Extended Forecast Discussion NWS Weather Prediction Center College Park MD 208 PM EDT Sun Mar 28 2021 Valid 12Z Wed Mar 31 2021 - 12Z Sun Apr 04 2021 ...Overview... The medium range period will begin Wednesday with an amplified mid-upper trough over the central U.S. that should shift eastward toward the East Coast through the end of the workweek before pivoting northward. At the surface, a cold front is forecast to sweep across the East, with rain (and snow in the interior Northeast) ahead of it and a spate of cooler temperatures behind it as a cool Canadian surface high comes in. Then, upper ridging will lead to a warm-up in the western/central U.S. late in the week, while a trough approaching the Pacific Northwest could lead to increased precipitation chances there by the weekend. ...Model Guidance and Predictability... 00Z/06Z model guidance continues to be in good overall agreement especially for the early part of the medium range period given the amplified pattern, with the longwave upper trough tracking across the central/eastern U.S. and the ridging behind. Once again the 00Z/06Z GFS suite was a little faster with the trough movement compared to the non-NCEP models that clustered well, so leaned toward the 00Z ECMWF/UKMET/CMC with that feature and the associated surface front timing by Friday. It appears one shortwave trough should move across southwestern to south-central Canada Thursday to Saturday, ahead of the potential for upper troughing to drop into the Northwest by the weekend. Model guidance varies quite a bit from run to run and model to model with this second trough in terms of position and potential for flow to split and a closed low to develop. Given this variability, it seemed prudent to shift toward a mainly 06Z GEFS/00Z EC ensemble mean blend by the weekend after a multi-model deterministic blend early on. Another feature to note is a southern stream shortwave trough moving eastward across the Pacific midweek and into the southern California/northern Mexico vicinity on Friday. Some model variability remains with its strength especially once it gets over land, with the GFS runs maintaining relatively stronger energy over the Southwest and even toward the Southern Plains over the weekend, and this leads to differences in the rain and thunderstorm potential for those areas. For now a multi-model solution sufficed there, indicating a weak shortwave feature. ...Sensible Weather and Potential Hazards... Widespread precipitation is forecast Wednesday into Thursday for the Appalachians to the Eastern Seaboard as moisture flows ahead of and into the vicinity of the aforementioned cold front. There is some potential for moderate to heavy rain causing flooding from the Southern Appalachians toward the Northeast Wednesday and Wednesday night. Precipitation is expected to change to snow across higher elevations of the Appalachians and across interior parts of the Northeast behind the lead cold front, and several inches of snow could fall from the Adirondacks to northern Maine. After that, generally dry conditions are expected to prevail across the contiguous U.S. as a surface high pressure system moves across, and as a frontal system in the north-central U.S. does not have much moisture to work with. The Northwest could see some light to modest precipitation though, with chances increasing over the weekend as the upper trough and a surface front approach. Other possibilities for light precipitation include the Southern Plains, southern Florida, and the interior Northeast. Colder than average conditions are forecast behind the potent cold front in the eastern half of the U.S. for the latter part of the workweek, with highs generally 10 to 25 degrees below normal. Daily record low minimum and maximum temperatures could be broken across the East as lows reaching the freezing mark are possible as far south as northern Georgia and South Carolina Friday morning. Temperatures should moderate toward normal across the East by the weekend as the upper trough lifts into eastern Canada. Meanwhile, temperatures are expected to soar to much above normal in most of the western and central U.S., with northern/central portions of the Plains seeing widespread 70 degree temperatures, about 20-25 degrees above normal. Temperatures in the 90s could occur in the Desert Southwest, and for many these temperatures could be the warmest of the calendar year. Tate 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