Extended Forecast Discussion NWS Weather Prediction Center College Park MD 359 PM EST Mon Feb 21 2022 Valid 12Z Thu Feb 24 2022 - 12Z Mon Feb 28 2022 ...Heavy to excessive rainfall threat from the Mid-South to the Central Appalachians Thursday along with a significant heavy snow/ice threat from the Mid-Mississippi Valley northeastward to the Northeast Thursday-Friday... ...Overview... A potent shortwave is forecast to track from the Four Corners region Thursday and likely combine with a northern stream shortwave in the Great Lakes/Ohio Valley Friday, while moisture streams ahead of the trough into the vicinity of a frontal boundary to cause precipitation across the south-central to northeastern U.S. through Friday. Cold high pressure will cause snow and ice on the northern/western side of the precipitation shield, along with much below normal temperatures for much of the country. The pattern should calm down somewhat by the weekend into early next week, though cold temperatures will persist for most areas other than Florida and a gradually warming West. ...Guidance Evaluation/Predictability Assessment... Recent model guidance continues to show reasonably good agreement for the overall large-scale pattern into the weekend with the aforementioned initial shortwave track, additional troughing/energy dropping into the Northern/Central Rockies Friday into Saturday, and amplified ridging over the eastern Pacific. Minor differences remain with the track of these features, with the GFS suite (including the deterministic runs and ensemble mean as well as the bulk of ensemble members as indicated by spaghetti plots and cluster analysis) shifted a bit east for both features as well as weaker with the second shortwave compared to the ECMWF suite. These are consistent with typical model biases, and consensus is close enough for the WPC forecast to use a multi-model blend of the latest available deterministic guidance (00Z/06Z) for the first half of the forecast period. By early next week, troughing should be shifting into the central and then eastern U.S. as energy spins around an upper low in eastern Canada, though with more differences in the phasing details. Ridging will move in behind the trough, though with uncertainty in the shortwaves coming in on the ridge's backside. As the medium range period progressed, shifted to a blend of deterministic (mainly maintaining the ECMWF) and ensemble (leaning toward the EC ensemble mean) guidance to lean toward the ECMWF suite, minimize individual model differences, and maintain good forecast continuity from the previous cycle. ...Weather Highlights/Threats... As the period begins Thursday with upper troughs digging over the West/Southwest and ridging over the Southeast, southerly inflow into a low pressure/frontal system will provide moisture for widespread precipitation from the Mississippi Valley to Tennessee and Ohio Valleys into the Mid-Atlantic and Northeast. Current forecasts show the threat for excessive rainfall is maximized across north-central Tennessee into eastern Kentucky and western West Virginia Thursday into Thursday night. To the north and west, there is a significant threat for snow and ice from the Mid-Mississippi and Ohio Valleys into the Northeast Thursday and Friday. Some moisture return into the southeastern quadrant of the country is possible over the weekend, but with likely lighter precipitation amounts compared to the previous events. Meanwhile some light snow is possible across the Great Lakes region for the weekend, while approaching frontal systems and shortwaves should lead to increasing precipitation chances over the Pacific Northwest. Cold Canadian high pressure will affect much of the contiguous U.S. through the period, spreading much below average temperatures to the bulk of the country, which could be record-setting. Especially frigid temperatures are likely from the northern High Plains to the Northern/Central Plains where daytime highs and overnight lows could be 30-40+ degrees below normal through Friday. After a warmer than average couple of days late this week in the southeastern U.S. with a few record warm maxes and mins possible under the ridge and ahead of the front, the cold air will spread into the East over the weekend, but modified/moderated. The Florida Peninsula will be the main spot hanging onto above average temperatures. Chilly weather could be reinforced by upper-level energy across the north-central U.S. into the Ohio Valley and Great Lakes early next week. Meanwhile the West can expect cool temperatures to begin the period but should warm to near/above average early next week given overall ridging. Tate Hazards: - Freezing rain/sleet from portions of the southern Plains across the mid-Mississippi and Ohio Valleys, and into portions of the interior northern Mid-Atlantic region, Thu, Feb 24. - Heavy precipitation across portions of southern New England, Fri, Feb 25. - Heavy rain from the Tennessee Valley to portions of the central/southern Appalachians, Thu, Feb 24. - Heavy rain across portions of coastal southern New England, Fri, Feb 25. - Heavy snow across portions of Missouri, across the Midwest and the lower Great Lakes into western New York, Thu, Feb 24. - Heavy snow across much of central to northern New England, Fri, Feb 25. - Flooding possible across portions of the lower Great Lakes, lower and mid-Mississippi Valley, the Tennessee Valley, and toward the southern Appalachians. - Flooding occurring or imminent across portions of the mid-Mississippi Valley and the lower Great Lakes. - Flooding likely across portions of the mid-Mississippi Valley and northern Indiana. - Much below normal temperatures across much of the Plains into the mid and upper Mississippi Valley as well as the northern and central Rockies, Thu-Sat, Feb 24-Feb 26. - Much below normal temperatures across much of the northern Plains, the Great Lakes, Ohio Valley and into the Appalachians, Sun-Mon, Feb 27-Feb 28. - Much below normal temperatures across northern Maine, Thu-Fri, Feb 24-Feb 25. 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