Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1201 PM EDT Tue Sep 17 2019 Valid 12Z Fri Sep 20 2019 - 12Z Tue Sep 24 2019 ...Overview and Guidance Evaluation/Preferences... Latest global guidance is similar on the large scale pattern into Sunday/Day 5 before divergence on the depth of a low over the southwest CONUS and how cut off it becomes into Day 7. There are some notable small scale differences, particularly with the Day 3/4 shortwave lifting over the northern Great Plains. The 06Z GFS is more amplified and farther south than the 00Z ECMWF/UKMET. This feature is much weaker in the 00Z CMC, so the CMC is excluded from the blend after Day 3. The 00Z UKMET has a similar approach to this north-central wave through Day 4 before diverging with a stronger shortwave crossing the central Plains on Day 5, so the 00Z UKMET is excluded after Day 4. The blend of Days 5-7 are a combination of the 06Z GFS/GEFS mean and 00Z ECMWF/ECENS mean. Both deterministic runs close the low over the southwest CONUS on Day 6 and cut it off on Day 7. There is considerable separation of the zonal northern stream trough over Canada and the low off the southern CA coast on Day 7 in the ECMWF while the 06Z GFS has a ridge over southwestern Canada with the low over the Great Basin. A climatology of the southwest CONUS does indicate a great increase in cutoff lows over the southwest CONUS from mid to late September, so this is a reasonable solution. A preference was given to the 00Z ECMWF/ECENS for Day 7 given its longer trend of a cutoff low. ...Weather Highlights/Threats... Deep tropical moisture will lift north to the east-central Plains to the middle MS Valley ahead of a trough crossing the northern Great Plains this weekend. This will focus heavy convection/runoff issues with cell training from the east-central Plains to the Mid-MS Valley/Midwest this weekend and into the Midwest early next week. There is a severe thunderstorm threat ahead of that northern Great Plains trough Friday into Saturday. 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