Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sun Oct 08 2023 Valid 12Z Wed Oct 11 2023 - 12Z Sun Oct 15 2023 ...Excessive rain threats for the Midwest to Northeast and central Gulf Coast/Southeast/northern Florida mid to late week... ...Overview... A stormy week on tap for our fine nation. A closed upper low will shift slowly eastward across eastern Canada mid-later week to end Great Lake effect rains and shift unsettled conditions under/around this amplified feature away from the Northeast. Far upstream, dynamic upper trough energies will work onshore and dive southeastward through the West. Early week rains will ease over the Pacific Northwest with system/frontal progressions to favor enhanced mountain snows from the Cascades to especially the northern Rockies with closed trough/low development and passage. This potent upper system will steadily track from the Plains to the Northeast Friday into next weekend. This will foster enhanced precipitation chances to spread in earnest from the central U.S./Midwest through the Northeast as Gulf then Atlantic moisture inflow deepens with deep cyclogenesis/frontogenesis. To the south, a frontal boundary with deepened tropical moisture will lift through the Gulf of Mexico to increase heavy precipitation chances across the central Gulf Coast and Florida/Southeast by mid to later this week before lifting off the East Coast. ...Guidance Evaluation/Predictability Assessment... Model and ensemble forecast spread continues to decrease through medium range time scales, now in a pattern with seemingly better than average predictability for flow evolution and main embedded weather focusing storms/systems over the next week in active flow. The WPC product suite was primarily derived from a composite blend of best clustered guidance from the 18 UTC GFS and 00 UTC ECMWF/Canadian and ECMWF ensemble mean along with the compatible 01 UTC National Blend of Models and WPC continuity. Latest 00 UTC guidance overall remains in close line. ...Weather/Hazards Highlights... Dynamic upper trough/height falls and surface system passage across the West into mid-later week will favor a swath of autumn mountain snows from the Cascades into through the Intermountain West and especially the northern Rockies. Downstream, precipitation chances will expand east throughout the week as a frontal system moves across the nation, reaching the Central U.S. by midweek. Deep cyclogenesis and wrapping anomalous moisture into a leading warm front lifting through the east-central U.S. will shift focus for emerging heavy rains from the Central Plains through the Midwest into Wednesday. The WPC Day 4/Wednesday Excessive Rainfall Outlook (ERO) shows a Marginal Risk over the Mid-MS Valley given risk for training and growing model and ensemble signals. Guidance suggests this heavy rainfall area will likely expand across the Midwest with continued system development and track/inflow that is covered at this point by a Marginal Day 5/Thursday ERO risk area. Meanwhile well south, a separate warm front lifting through the Gulf of Mexico and the Florida Peninsula brings a threat for heavy rainfall from the central Gulf Coast to the Southeast Wednesday/Thursday. This may be aided by an area of low pressure in the Gulf of Mexico and possible remnant tropical moisture to be monitored. Latest model guidance prompted an ERO marginal risk area for Day 4/Wednesday from the central Gulf Coast to the Florida Peninsula. A Day 5/Thursday ERO marginal risk area was also introduced downstream to span parts of the Southeast. These two main systems may increasingly interact to some degree to spread enhanced rainfall and runoff issues possible across the East/Northeast Friday into Saturday, with widespread enhanced backside winds and post-frontal falling Autumn temperatures. 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 forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw