Extended Forecast Discussion NWS Weather Prediction Center College Park MD 112 AM EDT Wed Apr 15 2020 Valid 12Z Sat Apr 18 2020 - 12Z Wed Apr 22 2020 ...Overview and Guidance/Predictability Assessment†The medium range begins Saturday with a shortwave moving through the Northeast with the guidance continuing to struggle mainly regarding intensity of this system as it exits New England. The 00z ECMWF remains the flattest solution, while the GFS has been very consistent in showing a more amplified system which results in a very deep cyclone off the coast of Nova Scotia by Sunday morning. The UKMET and the CMC help split the difference and so a general model blend seems to provide a good forecast which is stronger than the ECMWF solution, but still quite a bit toned down from the GFS. Meanwhile, whatever is left of a closed low off California at the end of the short range period should be entering the Southwest by Saturday. Guidance has come into better agreement since last night with the energy as it enters the Southern Plains early Sunday, likely getting absorbed by later Sunday/Monday into the broader scale troughing across the Central and Eastern U.S.. The models continue to exhibit less predictable detail differences but a blend of the deterministic models with ensemble means helps mitigate this. Behind the aforementioned Southern tier shortwave, upper level ridging will follow into the Western and eventually Central U.S. while another possible closed low/amplified trough drifts slowly eastward towards the West Coast early next week. Energy rotating around the base of this trough should send another frontal boundary into the Southwest U.S. which reaches the Southern Plains by Day 6-7/Tuesday-Wednesday. Models struggle as early as day 4-5 when the system is still offshore, and even more so once the energy moves into the Four Corners region on Tuesday. As a result, preferred a blend of the better clustered ensemble means with smaller contributions from the ECMWF which was the deterministic solution closest to the means. ...Weather/Hazard Highlights... As the unsettled California low enters the Southwest/Four Corners region this weekend, it should begin to tap a return of downstream Gulf of Mexico moisture to fuel showers and thunderstorms back into the forecast over the South. Models continue to show potential for heavy rainfall associated with this system, mainly from the lower Mississippi Valley into the Southeast, although differences in the details results in low confidence of any specifics at this time. Showers and storms should also extend northward along the exiting cold front across the Mid-Atlantic and Northeast Sunday-Monday. The next system entering the Southwest mid-to late period will promote unsettled weather across parts of the West Coast early next week eventually moving into the Southern/Central Plains by Tuesday. Again, moderate to heavy rainfall is possible, although with so much model uncertainty looming, any such scenario will need to be closely monitored. For Temperatures across the CONUS, locations from the Midwest to the Northeast will begin the period below normal, though quickly should moderate into early next week back towards normal. Meanwhile, temperatures should trend warmer out west and eventually into the Plains as upper ridging follows behind the Southern U.S. system. 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