Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1250 PM EST Sun Feb 14 2021 Valid 12Z Wed Feb 17 2021 - 12Z Sun Feb 21 2021 ...Much below temperatures will continue this week across much of the central part of the Nation... ...Stormy weather this week coast to coast with potential for significant storm system to impact Southeast and East Coast late this week... ...Overview and Guidance Evaluation... After a lengthy period of a highly amplified upper level pattern over parts of the CONUS, there are signs for a pattern change with increasing chances of a flattening/zonal upper level pattern by next weekend. This setup would allow for a moderation in temperatures across much of the lower 48 and a less active storm pattern from the central/eastern U.S.. In the meantime and leading up to that potential pattern change, the prevailing amplified mean trough over the central U.S. will feature upstream western energy digging into the Plains/northern Mexico by Thursday and then progressing through the eastern half of the country. The associated low pressure/frontal system will emerge from the Gulf and continue northeastward late in the week. With cold air remaining in place, a widespread area of wintry weather and area of heavy rainfall is likely to extend from the Southern Plains through the Northeast. Overall, given the amplified pattern in the day 3-5 time frame, there is reasonably good agreement between the latest guidance. Compared to the previous cycle, the Southeast to East Coast QPF footprint shifted some south/southeast. The WPC blend incorporated mostly a near equal blend of the ECMWF/GFS/CMC/UKMET early on (day 3-5) followed by mostly a blend of the ECMWF/ECENS and GFS/GEFS for day 6-7. ...Weather/Threats Highlights... The storm system brewing over the Gulf that is expected to lift through the Southeast toward the Northeast late this week will bring a variety of hazards, including potential for severe weather, heavy rainfall, and a swath of winter precipitation on its northern edge. The risk for heavy rainfall is mainly confined to portions of the Gulf Coast through the Tennessee River Valley and portions of the Mid-Atlantic, while the Storm Prediction Center is monitoring potential for severe weather over the central Gulf Coast states. On the cold side of this system, a swath of snow/wintry mix is increasingly likely from portions of the Arklatex region through the Ohio Valley and portions of the interior Mid-Atlantic and Northeast. The latest WWO has moderate to high probabilities for 0.25 inch liquid equivalent of snow/sleet. Details on the individual hazards and fine tuning the rain/snow/wintry mix transition zones will become clearer over the course of this week. Behind this system, another couple fronts reaching the Northwest between Thursday and Saturday should bring the potential for additional focused rainfall along coastal portions of Washington/Oregon with heavy mountain snows in the Washington/Oregon Cascades and northern Rockies. Meaningful rain/high elevation snow may extend into parts of northern California as well. For temperatures, the record cold and much below normal temperatures over the central U.S. will moderate somewhat while shifting eastward toward the East Coast. Widespread readings 20F to as much as 40F below normal will be possible Wednesday and Thursday over the Southern Plains, while readings of 10-20F below normal will be possible from the Ohio Valley and Mid-Atlantic/Northeast late this week. Temperatures in the West will be near to moderately below normal through midweek followed by a warming trend, especially over the Southwest where highs may reach 5-10F or so above normal Friday-Sunday. The extreme Southeast/Florida will be the one area of persistent warmth through early Friday, with morning lows in particular expected to be well above normal. However, below normal temperatures should spread across the Sunshine State by later Friday/Saturday after passage of the front anchored by the system affecting much of the East. Taylor/Santorelli Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook 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