Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sat Nov 03 2018 Valid 12Z Tue Nov 06 2018 - 12Z Sat Nov 10 2018 ...Guidance/Predictability Assessment... Recent models and ensembles offer reasonably good solution clustering days 3-5, but differences and run-run variance becomes problematic into days 6/7 at mid-smaller scales. Accordingly, the WPC medium range product suite was primarily derived from a composite model and ensemble blend days 3-5 before quickly transitioning to mainly an ensemble mean blend by days 6/7 consistent with increasing forecast spread/uncertainty. ...Pattern Overview/Weather Threats... Broad cyclonic flow/upper-level troughing spreads over much of the lower 48 next week between upper ridges that hold over the eastern Pacific and western Atlantic. The mean trough will be reinforced by a series of shortwaves originating in the north Pacific that potentially interact/amplify over the Plains with addition of shortwave energy of polar/arctic origin. There is ample threat for deepening low pressure to lift into the Midwest/Great Lakes by Tuesday to track over eastern Canada mid-later week. This will force a precipitation focusing frontal system across the central then eastern states. Colder Canadian air to dig into lower 48 in the wake of system passage supports organized snow on the northwest system periphery, mainly over the Upper Midwest. Stream phasing/separation specifics are much more uncertain later period and individual model runs are varied with subsequent surface low/organized precipitation development, but the potential as energy digs into the mean trough is certainly there even as WPC progs currently offer a more conservative deterministic solution. In this pattern much of the east-central U.S. will see widespread precipitation early-midweek as dynamic support aloft combines with increasingly favoravble return thetae advection with storm/frontal advance and deepening. An expanding areas of rain will spread northeastward ahead of the system. Over the East, a lingering front may bring lead potential for precipitation back to the I-95 corridor from the Southeast all the way northward to New England. Later week more modest precipitation may renew over the s-central/southern U.S./Gulf of Mexico as additional shortwave energies dig into the base of the longwave trough aloft and feed upon moisture pooled along a stalled wavy/trailing front. The extent that a wave along this front will develop and lift northward over the east-central to eastern U.S. Fri-next Saturday is uncertain. Meanwhile, periods of moderate rains and higher elevation snows will be possible for the Pacific Northwest early-later next week, with snows spreading to the Rockies as upper shortwaves and surface fronts traverse the region to the lee of the eastern Pacific upper ridge. Temperatures will be below average from the northern Rockies through the Plains into the Great Lakes and Ohio Valley as reinforcing cold fronts drag cool/cold Canadian air through the region. The west will see near to above average temperatures thanks to upper ridging while the east will be a bit variable -- warming up ahead of the Great Lakes system Tue/Wed then cooling off after the front passes. Some records highs may be possible ahead of the front across the Southeast/Florida Tue/Wed. Schichtel WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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