Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1206 PM EDT Fri Aug 16 2019 Valid 12Z Mon Aug 19 2019 - 12Z Fri Aug 23 2019 ...Weather Pattern Overview... A zonal upper level flow pattern is expected across the north-central U.S. with a broad upper level ridge over the southern tier states to start the work week. By mid-week, the pattern is expected to become more amplified as a powerful low pressure system develops off southeast Alaska, driving an upper level ridge to develop up the Rockies and into the Canadian Prairies and shunting low pressure toward eastern Canada. By the end of the week, a cold front associated with the eastern Canadian trough/low is expected to have crossed much of the eastern U.S. with the upper level trough axis situated over the northeast U.S. ...Guidance/Predictability Assessment... There is good overall deterministic model and ensemble agreement with the overall synoptic scale pattern through the period with details to the main two lows (one moving into southeast AK Tuesday and the other crossing eastern Canada middle to late in the week) differing particularly with magnitude of the parent low and timing of amplifying shortwave troughs around these lows. The GFS remains the deepest with the eastern low as it crosses northern Ontario from the 20th to the 21st which slows its progression toward Labrador and makes for less troughing in the northeast U.S. for Days 6/7. The 00Z ECMWF deterministic continues to eject the trough across the Canadian Rockies on the 22nd/Day 6 faster than the 00Z ECENS mean which is east of the 00Z/06Z GFS/GEFS trough axis. To address these differences, the medium range forecast was based mainly on a deterministic model blend with slightly greater weighting towards the ECMWF through Day 5, and then heavily toward the GEFS and EC means for Days 6 and 7. ...Sensible Weather... Temperatures are expected to remain above average across a large portion of the nation into Wednesday with cooler than average temperatures expected to spread east from the Plains to the northeast downstream of the developing ridge over the Rockies and warmer than normal conditions upstream. The heat is expected to be most pronounced across the southern High Plains Monday with highs of 10 to 15 degrees above normal. This will equate to widespread triple digit heat for those areas. Cooler and less humid conditions will likely be in place across much of the north-central U.S. and extending to the East Coast to close out the week after the passage of the cold front while the west remains several degrees above normal. Heavy rainfall is expected to be quite limited across the central and eastern U.S. given a progressive cold front, though there are indications the western end of the front may be slower over the southern Plains where enhanced heat and humidity could cause local issues due to heavy rain Wednesday into Friday. Jackson 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