Extended Forecast Discussion NWS Weather Prediction Center College Park MD 249 AM EDT Tue Apr 28 2020 Valid 12Z Fri May 01 2020 - 12Z Tue May 05 2020 ...Much above normal temperatures spread from the West to the Deep South... ...Stormy weather for the Northeast Friday into Saturday... ...Pattern Overview and Guidance/Predictability Assessment... Upper flow over the lower 48 will become less amplified Fri into the weekend which often corresponds to decreasing predictability. Late week initial Pacific energy will start to flatten and push eastward an upper ridge over the Plains while a deep upper trough with embedded low drifts over the Northeast. This eastern system will bring a heavy rainfall threat to parts of the Mid-Atlantic/Northeast. Stronger Pacific energy will cross the western U.S. Sun/Mon, supporting precipitation from the Pacific Northwest into the Northern Plains, while convectively active downstream flow to the east continues to lose amplitude and become more progressive. This evolution should lead to a gradual suppression/eastward spread of the hot temperatures shifting from the West through the South. There is some signal for renewed flow amplification early next week, but run-run continuity has been less than stellar at long time frames. The WPC medium range product suite was primarily derived from a blend of reasonably clustered guidance of the 12 UTC GFS/ECMWF and GEFS/ECMWF ensemble means days 3-7. The 12 UTC GFS/ECMWF seemed the best model fits with ensembles. The 00 UTC GFS/ECMWF also now fits this mold better than the 18 UTC GFS. This composite solution maintains good WPC continuity and acts to mitigate less certain smaller scale variance. ...Weather/Hazard Highlights... A deepened low/system affecting the Northeast will offer some potential for lingering heavy rainfall over the Northeast Fri into Sat. Coastal low redevelopment and a windy/tight gradient between low pressure/frontal system and high pressure tracking off the Canadian Maritimes will wrap moisture inland to enhance rainfall. Some locations could experience some runoff/flooding concerns due to wet ground from recent events. Meanwhile well upstream, a Pacific shortwave and cooling frontal system will bring modest precipitation across the Northwest into the Northern Plains late this week, with low level upslope flow behind the front possibly helping activity to persist over parts of the north-central Rockies/High Plains into the weekend. Another Pacific system should bring an episode of enhanced precipitation to the Pacific Northwest this weekend with continued eastward progression across northern parts of the West and into the Plains. Higher elevations may see periods of snow. As an associated front settles into the south-central Plains and extends into the Mid-MS/OH Valleys and south-central Appalachians by the weekend/early next week, expect increasing potential for some locally moderate to heavy rainfall in its vicinity. Energy aloft emerging from the West may enhance convective activity. Still uncertain specifics by this time frame portends relatively low confidence in the smaller scale details. Much above normal temperatures will linger over areas from the Great Basin/Southwest through the Rockies into the Plains Fri, with a broad area of plus 10-25F anomalies. By Sat-Mon the flatter trend for flow aloft will lead to the warmest temperatures extending farther eastward and being confined to the southern tier, with moderation of anomalies into the plus 5-15F range. Daily records for highs/warm lows should be most numerous through Fri, but even with the moderating trend temperature anomalies may be sufficient to produce some daily records across the South into early next week. Schichtel 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