Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sun Sep 13 2020 Valid 12Z Wed Sep 16 2020 - 12Z Sun Sep 20 2020 ...Sally to become a Hurricane by midweek central Gulf Coast states landfall to offer a significant heavy rainfall/flood threat to spread Thu-Fri to the Southern Appalachians... ...Some welcome rains for Northwest/Northern California this week... ...Guidance/Predictability Assessment... The 00 UTC GFS/GEFS mean have come into better agreement with latest ECMWF/UKMET and ECMWF ensembles and despite lingering forecast spread a composite blend now seems reasonable for the overall pattern over the CONUS and Sally. Please though refer to the latest NHC advisories on Sally. ...Overview and Weather/Hazard Highlights... With Sally forecast to head toward the central Gulf Coast and intensify into a hurricane, the threat of heavy rainfall, damaging winds, and storm surge have continued to increase along the Gulf Coast into mid-week. A lingering and slow moving front draped atop will likely help to focus very heavy rainfall along the eastern Gulf Coast into the Florida Panhandle as well as along the western Gulf Coast well into later week. But the highest threat of heavy rain in addition to high winds and storm surge may ultimately be near and just east of where Sally makes landfall. Deep moisture and slow system translation suggest that a significant heavy rainfall and flooding threat will work from the central Gulf Coast states/TN Valley to the southern Appalachians and also over the Southeast/Southern Mid-Atlantic as a weakening but still deeply wet system as dependent on the degree of extratropical interaction with northern stream upper trough and front approach. Meanwhile, a complex evolution over the northeastern Pacific should yield a fairly deep trough/closed low that is slated to slowly bring some welcome rainfall and cooler temperatures into the fire stricken Northwest and northern California by midweek, lingering into late week in a wet late summer pattern. Schichtel 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