Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 PM EDT Thu Oct 03 2019 Valid 12Z Sun Oct 06 2019 - 12Z Thu Oct 10 2019 ...Overview and Guidance/Uncertainty Assessment... Model and ensemble guidance shows a fairly progressive and moderately amplified pattern which averages out to broadly cyclonic flow in the multi-day means. There will be two primary upper troughs of note during the period, spaced a few days apart, supporting leading cold fronts at the surface. The first upper trough should extend from northwest Ontario into the central Rockies as of early Sun and then progress through the East during the first half of next week. The second trough will drop southeast from the Gulf of Alaska/northeastern Pacific and most likely reach the northern Plains and central-southern Rockies by day 7 next Thu. Starting with adjustments made by the ECMWF/ECMWF mean/CMC in yesterday's 12Z cycle toward the more progressive GFS/GEFS/UKMET, guidance now clusters quite well for the Gulf of Alaska to Plains-Rockies trough. The 00Z CMC may be a bit overdone with its amplitude late in the period though. The leading trough crossing the East still presents some forecast problems. Individual models and ensemble members diverge considerably for if and where some embedded energy may try to separate from the westerlies. Trends toward what has been the more consistent and progressive GFS cluster with the trough coming into the West, and the latest ECMWF run waiting to close off its upper low until the energy reaches farther eastward, suggest decreasing potential for meaningful shortwave energy to linger over the East whether in the form of a closed low or open wave. The 00Z/06Z GFS runs close off a low over the Maritimes but northeast of the 00Z ECMWF so there is still potential for such a feature somewhere over that area. A blend using the 00Z-06Z GFS and 00Z ECMWF/UKMET/CMC represented consensus well early in the period while resolving low confidence detail differences for the shortwave reaching the eastern states. The forecast transitioned to a model and ensemble mean (06Z GEFS/00Z ECMWF mean) blend by days 6-7 Wed-Thu to reflect the large scale agreement in the guidance over most areas. ...Weather Highlights/Threats... A fairly strong low pressure system tracking north of the Great Lakes on Sun will bring a reinforcing push a cool air from Canada into the northern states with a brief period of blustery winds. The trailing cold front with one or more possible embedded waves will provide a focus for locally heavy rainfall from the Tennessee Valley/south-central Mississippi Valley into the Northeast during Sun-Mon. This rainfall will be beneficial over areas currently experiencing drought of varying intensity. Also during Sun-Mon the warm sector ahead of the front will contain will contain much above normal morning lows. By Tue-Thu the front should settle over the Florida Peninsula and possibly lead to some rainfall enhancement in its vicinity. There is considerable uncertainty for rainfall intensity though. The upper trough dropping southeast from the Gulf of Alaska will bring a period of rain and higher elevation snow to the Northwest during the first half of next week with highest totals over favored westward-facing terrain. The cold air behind the leading surface front will progress south and east into the West/Plains--bringing high temperatures down to at least 10-20F below normal over the northern Rockies/Plains on Wed and over much of the northern-central Plains by Thu. Expect some rain to develop along the front as it reaches the Plains. Rausch/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 Hazards: - Heavy rain over portions of the Central Plains, the Middle Mississippi Valley, and the Upper Mississippi Valley, Sat, Oct 5. - Flooding possible across portions of the Central Plains, the Middle and Upper Mississippi Valley, and the Great Lakes. - Flooding occurring or imminent over portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, and the Northern Plains. - Flooding likely across portions of the Central Plains, the Middle Mississippi Valley, and the Great Lakes. - Much above normal temperatures across portions of the Southeast, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Sat, Oct 5. 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