Extended Forecast Discussion NWS Weather Prediction Center College Park MD 222 PM EDT Sat May 30 2020 Valid 12Z Tue Jun 02 2020 - 12Z Sat Jun 06 2020 ...Well above normal temperatures for the Great Basin/Rockies/Plains... ...Overview and Guidance/Predictability Assessment... Guidance overall agrees in showing a persistent and highly amplified/blocky large scale flow pattern over the CONUS and vicinity highlighted by mean upper troughs over the West Coast and Northeast that sandwich a hot south-central U.S. upper ridge. Predictability at the large scale is above average, but not so especially days 4-7 with the timing of small-mid scale embedded features embedded within the flow. A reasonably well-clustered guidance blend including the ECMWF/GFS seems reasonable for Tue-Wed. However, opted to gradually switch to a GEFS/ECMWF ensemble mean blend starting on day 5 (Thu) in an effort to mitigate numerous less predictable smaller-scale model timing and detail differences. Applied somewhat greater weighting to the overall less progressive ECMWF ensemble mean to maintain best WPC product continuity. The ensemble means favor a slow ejection of closed southern CA upper trough next week, and in general the models have trended a bit slower with this feature over the past several runs, but the GEFS members remain generally faster than the ECENS members. The generally blocky pattern nature seems to favor the slower side of guidance spread. The ensemble means also agree better than individual model runs for cooling and unsettling trough energy that works into the Northwest later next week. Guidance continues to have difficulty downstream with the path and evolution of a series of lead shortwave energies that eject from the West and track on/into the northern periphery of the central U.S. upper ridge and into the Northeast/Eastern U.S. upper trough position. Feature predictability is low due to their small scale, but they will drive locally organized diurnal convection and meso-boundaries/fronts across the broad region. Guidance especially continues to vary with respect to the progression and focus of these boundaries. ...Weather/Hazard Highlights... Highest anomalies within the area of much above normal temperatures centered over the west-central U.S. should be over the north-central Rockies/Plains Tue with readings up to 15-20F above normal and some daily record highs/warm lows possible. Temperatures should become less anomalous by Wed-Thu, but a broad area of plus 5-15F anomalies for highs may persist through the end of the period from parts of the central U.S. into pre-frontal Great Basin/interior CA. The pattern should favor multiple episodes of showers/thunderstorms with best potential of locally moderate to heavy downpours from the Mid-Upper MS Valley and Great Lakes/OH Valley to the central Appalachians/Mid-Atlantic. The uncertainty in surface wave/frontal specifics keeps confidence fairly low for details on magnitude and location of highest rainfall totals. Farther west, a wavy front extending into the Northern Plains/Rockies may provide a focus for rainfall but again there is still poor agreement on the specifics. Potent upper troughing is expected to bring height falls through the Northwest into later next that will generate some rainfall, while diurnal rainfall should continue over the central/southern Rockies. Other parts of the West may see scattered activity depending on shortwaves within the overall West Coast upper trough. Southern parts of Texas and Florida may also see some rain near a front that settles into the Gulf of Mexico. There is some potential to monitor for moisture working northward from the unsettled tropics to enhance rainfall late next week over the Gulf of Mexico/vicinity with approach of a ridge penetrating upper trough slated to drop down from the southern Plains. Schichtel/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