Area forecast discussion...updated National Weather Service Huntsville Alabama 1001 PM CDT Tuesday Jun 18 2013 Update... evening forecast update && Discussion... as the weak frontal boundary continued to slide south of the Tennessee Valley this evening...showers along the boundary quickly dissipated following sunset. The wind shift that followed behind the boundary has brought slightly drier air to the Tennessee Valley but low to middle 60s dewpoints remain across much of the County Warning Area. While temperatures have cooled across the forecast area...it seems to be more attributed to diurnal cooling than any strong cold advection behind the front. 9pm temperatures still ranged from the upper 60s (at Tullahoma/Winchester and vinemont) to the middle 70s (khsv)...which are not significantly different from surrounding cwas on both sides of the boundary. The going forecast was modified slightly to account for the effects from some lingering high level cloud cover streaming our way ahead of the next middle level trough axis. Scattered to bkn250 clouds should continue to track across the southeast through the overnight period and help dampen the expected diurnal cooling...and therefore help prevent dense fog development. Am still leaving fog wording in the grids for overnight though since there should be enough cooling to at least produce some patchy fog (helped by all the ground moisture remaining from recent rains). Have otherwise updated products to remove mention of rain chances through 06z as all the precipitation has dissipated and increased overnight lows by a degree or two due to the high clouds. Ccc && Aviation... /issued 629 PM CDT Tuesday Jun 18 2013/ for 00z tafs...with the exception of potential fog development overnight...VFR conditions should be predominant at both terminals for the period. Due to recent rainfall and expected clearing of cloud cover overnight...MVFR fog should begin to develop by around 08z and continue to drop visible through the early morning. At this time am expecting kmsl to see the lower visbys (to IFR/2sm at times) but if more of the high clouds dissipate...fog could become much thicker at both terminals. Will be monitoring evening trends closely for updates. Ccc && Previous discussion... /issued 340 PM CDT Tuesday Jun 18 2013/ Tennessee Valley weather has been relatively quiet today, all things considered, because a fairly deep shortwave trough passed through overnight. There are three surface boundaries of note this afternoon: an initial front now along/south of I-20, a secondary boundary draped from ktup to Vinemont/3a1 to between Winchester/bgf and kcha, and a third more robust boundary draped across Iowa to the Ohio Valley. A weakening band of showers is focused along the 2nd boundary in north Alabama, but there is little else now in the hun County warning forecast area. Not surprisingly, the off-and-on rain and clouds has kept temperatures from getting out of the lower 80s. While the wettest and most unstable period is coming to an end, we are not going to be totally dry for the next 7 days. First, the shortwave trough over Texas should stay mostly south of the area. Once showers clear out of the area this evening, we will need to watch for fog formation late tonight, especially if there is any decent clearing. However, a shortwave trough currently over the Missouri Valley will drive the 3rd boundary noted above southward into the Tennessee Valley tomorrow. The trough and boundary will get hung up, and some additional forcing could arrive Thursday. While forcing will not be terribly robust either day, there should be sufficient moisture, convergence, and heating to drive a few showers and storms during the afternoons--no more than a 15 to 20 percent pop, but just enough to mention in the forecast. The increased sunshine should easily push temperatures into the 90s. The synoptic scale pattern becomes increasingly murky by the weekend. Energy from the Wednesday/Thursday trough gets caught up/trapped on the eastern flank of a building ridge. Medium-range models disagree on the location and amplitude of the resulting trough, but agree on its presence and persistence. The European model (ecmwf) model maintains some sort of weak troughing or upper low over the southeast for the entire remainder of the forecast, and the GFS and GFS ensembles solutions are similar. Unless more robust subsidence or drier air pushes into the region, it is tough to go with a dry forecast during this time of year, so will maintain the 20-pop parade through the entire forecast. There will be days with higher coverage and those with lower coverage, but those details are too mesoscale to resolve at this kind of time range. Temperatures offered by the European model (ecmwf) and GFS are largely climatology-based, with highs around 90 and lows in the upper 60s (and little variation among the various ensemble members). These are acceptable with the expected pattern, since the troughing should keep the high-amplitude ridge (and hotter conditions) at Bay. Bcc && Hun watches/warnings/advisories... Alabama...none. Tennessee...none. && $$ For more information please visit our website at weather.Gov/Huntsville.