Extended Forecast Discussion NWS Weather Prediction Center College Park MD 326 AM EDT Tue Oct 01 2019 Valid 12Z Fri Oct 04 2019 - 12Z Tue Oct 08 2019 ...Central U.S. heavy rain threat diminishes late this week but could return/extend eastward by the weekend and early next week... ...Record warmth continues for the Southeast into Thursday... ...Overview and Guidance/Uncertainty Assessment... A less amplified and more seasonable mean flow aloft is expected to begin the medium-range period before the pattern possibly becoming more amplified again by early next week. Models have come into better agreement with an intensifying low pressure wave to move quickly off to the east of New England on Friday. The trailing cold front will bring an end to the record heat over the eastern U.S. Meanwhile, an upper-level trough is forecast to progress steadily through the western U.S. and should reach the Plains during the weekend. Model guidance appears to indicate a trend toward a more amplified broad scale pattern, with larger than normal uncertainty regarding the subsequent evolution of this trough as it heads toward the East Coast early next week. The WPC forecast grids were derived mostly from a blend of the 18Z GFS and the 12Z ECMWF, with more weights given to the ECMWF. Some 12Z UKMET and 12Z Canadian solutions were also used. It was noted that the ECMWF, UKMET, and Canadian models showed a more amplified/sharper configuration near the base of the upper trough over the western U.S. which was different from the less amplified version indicated by the GFS. The most amplified solution, as shown by the 12Z ECMWF, led to cyclogenesis over the southeastern U.S. by next Tuesday. This seneraio was not yet supported by its ensemble mean however. Therefore, a more conservative approach was used to handle the uncertainty by blending the 12Z EC mean, 18Z GEFS, and some 12Z NAEFS for days 6 and 7. This yielded good continuty with the previous WPC medium range package. ...Weather Highlights/Threats... The low pressure system moving pass New England Thursday night will bring focused rainfall to areas near/north of the low track. Rainfall along the trailing front will diminish except for some activity persisting over the southern Rockies/High Plains where the front will stall for a day or so. The system emerging from the West and into the Plains should bring scattered rain/high elevation snow to northern parts of the West late this week and then support some areas of locally moderate to heavy rain over the central U.S. by this weekend. The forecast becomes more uncertain by Sun-Mon given poor agreement regarding upper level flow details that will determine frontal timing/waviness and how much moisture may flow northward from the Gulf of Mexico. At the very least there is the potential for some areas to see significant rainfall but at this time confidence is very low for specifics. Locations along the eastern half of the Gulf Coast may also see periods of enhanced rainfall with moisture around the periphery of Gulf of Mexico low pressure and near a potential upper level weakness/low. Record warmth over the eastern and southeastern U.S. should largely come to an end on Friday behind a cold front. Meanwhile, expect unseasonably cool readings over the Northwest (10-20F below normal) to persist late this week and then trend closer to normal over the Pacific Northwest followed by the northern Rockies. Kong/Rausch 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