Extended Forecast Discussion NWS Weather Prediction Center College Park MD 124 PM EDT Wed Apr 08 2020 Valid 12Z Sat Apr 11 2020 - 12Z Wed Apr 15 2020 ...Easter Weekend Heavy Rain/Runoff and Severe Weather Threat for the South then Appalachians/Eastern Seaboard into Monday around a Windy/Deep Ohio Valley Low... ...Heavy Snow Threat/Cold Winds to dig through the Rockies/High Plains Sat-Mon... ...Overview and Guidance/Predictability Assessment... A broad upper-level ridge across the northeast Pacific is forecast to expand northward across Alaska then eastward into western Canada during this extended forecast period. This will promote a broad region of downstream cyclonic flow across much of the CONUS. An upper-level low initially across the Southwest U.S. is forecast to slowly move eastward, eventually interacting with a broad northern stream trough forecast to develop across the central/eastern U.S. The speed with which the upper low moves east and interacts with the northern stream remains a point of some contention among the guidance, but spread continues to decrease through time. The GFS continues to trend slower, but remains faster than all other guidance (which has also slowed down slightly). The ECMWF/ECMWF ensemble mean have been more consistent with this system over recent days, and these solutions were preferred for handling of this feature this weekend as initially closed systems tend to eject on the slower side of the full envelope of solutions. These solutions indicate quick deepening of a surface low across the Southern Plains Sun as the upper-level system moves east, with energy quickly transferring to development of another surface low. The new low is forecast to move rapidly northeastward across the Tennessee/Ohio Valleys later Sun into Mon and deepen. Forecast spread by Easter Sunday (day 4) starts to increase along with WPC preference for the ECMWF ensemble mean. The ECMWF ensemble mean remains less progressive than the GFS/GEFS and more in line with but not quite as slow as the ECMWF, adjusting known model bias. ...Weather/Hazard Highlights... Showers and thunderstorms are expected to become increasingly widespread from Texas and the lower Mississippi Valley/Gulf Coast to the Southeast over the weekend as an initially stationary front in the Gulf of Mexico moves north as a moisture focusing warm front ahead of the developing Southern Plains/western Gulf Coast low pressure system and supporting upper trough/jet approach. Models/ensembles show an increasingly strong signal for potential heavy rain/flooding concerns from the lower Mississippi Valley to the Southeast and Southern Appalachians Sat-Sun. As low pressure moves northeast across the lower Mississippi and Tennessee Valleys and quickly deepens, gusty winds may also pose a threat. Additionally, severe weather may also pose a threat across portions of the Southern Plains into the Arklatex on Sat, spreading east into portions of the Gulf Coast and Southeast on Sun. As the deep low lifts through the OH Valley and the overall system moves north and east Mon, expect widespread precipitation will spread up through the Mid-Atlantic and Northeast, with potential coastal low development leading to a possible band of enhanced precipitation across New England. With the parent low pressure system farther west a bit stronger in the recent guidance, the setup appears warmer than previous model cycles across the Northeast where the winter weather threat appears low. The deep low will support some risk for enhanced wrapping snows/winds back through the Upper Midwest and Upper Great Lakes. A strong/windy cold frontal passage will spread anomalously cold air southward from Canada this weekend. High temperatures 20 to 30 deg F below average are forecast across the northern Rockies and adjacent High Plains Sat, spreading southward across much of the Rockies and central U.S. Sun-Mon. Additionally, the system is also expected to produce a threat for heavy snow, working its way southward through the Rockies and High Plains Sat-Mon. Ryan/Schichtel 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