133 FXUS63 KLMK 082359 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 659 PM EST Fri Mar 8 2019 ...Updated Aviation Discussion... .Short Term...(This evening through Saturday) Issued at 301 PM EST Fri Mar 8 2019 ...Breezy with Strong to Severe Storms Possible Saturday... The morning snow is becoming a distant memory today as warmer air works into the region. Most obs in the area generally range from upper 30s to mid 40s with lots of overcast skies. Some showers are ongoing near the TN/KY border now, and should persist through the next several hours before tapering off this evening. Overnight, we should remain dry. A stationary front will remain draped across the lower Tennessee Valley, and most of the precipitation associated with that front will stay south of the KY state line. Clouds/stratus will linger here overnight, and we could see some patchy fog or mist develop late. Strong low pressure ejects out of the Plains tomorrow and heads toward the Midwest, setting the stage for potential active and severe weather. We'll start out the morning well north of the warm front, but as the low slides MO/IA/IL, we'll see the warm front try to gradually lift northward. Most models indicate some showers and elevated convection moving into our area between 12-15z Saturday. The main threat with the morning storms will be heavy rainfall, as a substantial surface inversion will eliminate any wind/tornado threat despite strong shear profiles. Can't rule out some small hail in the stronger storms, though the lack of dry air in the mid levels of the atmosphere won't be very conducive for bigger hail in the morning. As we head into the afternoon hours, models begin to surge a corridor of +60 dewpoint air into western Kentucky and southwestern Indiana as the warm front lifts northward. Drier air aloft may allow for a lull in showers/storms and potentially some breaks in clouds to form in these areas. It's during this timeframe that we'll begin to see a transition from elevated instability to surface based instability as the near-surface CIN is eroded. Storms then look to form in the warm sector ahead of a pre-frontal trough in far western KY and southern IL, tapping into the surface based instability. Storm mode via high-res models indicate a mix of linear/bowing segments and discrete convection as it pushes eastward. Model forecast hodographs within the warm sector show substantial long, clockwise curvature, indicating very strong low level shear and veering with height. This will result in an environment with ample storm relative helicity that will be supportive of a potential tornado threat, assuming any surface based instability can be realized. But that's the big question for tomorrow... how far north and east does the surface based instability translate? Most models indicate that the peak surge of higher dewpoints and surface based instability will be west of I-65, with a gradual waning in those parameters after 00z. There appears to be a small window of opportunity in our region for severe storms, from late afternoon into early evening, where a zone of surface based instability and shear parameters could align. Storms in this zone would be capable of all facets of severe weather, including damaging straight line winds, heavy rainfall (resulting in localized flooding), hail, and isolated tornadoes. The tornado threat will have to watched especially closely with any discrete supercells that form within the warm sector. A number of high-res models show storms weakening as they approach the I-65 corridor, which makes sense given the sub-par thermodynamics along and east of this area. Still can't rule out isolated severe storms east of I-65, but the overall thermodynamic environment just won't be very supportive of it. Think the current SPC Day 2 Outlook highlights the severe threat very well. In a nutshell, here's what we're thinking for specifics of the potential severe setup: * Timing: 4pm - 10pm * Storm mode: Mix of linear/bowing segments and discrete storms * Threats: Straight-line damaging winds, heavy rainfall, and hail, with an isolated tornado threat, mainly west of I-65. One other thing worth mentioning... with such strong wind fields in place, it won't take a lot of mixing to get some stronger gradient wind gusts to reach the surface. Went ahead with a wind advisory mainly south of the I-64 corridor and west of the I-65 corridor, where the best potential for +40mph gusts will be during the afternoon and early evening hours. .Long Term...(Saturday night through Friday) Issued at 230 PM EST Fri Mar 8 2019 ...STRONG STORMS POSSIBLE MID-LATE NEXT WEEK WITH POTENTIAL FOR MORE HEAVY RAINFALL... A quiet period of weather will get us started Sunday and continue at least through Tuesday. With the cold front clear of the region Sunday morning, expect this period to linger around normal temperature wise as well. Then we flip the active weather switch back on again midwekk, with temperatures rising well above normal and winds picking up from the southeast and then south as another low pressure center develops across the Central Plains and moves into the Midwest. The GFS/GEFS hints at some warm advection type showers Tuesday night as this switch turns on. Will cap pops in the 20-30 percent range for this potential and as most other models, including the FV3 keep us dry. Our eyes then turn to the cold front dragging behind this surface low. Model start time for storms to move into our area range from Wednesday afternoon through night. With the flow aloft becoming parallel to the front, it looks like this boundary could stall and even back up as further waves travel through that flow. The CMC/GEFS/Euro all keep some QPF in through Friday though the GFS and FV3 both push it east more quickly. Previous forecast was similar and SuperBlend keeps pops lingering into our I-75 zones into the daytime Friday. Will not stray too far from that thinking for now. In doing that, will keep Wed to Thu night above normal and then drop temperatures back to normal to close out the work week. && .Aviation...(00Z TAF Issuance) Updated at 635 PM EST Fri Mar 8 2019 MVFR/IFR conditions are expected this evening with HNB/SDF deteriorating to IFR tonight as well. Low cigs and some light fog are expected tonight as we sit in a moist low level environment to the north of a warm front. Drier conditions will exist at HNB/SDF so they may not see much light fog but will most likely experience IFR cigs later tonight. The warm front will lift north through the area tomorrow morning bringing the first of multiple rounds of showers/storms. South of the front tomorrow afternoon, southerly winds will become gusty with continued chances for showers and storms. The best time frame for strong storms will come tomorrow late afternoon through the end of the TAF period. These may contain heavy rainfall reducing flight conditions to IFR/LIFR and strong winds. Showers/storms should diminish just beyond the end of this TAF period. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...Wind Advisory from 1 PM EST /noon CST/ to 10 PM EST /9 PM CST/ Saturday for KYZ023-024-026>028-053-061>064-070>076. && $$ Short Term...DM Long Term...RJS Aviation...AMS