Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1218 PM EDT Tue Jul 10 2018 Valid 12Z Fri Jul 13 2018 - 12Z Tue Jul 17 2018 ...Overview, guidance evaluation and preferences... Model guidance this evening shows good overall agreement on the evolution of the synoptic pattern through next Tuesday. For the 500 hPa heights, pressures, and winds, used a compromise of the 00z Canadian, 00z UKMET, 00z ECMWF, and 06z GFS into Sunday morning. Thereafter, started blending in some 00z NAEFS mean and 00z ECMWF ensemble mean to deal with the uncertainty inherent at longer ranges. The temperatures, dew points, clouds, weather, and precipitation chances were derived from a 50/50 mix of deterministic and ensemble mean solutions. The preliminary days 4-7 QPF starts with a four-way blend of the 06z GFS, 00z Canadian, 00z ECMWF, and the 12z National Blend of Models. Should the 12z GFS prove useful, its thoughts could be included as well. ...Weather highlights... Although the dominating subtropical high will bring heat across a large portion of the country through early next week, there will be bouts of cool air intrusion from Canada following occasional frontal passages across the Northern Tier. A cold front will initially bring showers and thunderstorms across the northern Plains into the Great Lakes Friday but as the front is forecast to become more diffused with time, more isolated coverage in the Northeast will be the result during the weekend. Meanwhile, the next front will move out of Canada this weekend with scattered showers and thunderstorms along/ahead of its boundary. Cool air in its wake will break the heat wave across the northern Rockies and is forecast to drop temperatures more than 10 degrees below normal across the northern Plains early next week. Ahead of the front, temperatures will be about 5-10 degrees above average (80s and many 90s), and initially near or above 100 over portions of the interior Pacific Northwest/Great Basin on Friday. But triple-digit heat is expected to continue in parts of interior California. From the southeastern U.S. westward along the Gulf Coast, a dissipating front will keep a chance of showers and thunderstorms in the vicinity through the weekend. Monsoonal moisture will linger across the Four Corners area where locally heavy downpours are possible through early next week. Temperatures will generally be near or below average in the Southwest under limited solar insolation and a daily chance of showers/storms. Roth/Kong/Fracasso 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