Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1202 PM EDT Fri Sep 27 2019 Valid 12Z Mon Sep 30 2019 - 12Z Fri Oct 04 2019 ...Heavy rainfall potential from the southern High Plains into Great Lakes early to middle of next week... ...Anomalous warmth to persist over the central to eastern U.S., while very chilly conditions remain across the northern and northwestern states ... ...Pattern Overview and Guidance/Uncertainty Assessment... Through the extended period a highly amplified mean trough will be positioned over the West with a broad ridge over the South and Southeast. This pattern will largely remain unchanged over the next 7 days; which will keep a much cooler airmass over the Pacific Northwest and Intermountain Regions and a warmer one over the central and eastern states. A wavy front is forecast to gradually move across the central and eastern U.S. providing a focus for precipitation from the Southern Rockies/High Plains, through Midwest and Great Lakes regions to the Northeast. Ensemble consensus remains quite good and the latest runs of the deterministic guidance continues to be faster with ejecting energy from the western trough eastward across the north-central U.S. toward the Northeast. The Canadian model is persistent with focusing more energy with the trough over Canada/Northeast U.S. than others, but still usable in small quantities. The forecast comprised of a blend of the 00Z ECWMF, 00Z/06Z GFS with lesser weighting of the 00Z UKMET/CMC and the ensemble means. ...Weather Highlights/Threats... The Heavy snow/rain over the Northern Rockies will taper off by Monday as the the surface low pressure system moves further into the Northern Plains. The trailing front will become more zonal thanks to the ridge over the Southeast. Flow around the western periphery of the Ridge will draw tropical moisture from the eastern Pacific Ocean northward along the boundary, aiding in the development of scattered to widespread precipitation spanning from New Mexico to Maine. Multiple days of precipitation, potentially heavy at times, over nearly the same locations may increase the threat for flash flooding. This is especially the case for portions of the Central Plains and Great Lakes. Deep-layer easterly flow, associated will the decaying Tropical Storm Karen, will promote an increase in rain/showers over Florida. Please monitor NHC forecasts for the latest information regarding Karen. The western U.S. into Northern Plains are expected to have daily temperatures averaging 10-25F below normal with localized areas in Montana seeing highs at least 30F below normal. Daily records for cold highs are most likely on Sunday but some are possible in the days to follow. Many locations from the Gulf Coast to New England will be averaging 10-20F warmer and numerous daily records may be broken. As the pattern aloft begins to trend less amplified, expect a gradual moderation of chilly western U.S./northern Plains temperatures. However, record highs/warm lows remain a distinct possibility over the southeastern U.S. through late next week. Campbell 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 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