Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1153 AM EDT Mon Apr 15 2019 Valid 12Z Thu Apr 18 2019 - 12Z Mon Apr 22 2019 16Z Update: The deterministic models remain in above average agreement across the continental U.S. through Saturday with an amplified upper level pattern in place. The 6Z FV3 GFS solution is closer to the ensemble means with the main surface low across the Great Lakes for the end of the week, whereas the operational GFS is farther south with the closed low over the Tennessee River valley, so more of the FV3 was incorporated into the forecast. The operational ECMWF has indicated better run-to-run continuity with the East Coast storm system compared to the other guidance, and was also part of the forecast process. The more uncertain aspect to this forecast relates to the likely development of a secondary low off the East Coast by Sunday, and the models are still resolving this potential feature. By the end of the forecast period next Monday, a new surface low will likely evolve across the High Plains in response to the next Pacific trough moving across the western U.S., with the operational GFS among the most amplified solutions. This storm system may be the next significant weather event going into the beginning of next week. The previous overnight discussion is appended below for reference. Hamrick ...Overview... Progressive but amplified pattern will support a dynamic system moving through the central states Thu/Fri into the east by the weekend but possibly taking until next week to fully move offshore. The west will see a front move into Washington/Oregon early Friday and then progress eastward and southward into the Plains and southern Rockies late this weekend into next Monday. ...Guidance Preferences... Blend of the 18Z GFS/GEFS and 12Z ECMWF/ECMWF ensemble mean offered a reasonable starting point to the medium range period, with a deterministic-centered blend including the UKMET/Canadian to start and a 2/5ths ensemble weighting by next Monday. This maintained good continuity overall as the pattern remains fairly well-handled by the ensembles after earlier uncertainties. Still, questions remain in how the eastern system evolves depending on the strength/track of mid-level shortwaves not easily resolved at this lead time. Ensemble clustering suggested a slowing of the front along or just off the east coast with a new surface low/wave developing near the Mid-Atlantic before turning northeastward. Residence time near New England should be limited due to the approaching system from the west by that time. ...Weather Highlights/Threats... Multi-inch rainfall totals with local flooding are probable (enhanced in embedded convection) along/ahead of the front over the lower Mississippi Valley (possibly into parts of the Southeast and Mid-Atlantic) with lesser amounts in a local max area to the north/northeast of the surface low across Wisconsin. Consult SPC for the latest on the severe weather risk. Mild temperatures will precede the front (10-15F above average) to be replaced by cooler than average temperatures after its passage. The Northwest will see generally light precipitation along a front push through the Great Basin and central Rockies this weekend into next Monday. Fracasso 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