Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1219 PM EDT Tue Jun 05 2018 Valid 12Z Fri Jun 08 2018 - 12Z Tue Jun 12 2018 ...Pattern overview... Guidance shows a general trough-ridge-trough pattern aloft persisting through a majority of the forecast period. Passage of a vigorous shortwave trough across the Northwest during the weekend followed by low amplitude North Pacific flow will likely serve to flatten/broaden the overall mean trough over western North America late in the period and push the downstream ridge into the east-central part of the continent. However northeastern U.S. mean troughing may be reluctant to depart in spite of the broadening evolution to the west. Mean ridging aloft anchored over the southern Plains may weaken a bit during the weekend and rebuild over/near the southern Rockies around next Tue. Farther east there will be a weakness aloft over the eastern Gulf of Mexico/Florida. This feature will weaken gradually through the period. ...Model guidance/predictability evaluation/preferences... For the days 3-5 Fri-Sun part of the forecast a blend of latest operational model guidance represented consensus well for features that have a reasonable degree of synoptic predictability. The western-central pattern will sharpen as the strong upper trough and leading surface cold front reach the western U.S. while the central Canada ridge builds. This will start the process of reloading the eastern trough aloft with initial weak northern U.S. energy contributing to frontal waviness that reaches the East by Sun. Wave details will have low predictability and likely display meaningful run to run variability. By days 6-7 Mon-Tue the forecast starts to incorporate GEFS/ECMWF means along with latest operational runs as detail uncertainties increase. Timing spread develops for the western trough with ECMWF/CMC ensemble members tending to show faster ejection than a majority of GEFS members, while solutions are all over the place for the shortwave details of low amplitude flow immediately upstream. Issues with the western trough ultimately affect the front that reaches the Plains. The average of guidance yields a faster adjustment versus continuity but would like to await confirmation from further runs before trending as fast as the 06Z GFS/00Z ECMWF runs. Models/means appear somewhat more agreeable for persistence of the northeastern U.S. trough but some individual ensemble members show potential for higher heights aloft late in the period. At this time prefer the majority scenario that favors persistence of this trough. ...Weather highlights and hazards... Ridging aloft will support hot temperatures from the Desert Southwest eastward into the Plains, though with anomalies for daytime highs tending to be less than plus 10F. Greater anomalies for max/min readings are likely to extend from the Intermountain West into the northern-central Plains from Fri into Mon ahead of the cold front that pushes into the West. This cold front will bring some chilly temperatures into the West with the weekend likely featuring some highs up to 10F or so below normal from the northern half of the West Coast northeastward. Upper troughing will promote near to below normal readings near the East Coast. Multiple mesoscale complexes will likely extend from the Northern Plains into the Great Lakes/Ohio Valley region. The wavy front from the Plains to East Coast late this week through the weekend will provide a significant focus for locally heavy/strong convection. Amplifying upper troughing will also promote wet conditions over the East during the weekend. Farther south, expect showers/storms across Florida and parts of the Southeast, especially late this week into the weekend in association with the weakness aloft. The strong upper trough/surface front affecting the West will bring abundant precip to the Pacific Northwest/northern Rockies and eventually may generate some convection over the northern Plains. Rausch 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