Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 PM EDT Wed Apr 13 2022 Valid 12Z Sat Apr 16 2022 - 12Z Wed Apr 20 2022 ...Overview and Guidance Evaluation/Predictability Assessment.. Relatively low amplitude mean flow aloft should prevail over the lower 48 through the weekend, in the wake of a departing deep upper low working from the Great Lakes/Northeast to the Canadian Maritimes. Guidance shows a gradually amplifying shortwave trough and associated rain/snow focusing system progressing into and through the West during the weekend onward to the north-central U.S. by early next week. However, the pattern over the lower 48 is then expected to transition to more amplified flow, likely in part due to effect from the upstream progression as a deep extratropical low to the Aleutians of current west Pacific Typhoon Malakas. As such, an amplified upper trough reaching the West Coast by Tuesday would build downstream upper ridging to also allow potential to dig/carve out a closed low over the Great Lakes/Midwest that is expected to work in earnest into the Northeast by midweek. Accordingly, the WPC medium range product suite was primarily derived from a composite blend of the 00 UTC ECMWF/Canadian and ECMWF ensemble mean that offer a decently clustered overall solution that is on the more amplified side of the full envelope of guidance soltuions. Latest 12 UTC guidance is trending toward a more common pattern amplitude evolution. This raises forecast confidence to a degree, albeit with overall flow not quite as amplified as the earlier derived WPC guidance blend, but more amplified than the 00/06 UTC GFS/GEFS mean. ...Weather Highlights/Threats... The departing low pressure system north of the Great Lakes should continue to produce some generally light to moderate precipitation across the Great Lakes/Northeast as a secondary surface low lifts off the coast. Moisture and instability interacting with a warm front lifting through the South/Southeast this weekend and approach of a cold front from the north should bring areas of moderate to locally heavy rainfall to parts of those areas, but for now with low confidence in exact placement of heaviest totals. Farther west, a system forecast to reach the West by Saturday should continue to focus rain/mountain snow over the central and northern West Coast into the northern Rockies late this week into the weekend. Moisture should spread east beyond the Rockies Sunday onward as low pressure/fronts reach the central/eastern U.S.. At least some precipitation across the northern tier may be in the form of snow, again. Guidance is trending signifcantly upward the precipitation potential/intensity over the East. This seems especially evident over New England as the expected approach of the aforementioned upper low may spawn deep surface cyclogenesis. This will offer the potential for runoff issues outside of northern areas in an emerging threat area for wrapping/windy spring snows. meanwhile, the central Rockies/High Plains could see a brief period of strong winds around Sunday with system passage. Upstream, expect another episode of precipitation from the Pacific Northwest/northern California into the northern Rockies through early next week, with some enhanced totals possible over favored coastal/terrain areas. Precipitation potential may increase into next midweek with approach of another amplified upper trough and frontal progression. The core of below normal temperatures across the northern Plains and vicinity will likely persist into early next week, with daytime highs generally 20-30F below normal, and moderating slowly with time. Over the West, temperatures should moderate in between systems as a period of upper ridging moves through. Saturday will feature chilly readings over the northern half of the region (minus 10-15F anomalies for highs) and closer to normal temperatures farther south. As the upper ridge builds over the region by the start of next week, northern locations should trend toward normal and southern areas above normal. The Great Basin and Southwest could see highs as warm as 10-15F above normal. The East should stay near normal on Saturday, but the system potentially reaching the Midwest/East early next week could draw some of the chilly northern Plains air southward and eastward behind it, with expanding coverage of minus 10-20F anomalies. The southern Plains will see highs 10-15F above normal next weekend followed by a cooling trend. Schichtel/Santorelli 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