During the week, an upper level shortwave trough will be moving eastward across the country, originating in the Pacific northwest and setting up over the Midwest Thursday into Friday. Ahead of the trough, a surface low pressure system is expected to form over the Great Lakes region and track eastward with the trough. A cold front extending southward from the system will likely affect the track on Friday and/or Saturday. The disparity as to what day the front will pass through is due to the GFS and ECMWF in disagreement. The Euro indicates the frontal passage in the late afternoon or evening on Friday while the GFS shows the front passing Friday night. In both cases, precipitation is expected behind the front and with the front moving through earlier with the Euro, a chance for rain to disrupt on track sessions in the afternoon; precipitation would move through overnight according to the GFS.
With the front passing through, warm winds from the southwest will be expected at the surface, raising air temperatures to the lower 90's in addition to bringing moist air from the south to the region. The increased humidity at the surface will result in heat index values in the mid to upper 90's.
On Saturday, the center of the upper level trough will move through the Mid-Atlantic, continuing to push moisture into the region from the west and southwest. Through much of the region, there will be a slight chance for scattered showers, especially in the afternoon. Where there aren't showers, partly cloudy conditions are expected as moisture persists in the low levels. Surface winds from the west will continues to keep temperatures in the 90's, with dew points in the upper 60's causing heat index values to reach the mid 90's.
For Sunday, the trough will be to the east of the region, tracking into the Atlantic Ocean, resulting in the track being upstream of the center of the trough. Winds in the upper levels will be from the west to northwest bringing drier air to the region. Partly cloudy conditions are expected as the low to mid levels of the atmosphere will have moderate amounts of moisture and with the dry air above, conditions will likely remain the same for the majority of the day. Light winds at the surface from the north and northeast will keep temperatures around 90, though with dew point temperatures in the upper 60's, heat index values will be in the low 90's.