Day 1-5 (Today (8/18) through Sunday (8/22))
An axis of heavy rain continues around the edges of a southeast ridge today with heavy rain over the lower Mississippi River Valley in association with the remnants of TD #5, and a batch of heavy rain from TN/KY into the mid-Atlantic and to just south of New York City. A surface low will form off the mid-Atlantic coast today and track just south of New England the next 24 hours. Several inches of rain are possible today over Louisiana and southern Mississippi, and also from North Carolina to Kentucky, Virginia, West Virginia, Maryland, eastern PA, and NJ. Severe weather will be possible the next several days in the upper Midwest.
The day 1-5 temperature anomalies http://raleighwx.easternuswx.com/models/00z1-5daytemps.html show the best heat over the High Plains and most of the central US being warmer than normal. In fact most of the country will be above normal the next 5 days except for the Pacific Northwest coast, and northern New England. The southern plains will continue to roast with temperatures near or exceeding 100 in Dallas for the foreseeable future and extending back into Oklahoma City, Tulsa, Little Rock, and Shreveport by the weekend. Significant heat could slide into Chicago and Cincinnati by Friday and the weekend with low to mid 90s possible there. Temperatures near and exceeding 100 are being shown Saturday and Sunday over parts of southeast Montana, northeast Wyoming, and the western Dakotas which could break records. This could include the Rapid City area.
Day 6-10 (Monday (8/23) to Friday (8/27))
I will lean on the GFS and ECMWF ensembles this period which will feature the best heat across the Mississippi River Valley into the Midwest and Lakes region, as well as building heat in the southwest US. The east coast will be tricky as the evolution of an eastern US trough is being debated by the models. The operational ECMWF is much deeper with this trough than the ensemble guidance and also the GFS. The ensembles paint a compromise which would keep the east coast slightly above normal. The Pacific Northwest is also a bit tricky but I favor a cooler pattern there.
The hottest spots could include southern California, Las Vegas and Salt Lake City this period.
A zone of storms could set up from the Front Range into the northern Plains and upper Midwest.
Day 11-15 (Saturday (8/28) to Wednesday (9/1))
It seems like the 6-10 day pattern will continue into the 11-15 day period with a southern US upper ridge amplifying and leading to a warm look for most of the US outside the northwest US. The location of the ridge axis could mean the axis of the warmest temps will extend from the 4 Corners to the central plains to the Midwest to the northeast US. The Gulf Coast and Florida could see less in the way of heat. Right now this pattern looks to stick around until at least early September.
We will also have to watch the tropics would could greatly affect temperatures and rainfall in the southeast US including Florida.
Images related to this discussion are in the slideshow below.