Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Tue Apr 27 2021 Valid 12Z Fri Apr 30 2021 - 12Z Tue May 04 2021 ...Guidance/Predictability Assessment and Preferences... Guidance this morning continues the theme of a relatively 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 becomes more amplified again early next week with trough development over the West and ridging over the East. There are a couple of areas where models continue to show below normal predictability--(a) the extent of phasing between southern and northern streams late week into the weekend across the northern tier states, as evidenced by erratic embedded system run to run timing flip-flops; and (b) the westward extend of precipitation along the Gulf Coast during the weekend. There has been a general model trend this morning for a faster eastward progression of the northern stream energy. Meanwhile, the ECMWF and the CMC favor more QPF to linger over the western Gulf Coast region due to a much slower progression of an upper low/trough over southern Texas relative to the GFS/GEFS. Both the EC and CMC ensemble means are more progressive though. Given the uncertainty, opted again to take a middle-of-the-road approach with a composite blend of the 06Z GFS/GEFS mean, 00Z ECMWF/EC ensemble mean and a smaller contribution from the 00Z CMC/CMC mean, with increasing proportion of the ensemble means toward Day 7. This blend yielded a faster northern stream progression while maintaining a weak reflection of a western Gulf Coast wave along a warm front that later washes out as it lifts into the East Coast early next week. ...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 while some precipitation may linger into the western Gulf Coast region. 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 pattern focusing rainfall over the northern to central High Plains early next week that should later shift eastward along an increasingly sharp front extending into the Northeast with above normal temperatures for much of the East and the South. Kong/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