Extended Forecast Discussion NWS Weather Prediction Center College Park MD 237 AM EDT Tue Apr 27 2021 Valid 12Z Fri Apr 30 2021 - 12Z Tue May 04 2021 ...Guidance/Predictability Assessment and Preferences... Guidance overall agrees in showing a rather benign larger scale pattern evolution as we transition into May. The upper flow will be highlighted by an amplified ridge over the West and trough over the East later this week, likely followed by a period of flatter flow that leads into trough development over the West and a ridging into the East early next week. There is in particular below normal predictability with respect to the sensitive extent of phasing between southern and northern streams late week into the weekend that has given the models fits recently as best evidenced by erratic embedded system run to run timing flip-flops. Given uncertainty and with an eye toward best possible WPC product continuity, opted again to take a middle of the road approach with a composite blend of reasonably well clustered guidance of the 18 UTC GEFS mean, 12 UTC UKMET, 12 UTC ECMWF ensemble mean and the 01 UTC National Blend of Models. The 00 UTC models still do not seem to present much of a common forecast trend with embedded system and phasing issues, but the WPC blend remains in line with the ensemble means. ...Weather/Hazards Highlights... Uncertain upper trough energies are slated to focus convergence into wavy lead fronts, with moisture and instability pooling contributing to enhance rainfall that will spread over the East Friday. The front will settle over Florida to remain a focus for convection into the weekend. Meanwhile, an amplified upper ridge over the West will spread much above normal temperatures with 15-20+F above normal anomalies Friday into Saturday across the West and into the High Plains. Some locations may reach daily records for highs/warm lows. An approaching Pacific trough aloft and leading cold front will start a pronounced cooling trend back toward climatology by the weekend and focus generally modest Pacific Northwest to northern Rockies precipitation. Steady system progression and lead impulse ejections may combine with measured Plains cyclogenesis/frontogenesis to favor an emerging strong convective pattern focus over the central U.S. early next week. Schichtel 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