Extended Forecast Discussion NWS Weather Prediction Center College Park MD 301 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 remains to be favored across 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 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. Thus, half of WPC morning medium-range forecast was based on 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 impact 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 with widespread light to moderate precipitation likely to impact the Eastern states on Sunday. This system could undergo cyclogenesis on Monday as it nears the New England coast. The trend should be towards warmer and drier weather out West 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. The eastern third of the country will start warm and above normal through the weekend, with the greatest anomalies (+15 to +20F) across the Mid-Atlantic and Northeast on Friday. 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. Out West, temperatures should trend warmer after this week as upper level ridging builds across the region. Kong 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