Area forecast discussion National Weather Service Detroit/Pontiac Michigan 709 am EDT Sat may 18 2013 Aviation... //discussion... VFR conditions will persist as we will remain on the western periphery of large high pressure system over eastern Canada today. Winds will be easterly through the day before veering to the southeast by Sunday morning. The easterly flow will continue to pump dry air into the low level keeping ceilings generally at or above 7kft this afternoon. An increase in low level moisture will occur behind a passing warm front Saturday night which will allow visibilities and ceilings to drop to MVFR by early Sunday morning. This will quickly mix out after sunrise. //Dtw threshold threats... * medium confidence ceilings will drop below 5kft early Sunday morning. && Previous discussion...issued 339 am EDT Sat may 18 2013 Short term...today and tonight Middle/upper level ridging will continue to build into the region today while we remain on the western extent of a dome of high pressure at the surface centered over eastern Canada. Easterly winds will persist through tonight due to the surface high. The continued feed of dry Continental air will keep dewpoints in the 40s once again. Model soundings in fairly good agreement with the 00z DTX sounding with the depth of dry air in the boundary layer currently around 9kft. The 700mb warm front lifted through Friday afternoon and models show the weaker 925 mb front will follow northward through today. Hard to find any additional support to help this kick off any showers this afternoon. Models keep most of the showers over the Ohio Valley where surface moisture is much higher. The likely result will end up being a lowering of the cloud deck to around 6-7kft. Weak warm air advection will allow temperatures to rebound a few more degrees today into the middle/upper 70s with cooler temperatures for areas in the Lake Shadow. Long term...Sunday through Friday Stabilizing influence of upper ridging should help keep the area dry on Sunday. Although a surface warm front will lift north through the County Warning Area early on Sunday...dry conditions are expected to continue despite MUCAPE values approaching 1000 j/kg during the afternoon hours given the very dry and in place and stabilizing effect of downward motion from the upper level ridge. The passage of the warm front will bring warmer air to the region...with daytime highs around the 80 degree mark away from Lake Huron. Warm air will continue to stream in behind the warm front early in the work week as southerly winds bring a marked increase in moisture across southern Michigan. The increased moisture as well as the shift east in the upper level ridge will bring an increase in rain chances to Southeast Michigan as the week progresses. Although an upper level low will sit off to the west during the early part of the week...several embedded shortwaves will take advantage of the increased instability of 1000 to 2000 j/kg Monday and Tuesday. The upper level dynamics and instability will bring the possibility for several rounds of showers and thunderstorms to the area. Despite the decent cape values...shear will be very weak in the low levels with a rather unimpressive hodograph and meager helicity values. Monday looks to be the warmest day of the upcoming week with high temperatures getting into the lower to middle 80s across much of the County Warning Area. Although model differences still exist...there appears to be more agreement in handling the cut off low out to the west as it progresses east during the middle of the week. The GFS and European model (ecmwf) solutions merge this low with the northern stream low over Hudson Bay...absorbing the low as a positively tilted trough tracking through the central Great Lakes region. Although thunderstorms are still possible during the middle of the week...the best instability will be well to the south. However the system will have enough moisture to produce some heavy rain showers during the middle of the week as the surface low tracks through the southern Great Lakes region. Canadian high pressure builds in behind the low late in the week...bringing dry conditions and much cooler daytime highs in the 60s to Southeast Michigan. Marine... Easterly flow will continue through tonight as we remain under the influence of high pressure over Canada. The favorable fetch will allow waves to be slightly high over Western Lake Erie...but a decreasing trend will keep them below Small Craft Advisory criteria. Winds will veer to southerly by Sunday night before increasing next week as low pressure lifts out of the plains. This low will bring a chance of thunderstorms Monday through at least Wednesday and will be accompanied by a modest increase in southerly winds by Monday afternoon. A middle-week wind shift to northerly can then be expected as a cold front pushes across area waters. && DTX watches/warnings/advisories... Michigan...none. Lake Huron...none. Lake St Clair...none. Michigan waters of Lake Erie...none. && $$ Aviation.....Drk short term...drk long term....kurimski marine.......drk You can obtain your latest National Weather Service forecasts online at www.Weather.Gov/Detroit (all lower case).