Extended Forecast Discussion NWS Weather Prediction Center College Park MD 236 AM EDT Sun Jun 17 2018 Valid 12Z Wed Jun 20 2018 - 12Z Sun Jun 24 2018 ...Heavy rain threat for southern Texas and the north-central U.S... ...Pattern Overview and Guidance/Predictability Assessment... Short range western U.S. closed low energy and height falls eject to the Plains midweek and Mississippi Valley late week. Strong Pacific Northwest ridging shifts eastward as a shortwave trough breaches the Northwest Friday. Meanwhile, the northern periphery of downstream ridging over the East/Southeast is eroded by northern stream cyclonic flow over the Great Lakes and the Northeast, which should suppress the oppressive heat and humidity expected early this week. Overall, the models and ensembles show a reasonably similar larger scale pattern over the next week, but smaller mid-scale embedded features still offer a bit of forecast spread. This cycle of the WPC medium range suite was mainly derived from a blend of the latest runs of the GFS/ECMWF with their ensemble means. Leaned weighting in this composite in favor of the ensemble means and euro guidance to de-emphasize the less predictable smaller scale features which still remain highly uncertain. This forecast methodology maintains good WPC continuity. ...Weather Highlights/Threats... A main and persistent/wavy frontal boundary remains quasi-stationary this week from the Plains to the Ohio Valley and Mid-Atlantic. Periods of locally excessive convection will focus along this boundary and in the warm sector aided by early period tropical moisture influx from the Gulf of Mexico. WPC medium range QPF forecasts show the heaviest potential over southern TX due to a potential tropical wave/disturbance now followed by NHC. Moisture streaming inland intersects the wavy boundary to the north to fuel strong/severe convection as per SPC and periods of potentially excessive rainfall centered over the N-central U.S. As the trough and front shifts slowly eastward into later week, the heaviest rainfall may increasingly spread along the surface boundary as enhanced by any potential wave developments/convective system propagations into the Midwest/Ohio Valley states and Mid-Atlantic. Schichtel WPC medium range forecasts of 500 mb heights, surface systems, weather grids, quantitative precipitation, and winter weather outlook probabilities can be 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