Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Sat Jul 07 2018 Valid 12Z Tue Jul 10 2018 - 12Z Sat Jul 14 2018 ...Pattern overview/Guidance evaluation/Preferences... A persistent mid/upper-level ridge across the western/central U.S. will remain fixed over the region while flattening in time in response to amplification along the international border with Canada. While 500-mb anomalies should weaken from the expected 2 to 2.5 sigma values early in the week, the anticyclone will likely set up across Four Corners into the Southern Plains by Day 6/7, July 13/14. To the north of this positive height anomaly, an active pattern is anticipated as a pair of amplified systems track from the Pacific Northwest/southern British Columbia toward Hudson Bay. Each will likely be fairly impressive in nature with attendant deep surface cyclones tracking through central Canada. Ultimately this will have the influence of flattening the northern extent of the prevailing ridge across the western/central states. Meanwhile, what is expected to become Tropical Storm Three should gradually migrate northeastward away from the Gulf Stream after stalling during the short range period. The parent elongated upper trough which helps steer this tropical cyclone out to sea which linger over the eastern U.S. through Thursday before moving offshore. Overall guidance has been struggling with the handling of the tropical cyclone with a few random solutions taking the system toward the Eastern Seaboard. However, the 00Z guidance has shifted eastward which more closely mimics the forecast from the National Hurricane Center. Considering the remainder of the country, models have bounced around a bit with the timing of the lead system tracking across central Canada mid-week although they agree on the evolution of a rather defined surface low. In its wake, the guidance has trended deeper with the trailing upper trough which accelerates into British Columbia/Alberta by Friday with some southward extension into the northwestern U.S. At this point, the ensemble means sufficiently smooth out the pattern but are in agreement in maintaining the tightest height gradient along the international border with Canada. In terms of preferences, generally followed a combination of the 18Z GFS/GEFS mean, 12Z ECMWF/ECMWF ensemble mean, and 12Z NAEFS mean with decreasing operational influences deeper into the forecast period. ...Weather threats/highlights... While a vast majority of the country can expect above average temperatures next week, the exception will be the Desert Southwest eastward into the Southern Plains. An active monsoonal flow regime should maintain enhanced cloud cover and widespread showers/thunderstorms across the Four Corners. This should keep numbers several degrees below climatology for much of the period. Meanwhile, the most pronounced warmth will likely focus over the Pacific Northwest starting Wednesday with widespread 90s expected inland with cooler readings closer to the coast. In terms of precipitation, the most organized area of convection will be via the active monsoonal flow while diurnally forced activity is expected across the southern U.S. To the north, some frontal precipitation is possible over the north-central states in response to warm advection ahead of the next potent shortwave. Rubin-Oster 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