Extended Forecast Discussion NWS Weather Prediction Center College Park MD 201 AM EDT Sat Apr 06 2019 Valid 12Z Tue Apr 09 2019 - 12Z Sat Apr 13 2019 ...Overview and Guidance Assessment/Preferences... On Day 3, the eastern upper trough indicate height falls over the northeast leading to low pressure development on the front as it moves off the New England coast, with a trailing trough across the region. The southern portion of the front slowly progresses across the southeast on Tue before moving off the coast Wed. The ECMWF was on the fast edge of the cluster of solutions with the upper trough progression, with the 12z ECMWF ensemble mean several hours slower and clustering well with the GEFS Mean, so the means were given more weighting given better overlap. Attention turns west with the the first of the western troughs crossing the Great Basin to the WY/CO Rockies. Low pressure develops on the high plains by Wed morning and continues moving northeast towards the mid MS Valley Thu and Great Lakes Fri while occluding. On Sat a triple point low develops near the New England coast and eventually depart into the Canadian maritimes. For this system, the 18z GEFS/12z ECMWF ensemble means hold good run to run continuity and overlap with one another , as the operation the 12z ECMWF/18z GFS were bookends on either side of the means (ECMWF/GFS south). The next in the series of upper-level waves should amplify along the West Coast Thu-Fri and continue into the Great Basin and southwest Fri with a surface frontal system develops in the southwest. The 12z ECMWF has the highest amplitude/shorter wavelength upper ridge approaching the Pacific northwest, leading to higher amplitude/slower moving trough across the southwest. Most ECMWF ensemble members have a lower amplitude coupled northeast Pacific ridge and downstream southwest trough, so more weighting was given towards the mean solution, again with support from the 18z GEFS Mean. ...Weather Highlights/Hazards... Showers and thunderstorms with locally heavy rains are possible in the Southeast to southern mid Atlantic Tue as the first southern stream shortwave/low pressure system moves slowly across the region. The second and most significant southern stream system during the period should produce widespread rains and mountain snows (some potentially heavy) across the central/northern Rockies Tue. As the system reaches the central U.S. by the middle of next week, a band of precipitation along the l0ow level frontogenesis maxima is expected to develop from the Central to Northern High Plains to the Midwest and Great Lakes. A band of moderate to heavy snow appears probable north and west of the surface low track, with a transition zone and areas of moderate to heavy rain as well. See the Storm Prediction Center outlooks for severe convective weather potential. Once the system moves into the lakes, the precip should progresses across the Great Lakes to the mid Atlantic and northeast next Fri-Sat 13 Apr. The next west coast trough brings valley showers and mountain snow showers across the Great Basin to the central Rockies Fri into Sat 13 Apr. Warm temperatures are expected across much of the central and eastern U.S. during the early to middle portion of next week. High temperatures ranging from 10 to 20 deg F above average are possible Mon-Wed over a large area, with the greater anomalies across the southern Plains to lower MS Valley Tue-Wed. Colder air and further amplification of upper troughing across the West in the wake of the mid-week system will support below average temperatures, with highs 5 to 15 deg below average across much of the interior West Wed and into the Central/Northern Plains Thu-Sat. Very little of the country is forecast to be above normal Sat 13 Apr, mainly focused on FL and northwest WA. Petersen 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