area forecast discussion National Weather Service Louisville Kentucky 1254 PM EDT Friday may 24 2013 ..updated aviation discussion... Forecast update... issued at 640 am EDT Fri may 24 2013 Current forecast continues to be on track. Drier air is starting to win out as low-level cloud deck is start to erode nicely across southern Indiana. Expect partly cloudy skies to give way sunny skies as we head through the rest of the morning hours. Temperatures should continue to fall over the next hour or so bottoming out in the mid-upper 40s in the far north with upper 40s to around 50 near the river...and in the lower 50s across southern Kentucky. Afternoon high temperatures in the mid to upper 60s still look on target. && Short term (now - saturday)... issued at 325 am EDT Fri may 24 2013 Surface cold front continues to plow on off to the southeast this morning. Rain showers have long ended across southern Indiana and central Kentucky, but plenty of low clouds remain in place across the region. Drier air is trying to work in from the west, but a persistent north to northeasterly planetary boundary layer flow is allowing the low clouds to continue to flow southward this morning. In the near term, expect mostly cloudy conditions to remain in place, though our western sections will probably see a little more clearing due to the closer proximity to the drier air in place to our west. Temperatures will continue to fall with cold air advection place...and we expect readings to fall into the mid-upper 40s by sunrise. For today, high pressure will slowly build in from the northwest. Dry punch of air will continue to make headway into the Ohio Valley, so we should see a rapid decrease in clouds during the morning hours with mostly sunny skies expected today. Dewpoints will likely drop into the 30s this afternoon and with a good amount of mixing and cooler air aloft, we're likely to see a bit of a temperature gradient across the region. Afternoon highs will likely only top out in the 61-66 degree range across the Bluegrass region of central Kentucky with 65 to 70 degree readings in the I-65 corridor and points west. Surface winds will be out of the north to NE and will slacken later in the afternoon and into the evening hours. For tonight, high pressure and light winds will be in place which should set up a good radiational cooling period. The question remains whether we'll see the development of fog or a potential frost. From a climatological perspective, the threat of frost is fairly low here in KY/in. For the most part, it looks like temperatures will probably remain warm enough that we'll see mostly patchy fog develop. However, some of our eastern counties may get a touch of frost...especially in our typical cold spots. For this reason, we will issue a Special Weather Statement this morning highlighting the potential frost threat in the typical colder spots in the eastern Bluegrass region. Lows tonight will likely be in the upper 30s in the east with lower 40s in the central and western sections. Quiet and warmer conditions are expected for Saturday as high pressure moves on off to the east. This should kick our surface winds around to the south and eventually the southwest. Temperatures should moderate a bit on Saturday with highs in the 65-70 degree range in the Bluegrass with 70 to 75 in the central and western sections of the forecast area. Long term (saturday night through thursday)... issued at 310 am EDT Fri may 24 2013 A amplified yet slowly progressive 500mb pattern will feature deep troughs across New England and the Pacific northwest late Saturday. Eventually, ridging over the Western Plains will expand towards the lower Ohio Valley. This will enable temperatures to warm substantially beginning Monday. High temperatures may actually approach 90 towards the end of the next work week. Canadian high pressure ridge axis will lie right over the Great Lakes late Saturday, extending southward across the commonwealth. Cool weather with low dewpoints will continue through Sunday, along with light winds. Despite the possibility of some increasing high cloudiness associated with a warm front to our southwest, lows early Sunday will fall well down into the lower to mid 50s. Quite a bit of uncertainty and disagreement exists between some of the long range guidance for the Sunday through Tuesday time frame. Overall, warmer more moist air will attempt to move northeast into the lower Ohio Valley. However, a deep slow moving low over New England and persistent northwest flow aloft over the commonwealth will retard the northeast progress of this boundary. It is likely during the first couple of days of next week that several convective clusters will develop across the Midwest, aided by moisture advection and the presence of a nocturnal low level jet. These periodic thunderstorms may slide southeast, bringing at least a chance of difficult-to-time thunderstorms beginning Sunday afternoon and possibly continuing through Tuesday. Both the European model (ecmwf) and the GFS forecast the surface boundary to stretch early Sunday from northern Missouri southeast towards central Tennessee. The consistent European model (ecmwf) has been slower in bringing this boundary north across the commonwealth than the GFS. However, by Tuesday afternoon, both of these models have this boundary as far north as southern Ohio. Will continue our forecast of at least a chance of thunderstorms Sunday afternoon through Tuesday, with an admittedly low confidence on attempting to time any areas of convection moving southeastward along this boundary. Highs on Sunday will likely remain in the 70s, warming to the lower to mid 80s by Tuesday. For Wednesday and Thursday, mid-Summer like ridging will develop over the Tennessee Valley. Expect that these two days will stay dry with quite warm temperatures in the mid to upper 80s. && Aviation (18z taf issuance)... issued at 1253 PM EDT Fri may 24 2013 High pressure is building into the region and will hold influence through this forecast cycle. This will keep conditions dry and VFR. Few - sct cu should gradually mix out through the afternoon with a steady north-northwest wind between 5 and 10 mph. Winds will go nearly calm to calm tonight. Expect a light easterly wind on Saturday with few to sct upper level clouds beginning to move overhead. && Lmk watches/warnings/advisories... in...none. Kentucky...none. $$ Update...........mj short term.......mj long term........jsd aviation.........Bjs