Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 AM EDT Fri Apr 30 2021 Valid 12Z Mon May 3 2021 - 12Z Fri May 7 2021 ...Heavy rainfall becoming more likely across the Deep South Tuesday into Wednesday... ...Guidance/Predictability Assessment and Preferences... An active weather pattern is forecast to continue going into the medium range period next week as two significant troughs cross the southern tier states and result in heavy rain and strong thunderstorms. Meanwhile, an upper level ridge becomes established over the Intermountain West towards the end of the week ahead of the next Pacific storm system that will likely reach the West Coast by next Friday. The 00Z model suite is in above average agreement through Tuesday across the continental U.S., and for this time period a general blend of the UKMET/GFS/ECMWF/CMC sufficed as a starting point in the forecast process. By Wednesday, the guidance diverges more on timing of smaller individual shortwaves in the northern stream flow, and thus precipitation coverage and placement across the northern Plains and Upper Midwest later in the forecast period is less certain. By Friday, there is good agreement that an organized Pacific storm system will affect the West Coast, with the GFS a bit more progressive than the slower ECMWF/CMC solutions, so leaning towards the slower timing seems prudent for now. There is also some indication of a potential coastal low near the Mid-Atlantic region to close out the week, although details remain uncertain. More of the NAEFS/EC means were incorporated for the Thursday through Friday time period. ...Weather/Hazards Highlights... Multiple rounds of moderate to heavy rainfall are likely across portions of the central and southern tier states next week as multiple disturbances cross the region. The region that appears most favored for excessive rainfall is the Deep South, mainly from northern Louisiana to the southern Appalachians, where 3 to 5 inches of rain may be realized in some areas. Most of this should fall during the Tuesday-Wednesday time period ahead of the slow moving cold front. This may be enough to cause some flooding, particularly where convective training develops or across areas that will have already received noteworthy rain prior to Monday. Across the Wyoming and Colorado Rockies, a late season snow event is likely for the higher elevations west of Denver and Cheyenne, with several inches of accumulation possible. In terms of temperatures, highs are expected to be about 5-15 degrees above average for much of the eastern U.S. ahead of the front for early next week, with some 90 degree readings likely across portions of the Virginia and North Carolina Piedmont on Tuesday. This will be followed by a return to more seasonal temperatures to close out the week behind the cold front, and perhaps slightly below normal. Across the western U.S., heat is expected to build in response to the upper level ridge, with highs 10-20 degrees above normal possible for the middle to end of the week for portions of the Intermountain West and the Desert Southwest. This will equate to some 100+ degree high temperatures for the lower elevations of eastern California and southern Arizona. Hamrick 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