Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Mon Jun 18 2018 Valid 12Z Thu Jun 21 2018 - 12Z Mon Jun 25 2018 ...Guidance/Predictability Assessment and Weather Highlights/Threats... Models and ensembles are in closer agreement with overall pattern timing and evolution, bolstering forecast confidence, with a composite trending slightly more progressive with mid-latitude flow and more amplified northern stream flow over Canada. Central plains closed trough/low energy Thursday slides east-northeastward over the east-central U.S. then the northeast late weekend. This occurs as a kicker shortwave trough pushes inland over the NWRN U.S. Friday and through the Rockies into the central states. Guidance has also trended to produce a more developed series of surface lows to run along a main frontal boundary from the Plains to the Ohio Valley and Mid-Atlantic. Expect periods of locally excessive convective complexes/rains to focus along this boundary and in the warm sector aided tropical moisture influx from the Gulf of Mexico. Guidance differences are indeed more stark underneath with the short and medium range heavy rain threat over Texas associated with a tropical disturbance now over the Gulf of Mexico. This system in some form is expected to lift over Texas with parts lingering back toward the Rio Grande Valley. The operational ECMWF and UKMET still both show a much better defined system and extremely heavy rainfall, while the GFS and ensemble means offer much less. Tropical nature and slow translation should combine to pose a heavy/excessive rainfall threat, leaning WPC QPF in the direction of the wetter lingering scenarios. Otherwise, the WPC medium range product suite was primarity derived from a composite model blend across the mid-latitudes. 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