Extended Forecast Discussion NWS Weather Prediction Center College Park MD 519 PM EDT Tue Mar 23 2021 Valid 12Z Fri Mar 26 2021 - 12Z Tue Mar 30 2021 ...Heavy rain possible across parts of the interior Deep South/Tennessee Valley on Saturday... ...Overview... An unsettled and active weather pattern is forecast for the eastern two-thirds of the country through this weekend into early next week, as shortwaves/troughs from both the northern and southern streams tend to interact/merge across the region. A compact and possibly intense low pressure system is forecast to track through the Great Lakes and New England Friday to Saturday before another developing system tracking across the same regions Sunday into Monday with cyclogenesis possible near the New England coast. A swath of moderate to heavy rain is forecast for parts of the Deep South to the Tennessee Valley on Saturday under this pattern. Meanwhile, much of the West should trend warmer/drier as upper ridging builds into the weekend before the next system enters the Pacific Northwest and brings another round of rain and mountain snows to the region. ...Model Guidance/Predictability Assessment... Among all of the model guidance, the ECMWF has been showing the best level of consistency for the past few runs although it has been generally the slowest piece of the guidance through the medium-range period. The GFS has been on the fast side while the CMC has been somewhere in between through Day 5 and then closer to the fast solution through Day 7 for the Pacific Northwest system. The preference for this morning's WPC medium-range forecast was to use 50% 00Z ECMWF/EC mean. The 06Z GFS/06Z GEFS, and the 00Z CMC/CMC mean made up the second half. More of the ensemble means were incorporated for Days 5-7 to account for the increasing uncertainty. Very good WPC continuity was maintained with a slightly faster eastward progression of each system than the previous forecast. ...Weather/Threats Highlights... There is increasing model signals for a compact and possibly quite intense low pressure system to track through the Great Lakes and New England Friday to Saturday, bringing the potential for strong and very gusty winds to the Northeast. Some heavy wet snow could fall across northern Maine Saturday morning as the low pressure center likely passes to the south. The trailing frontal boundary in the Gulf of Mexico should lift northward as a warm front focusing another round of moderate to heavy rainfall across parts of the Deep South to the Tennessee Valley on Saturday. The next system sends another cold front into the East on Sunday with widespread light to moderate precipitation likely to impact the Eastern states. This system could undergo cyclogenesis on Monday as the center nears the New England coast, and could bring another round of wintry precipitation for northern New England. Out West, the trend should be towards warmer and drier weather this weekend, ahead of the next system into the Pacific Northwest which should bring another round of rain and mountain snow to the region early next week with a return to cooler than normal temperatures. The eastern third of the country will start out very warm Friday afternoon with the greatest anomalies (+15 to +20F) across the Mid-Atlantic and Northeast, and will remain warmer than normal through the weekend. Morning lows will be even more so anomalously warm, with several record high minimum temperatures possible late this week stretching from Florida to the Northeast. Troughing entering the region early next week should bring temperatures back down towards normal next Monday and Tuesday. Kong/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 Hazards: - Heavy precipitation across portions of the Northeast, Fri, Mar 26 and Sun, Mar 28. - Heavy rain across portions of the Southeast, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Sat, Mar 27. - Heavy snow across portions of the Pacific Northwest and the Northern Great Basin, Sun, Mar 28. - Heavy snow across portions of the Southern Rockies, the Central Rockies, the Central Great Basin, and the Southwest, Fri, Mar 26. - Flooding possible across portions of the Central Plains, the Middle/Lower Mississippi Valley, the Tennessee Valley, the Southeast, and the Ohio Valley. - Flooding occurring or imminent across portions of the Middle Mississippi Valley and the Ohio Valley. - Flooding likely across portions of the Central Plains. - High winds across portions of the Great Lakes, the Mid-Atlantic, the Northeast, the Central Appalachians, and the Ohio Valley, Fri, Mar 26. 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