Extended Forecast Discussion NWS Weather Prediction Center College Park MD 118 AM EST Sun Feb 14 2021 Valid 12Z Wed Feb 17 2021 - 12Z Sun Feb 21 2021 ...Well below normal temperatures expected to continue across much of the central part of the nation into Friday... ...Stormy pattern with wintry precipitation events from coast to coast and late week heavy rainfall potential across parts of the East... ...Overview and Guidance Evaluation... By the end of next week and weekend the models and ensembles are still advertising a flattening trend for mean flow aloft across the lower 48. This evolution would bring a drier period and more moderate temperatures to areas east of the Rockies by the end of the forecast, while primarily focusing rain/mountain snow from the northern half of the West Coast into the Rockies. In the meantime, the prevailing pattern with an 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 after midweek. With record cold air in place over the Plains/Mississippi Valley at the end of the short range period and only gradual moderation expected thereafter, a widespread area of wintry weather is likely to extend from the Southern Plains through the Northeast. The guidance has come into better agreement on the late week eastern system, though the ECMWF continues to be just a hair faster and stronger than the GFS/CMC. This results in a little flatter western-central U.S. flow late in the period from the ECMWF, while the GFS/CMC continue to suggest some degree of mean ridging ahead of the next shortwave expected to arrive into the Pacific Northwest by day 6/Saturday. Of course, even small differences in the details like this would have more meaningful impacts to exact areas of heaviest rainfall and/or more significant winter weather. The WPC progs reflect a blend of the deterministic solutions early in the period, with some increasing contributions from the means beyond day 5 to mitigate detail differences, especially with the next PacNW shortwave next weekend. This approach maintains good continuity with the previous shift. ...Weather/Threats Highlights... Precipitation over the Southern Plains/Lower Mississippi Valley will be increasing in coverage by the start of the medium range period, eventually reaching into the East by Thursday and Friday. Moderate to heavy rainfall is likely from the Gulf Coast through Tennessee Valley/southern Mid-Atlantic, with a broad area of winter weather impacts on the northwest/northern side of the precipitation shield from the ArkLaTex region northeastward into the Northeast. Also to note, the Storm Prediction Center continues to mention severe weather potential within the warm sector of this system, with details to be better resolved over the coming days. 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. In terms of temperatures, widespread record cold at the end of the short range period should begin moderating somewhat by Wednesday, though widespread 20-40F below normal is still expected across the central/southern Plains and the Mississippi Valley into Friday with some potential for more daily records across southern areas. Upper ridging should finally allow for some recovery of temperatures back closer to normal by next weekend across this region. Given the less extreme anomalies over northern areas to start with, the moderating trend over the Plains may be sufficient to yield modestly above normal highs over parts of the Dakotas and vicinity by next Saturday. 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. Santorelli/Rausch 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