Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1152 AM EDT Fri Jun 01 2018 Valid 12Z Mon Jun 04 2018 - 12Z Fri Jun 08 2018 ...Heat wave to continue across portions of the Southern U.S... Pattern overview and guidance evaluation ---------------------------------------- Two prominent large scale features will be present throughout the extended periods; a broad ridge across the southern CONUS and trough over the Great Lakes and Northeast region. Shortwave troughs will move onshore the Pacific Northwest Coast and ride over the ridge top, which will then reinforce the trough over the trough over the East. For the latest run of the model guidance, the ensemble means are actually having a better handle on the evolution of individual fronts in terms of clustering and timing. The 00Z ECWMF run for the first 3 days of the extended was more positively-tilted and more progressive with the surface lows moving up the Northeast Coast than all of the other solutions, but then slowed significantly for the later periods. The 06Z GFS favored a more neutral-slightly negatively tilted trough, which favored a slower progression through the eastern third of the U.S. The ensemble means took a middle ground approach, not only on the depth of the lows but also the timing and track. With such a significant difference within the operational models, the preferred blend for the entire extended forecast comprised of equal parts of the 00Z ECWMF/GEFS/NAEFS means. The one of greatest interest will be a possible nor'easter southeast of New England through early Tuesday, and there has been a trend for this to be closer to the coast and slower to depart the region. Farther upstream across the northern plains and Midwest states, the models are having difficulty with the progression of embedded shortwaves in the northern stream flow that eventually amplify the large scale trough over the eastern U.S. The guidance continues to agree well on the placement and amplitude of the upper ridge over the southern plains. Weather highlights and hazards ------------------------------ Precipitation can be expected from the north-central states to New England with the upper low and trough, along with a surface low developing offshore. There has been a trend for heavier rainfall from this coastal low to affect parts of the northeast U.S., with the possibility of a late season nor'easter affecting coastal New England for early next week. Another area of concentrated showers and storms is expected across the Dakotas and the Upper Midwest by the middle of next week as a disturbance crosses near the Canadian border. Model guidance is also signaling possible mesoscale convective systems (MCS) developing from Oklahoma and propagating southeast in northwest flow aloft early in the week. The ridge over the South will result in a heat wave from southern California, the Desert Southwest and the Southern/Central Plains. Several locations across Texas, Oklahoma and into Kansas will observe afternoon high temperatures exceeding 100 degrees- a few locations may approach 110 degrees over western Texas. Daily records for high temperature will likely be tied or broken in the coming week. Above normal temperatures are also expected across the Rockies and extending northward across the north-central U.S. More pleasant temperatures can be found for the Northeast U.S. and the Pacific Northwest, which will be under the influence of the upper level troughs. After an unusually warm month of May, the beginning of June appears to be below average for temperatures next week from the mid-Atlantic and extending northward to New England, with cooler northerly flow behind the low pressure system offshore. 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 Campbell/D. Hamrick