Extended Forecast Discussion NWS Weather Prediction Center College Park MD 402 PM EDT Mon Oct 21 2019 Valid 12Z Thu Oct 24 2019 - 12Z Mon Oct 28 2019 ...Guidance/Uncertainty Assessment and Weather Highlights/Threats... Guidance agrees that the active flow pattern will reload over the cooling/unsettled West Wed/Thu as digging upper impulse/jet energies support some enhanced Rockies snows. Height falls should then act to carve out an amplified central U.S. upper trough later week. Pattern evolution uncertainty grows quickly thereafter, resulting in low forecast confidence for the southern and eastern U.S. Guidance continues to indicate two possible scenarios by this weekend: (1) A more amplified upper trough draws in deep moisture from the Gulf and results in a low pressure system that spreads heavy rainfall well inland, as represented by ECMWF/UKMET and CMC solutions; or (2) less flow separation between the northern and southern streams will keep a cold front moving steadily across the southern and eastern U.S., as represented by recent GFS runs. Overall, the most recent operation models that indicate scenario 1 show a trend toward a slower eastward ejection of the amplified upper trough. On the other hand, the UKMET is hinting at a tropical low center lingering off the Texas coast as the upper trough approaches. The GEFS/EC/CMC ensembles are mixed, with ECMWF ensemble members showing scenario 1 but with highly variable forward motion of the associated upper-level shortwave. With the consideration of the amplitude of the upstream upper ridge, the next main upper trough should bring renewed cooling with enhanced precipitation/mountain snows through the Northwest then Rockies until next weekend. So, wavelength spacing with the downstream system seems sufficient to allow for at least some southern stream separation. WPC progs modestly lean the forecast to show such potential. However, with the ensemble means continue to support a less prominent system due to the high degree of uncertainty, the new WPC prognostic charts now show a less prominent frontal wave moving across the Southeast during the weekend compared with previous progs. Schichtel/Kong 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 - Heavy rain across portions of the Southeast, the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Thu-Fri, Oct 24-Oct 25. - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Southern Appalachians, the Southeast, and the Ohio Valley, Sat, Oct 26. - Flooding likely across portions of the Pacific Northwest and the Northern Great Basin. - Much below normal temperatures across portions of the western High Plains and the Northern/Central Rockies, Mon, Oct 28. - Enhanced wildfire risk across portions of southern California, Thu, Oct 24. 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