Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1155 AM EDT Sat Jul 07 2018 Valid 12Z Tue Jul 10 2018 - 12Z Sat Jul 14 2018 ...Pattern overview/Guidance evaluation/Preferences... A mid/upper-level ridge will persist across the western/central U.S. through the period. While 500-mb anomalies should weaken from the expected 2 to 2.5 sigma values early in the week, the anticyclone will most likely set up across Four Corners/Great Basin into south-central portions of the Plains by Days 6/7, July 13/14. The northern periphery of the mean ridge should flatten with time due to an active pattern involving a pair of amplified systems tracking 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. Their trailing fronts should extend into the Northern Tier states. Meanwhile the National Hurricane Center is issuing advisories for what is currently Tropical Depression Three over the western Atlantic, with strengthening anticipated over the coming days while the system initially stalls and then tracks northeastward offshore the East Coast. Consult NHC products for latest information on T.D. Three. An elongated upper trough that helps to steer this tropical cyclone out to sea should linger over the eastern U.S. into late week before weakening/moving offshore. Early in the period 00Z-06Z GFS runs and the 00Z ECMWF/CMC offered good agreement with significant features (aside from T.D. Three) and had good support from the ensemble means, so those solutions provided the basis of the forecast into Day 5 Thu. At that time guidance began to diverge in response to differences that develop with North Pacific/Alaskan flow. Of particular note the 06Z GFS became out of sync relative to the 00Z GFS/ECMWF/CMC and their ensemble means so the updated blend removed that run after Thu. Meanwhile by Fri-Sat consecutive operational model runs and individual ensemble members suggest decreasing detail confidence within a pattern that at least shows a general theme of broadly cyclonic flow over the western half of Canada and extending into the Northern Tier U.S. As a result the forecast trended much more toward the 06Z GEFS/00Z ECMWF means late in the period. Latest guidance consensus shows the front that drops into the eastern U.S. Tue onward pushing farther south than prior forecast as well as persisting for a longer time before weakening. There is also more of a signal for some degree of waviness (frontal or otherwise) near the southern Mid Atlantic coast during the latter half of the period. ...Weather threats/highlights... A majority of the country can expect above average temperatures next week, with the primary exception being 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, keeping high temperatures several degrees below climatology for much of the period. The eastern U.S. cold front and trailing high pressure should bring a couple days of near to slightly below normal temperatures to the Northeast/Mid Atlantic around midweek. Expect the Interior West into northern Plains to see well above normal readings Tue-Wed ahead of the first front progressing into/across the Northern Tier. Then the Pacific Northwest will see a pronounced warming trend by Wed-Thu ahead of the next front. In both cases some plus 10-20F anomalies are possible. In terms of precipitation, the most organized and persistent area of convection will be via the active monsoonal flow over and near the Four Corners states while diurnally forced activity will occur across the southern U.S. The cold front pushing into and eventually stalling over the eastern U.S. may add some focus for convection. To the north, some locally heavy convection is possible with the front crossing the northern Plains/upper MS Valley around Tue-Wed with amounts tending to be lighter farther south/east of this region. There may be another period of convection over the Northern Tier late in the period as the trailing part of the front returns northward and the second front from western Canada approaches. Rausch/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