Extended Forecast Discussion NWS Weather Prediction Center College Park MD 155 AM EST Sun Feb 02 2020 Valid 12Z Wed Feb 05 2020 - 12Z Sun Feb 09 2020 ...Excessive Rainfall Threat for the South/Southeast/Appalachians... ...Heavy Snow/Ice Risk from the Mid-Mississippi Valley northeastward to the Northeast... ...Overview and Guidance/Predictability Assessment... The medium range period begins Wednesday with amplified broad troughing across the Central U.S. with northern stream energy racing eastward across the Great Lakes and developing southern stream energy shifting from the Southern Plains to the Southeast and eventually up the Northeast coast late next week. Developing low pressure along the front lifts across the Appalachians on Thursday, landing somewhere near the northern Mid-Atlantic/interior Northeast by Friday. Models are in fairly good agreement with the overall flow pattern, though still struggle with the details which do have implications for surface low placement on Friday. The UKMET is the slowest/strongest of the solutions and was not included in today's blend. Past day 4, the ECMWF/GFS/CMC exhibit minor timing differences both with the main system, and also shortwave energies dropping in behind this system, but neither were bad enough to exclude from the blend. Ensemble means are in good agreement and were blended in past day 4. The next system/shortwave enters the Pacific Northwest next weekend, and models indicate this could drop down the West coast resulting in a possible closed low over central California by day 7. The GFS has been much more consistent with this feature than the ECMWF which has shown wildly different solutions the past few runs. The GFS is also a lot stronger/deeper with the closed low, as compared to the ECWMF and CMC. An ensemble blend approach is preferred, keeping some contributions from the operational models for wave definition. ...Weather/Hazard Highlights... The amplified troughing across the Central U.S. will drive a cold front through the South and East coast states Wednesday and Thursday. Leading/increasing Gulf of Mexico moisture inflow and instability in advance of this system continue to favor an emerging threat for excessive rainfall, especially across the South/Southeast and into the Southern Appalachians and southern Mid-Atlantic. SPC also highlights a risk for severe weather from the Lower Mississippi Valley/central Gulf Coast on Wednesday, into the Southeast on Thursday. On the north side of the precipitation shield, there is an increasing signal indicating that sufficient cold air will settle in place resulting in a swath of possibly heavy snow from parts of the Mid-Mississippi Valley to the Northeast. A period of freezing rain is also possible in the transition zone region between rain/snow. In the West, persistent onshore flow running overtop a building western U.S. upper ridge will bring rounds of heavy precipitation to the Pacific Northwest next week that work inland across the northern Great Basin and north-central Rockies. Locally heavy mountain snow is likely. As the better onshore flow gets cut off a bit, precipitation should wane across these regions next weekend, while slowly drifting southward towards northern/central California and the central Great Basin. Some more enhanced precipitation is possible along the favored terrain. Temperatures across the U.S. begin much above normal across parts of the Southeast and southern/Mid-Atlantic with slightly above normal temperatures also reaching up into New England. Meanwhile, temperatures should be well below normal underneath the upper level trough across the Southern Plains and southern to central Rockies. After Thursday, temperatures look to moderate back towards normal nationwide with closer to normal values expected by next weekend. 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