Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1202 PM EDT Sun Sep 15 2019 Valid 12Z Wed Sep 18 2019 - 12Z Sun Sep 22 2019 ...Overview and Guidance Evaluation/Preferences... The two main weather features through the medium range period are the trough digging over the Great Basin through Thursday then ejecting northeast across the northern Great Plains through next weekend and Humberto. For the western trough, the 00Z/06Z models and ensembles are in good agreement through Day 4/Thursday before the 06Z GFS becomes more progressive than the 06Z GEFS mean while the 00Z ECMWF and 00Z ECENS mean keep good timing into Day 6/Saturday. However, the 00Z GFS remains well aligned with the 00Z GEFS mean into Day 5. Therefore the 00Z GFS is used in the blend through Day 5 with a switch to the 06Z GEFS mean for the remainder of the period. The 00Z UKMET is quicker to eject the trough out west like the GFS, so a small amount of it was included through Day 4/the limit of its availability at WPC. There are differences again on Day 7 with the progression and strength of the next trough toward the Pacific Northwest with the 00Z ECMWF much more progressive than both the 00Z and 06Z GEFS. However, the ensemble means are not that far apart, so a heavy reliance on ECENS and GEFS means is used for Days 6/7. The 00Z CMC never ejects Humberto east of Bermuda like the rest of the global models. In fact, the 00Z CMC brings Humberto back toward NC on Day 5, so it was completely disregarded for this blend. ...Weather Highlights/Threats... Tropical Storm Humberto continues to be forecast by NHC to be a hurricane as it shifts east near Bermuda during the midweek. As the upper trough amplifies from the Pacific Northwest expect widespread rains (some very high elevation snow) to WA/OR Wednesday, spreading inland/south to MT/ID and northern NV/CA on Thursday. As the associated surface low spreads onto the northern Plains, expect an organized convective focus with locally heavy downpours shifts to the northern Plains Friday into Saturday before shifting east to the Great Lakes and central Plains Midwest next weekend. Increased moisture inflow up the Plains ahead of this system will lead to near record high minimum temperatures Wednesday with above normal temperatures there continuing through the rest of the period. The upstream pattern meanwhile reloads again over the West to reach the north-central states again next weekend. In this pattern expect subtropical moisture out of Mexico on southwest flow aloft over the Southwest/Four Corners states with rain chances mainly on Days 4/5. This moisture may fuel support for aforementioned potential convection downwind into the north-central U.S. Strong ridging downstream over the east-central U.S. will favor well-above average temperatures next week with some near record Deep South heat. Nearby in the western Gulf of Mexico, a trough/wave associated with an upper low favors a potentially heavy over coastal Texas midweek and weak steering aloft may allow this area of rain to persist through late week. 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