Extended Forecast Discussion NWS Weather Prediction Center College Park MD 254 AM EDT Sun Jul 08 2018 Valid 12Z Wed Jul 11 2018 - 12Z Sun Jul 15 2018 ...Pattern overview/Guidance evaluation/Preferences... Model guidance this evening is in excellent agreement on the general evolution of the synoptic pattern across North America through next weekend. An upper-level trough moving into the Northeast early in the week is forecast to lift toward southeastern Canada by midweek. This will bring a cold front through the Northeast into much of the Mid-Atlantic and help accelerate what is still Tropical Depression Three off the North Carolina coast toward the northeast. The UKMET has been advertising the storm to linger a bit longer off the Southeast U.S. coast before accelerating it just off or across coastal New England around the Day 4-5 time frame. This scenario has been discounted. Consult NHC products for latest information on T.D. Three. As the upper trough lifts out of the Northeast, models are in unanimous agreement that the warm subtropical high will reestablish and anchor itself over the central Plains with a slight tendency of extending a ridge westward into the western U.S. through next weekend. Meanwhile, a couple of shortwave troughs are indicated to traverse western Canada just north of the U.S.-Canadian border. Despite their relatively fast zonal movement, models are in excellent agreement on their speeds of motion and amplitudes. The associated cold fronts will likely move across the northern tier states through the medium-range period. Therefore, the evening WPC medium-range grid package was a consensus of the 12Z and 18Z GFS together with the 12Z ECMWF with more of the 12Z GEFS mean and 12Z EC ensemble mean included toward Days 6 and 7. The 12Z GEFS was chosen instead of the 18Z GEFS due to better agreement with the 00Z EC mean on the surface features in central Canada. Their U.S. surface features are in excellent agreement however. ...Weather threats/highlights... With the subtropical high forecast to reestablish over the central U.S., temperatures are expected to remain above average across the region through next weekend. Farther north across the northern tier into the Northeast and Mid-Atlantic, periodic cold frontal passages will bring occasional breaks in the heat and humidity along with passing showers and thunderstorms. South of the center of the subtropical high, an active monsoonal flow regime should keep temperatures below normal with showers and thunderstorms likely across the Four Corners region. Over the western U.S., expect well above normal readings to persist across the interior Pacific Northwest throughout the end of the week with triple-digit heat most likely on Thursday. Meanwhile, a good chance of showers and thunderstorms can be expected to persist across the southeast U.S., Florida and along the Gulf Coast through this week, keeping temperatures near or slightly cooler than normal. Kong WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found at: http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 http://www.wpc.ncep.noaa.gov/heat_index.shtml