Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Mon Mar 28 2022 Valid 12Z Thu Mar 31 2022 - 12Z Mon Apr 04 2022 ...A deep and windy storm to bring a late week threat of Upper Great Lakes heavy snow and heavy rain/severe weather to the East... ...Guidance Evaluation/Predictability Assessment... The WPC medium range product suite was primarily derived from a composite of best clustered guidance from the 18 UTC GFS and 12 UTC ECMWF/Canadian along with the 01 UTC National Blend of Models days 3/4 (Thursday-Friday) in a stormy pattern with above normal predictability. This blend is also well supported by ensembles and 00 UTC model guidance. Embedded smaller scale system differences in the main two flow streams and run to run continuity variance becomes more problematic from the weekend onward despite reasonably similar larger scale pattern evolutions. A blend of more compatible guidance from the 18 UTC GEFS mean and 12 UTC ECMWF ensemble mean tends to mitigate the less predictable forecast components while inclusion of the most compatible model, the 12 UTC ECMWF, provides a bit more detail consistent with a pattern with near average predictability. Overall, WPC product continuity is well maintained with this strategy and the forecast seems in line with a composite of 00 UTC guidance. ...Overview and Weather Highlights/Threats... A deep and windy storm set to lift from the Great Lakes to eastern Canada Thursday into Friday offers a threat for wrapping heavy snows north of the low track. Heavy rainfall will sweep across the Eastern Seaboard with frontal system progression Thursday along with a severe weather threat focus over the Mid-Atlantic as per SPC. A protracted series of more modest upstream upper trough energies and frontal systems forecast to dig with some uncertainty through the West later week into next week could each provide an opportunity for enhanced rounds of wintry weather, mainly for the north-central Intermountain West/Rockies. Potential system amplitude and progression into next weekend/early next week would favor return moisture into a wavy frontal pattern. This may support a heavy rainfall focus from the Gulf Coast states to the Southeast/Mid-Atlantic. By early next week there is also a guidance signal to bring more energetic Pacific flow toward the West Coast in two streams to be monitored. Schichtel 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml