Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Thu Nov 16 2023 Valid 12Z Sun Nov 19 2023 - 12Z Thu Nov 23 2023 ...Pattern Overview... A split flow pattern will persist well into next week. Systems in a northern stream will track east across Central/Southern Canada and U.S. northern tier while systems in a southern stream will track east across the southern United States and curve northeast over the East Coast. This will fuel an emerging wet pattern across this broad area of our fine nation next week. ...Guidance Evaluation/Predictability Assessment... Model and ensemble solutions remain in better than average agreement through medium range time scales and overall seem to provide a reasonable forecast basis. The WPC product suite was primarily derived from a composite blend of the 18 UTC GFS and 12 UTC ECMWF/UKMET/Canadian along with the 01 UTC National Blend of Models and WPC continuity to provide max detail consistent with a pattern with seemingly above normal predictability for Sunday-Tuesday. Newer 00 UTC guidance remains reasonably well in line during this period. Opted to add modest influence from the 18 UTC GEFS mean and 12 UTC ECMWF ensemble mean to the aforementioned composite blend to best maintain continuity into next Wednesday/Thursday amid slowly growing forecast spread and run to run variances. ...Weather/Hazards Highlights... Colder air wrapping around the backside of an exiting Northeast system and lead coastal low into Sunday will allow for some lingering wintry precipitation over northern New England and downstream of the Great Lakes. Elsewhere, heavy rainfall potential will remain low through the weekend, but will increase across the south-central to eastern U.S. next week as a main low pressure system deepens and tracks across the region. The low will develop in the lee of the Rockies over the central/southern Plains on Sunday and move to the east-central states early next week before curving towards the Northeast mid-week. The tightening pressure gradient as the low spins up will likely produce a period of high winds across the High Plains early next week. There is now a signal for heavy rainfall by Monday with focus over the central Gulf Coast states and vicinity, A WPC Excessive Rainfall Outlook "Marginal Risk area was introduced to address this emerging threat. Ample moisture will stream into the southern and eastern U.S. ahead of the system as it works downstream, so despite progression over time may lead to some localized runoff issues in the vicinity of the central/southern Appalachians on Tuesday and the Mid-Atlantic and Northeast on Wednesday. Urban flooding potential may be a concern especially for the metro areas up through Mid-Atlantic and the Northeast. There is some possibility for snow on the northern periphery of this precipitation shield. In the West, unsettled weather including a burst of mountain snows is expected Sunday as northern stream upper trough energy digs through the north-central Intermountain West/Rockies. An amplified upper ridge will then build over the West Coast early next week, resulting in more stable and dry weather. However, upstream Pacific system energies may work into this ridge enough to bring another opportunity for organized precipitation into the Pacific Northwest next Tuesday/Wednesday. 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