A quick update,
Rain continues tonight and into Friday as instability hangs around from the approachng trough. After a quick chance for mid to upper 80s this weekend with warmer 850's and a SW flow, most models show a reloaded trough moving back east that could be stronger and more vertically oriented, or more zonal than this past one, either way keeping us below average for most of next week. As i mentioned, i  think the question is how  below average we will get. Models agree on moving in a trough, but their is a discrepancy on how vertically oriented and strong the trough itself will get. taking a look at the GFS and GEM discrepancy at the 500mb heights. Both show a strong ULL over Canada between 136 and 150 hours,

The GEM has a 594 DM high popping a strong + PNA ridge in the west. You can also notice the HP center is further west itself. This allows the Upper Level Vort over Canada to react and form a sharper and stronger vort with tighter pressure gradients over the Eastern US and Build a strong 1023mb high on the back side of the trough

 

With the tight trough over the Eastern US with a strong Vort Max over Canada it allows even cooler air to filter in behind the departing ULL bringing much below average 850's and in turn temperatures.

 

The GFS on the other hand has a much weaker Hp is the SW that is displaced further east due to the GFS's accelerated movement of the ULL. With out the HP being further west and in a more stronger and dominating position, it is unable to form a more vertically oriented Positive ridge in the west, therefore not allowing the ULL to dive further south and enhance the trough, making the pattern in the Eastern US more zonal than the GEM.

 

At 150 hours you can easy see the difference between the GFS and GEM, the GFS has the ULL much father to the east than the GEM, and a almost complete zonal pattern with little vertical tilt to the Jet stream. this allows more seasonable temperatures to stay in the area with a west wind rather than a cool NW or N wind  and allowing the bulk of the cooler weather to the west.

 

Their has been a trend to a weaker trough in the east in this time period over the last day or two. If this trend continues we will not see much below average temps, but if the global guidance holds suite we could be in for a even more pronounced cool down. We will see how models trened the next couple days.