Extended Forecast Discussion NWS Weather Prediction Center College Park MD 114 AM EDT Thu Jun 11 2020 Valid 12Z Sun Jun 14 2020 - 12Z Thu Jun 18 2020 ...Overview... An upper low is forecast to meander around the Mid-Atlantic states next week which could bring a multi-day rain to the region. In the West, one upper low will rotate out of Washington/Oregon late this weekend as another slides in from the Pacific late Tue into Wed. Ridging will lie in between, centered over the Southern Plains. ...Guidance/Predictability Assessment... Through the 12Z/18Z cycle, the ensemble means were in good agreement through the period with a bit less agreement over the Northwest due to a continued somewhat uncertain Pacific flow. The deterministic models still showed even larger differences in the West but less disagreement over the central states. In the East, models have wavered on the track of the upper low that will likely meander for a few days over the central Appalachians/Mid-Atlantic which will influence how much rainfall is expected. The 12Z GFS/Canadian closed off the upper low near the coast and moved it bodily eastward into the Atlantic, effectively rendering a much drier pattern for the region. However, the 18Z GFS and 12Z ECMWF/UKMET were closer to the ensemble consensus and continuity which keeps the upper low inland and the associated surface front along or just offshore the coast. With essentially no trend in the ECMWF ensembles the past four cycles, preferred to stay near the larger consensus of the 18Z GFS/12Z ECMWF. This also served well for the rest of the CONUS, with the possible exception of the Northwest where the GFS/GEFS were much deeper than the ECMWF and its ensembles around Tue. Gave a slight edge to the ECMWF and its ensembles over the GFS/GEFS but a deeper solution is within the realm of possibility considering upstream amplification between Alaska and Hawai'i. ...Weather/Hazard Highlights... Temperatures 5 to 15 degrees above normal are forecast for the Plains throughout the period and should build toward the Midwest/Great Lakes Tue/Wed. Behind the western front, cool temperatures with highs 5 to 10 degrees below normal are forecast for the Northern Rockies (especially on Sunday) before slightly moderating. With the prospect of a lingering upper low (and nearby front along the coast), abundant cloudiness could keep temperatures below normal by at least a few degrees over the Mid-Atlantic through the period, returning to near normal by the end of the period next Thu. Rainfall over the CONUS should be generally light through the medium range period with the exception of portions of the East. Given the upper low overhead and a stalled front along the Atlantic Coast, the Carolinas and Mid-Atlantic may see heavy rainfall for the first half of next week. Rainfall amounts and placement will depend greatly on the track of those features which will continue to be refined. Several inches of rain is possible over a multi-day period if the low stalls or meanders as forecast. The last 30 days has been drier than normal over VA/DC/MD/DE but wetter than normal over NC/SC, so where the heaviest rain may fall will be crucial to any future flooding concerns. Rainfall in the Northwest will generally be light with perhaps modest amounts on Monday over the coastal ranges and Cascades in Washington and northern Oregon. Fracasso Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml