Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 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. A blend of the 18Z GFS with the 12Z ECMWF, with more weights given to the ECMWF, was used to derive the WPC forecast grids. Some 12Z UKMET and 12Z Canadian solutions were also used. It is noted that the ECMWF, UKMET and Canadian models show a similar sharper configuration near the base of the upper trough in the western U.S. which is different from a less amplified solution in the GFS. ...Weather Highlights/Threats... Great Lakes through Northeast low pressure Thu-Thu 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 and a little north of the Southeast should continue into Thu before temperatures finally moderate. Expect unseasonably cool readings over the Northwest (10-20F below normal) to persist late this week and then trend closer to normal first over the Pacific Northwest and then eventually over 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 Hazards: - Heavy rain across portions of the Southern Rockies, the Southern Plains, and the Southwest, Thu-Fri, Oct 3-Oct 4. - Heavy rain across portions of the Mid-Atlantic, the Northeast, and the Great Lakes, Thu, Oct 3. - Flooding possible across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, the Ohio Valley, and the Upper Mississippi Valley. - Flooding occurring or imminent across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, and the Northern Plains. - Flooding likely across portions of the Central Plains, the Middle Mississippi Valley, and the Great Lakes. - Much above normal temperatures across portions of the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Great Lakes, and the Ohio Valley, Thu, Oct 3. - Much above normal temperatures across portions of the Southeast, the Mid-Atlantic, the Southern Appalachians, and the Tennessee Valley, Thu-Fri, Oct 3-Oct 4. - Much below normal temperatures across portions of the Central/Northern Rockies and the Central/Northern Plains, Thu, Oct 3. 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