Extended Forecast Discussion NWS Weather Prediction Center College Park MD 230 AM EDT Thu Jun 21 2018 Valid 12Z Sun Jun 24 2018 - 12Z Thu Jun 28 2018 ...North-Central U.S. Heavy Convective Rainfall Pattern... ...Guidance and Predictability Assessment... Models and ensembles continue to show above normal agreement with the overall medium range flow pattern evolution, bolstering forecast confidence. Nrn stream flow features a slowly translational e-central Canada upper ridge bookended by amplified w-central Canada/NW U.S. and ern Canada/NE U.S. cooling troughs. A modestly progressive pattern underneath for the CONUS has a tendency for embedded system amplification. Energy digging through the Rockies to the n-central U.S. tends to deepen/close off in a region of relatively weak upper flow beneath the Canadian ridge. This seems the case again Sun-next Thu when ample system height falls and instability/pooling moisture set the stage for slow moving convective clusters that would lead to a locally excessive rainfall threat centered from the central plains to the mid-upper MS valley states. A mix of a few GFS/Canadian model runs over the past few days have also dabbled with the threat of closing off a Northeast/Ern U.S. trough with organized coastal lows as early as Mon/Tue, but run to run variance in these models with these features have been less than stellar. Accordingly, the WPC medium range product suite was mainly derived from a composite blend of reasonably clustered and consistent guidance from the latest ECMWF and GEFS/ECMWF ensemble means. This maintains excellent WPC continuity. ...Weather Highlights and Threats... Lead trough/low energy continues to shear northeastward over the Northeast then Canadian maritimes Sunday. Post-frontal high pressure will settle a moderating and wavy trailing front far down over the ern U.S. next week and focus some convection. Upstream, a dominant amplifying shortwave trough digs from the NW U.S. southeastward over the Rockies to the north-central states. This system will produce an organized surface low along a main frontal boundary. Convective complexes/heavy rains will focus along the front and into the warm sector fueled by pooled moisture. Meanwhile further upstream, a late season cooling front with much more modest pcpn shows good promise to work earnestly from western Canada down across the NW U.S. and n-central Great Basin/Rockies next week as supported by amplified mid-upper level trough amplification and passage to the north. Schichtel WPC medium range forecasts of 500 mb heights, surface systems, weather grids, quantitative precipitation, and winter weather outlook probabilities 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