Extended Forecast Discussion NWS Weather Prediction Center College Park MD 252 AM 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 begin the forecast period early next week. By mid-week, the pattern is expected to become more amplified with a weak trough axis evolving across the eastern U.S. and the upper level ridge becomes more established over the Rockies, which is in response to a building trough over the northeast Pacific. By the end of the week, a cold front is expected to cross 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 synoptic scale pattern on Monday, with the main exception being a more amplified trough over the Ohio Valley with the past few runs of the GFS, with a few ensemble members also supporting this. This difference continues into mid-week with more troughing along the East Coast and more GEFS members supporting it. The UKMET appears stronger and more expansive with the upper level ridge over the south-central U.S. Towards the end of next week, model differences remain with the timing of the northeast Pacific trough as it tracks inland across southwest Canada. The 00Z ECMWF is faster with the progression of this trough axis over Alberta on Thursday, whereas the EC mean is farther back and the GFS/GEFS mean even slower. To address these differences, the medium range forecast was based mainly on a deterministic model blend with slightly greater weighting towards the ECMWF, and then more towards the GEFS and EC means for the end of next week. ...Sensible Weather... Temperatures are expected to remain above average across a large portion of the nation through Tuesday, compliments of the upper level ridge, with the exceptions being across parts of the Southeast owing to increased cloud cover and showers/storms, and also for the northern Plains. The heat is expected to be most pronounced across the central High Plains and across the Desert Southwest, 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. In terms of rainfall, there will likely be scattered areas of moderate to locally heavy rainfall across parts of the Midwest and also near the Gulf Coast, with most events resulting in less than 1 inch in any 24-hour period. At the end of the forecast period late Friday, it is worth noting that the GFS/GEFS ensemble members are hinting at the possibility of a heavy rainfall event near the central/western Gulf Coast region, but confidence in this scenario is limited at this time. Hamrick 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