211 FXUS63 KLMK 241619 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 1119 AM EST Tue Jan 24 2023 .Forecast Update... Issued at 1115 AM EST Tue Jan 24 2023 Current satellite imagery shows mostly sunny skies across the area, with temperatures beginning to warm into the mid to upper 30s after a chilly start to the day. Will continue to enjoy a few more hours of sunshine before high clouds begin to push in from the west this afternoon ahead of the approaching system. The 24/12Z model guidance is coming into better alignment regarding tonight's system, with increasing confidence in best snow chances being generally along and north of the Ohio River, while p-type remains as mostly rain across central KY. Expect precip shield to move in from the west shortly after 25/03Z and overspread the area, with periods of moderate to heavy precip expected to continue through 25/09-12Z. The dry slot will then cut into the area with precip rates tapering off Wednesday morning. Have not made any major changes to the forecast at this time, more in depth analysis will be available with the afternoon forecast package. && .Short Term (Now through Wednesday)... Issued at 255 AM EST Tue Jan 24 2023 Key Messages/Impacts... - Accumulating snow possible late tonight, mainly in southern Indiana - Small shifts in the low track and temperature profiles will have a large impact on precip type and potential snow amounts - Gusty winds in excess of 30 mph possible Wednesday, especially east of Interstate 65 Confidence: Medium-high on timing, low-medium on precip types and snow amounts. Discussion: After a tranquil and somewhat mild day, precipitation will spread into the Ohio Valley tonight as low pressure runs up the Lower Mississippi Valley. Rain will change over to snow across southern Indiana and parts of north-central Kentucky, with at least minor accumulation possible after midnight tonight into Wednesday morning. Snow chances will come to an end Wednesday morning, with gusty winds likely through the remainder of Wednesday. Closed upper low currently near El Paso is progged to eject ENE to near DFW by this evening, by which time we'll see a sfc low developing near the TX/LA border and isentropic lift extending into far western Kentucky. Precip will spread eastward through the night as a 60 kt low-level jet translates east, and temps will initially be warm enough to start out as rain. However, there should be just enough of a T/Td spread to drop temps by a few degrees, at which point southern Indiana and part of north-central Kentucky would change over to accumulating snow. By the time the sfc low reaches our longitude Wednesday morning, the track should be just one side or the other of the Ohio River. The window for snow accumulations will be mainly from 06-12Z on Wednesday, before mid-level dry air aggressively wraps into the system and we lose the ice aloft. Forecast temps remain just barely above freezing, but with strong dynamics and QPF approaching a half inch of liquid, rate-driven cooling is not out of the question and could allow snow to pile up. The transition could be a sharp one from all rain to several inches of snow, but the most likely scenario across our southern Indiana counties is 1 to 2 inches, with only about a 5 percent probability of hitting 4 inches from roughly Jasper to Madison. Will go with a Winter Weather Advisory from midnight tonight until noon Wednesday, covering all of our Indiana counties and north of I-64 in Kentucky, which is admittedly generous to allow for a farther south/east low track, and if the system were to overachieve. By midday Wednesday the low starts to become stacked over SE Indiana/SW Ohio, setting up a deformation band over central Indiana while a pronounced dry slot punches from SW to NE across central Kentucky and southern Indiana. Light rain or drizzle will be the predominant precip type as temps quickly recover into the 40s with a few locations warming into the 50s. Greatest weather impact in Kentucky will be strong S-SW winds with gusts easily hitting 30-40 mph east of I-65. After coordination with PAH and JKL, we'll hold off issuing any Wind Advisory, but one may very well be needed. .Long Term (Wednesday Night through Monday)... Issued at 330 AM EST Tue Jan 24 2023 Synopsis...The medium range portion of the forecast begins with broad cyclonic flow over most of the Conterminous US as negative upper height anomalies predominate over the Central US. Eventually, mid-level shortwave troughs will carry these anomalies to the Northeast US and off to the North Atlantic, allowing the quasi- stationary subtropical high to extend its ridge axis through the Southeast US and Mid Atlantic. Meanwhile, the mean position of the longwave trough axis will be draped along the West Coast. The aforementioned scenario reinforces an active weather pattern/storm track over the lower Ohio Valley. Model Evaluation/Confidence...There is good model agreement on the position and intensity of the large scale factors at play during the first half of the period (Thu-Sat). Both high and low resolution models support persistent snow showers on Thursday under the influence of shortwave energy riding the cyclonic flow in place. The second half, on the other hand, depicts high model variability regarding upstream energy digging through the Pacific Northwest. In this case, CMC and ECMWF exhibit a more amplified trough while the GFS is much more subtle, probably due to a ridge over Baja California. Thursday...Cloudy and breezy conditions will continue during Thursday as well as persistent cold air advection. In addition, shortwave energy and sufficient low-level moisture will support low- topped snow showers during the morning and afternoon hours. Forecast soundings show a saturated layer just below the DGZ, but decent low- level lapse rates. Therefore, a mix of snow/ice pellets is favored under a mostly sub-freezing thermal profile. It is important to mention that although 24-hr snowfall amounts stay below 1", there will be isolated accumulations over half an inch in narrow streaks oriented parallel to the low-level shear. Friday - Saturday...Partly cloudy with slightly warmer temperatures as the ridge starts to build in from the south. So far, dry weather is indicated for the start of the weekend, but notice that there could be some low PoPs reintroduced on Friday afternoon for southern Indiana and the Bluegrass given some mid-level energy clipping these areas provided there is enough moisture available. Sunday - Tuesday...Another weather system slowly approaches the area increasing PoPs. It seems that temperatures favor rain as the dominant p-type, but a wintry mix is possible towards Monday and/or Tuesday. Still, low confidence regarding temperature/moisture distribution for next week. && .Aviation (12Z TAF Issuance) Issued at 615 AM EST Tue Jan 24 2023 Impacts/Confidence: - High confidence on VFR conditions through this evening - High confidence in MVFR or IFR conditions toward daybreak Wed - Low confidence in precip types at HNB and SDF Discussion...VFR conditions through this evening with mainly cirrus ceilings and light S-SE winds. Look for a mid-level ceiling to move in this evening as isentropic lift develops ahead of a low pressure center. As precip breaks out conditions will quickly drop into low- end MVFR or even IFR after midnight tonight. Best opportunity for IFR cig/vis will be at HNB, where rain could mix with or change over to snow. Low-level jet cranking up to 50-60 kt will push the thresholds of wind shear late tonight/Wed AM, so will further assess that in later issuances. Easterly sfc winds will pick up as precip arrives, with gusts near 20 kt through Wed morning. Wednesday afternoon could get quite breezy as we warm up in the dry slot, with S-SW wind gusts over 30 kt possible especially at BWG and LEX. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...Winter Weather Advisory from midnight tonight to noon EST Wednesday for KYZ030>037. IN...Winter Weather Advisory from midnight EST /11 PM CST/ tonight to noon EST /11 AM CST/ Wednesday for INZ076>079-083-084- 089>092. && $$ Update...JML Short Term........RAS Long Term.........ALL Aviation..........RAS