Extended Forecast Discussion NWS Weather Prediction Center College Park MD 203 AM EDT Fri Jun 1 2018 Valid 12Z Mon Jun 4 2018 - 12Z Fri Jun 8 2018 Pattern overview and guidance evaluation ---------------------------------------- The forecast period begins on Monday with an upper trough over the Pacific Northwest, a ridge axis encompassing the central U.S., and a developing trough over the eastern U.S. with a surface low offshore. This overall synoptic scale pattern is expected to hold through much of the upcoming week, with disturbances tracking across the northern tier of the U.S. around the northern periphery of the upper ridge that will be building over the southern plains. In terms of the model guidance, the greatest uncertainty exists over the northeastern quadrant of the nation early in the week with two separate low pressure systems. 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. The deterministic ECMWF, GFS, UKMET, and CMC are now northwest of the ensemble means, and closer to the coast. 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. In terms of the WPC forecast, some of the deterministic GFS and ECMWF was incorporated for the first half of the forecast, and then mainly ensemble means by next Thursday and Friday. Some previous WPC continuity was used given the noteworthy changes in deterministic model runs. Weather highlights and hazards ------------------------------ The best prospects for noteworthy precipitation across the continental U.S. will be from the Great Lakes to New England in association 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. In the temperature department, the heat wave across Texas and Oklahoma is forecast to continue going into next week owing to the building upper level ridge in place and dry conditions. Widespread highs exceeding 100 degrees are expected as far north as Kansas early next week, and a few locations may approach 110 degrees over western Texas. Some record high temperatures are likely during this time. 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 D. Hamrick