Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 AM EDT Tue Mar 16 2021 Valid 12Z Fri Mar 19 2021 - 12Z Tue Mar 23 2021 ...Overview... Upper ridging initially over the High Plains and southern Canada will translate eastward through the period into southeastern Canada/Northeast by next week. A trough over the East Coast Friday will lift northeastward but trailing energy will likely linger move through the Southeast and off the coast, slowing the frontal progression away from Florida. A Pacific system will move through the Rockies this weekend and splitting into two pieces--the southern portion slowly exiting the Four Corners and eventually lifting northeastward next week toward the Upper Midwest. ...Model Guidance/Predictability Assessment... Through the 12Z/18Z guidance, a deterministic/consensus blend sufficed for the Fri-Sun period for the low and trailing front off the East Coast and the incoming western system. The 12Z Canadian was just a bit slower in the East but no unreasonably so. Trend off the Southeast continues to be a bit weaker and farther southeast from Florida, but may still be close enough to yield affects such as some showers and gusty northeast winds. Over the West, GFS/GEFS were a bit deeper with the upper trough than the ECMWF/ECMWF members, but within tolerance for the lead time. As the system deepens its southern extent over the Four Corners, 12Z Canadian/GFS became quicker than the ECMWF/18Z GFS and ensemble means. With solid agreement in the means saw no reason to deviate much from this pairing since the pattern remains progressive enough to stay in the middle of the road. 18Z GFS and 12Z ECMWF painted viable solutions. ...Weather/Threats Highlights... Exiting coastal system will maintain rain chances for the Mid-Atlantic on Friday before a drier weekend. Subsequent rainfall with the front may be confined to just coastal portions of the Southeast into Florida over the weekend and maybe Monday (South Florida) depending on how close the system may be. High pressure over the Northeast will maintain cool temperatures this weekend (especially the Mid-Atlantic into the Southeast) but then a warm-up next week. Temperatures may be 5-15 degrees above normal next week over the eastern Lakes into the Northeast (mid 50s to mid 60s). Western system will spread low elevation rain and higher elevation snow to the Great Basin and central/northern Rockies as the southern portion of the upper trough slows the system progression. Precipitation will expand eastward as surface low pressure organizes to the lee of the Rockies and lifts northeastward, eventually drawing in Gulf moisture ahead of the front. Cooler than normal temperatures behind the front are forecast for much of the West through the period. East of the Rockies, well above normal temperatures are expected for the High Plains into the Upper Midwest and Great Lakes (perhaps 15-20 degrees above normal). This could approach record highs near the Canadian border. Fracasso 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