Surface ridge bringing nice weather over much of the central and eastern U.S. will be replaced by a mid level ridge that will build heat into the southern plains and northeast late this weekend into next week. For the southern plains the 90 degree heat returns starting today with deeper moisture returning north owing to southerly return flow. Overnight lows will warm noticeably but daytime highs will remain in the lower to middle 90's. The triple digit heat will not be making a return but the heat index WILL come back into play. For the northeast heat, perhaps excessive builds in with high temperatures likely approaching the century mark in some locations. The heat will persist for much of the week.
A STRONG cold front will blast through the northwest by early week as a deepening cyclone develops over Canada. The cooler air will rush south by the weekend knocking temps back down into the lower 80's(some of the raw model data shows 70's) in the southern plains along with less humidity. This front will follow eastward ending the heat wave. However a particularly fast westerly flow undercutting a ridge will develop and lead to quick air mass changes. It appears that a pattern featuring deep cyclones over the northern plains/southern Canada bringing hot and humid air quickly northward followed by a push of cooler pacific air will develop next week. This may also lead to some severe weather setups for the northern and central plains. It's all a sign that fall is making its arrival and summer's days are numbered. Some of the longer range models show a very strong front coming in around mid september undercutting a ridge of high pressure. This is not to be taking literally for now as it's quite a ways off but my point is that the persistent heat has likely ended with cooler pacific(and at times modified canadian air) entering the synoptic pattern. Pushes of heat will still occur but will likely be short lived and not as intense as earlier this month.