Extended Forecast Discussion NWS Weather Prediction Center College Park MD 311 PM EDT Sat Apr 03 2021 Valid 12Z Tue Apr 06 2021 - 12Z Sat Apr 10 2021 ...Overview and Guidance Evaluation/Predictability Assessment... Model guidance this morning generally agrees that a shortwave will march across the middle to eastern portion of the country through the medium-range period as another upper trough with embedded shortwaves approaches/reaches the Pacific Northwest late next week. The ensemble means from the ECMWF, GEFS, and CMC are actually quite agreeable with one another through Day 7 regarding the overall pattern evolution across the U.S., with excellent timing agreement on the west-to-east motion of a low pressure system from the Plains to the East Coast. The GEFS mean and the CMC mean track the low slightly farther to the north toward the lower Great Lakes than the EC mean which takes it across the Ohio Valley. A blend of these ensemble means should yield a good starting point. As for the deterministic solutions, the GFS has continued to depict a deeper and larger low pressure system to form over the central Plains during the middle of next week compared with other models. As for the subsequent evolution of the system, the deterministic solutions are increasingly diverged, with the GFS tracking the system across the Great Lakes into Canada while the ECMWF and CMC generally carry it into the East Coast. The WPC medium-range package was based mainly on a composite blend of the 06Z GEFS, 00Z EC mean, a smaller contribution from the 00Z CMC mean, together with some from the 00Z ECMWF and a lesser amount from the 06Z GFS and the 00Z CMC. This resulted in a solution that depicts a low pressure system tracking from the central Plains to the East Coast with some coastal development by next weekend. ...Sensible Weather and Potential Hazards... The upper low emerging from the north-central Rockies along with developing Plains/Midwest low pressure should promote an axis of potentially heavy rainfall over parts of the north-central Plains and Midwest during Tuesday or Tuesday night through at least Wednesday. Some snow will be possible over the north-central Rockies and High Plains. With time expect this system to spread moisture into the East with some areas of locally moderate to heavy rainfall possible. Increasing uncertainty over system details after Thursday decreases confidence for determining highest rainfall totals and their location at that time, though existing signals suggest they would be within an area from the Ohio Valley into Tennessee Valley through parts of the Mid-Atlantic/Southeast. The Northwest should see one or more periods of rain and mountain snow during the period but uncertainty over shortwave details will keep confidence low for specifics of coverage/timing/amounts. From Tuesday into early Wednesday well above normal temperatures (at least plus 10-20F anomalies) will prevail from the southern Rockies/Plains into the Great Lakes. The greatest anomalies should be over the central Plains and Midwest where morning lows may be 20-25F above normal. This warmth will moderate somewhat as it continues eastward ahead of the Plains system. The East should generally see highs of 5-15F above normal mid-late week while clouds and rainfall will lead to warmer anomalies of plus 10-20F for morning lows. Farther west, parts of the north-central Rockies/Plains may see modestly below normal highs into midweek while the mean trough aloft nearby keeps the Pacific Northwest somewhat below normal for highs. Most of the Southwest and Great Basin will likely see highs 5-10F above normal from midweek onward. Kong/Rausch 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