Extended Forecast Discussion NWS Weather Prediction Center College Park MD 142 PM EST Thu Feb 06 2020 Valid 12Z Sun Feb 09 2020 - 12Z Thu Feb 13 2020 ...Heavy rain threat for parts of the Southern Plains/Lower Mississippi Valley to the Tennessee Valley next week... ...Overview and Guidance/Predictability Assessment... Upper pattern next week will shift toward western troughing and a resurgence of the subtropical ridge over Cuba. A lead shortwave dropping through the Great Basin to begin the period (Sunday) will deepen into a closed low by Monday over southern California. As this eventually weakens and lifts northeastward into the Southern Plains next Tuesday into Wednesday, a heavy rain threat will expand over the Southern Plains/Lower Mississippi Valley to the Tennessee Valley along a slow-moving frontal boundary. Yet another shortwave is forecast to sink southward out of British Columbia around next Tuesday into the Northwest, reinforcing the western trough. A deterministic blend (between the GFS/ECMWF/CMC) worked well for the Sun-Tue period. Thereafter, uncertainty increased with respect to: 1) the evolution of the system in the Southwest (how quickly it may lift northeastward), 2) the track/strength of reinforcing energy into the Northwest (GFS was flatter and farther east vs the more amplified ECMWF/Canadian), and 3) track of the downstream surface low over the middle or eastern section of the CONUS. Incorporated an increased weight of the ensemble means for next Wed/Thu, favoring the ECMWF/ECMWF ensemble mean along with the GEFS mean and continuity. Confidence remains above average in the overall pattern, though details remain expectedly less clear by the latter half of the period. ...Weather/Hazard Highlights... High pressure will exit the Northeast on Sunday as surface low and cold front from the Great Lakes move into the region by Monday. This may bring a band of accumulating snow out of the Upper Midwest/Great Lakes Sunday eastward to parts of the interior Northeast into Monday. The western U.S. closed low will bring light to modest rain and mountain snows to much of southern California and parts of Arizona Sunday/Monday into the central and southern Rockies by Tuesday. As the upper low moves through the Southwest and ridging increases over the Gulf, a frontal boundary will settle across the mid-Mississippi and Tennessee Valleys. Gulf moisture will increase initially into the Southern Plains/Lower Mississippi Valley Monday and then spread northward and eastward into the Tennessee Valley by Tuesday into Wednesday, with another surge of moisture moving into the same region next Wednesday into Thursday. Convectively-enhanced rainfall supports a locally heavy rain threat in these areas. Some snow is possible on the northern edge of the precipitation shield from the mid-Mississippi Valley to the Midwest, but any kind of significant accumulation remains in question. Highlighted this area on the day 4-7 winter weather outlook. The second shortwave dropping into the Northwest next Tuesday and settling across the West into Thursday will bring another round of modest mountain snows to the Northwest/Rockies and eventually into the Four Corners region. Behind this, cold high pressure settles southward into the north-central U.S. with daytime highs 20 to 25 degrees below average expected by next Thursday across parts of the Rockies and northern High Plains. Much of the East will see near to above average temperatures, increasing from north to south (5-10 degrees above average from the Mid-Atlantic northward and about 10-15 degrees above average over the South/Southeast). Fracasso/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