Extended Forecast Discussion NWS Weather Prediction Center College Park MD 142 AM EDT Mon Apr 13 2020 Valid 12Z Thu Apr 16 2020 - 12Z Mon Apr 20 2020 ...Overview and Guidance/Predictability Assessment... Models and ensembles show good agreement in broad troughing across most of the CONUS Thursday-Friday downstream of an amplified northeast Pacific mean ridge. Vigorous shortwave energy crosses the Rockies on Thursday, reaching the Midwest by Friday with guidance continuing to show support for a surface low lifting from the Midwest to the Northeast Friday-Saturday. Upstream, models are coming into better agreement compared to previous days on the handling of shortwave energy undercutting the Pacific Ridge late this week, likely closing off into an upper low. This low should slide southward along or just offshore California before progressing inland across the Southwest and southern tier states next weekend. By early next week, the question becomes whether any remaining energy stays separate from the northern stream troughing or more or less gets absorbed into the overall flow. This of course would have implications on rainfall potential across the Southern U.S. Sunday into Monday. The ensemble means are in line with the deterministic runs, but by nature are not as detailed showing a more washed out system, especially late in the period when individual ensemble member spread increases. The WPC preferred blend for this cycle of products prefers a majority deterministic model blend (between the latest runs of the GFS, ECMWF, and CMC) for days 3-4. Weighting of the ensemble means increases after day 5 in an attempt to smooth out the less predictable details, though at least 50% of the deterministic models were maintained through day 7 for added definition to individual systems. This also maintains good WPC continuity with the previous shift. ...Weather/Hazard Highlights... Shortwave energy digging southward through the Intermountain West will spread snow potential into the Central Rockies on Thursday. As an unsettled eastern Pacific closed low/trough enters the Southwest/Four Corners region next weekend, it should also begin to tap a return of downstream Gulf of Mexico moisture to fuel showers and thunderstorms back into the forecast over the South. Some models hint at the potential for heavy rainfall, though much of this is dependent on northern/southern steam interactions and evolution of this shortwave. Confidence in any kind of event remains low. For Temperatures across the CONUS, locations from the Rockies to the Midwest will be well below normal Thursday into Friday with daytime highs averaging 15 to 20 degrees below normal. Values should moderate back towards normal by this weekend and into early next week. Meanwhile, temperatures should trend warmer out west as upper ridging follows behind the late week California closed low. 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