Extended Forecast Discussion NWS Weather Prediction Center College Park MD 247 AM EDT Sat Oct 24 2020 Valid 12Z Tue Oct 27 2020 - 12Z Sat Oct 31 2020 ...Record cold in the central US Tue before relenting... ...Heavy rain threat from the southern Plains to the southeastern third of the CONUS next week... ...Guidance Evaluation/Preferences... Longwave pattern and evolution remain in good agreement within the models/ensembles but with lingering/ongoing timing differences. Through the 12Z/18Z cycles, the GFS was still quicker than the other models/ensemble means with the exiting Southwest closed low while the ECMWF/UKMET were on the slower side. The Canadian fell more or less in the middle, though not at all times, but the guidance was generally closer together than 24 hrs ago. Despite a bit quicker trend, still discounted the GFS after Tue in favor of the larger cluster near the ECMWF ensemble mean. Upper ridging is forecast to hold in place over the Southeast U.S. until Thursday, becoming squashed as the Plains system moves eastward. An additional factor is a possible tropical system in the Gulf of Mexico early in the week. Please consult the National Hurricane Center for more information. Regardless of development, rainfall will move into parts of the Southeast/Florida ahead of the Plains system and perhaps combine over the Carolinas. Much uncertainty remains in these details. ...Weather/Hazard Highlights... The very cold airmass out of the short range will moderate as it pushes eastward after Tuesday. More record lows (and low maxes) are likely for Tuesday as a large area over the southern/central Plains will see temperatures 20-40 degrees below normal. For Wed into Sat, temperatures will only be below normal by 5-15 degrees in the central to eastern states behind the front. Areas of the Northwest/Great Basin/California will see above normal temperatures by about 5-10 degrees. In the warm sector ahead of the front, showers and thunderstorms will focus over the southern Plains Tue into Wed before sliding east through the Ohio/Tennessee/lower Mississippi Valleys with some heavy rain possible. Based on latest guidance, tropical moisture could surge into the Southeast ahead of the upper low Tue-Wed before becoming absorbed into the larger frontal system Thu onward as it heads toward the East Coast. Some heavy rain may be possible but track of any tropical moisture will affect the timing/duration/intensity. Fracasso 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