956 FXUS63 KLMK 190750 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 350 AM EDT Thu Mar 19 2020 .Short Term...(Today and tonight) Issued at 345 AM Thu Mar 19 2020 ...Potential for severe storms and flooding rains tonight... The weather is quiet across central KY and south-central IN at this time, with a mostly cloudy sky. As we head toward daybreak, lower level clouds and some fog could develop as a warm frontal surface develops to our SW and begins heading toward the lower OH Valley. Not out of the question that isolated dense fog could develop over parts of southern IN, but this should be the exception. ASOS and KY Mesonet obs show temperatures remain mild at this time from about 57- 63 F at this time, and these will not fall too much more. The main concern for today is the potential for severe storms tonight along with heavy rain and flash flooding. The upper-level system to cause this is currently over the southwestern U.S. with lee side surface cyclogenesis occurring over eastern CO. For today, that low pressure system will move out into the central Plains. In response, areas of deep convection are already in progress ahead of the system across the southern Plains. For this morning, this convection will continue to expand and lift northeastward with development of additional showers and storms over AR into western TN in response to low-level warm advection and upward moisture transport. This axis of rain will lift quickly NE into SW/southern KY this morning, then spread across our entire region through early afternoon. Low-level instability will be marginal, but an axis of some elevated instability will exist so the rain should contain some convective elements that could produce brief heavy rainfall. As the warm front lifts NE during the day, rainfall will taper off this afternoon across our area, but scattered showers and isolated storms could remain in spots. The question then becomes how warm it becomes after warm frontal passage. Surface winds will kick up from the S and SW this afternoon over central KY with gusts to around 30 mph, which will continue tonight. Highs over southern KY could easily reach the mid 70s, with around 70 in southern IN. Tonight becomes quite interesting. From a severe standpoint, SHEF and NAM/GFS show increasing low-level wind shear as the mid-level system approaches and a nice elongated upper-level jet streak stretches SW to NE over the mid MS Valley. 0-1 km SRH values are forecast to increase to around 300 m2/s2, perhaps locally 300-400 as the low-level jet intensifies in response to the mid/upper-level divergence and forcing. Low-level instability will be greatest to our west this afternoon and evening, with some decrease in instability overnight. However, the boundary layer will remain well mixed tonight in our area with gusty gradient surface winds and temperatures that will fall little from daytime highs. Thus, models may be underplaying low-level instability somewhat. The pattern suggests a high shear-low instability QLCS with potential for some bowing segments and mesovortex development. As a result, swaths of damaging winds and isolated tornadoes are possible, particularly over the western and northern two-thirds of our forecast area with a decreasing severe threat over our eastern/southeastern KY counties. In addition, the pattern also favors high rainfall rates tonight in convective cells with potential for some SW to NE training of cells. Given past rains and with some brief heavy rain potential with the warm front today, flash flood potential will increase tonight, most likely centered roughly on the OH River. Thus, after much coordination with neighboring offices, we are issuing a Flash Flood Watch for tonight (00-12 UTC) for south-central IN and north-central and west-central KY. The timing and area of the Watch can be modified as later data dictates. && .Long Term...(Friday through Wednesday) Issued at 340 AM EDT Thu Mar 19 2020 Friday likely will feature a couple of bands of precip crossing the region...one out ahead of a strong cold front in the morning and the other closer to/right along that boundary in the afternoon. Gusty gradient winds are expected at least in the morning hours. That gradient should briefly loosen for a few hours right ahead of the surface trough, when the second widely scattered line of showers moves in. This line could bring some small hail with it, in addition to some gusty winds. Behind the front, the gradient will tighten again and perhaps bring gustier winds...30-40 mph wind gusts making for a brisk Friday evening. Saturday winds will take some time to die down, as high pressure builds in from the north. Most of the weekend will be dry and chilly under this regime. There are some indications that we could see a weak disturbance get into the area later in the day Sunday into Sunday night, bringing some light rains to southern KY. That system will be brief, and we should see high pressure dry us out to start the work week before another midweek system gets in here. Temperatures should get back above normal by Wednesday. && .Aviation...(06Z TAF Issuance) Issued at 145 AM EDT Thu Mar 19 2020 Currently, ceilings vary considerably at TAF sites, ranging from VFR at SDF and BWG to IFR (occasionally MVFR) at LEX and HNB. This variability should continue for next few hours, but in general, ceilings should remain or lower to IFR or perhaps low MVFR at each site before 12 UTC. Initial SW surface winds of 5-10 kts will become lighter S or SE by/before daybreak. Expect a band of showers and embedded thunderstorms to move from SW to NE across all TAF sites between about 12 and 18 UTC today associated with a warm front and increasing winds around 5 kft aloft from 30-40 kts. After this band of rain passes, surface winds will shift to the S to SW and increase to 10-20 kts with gusts 20-30 kts behind the warm front. Precip should become isolated to scattered in nature (perhaps end for a time) with lower ceilings lifting or breaking up, but holding much of the day at HNB. For tonight, as a low pressure storm system approaches from the west, showers and thunderstorms should become more numerous again, although timing at each TAF site is a bit nebulous at this time. But, expect rain after 02-03 UTC starting at HNB initially, then a little later at the other sites, especially BWG and LEX. Ceilings and vsbys should generally be MVFR during this period, but with IFR conditions at times given heavy rain in convective cells. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...Flash Flood Watch from this evening through Friday morning for INZ076>079-083-084-089>092. KY...Flash Flood Watch from this evening through Friday morning for KYZ023>040-045-061. && $$ Short Term...TWF Long Term....RJS Aviation.....TWF