Extended Forecast Discussion NWS Weather Prediction Center College Park MD 227 AM EDT Thu Jul 04 2019 Valid 12Z Sun Jul 07 2019 - 12Z Thu Jul 11 2019 ...Overview and Guidance/Predictability Assessment... Downstream of a Rex block across the North Pacific/Alaska, moderately progressive flow will pass between a building upper ridge across the CONUS southern tier, and a mean upper trough near Hudson Bay. A series of convection focusing shortwaves will traverse the zone of stronger flow, across the U.S. northern tier. This will act to push a cold front southeastward off the Eastern Seaboard on Thu, with the trailing end of the front expected to stall from the Southern Plains east to off the Southeast U.S. coast. Meanwhile, shortwave energy reaching the Pacific Northwest this weekend may separate into a more progressive northern component and a slower-moving shortwave crossing the Great Basin/northern Rockies through early next week, and the Northern Plains/Midwest by the middle of next week. A multi-model deterministic blend including the ECMWF/GFS/UKMET/CMC was used initially during days 3-4 (Sun-Mon). Model solutions were reasonably comparable to one another during this time frame, and a consensus/blend approach was favored. Starting on day 5 (Tue), deterministic solutions began to diverge substantially on the evolution of the western shortwave, and how much of the energy gets quickly sheared east in the stronger westerlies versus lingering in a deeper/slower western trough. In general, the trend has been to keep a somewhat more amplified and slower wave, with a less significant component shearing east in the polar jet. This idea has relatively strong support from the ensemble means, but as mentioned, deterministic solutions were much more variable. The solution most closely clustered with the ECENS/GEFS means was the 12Z CMC. Meanwhile, the 12Z run of the ECMWF was nearly out of phase with its own ensemble mean, moving much more of the energy eastward quickly. As a result of these differences, the forecast during days 5-7 (Tue-Thu) was based heavily on a blend of the ECENS/GEFS means and the deterministic 12Z CMC/GEM global. ...Weather Highlights/Threats... The frontal boundary crossing the central/eastern U.S. through much of the forecast period will focus areas of scattered to numerous showers and thunderstorms across a large area, including portions of the Central/Northern Plains, Ohio/Tennessee Valleys, and the Southeast/Mid-Atlantic through the middle of next week. Models show a signal for areas of heavy rainfall along the immediate Southeast U.S. coastline from Sunday onward. A renewed threat of more widespread convection may develop across the Northern Plains and Upper Midwest by Mon-Wed as the next shortwave/frontal system cross the region. Temperatures should be relatively close to seasonal norms across much of the CONUS through the medium range. Cooler temperatures (highs 5 to 8 deg F below average) are forecast across portions of the West early next week as the upper-level shortwave crosses the region. Ryan Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml