Extended Forecast Discussion NWS Weather Prediction Center College Park MD 148 AM EDT Fri Apr 10 2020 Valid 12Z Mon Apr 13 2020 - 12Z Fri Apr 17 2020 ...Heavy rain threat continues Monday for parts of the East/Northeast... ...Overview and Guidance/Predictability Assessment... Upper ridging should maintain itself through the period initially across the Northeast Pacific inching into western Canada by the end of next week. This results in broad cyclonic flow across much of the CONUS with multiple upper level shortwaves/impulses rotating through the flow. An initial vigorous upper level low/deepening surface low will lift from the Great Lakes into eastern Canada Monday-Tuesday, with a heavy rain threat likely along the attendant cold front as it pushes through the East. Models show fairly good agreement with this system, albeit minor timing differences so a general model compromise should suffice. A shortwave drops into the north-central U.S. next Wednesday continuing southward through the Central U.S. late next week. Models show typical timing/amplitude differences with this system. The bigger question arises by the middle of next week regarding a shortwave/possible closed low moving through the eastern Pacific ridge, and riding down along the West Coast next Thursday into Friday. At this point, the GFS remains the strongest by far with this system, though most of the deterministic models at least show a feature. This feature becomes fairly washed out in the means as expected given large spread on placement or even existence (a good number of ECENS members show a feature, which many GEFS members do not). In addition, even run to run continuity in the deterministic models is quite poor so forecast confidence is low for this particular feature. This cycle of the WPC fronts/pressures progs relied on a mainly deterministic model blend (ECMWF/GFS/CMC) for days 3-4, trending towards 50 percent ECENS mean by day 7 (with smaller contributions from the ECMWF and GFS). This blend at least maintains a semblance of a Western U.S. system, and also good continuity with the previous WPC shift. ...Weather/Hazard Highlights... A deepening surface low will lift from the Great Lakes into eastern Canada bringing with it a threat for high winds and heavy rainfall across the Northeast on Monday, with showers and strong to potentially severe storms from the southern Mid-Atlantic to northern Florida. Heavy snow is likely on the north side of the low across parts of the Upper Peninsula of Michigan on Monday, with the low tracking far enough west to limit any potential winter weather threat across the Northeast. After Monday, rain should clear most of the Eastern Seaboard as the cold front pushes into the Atlantic. The exception to this is across parts of the Gulf Coast/Southeast where showers and storms may linger into Wednesday associated with weak low pressure. The western portion of this boundary will become stationary into mid week before weakening across the Four Corners region with showers possible along the boundary. A weak cold front dropping into the Central Plains may bring some light showers to parts of the region, as well as the favored terrain of the northern/central Rockies. Elsewhere, much of the country will be dominated by high pressure, with reinforcing shots of cold air dropping into the Central U.S.. Daytime highs from the Rockies to the Midwest could be 20 to 30 degrees below normal Monday-Wednesday, before slowly moderating back towards normal as the airmass shifts into the East. Across the West, temperatures should trend warmer as upper level ridging builds. Depending on the evolution of the potential West Coast system, some rainfall may return to parts of the West late next week. Santorelli Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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