Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Sun Jul 29 2018 Valid 12Z Wed Aug 01 2018 - 12Z Sun Aug 05 2018 ...Pattern Overview and Guidance/Uncertainty Assessment... Model guidance this morning shows decent agreement on the synoptic pattern evolution across the U.S. through next weekend. An upper-level trough moving toward the eastern U.S. will be impeded and then weakened by a strong Bermuda High which is forecast to remain a dominate feature from the western Atlantic to the East Coast through much of this week. This will ensure tropical moisture to move up the East Coast with a good chance of precipitation. Meanwhile, models continue to show noticeable differences on the strength of a cool airmass moving into the northern Plains and the Great Lakes during the middle of the week, with the ECMWF continues to offer the warmest solution while the GFS solutions remain rather cool. This is reflected by a stronger high pressure system shown in the latest GFS (06Z) although not as strong as in previous runs. By next weekend, models agree that the Bermuda High will erode much of the upper trough axis along the Mississippi Valley with moisture lingering along the East Coast. Meanwhile, a significant upper trough/closed low would drop southeastward across the Gulf of Alaska toward the Pacific Northwest. Teleconnections relative to the positive height anomaly center near the Aleutians in D+8 charts favor a northeastern Pacific trough closer to the ECMWF/ECMWF mean. Therefore, the WPC morning grid fields were derived using a general compromise of the 00Z ECMWF with the 06Z GFS through Day 5 Friday. For Day 6 and 7, A 60% of the 00Z ECMWF/EC mean was blended with 40% of the 06Z GFS/GEFS mean. Kong ...Weather Highlights/Threats... The Southeast continues to show the best potential for highest rainfall totals during the period. Flow around the Bermuda high will support a persistent feed of low level Atlantic/eastern Gulf moisture into the region. This moisture should interact with the slow moving front over the East during the first half of the period. After the front dissipates expect convection to be somewhat less organized with increasing focus along terrain and localized boundaries. Convection/rainfall through the period may be problematic over areas that have received significant rainfall over the past two weeks. Expect some moisture/rainfall to extend into the Mid-Atlantic/Northeast, with pockets of moderate-heavy activity but in general less extreme totals than over the Southeast. Periods of convection with varying intensity will continue over the Four Corners states with showers/storms possibly extending into the southern High Plains at times. Across the northern states, advancing shortwave energy and surface low pressure/leading warm front should encourage convective development within an area from the northern Plains into western Great Lakes from late week into the weekend. Some thunderstorms may produce heavy rainfall. Across the West, flatter flow aloft over northern areas will bring temperatures down to near or slightly below normal. Expect the Great Basin/Southwest to see above normal min temps through the period but highs will likely be more moderate. A wavy front pushing into the northern U.S. will bring an area of well below normal readings into the northern Plains/upper MS Valley Wed-Thu. Then flattening of the upper pattern will encourage a warming trend to above normal levels, progressing from the northern Plains into Great Lakes during Fri-Sun. Clouds/rainfall should keep the Southeast below normal for highs on most days. Flow around the Bermuda high will promote above normal lows over the Mid-Atlantic/Northeast. Rausch WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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