Extended Forecast Discussion NWS Weather Prediction Center College Park MD 205 PM EDT Sun Apr 11 2021 Valid 12Z Wed Apr 14 2021 - 12Z Sun Apr 18 2021 ...North-Central Rockies/High Plains Heavy Snow Threat Midweek... ...Overview and Guidance/Predictability Assessment... The medium range period begins Wednesday with a deep closed low over the Great Lakes, which pushes a cold front/deepening surface low off the East Coast by Thursday/Friday. Models/ensembles (especially the 00z ECMWF) are trending towards a more amplified/less progressive solution, and show relatively good agreement through much of the period with this feature. Meanwhile, out West, a closed low will settle over the Great Basin region during the middle of the week before a building ridge over the West Coast/western Canada acts to push the energy eastward into the Plains by next weekend. The models show good agreement the first half of the period, but begin to diverge with the details of energy ejection days 5-7. A solution close to that of the ensemble means should help to mitigate these detail differences. This cycle of the WPC medium range product suite was primarily derived from a majority blend of the deterministic models (GFS/ECMWF/CMC) through day 5, quickly increasing the weighting of the ensemble means thereafter. This maintains overall good WPC continuity, with one exception being a slower/farther west cold front progression off the East Coast days 3-4, consistent with the latest model trends. ...Weather/Hazards Highlights... Combination closed low held over the West and lead cold Canadian High Pressure (with temp anomalies ~10-20 degrees below normal) sets the stage for a potentially heavy upslope snow event over the North-Central Rockies/High Plains through midweek. Some deformation and terrain enhanced precipitation is also possible over the Great Basin. Confidence is increasing on a moderate rain focus shifting into the Plains Thursday-Friday. Meanwhile, a wavy frontal boundary will settle/linger this week into the northern Gulf of Mexico and focus periods of moderate to heavy rains over the Florida/Gulf Coast/Lower Mississippi Valley/Southern Plains through the entire period. Amounts don't look very high, but the Central Gulf Coast states have had much above normal rainfall recently, so there may be flooding concerns. Farther north, guidance has noticeably trended upward with respect to rainfall across parts of the East Coast/Northeast Thursday-Friday. Some models suggest moderate to locally heavy rainfall to accompany the cold front/surface low as it traverses the region. Coastal low genesis may also present some maritime/coastal threats across New England late week/next weekend. Santorelli Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook 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