Area forecast discussion National Weather Service Detroit/Pontiac Michigan 104 am EDT Thursday Jun 20 2013 Aviation... //discussion... High pressure centered over Lake Huron will provide a strong influence across the region through Thursday night. This will maintain mostly clear skies and light southeasterly winds during this time. //Dtw threshold threats... * none && Previous discussion...issued 329 PM EDT Wednesday Jun 19 2013 Short term...tonight Confluent northwest upper level flow will continue to provide clear/mostly clear skies to the region...allowing for another another cool night. Surface high pressure (1023 mb) over Lake Huron will just slowly retreat off to the east. Temperatures today (19z) are exceeding yesterday afternoon's readings by two or three degrees on average...and expecting mins about 2 degrees warmer tonight compared to this morning due to the airmass modification. Also...we do begin to get into the return flow toward sunrise...which should help offset the currently low dew points in place this afternoon. Long term...Thursday through Tuesday WV imagery shows energy that entered the Pacific northwest is now progressing eastward toward central California and Nevada where the 500 mb trough remains...but continues to weaken. East of The Rockies the upper ridge continues to build and will do so through this weekend. Surface high pressure will be centered east of the County Warning Area to start Thursday...but it's influence and the orientation of the low level jet will still succeed in coaxing a couple surface lows north of our focus area. Thursday and Friday will be similar to each other with fair weather cumulus in the afternoon and plenty of sunshine. Temperatures will gradually increase on Friday as the upper ridge nears and the return flow from an exiting surface high keeps south winds pumping in warmer and drier air. The major forecast challenges and changes start on the weekend. Models mainly agree that there will be a Stout (590 dam) 500 mb ridge in place along with warm 18-20c 850 mb temperatures. Mixing from 850 mb to the surface should get US to the middle or upper 80s. The main limitation to that is the 1500 to 2000 j/kg of cape and the potential for an upstream mesoscale convective system tracking into the region. Due to the conditional nature of convection and the strength of the capping inversion...will lean towards higher temperatures and lower probability of precipitation for Saturday. Sunday looks like a better chance to hit 90 as the upper air setup is very similar...except there will be an even stronger cap in place. Dewpoints will be near 70 and cape values will again be in the 1500-2000 j/kg range so the potential for strong to severe thunderstorms is certainly there. Monday will be continued hot and muggy with storm chances under a similar pattern to the weekend. Flow turns more zonal or trough-like on Tuesday with only slight moderation to the temperature and dewpoints. Though we may fall short of a definitive heat wave...we will likely see heat index values over 90f for 4-5 days. Adding to the high heat threat is a recovery only to 70f or so each night. Marine... High pressure over the central Great Lakes will be slowly sliding to the east. Light southerly winds tomorrow into the weekend will allow warmer and more unstable air to move into the area...allowing for a chance of showers and thunderstorms....especially on Saturday. && DTX watches/warnings/advisories... Michigan...none. Lake Huron...none. Lake St Clair...none. Michigan waters of Lake Erie...none. && $$ Aviation.....Mr short term...sf long term....mm marine.......sf You can obtain your latest National Weather Service forecasts online at www.Weather.Gov/Detroit (all lower case).