .Forecast Update... Issued at 1045 AM EST Sat Feb 6 2021 Forecast remains on track this morning. Minor tweaks made to temperatures given a slower warming response with the cloud cover over central Kentucky... otherwise, still expecting to see highs top out in the upper 30s in southern Indiana and low to mid 40s across central Kentucky. Far southern Kentucky could see highs briefly hit the upper 40s by late afternoon. Clouds will continue to increase in coverage and thickness ahead of our next system tonight. && .Short Term...(Today and tonight) Issued at 330 AM EST Sat Feb 6 2021 Current satellite imagery shows thinning band of cirrus over southern KY while a band of mid-level clouds streams across southern IN and northern KY. Continue to see some light snowfall and flurries out of this mid-deck as area surface observations indicate lowest levels have saturated enough for precip to reach the ground. However, not expecting more than a dusting with these snow showers as they diminish over the next couple of hours. Otherwise relatively quiet weather in store for the first part of the day with increasing cloud coverage throughout the day ahead of an approaching system. Temperatures will warm into the upper 30s to lower 40s across southern IN and northern KY and into the mid to upper 40s across southern KY. As we move into this evening, expect a couple waves of energy swinging across the TN Valley and Great Lakes region to bring increasing precipitation chances to the area. Precipitation will begin to move in shortly after sunset, when temperatures across northern portions of the area will be in the lower to mid 30s and temperatures across southern KY will be in the lower 40s. This will result in p-type starting as snow along and north of I-64, rain across southern KY, and a rain/snow mix between the Parkways and I- 64. As temperatures continue to crash overnight however, expect precip to changeover to all snow between 12-3 AM EST. Snow will then continue overnight before ending from west to east towards sunrise Sunday morning. Accumulations will generally be around a half inch or less, but higher amounts to around an inch will be possible mainly along and north of I-64 as well as across the eastern edge of our CWA. With temperatures ranging from the upper teens over southern IN to the upper 20s across southern KY, any wet surfaces may freeze and create slick spots. .Long Term...(Sunday night through Friday) Issued at 339 AM EST Sat Feb 6 2021 A very challenging, complex, low confidence forecast as the region sits in the battleground between air masses to our north and south. Sunday and Sunday night Canadian high pressure will nose southeastward into the region with dry, cool weather. Highs on Sunday will be in the 30s but we'll drop into the mid teens to lower 20s Sunday night with partly cloudy skies. Monday a warm front will set up from a weak area of low pressure over the TX/NM border to the central Appalachians. During the day precipitation associated with this feature will remain to our north. However, Monday night into Tuesday morning the boundary is expected to slip southward as a cold front as low pressure rides along it, bringing us some light precipitation. Will stick with rain/snow mix in the forecast for now, however it should be noted that soundings over southern Indiana and north central Kentucky show little if any ice nucleation aloft given a shallow layer of low level moisture while surface temperatures fall into the middle and upper 20s...suggesting freezing drizzle or light freezing rain may be a possibility by the Tuesday morning commute. Something to keep an eye on. Mid-week confidence remains low, similar to previous forecast packages, as we sit between cold air and more vigorous mid/upper energy to our north and more temperate air to our south. CFSv2 16 member ensemble mean shows cold air spilling from Alaska and Canada into the Plains/Great Lakes/Midwest and a baroclinic zone setting up from the Ozarks through the Tennessee Valley to the mid-Atlantic. EPS and GEFS are similar but have the baroclinic zone slightly farther north, more over the Ohio Valley than the Tennessee. The location of this zone will have an impact on how much precipitation we receive and what type of precipitation we receive depending on how deep into the cold air we are at the surface and aloft. Tuesday-Tuesday night we're in between systems but ensembles do show the possibility of some very light precipitation in the area so will continue to carry a low PoP with very low QPF. Right now will prog highs Tuesday afternoon ranging from around freezing in southern Indiana to near 50 along the Tennessee border...which provides a good illustration of how we are treading the tightrope between cold and warm. A shift of just a hundred miles in that temperature pattern will spell huge differences in the forecast, especially as we continue into mid- and late-week. Speaking of which, Tuesday night-Wednesday night the operational GFS brings significant wintry weather to the region in two waves. The first wave would come late Tuesday night into Wednesday morning and has support from the CMC and now from the latest ECMWF as well. The second wave would then come in Wednesday night and possibly into Thursday. Though the models have not done a great job with the extended over the last few days and there is still some run-to-run inconsistency showing up as the models struggle with the transition zone, this is something to keep a close eye on with the GFS/EC/CMC all starting to come together. We'll have southerly low level flow bringing warmth and moisture northward overrunning a surface trough from the Mississippi Delta to the central Appalachians and flowing above above shallow cold northeasterly winds at the surface coming off of Canadian high pressure stretching from the northern Plains to New England. This set-up would encourage impactful winter weather. Thursday-Friday low pressure is expected to lift from the western Gulf into the upper Ohio Valley and bring us another chance of precipitation and once again the advancement, or lack thereof, of the cold dome to our north will make a big difference in the resulting precipitation type. Operational GFS is a little more aggressive with the late week cold invasion than the model mean and there is a 58 degree spread in 2m temperatures Friday evening among the model members at Louisville. Will lean on what the NBM delivers for now...plenty of other fish to fry in the meantime. Thanks to neighboring offices for collaboration this morning. && .Aviation...(18Z TAF Issuance) Issued at 1201 PM EST Sat Feb 6 2021 VFR conditions will be in place at the start of the forecast period, but flying conditions will decline tonight as a system moves in from the west. Rain and/or snow showers will begin shortly after 00z for TAF sites west of I-65, and eventually spread to the I-75 corridor after midnight. Cigs/Vis will drop to MVFR levels, perhaps briefly hitting IFR levels, for several hours. Visibilities will improve after the rain and/or snow moves out, but MVFR cigs will linger well into tomorrow morning before drier air from the northwest scatters out the stratus deck. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Update...DM Short Term...JML Long Term...13 Aviation...DM