138 FXUS63 KLMK 140125 AFDLMK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOUISVILLE KY 924 PM EDT WED MAR 13 2013 .Forecast Update... Issued at 924 PM EDT Wed Mar 13 2013 Made a quick update this evening to lower minimum temperatures tonight. Current observations are running 2-3 degrees below the going forecast, despite the lingering cloud cover. Once skies clear out and the winds die down, radiational cooling effects will allow temperatures to dip into the lower 20s and even upper teens in some of the cold spots. The remainder of the forecast looks well on track. && .Short Term (Tonight through Thursday night)... Issued at 325 PM EDT Wed Mar 13 2013 Strong surface high pressure over the Plains is helping to draw unseasonably cold air into the Ohio Valley. Dry weather will be short-lived as fast NW flow aloft continues, and the next disturbance is just emerging from the Canadian Rockies. Low-confidence forecast hinges on the timing and exact path of this disturbance, and precip type and chances as it crosses the Ohio Valley. This afternoon's gusty winds will diminish around sunset, and the residual strato-cu should clear quickly, giving way to a cold night. Most locations will be in the lower/mid 20s, but can't rule out some of the typical cold spots dipping into the the teens. Will start off mostly clear Thursday morning, but mid-level clouds will stream in from the NW ahead of the Clipper. This makes the temp forecast rather tricky, and it is likely that we will see a sharp SW-NE gradient somewhere across Kentucky. Have opened a range from lower 40s across the Bluegrass to around 50 near Bowling Green, but the actual spread could be even larger, and quite sharp somewhere in between. Precip arrives late in the afternoon across southern Indiana, and by early evening over central Kentucky. Still some model discrepancies as the NAM and GEM keep most of the precip over the Bluegrass, while ECMWF and GFS spread it farther west. Expect that the precip will be mostly rain, as most of the ice aloft will be lost before the boundary layer can saturate. However, there will be a narrow window for precip to fall as snow, so this forecast will show a rain/snow mix where low-level temps get cold enough. This will be a quick-hitting system with most, if not all the precip exiting around midnight Thursday night. Fri morning lows will generally be near freezing or just above, mitigating most re-freezing concerns. .Long Term (Friday through Wednesday)... Issued at 300 PM EDT Wed Mar 13 2013 A fast moving shortwave in northwest flow aloft should be exiting the southeast forecast area by about daybreak Friday, with dry conditions expected through the day. Temperatures ranging from the mid 50s in the northeast to low 60s in the southwest appear on track Friday, with southwesterly low-level winds expected. Low-level clouds will exit, while higher clouds move in through the day as our next system approaches for Friday night. The next shortwave will arrive late Friday night and last through Saturday afternoon, as the surface boundary sliding south. Temperatures will only fall into the upper 40s and low 50s Friday night, with temps Saturday being highly dependent on the frontal boundary placement. Warmer temps, perhaps in the 60s will be across the south, with lower 50s across the north on Saturday. The bulk of this precip Friday night into Saturday morning appears to favor our northeastern half of the CWA, with continued or new development along the front across south-central Kentucky during the late morning and afternoon hours. Expecting all rain with this event and could have some rumbles of thunder, as soundings indicate some elevated instability. This frontal boundary will become quasi-stationary across the Ohio and Tennessee Valleys Sunday through Tuesday, as more zonal flow aloft becomes established. This will provide a chance of rain Sunday through early morning Tuesday as several waves pass across the area. There should be brief breaks in precip between the waves, but a little too difficult to time this far out with noticeable ensemble spread. The next shortwave arrives Sunday, but we should start to see rain Saturday night with rain dissipating sometime Monday morning. The location of the quasi-stationary boundary remains a fairly big difference amongst models, but an ensemble approach would place it directly west-east across the CWA. Temperatures could have quite a gradient from north to south if this occurs. For now, mid and upper 40s across our far north to low 60s across our far south for Sunday seem reasonable. Temperatures should warm more for Monday as the boundary lifts north with our next weather system quickly moving in. So, while precip diminishes Monday morning from the Sunday system, rain will quickly overspread the region during the day Monday and last through early Tuesday morning. For our final system Monday, two broad areas of low pressure appear to form and sweep across the Ohio Valley. The trailing front will push all activity to the eastern CONUS Tuesday, with dry high pressure settling across the area Tuesday through Wednesday. Cannot rule out some upslope development in our east during the late morning and afternoon hours Tuesday, but chances seem small at this time. With the boundary setting up across the CWA and several waves of precip expected, rainfall totals from Sunday through early morning Tuesday of up to two inches are possible. However, the key factor will be the exact placement of the quasi-stationary boundary. High temperatures generally in the 40s, maybe low 50s in the south are on tap Tuesday. Will see several degrees of warming Wednesday, with mid and upper 50s anticipated. && .Aviation (00Z TAF Issuance)... Issued at 725 PM EDT Wed Mar 13 2013 VFR stratocumulus deck will continue to drift off to the east as it dissipates with the loss of daytime heating. Therefore, expect all terminals to go SKC by late this evening, which will last through the overnight hours. NW winds will also die down in the next hour or two as mixing wanes. VFR conditions will continue through the majority of Thursday. The next upper-level system will first spread a mid-level deck across all sites through the day on Thursday. By late in the afternoon, a few showers (mostly rain with perhaps some snow mixed in) and a lowering VFR ceiling (FL040-FL060) will spread across mainly KSDF and KLEX. The bulk of the precipitation looks to remain north of KBWG at this time, so will leave VCSH wording out. This system will be quick-moving, clearing out of KSDF by the end of the planning period. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...NONE. KY...NONE. $$ Update...........KD Short Term.......RAS Long Term........MJP Aviation.........KD