Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM EST Sat Feb 01 2020 Valid 12Z Tue Feb 04 2020 - 12Z Sat Feb 08 2020 ...Heavy Rainfall Threat for the South/Southeast/Appalachians Wednesday/Thursday... ...Overview and Guidance/Predictability Assessment... An amplified shortwave/closed low will dig out of the Rockies and into the Central U.S. Tuesday into Wednesday. Models show good agreement that this feature will split into northern/southern stream pieces of energy, with the northern part tracking towards the Great Lakes on Thursday. Meanwhile, the southern piece should be reinforced by additional upstream western U.S. energy resulting in amplified broad troughing over the Central U.S. late next week, which then progresses eastward by next weekend. Given an increasingly deepening moisture surge out of the Gulf, this favors development of a heavy rainfall/severe weather threat across the South and Southeastern U.S. Across the West, upper ridging should prevail much of the period, though shortwave energy looks to move back into the Pacific Northwest by late week into next weekend. Models struggle with the timing of this system, with the latest runs of the GFS/CMC showing energy over the Northwest by 12z next Sat, while the ECMWF is displaced quite a bit west. Although models may be trending slower with this, prefer the GFS/CMC placement for now because of better agreement with the ensemble means. Confidence is above normal in the large scale/synoptic flow pattern, though closer to average on the flow details past midweek. WPC medium range favors a deterministic model blend days 3-4, with increasing contributions from the ensemble means thereafter. Slightly more weighting was placed on the GFS than the ECMWF across the Northwest on day 7 for the reasons outlined above. This maintains good continuity with the previous WPC shift. ...Weather/Hazard Highlights... Showers and thunderstorms are likely by mid-week across parts of the south-central U.S. into the Tennessee Valley and Mid-Atlantic/Northeast. Frontal wave development and leading/increasing Gulf moisture inflow suggest a threat for heavy rainfall especially across parts of the Gulf Coast/Southeast and into the southern Appalachians/southern Mid-Atlantic. SPC also highlights a risk for severe weather shifting from the Lower Mississippi Valley to the Southeast Tues-Thurs. On the north side of the precipitation shield, sufficient cold air may be in place for wintry precipitation from the Central Plains to the lower Great Lakes on Tuesday. With several waves of low pressure expected to move through the Mid-Atlantic, a couple of days of wintry precip is possible from the lower Lakes to the Northeast. Potential surface wave development riding up the Northeast coast next Friday into Saturday could bring a round of heavier snows to parts of northern New England. Meanwhile, persistent onshore flow will bring a round of heavy precipitation to the Pacific Northwest mid-later next week. Heavy mountain snows are possible initially over the Cascades on Tuesday, eventually working inland to the Northern and Central Rockies Wednesday-Friday. Temperatures from the Southern Plains to the Mid-Atlantic will average 15 to 20 degrees above normal to start the period, trending back towards normal following the cold frontal passage. Temperatures out west could be much below normal Tuesday, warming back to normal or slightly above normal by the end of the week as upper level ridging builds aloft. Santorelli 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