Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Fri Jun 22 2018 Valid 12Z Mon Jun 25 2018 - 12Z Fri Jun 29 2018 ...Overview and guidance/predictability assessment... Models and ensembles continue to agree that the split upper-level pattern across North America will gradually become more consolidated by the middle of next week as heights are forecast to rise over the central and eastern U.S. First, the positively-tilted trough digging down into New England on Monday should move off into the Canadian Maritimes Monday night. The GFS shows a surface low closer to the New England coast on Monday while the GEFS centers the low farther east, which is in better agreement with both the ECMWF and Canadian models. Meanwhile, another compact shortwave trough/low should emerge from the northern Rockies into the northern Plains. This system should help the development of mesoscale convective systems over the central Plains where excessive rainfall is possible Monday into Tuesday. Models agree that the shortwave will lift toward the Great Lakes and weakens will time. The intensity of the precipitation should decrease as the system moves into the Midwest and Great Lakes during midweek next week. By late next week, there is excellent agreement on a Pacific front moving through the northwest U.S. into the northern tier where moisture supply appears somewhat lacking. Therefore, the WPC medium range morning product suite was derived from a composite blend of the 00Z ECMWF, 06Z GFS, and a small portion from the 00Z Canadian model, trending toward their ensemble means through Day 7. This maintains good WPC continuity. ...Weather threats/highlights... An area extending from the northern-central Plains into the western Great Lakes will be one focus for heavy rainfall during the period. The majority of convection will be supported by the system tracking from the Plains into Great Lakes Mon-Wed. Some moisture will eventually extend into the East but rain should trend lighter as upper dynamics weaken/lift farther north. The front moving into the West early in the week may bring light/scattered precipitation to extreme northern parts of the West and then some light-moderate rainfall over the northern Plains. As this front stalls, it may become a more prominent focus for convection over the northern tier states toward the end of the week. This latter potential episode will have to be monitored for any overlap with locations receiving significant rainfall earlier in the week. Meanwhile some areas over the Southeast/Florida may see one or more days of locally heavy rainfall in diurnally favored convection. A cold front dropping into the Southeast and eventually weakening will likely enhance showers/thunderstorms at times. After eastern U.S. surface high pressure departs into the Atlantic after Tue, the expected pattern evolution at the surface and aloft should promote an expanding area of heat/humidity over the central/eastern states. Greatest anomalies for min/max temperatures (plus 10-15F) by Thu-Fri should extend from parts of the Central Plains through the MS Valley into portions of the Great Lakes/OH Valley. Dew points reaching well into the 70's F over some areas may contribute to high heat index values. Another area of persistent warmth albeit with lower humidity should be over the Great Basin/Four Corners region, with min temps tending to be somewhat more above normal than maxes. The initial High Plains system will lead to cool daytime highs on Mon. The Northwest will see near to below normal highs behind the early week front and then with upper troughing moving in late in the week. A warming trend is expected for the central and eastern U.S. next week where temperatures are forecast to reach the century mark at some locations. Kong/Rausch 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