Extended Forecast Discussion NWS Weather Prediction Center College Park MD 948 AM EDT Thu Aug 02 2018 Valid 12Z Sun Aug 05 2018 - 12Z Thu Aug 09 2018 ...Pattern Overview and Guidance/Uncertainty Assessment... The guidance shows very good agreement on timing of systems in and near North America, with some depth issues noted. Overall, the guidance has maintained better day to day consistency than seen this time yesterday. While the 00z Canadian is stronger than other guidance with troughing developing near the Great Lakes, it was the first to start the trend towards what the guidance now advertises. The 500 hPa heights, surface pressures, fronts, and winds are based on a blend of the 00z Canadian, 00z UKMET, 00z ECMWF, and 06z GFS through Tuesday morning to deal with the small differences seen in the guidance. Thereafter, incorporated increasing amounts of the 00z ECMWF and 00z NAEFS means which ramp up to 40% of the blend by next Thursday. The weather, dew point, cloud, temperature, and rain chance grids will reflect a more even blend of the deterministic and ensemble guidance. The days 4-7 QPF is likely to reflect a rough blend of the 06z GFS, 00z Canadian, 00z ECMWF, and 12z National Blend of Models. Should the 12z GFS have reasonable mass fields, it could be included as well. ...Weather Highlights/Threats... With the latest cycle of guidance either consistent with or furthering trends toward keeping the eastern Pacific upper low well offshore through the period while upper ridging builds over the West, confidence is increasing that most of the western U.S. should see a warming trend to above normal temperatures by Tuesday into next Thursday. Dry conditions will likely prevail over most areas as well, aside from diurnally favored convection at times over parts of the Four Corners states. Before this warm-up locations from the central West Coast into the northern Rockies may see below normal highs especially on Sunday. Record high minima are forecast across the Desert Southwest and southern California. Farther eastward the gradual development of upper troughing will help to push an initial wavy front over the northern Plains southeastward with time. As a result the focus for areas of potentially heavy/strong convection will shift from the upper MS Valley/Great Lakes/north-central Plains toward/into the eastern-southern states. Some rainfall is also possible with another front that may drop into the northern states late in the period but less available moisture should lead to lower totals than with the activity earlier in the period. Ahead of these fronts early in the week, a typical summer-like airmass across portions of the South and East may see scattered and generally light-moderate showers/thunderstorms. For temperatures east of the Rockies expect areas from the Great Lakes into the Northeast to see the warmest readings versus normal (especially for morning lows) in the Sunday-Tuesday time frame. The expected pattern evolution should yield near to slightly below normal highs over a majority of the East by next Wednesday-Thursday. Due to the available moisture and slowly declining temperatures/averages normally seen in August, record high minima are expected across southern New England. Roth/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