Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 PM EDT Fri Apr 10 2020 Valid 12Z Mon Apr 13 2020 - 12Z Fri Apr 17 2020 ...Heavy rain threat Wednesday night/Thursday for parts of the Southeast and southern Mid-Atlantic... ...Overview and Guidance/Predictability Assessment... The synoptic pattern remains fairly consistent through the extended periods, with an expansive ridge over the eastern Pacific/West Coast and a broad longwave trough over much of the central and eastern CONUS. Within this cyclonic flow will be multiple upper level shortwaves/impulses rotating through. The main feature on day 3 will be an explosive upper level low/deepening surface low that will lift through the Great Lakes into eastern Canada by Tuesday. Model remain in fairly good agreement with the timing and evolution, as well as, a shortwave diving into the north-central states Wednesday progressing south through the Central U.S. late next week. Model guidance has been hinting that shortwave energy will undercut the ridge over the eastern Pacific the last few runs. There continues to be disparity on the 14th and 15th but lock onto a low offshore the central California coast for the 16th and 17th. The CMC had the feature but it was positioned near the Oregon/California coast. This feature is fairly washed out in the means, but at least shows an open wave present near California. This cycle of the WPC fronts/pressures progs consisted of heavier weighting toward the 00Z ECWMF/EC ensemble means and the 06Z GFS, with lighter weighting of the 00Z CMC/UKMET. ...Weather/Hazard Highlights... A robust and rapidly deepening surface low will lift from the Great Lakes/Ohio Valley region into Canada while ushering in strong winds and snow from the central U.S. to the Great Lakes region. Locally heavy snow possible for Michigan. The main surface low will continue to track northeast through Canada while the trailing cold front extends south along the Mid-Atlantic/ Southeast Coast and across Florida. Impulses of energy will move through the Upper Mississippi Valley and Great Lakes region in the days to follow keeping this region unsettled. Meanwhile, Strong, possibly severe, thunderstorms will be possible for parts of the Mid-Atlantic and Southeast. Periods of heavy rain may lead to areas of rapid runoff or urban ponding. A weak wave will develop along the frontal boundary near the Gulf Coast/Southeast; which will keep showers and thunderstorms in the area. 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, snow to some of the favored higher terrain of the Northern/Central Rockies. A majority of the lower 48 will have a broad area of high pressure, which will maintain a colder than average airmass for mid-April.Afternoon highs are expected to be 20 to 30 degrees colder from the Rockies east to the Midwest through midweek. This chilly airmass will drift to the east by the end of the week. With the ridging building into much of the West, temperatures will be on the warmer side. Rainfall may return to parts of the West late next week as system develops offshore California. Campbell 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