Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Fri Feb 12 2021 Valid 12Z Mon Feb 15 2021 - 12Z Fri Feb 19 2021 ...Widespread record cold temperatures over the Plains and Mississippi Valley into early next week followed by only gradual moderation... ...Stormy pattern will bring multiple wintry precipitation events from coast to coast, with heavy rainfall potential across parts of the East late next week... ...Overview and Guidance Evaluation... Models and ensembles maintain a very active synoptic pattern through much of the medium range period, with a series of systems digging into and ejecting from a long-term mean trough aloft anchored over the contiguous U.S.. These systems will bring periods of active weather for the Western states, as well as parts of the Southern Plains to the Northeast. Across the Plains and into the Mississippi Valley, record cold is likely through at least mid-week. By late next week, models seem to indicate mean troughing progressing eastward while upper level ridging tries to build again over the central part of the country. The latest guidance does continue to generally cluster well for individual systems through the period. There are some minor timing differences with shortwave energy exiting the Northeast around Tuesday-Wednesday which of course has implications for placement of a surface low off the coast. A general model blend though gave a good middle ground solution. Concerning the next shortwave to drop through the West mid next week, the CMC is more amplified/slower than the rest of the guidance on this shortwave as it moves into the Southern Plains, while the GFS/ECMWF and ensemble means are a bit more progressive. Although, differences are pretty minor at least compared to typical spread in the day 6-7 time frame. The blend for this cycle of the WPC medium range forecast used the deterministic models (GFS/ECMWF/UKMET) for days 3-4, with modest inclusion of the ensemble means beyond that to account for the typical late-period detail uncertainty. This helps to maintain good continuity with the previous shift. ...Weather/Threats Highlights... The period starts out with a surface low tracking from the Gulf into the Eastern U.S. Monday-Tuesday accompanied by a broad area of precipitation. The greatest winter weather threats will extend from the lower Mississippi Valley, across the Ohio Valley, and into the Northeast. Snow will fall sufficiently far into the cold air, but there will be potential for areas of significant sleet/freezing rain south of the snow area. Farther south/east across the Tennessee Valley/Southeast/southern Mid-Atlantic, rain may be locally moderate to heavy at times. The next system into the Northwest early next week should bring a couple of waves of precipitation into the Pacific Northwest/northern California with snow mainly confined to the mountains. The moisture will continue southeastward through the Great Basin and the Rockies, followed by increasing coverage and intensity of precipitation over the Southern Plains/Lower Mississippi Valley into the East from Wednesday to Friday. As upper ridging from the Atlantic builds toward southern Florida and the upper trough heads into the Plains/northern Mexico, combined with a more favorable surface evolution, the system may feature a stronger flow of moisture from the Gulf than the preceding system early in the week. Therefore the heavy precipitation potential will require monitoring over the coming days. As with the previous system, expect a broad area of winter weather impacts from the Southern Plains northeastward. Yet another system should bring rain/mountain snow to the Northwest after midweek. There should be potential for many daily records to be broken for both min and cold high readings over portions of the Plains and lower/mid Mississippi Valley into Tuesday with temperatures of at least 30-45F below normal. Although the central U.S. will see moderating temperatures by mid-late week, this may involve anomalies recovering to "only" 20-30F below normal. Some of this cold air will extend in modified fashion into the Ohio Valley and vicinity, and at times farther eastward. Temperatures in the West will be near to moderately below normal with some variability associated with system progression. The extreme Southeast/Florida will be the one area of persistent warmth, with lows in particular expected to be well above normal most days. Though by day 7/Friday, below normal temps may begin to creep into the Sunshine State. 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