Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Sat Nov 11 2023 Valid 12Z Tue Nov 14 2023 - 12Z Sat Nov 18 2023 ...Heavy rainfall potential for the central Gulf Coast and parts of the Southeast into Thursday... ...Moisture directed into California could lead to heavy rain and snow Tuesday-Thursday... ...Pattern Overview and Guidance Evaluation/Predictability Assessment... The medium range period (Tuesday-Saturday) features shortwave energy exiting the Northeast and additional troughing moving through the Deep South, with early-mid week heavy rainfall potential along the Gulf Coast and into parts of the Southeast/Florida. Meanwhile, East Pacific troughing looks to split, with an amplified northern stream shortwave moving quickly eastward through the northern tier, reaching the Great Lakes/Northeast by Friday-Saturday. A southern stream deep upper low looks to meander off the California coast until about Friday, eventually ejecting inland by next weekend. Models show good enough agreement Tuesday-Thursday for a purely deterministic model blend as a starting point for the WPC medium range forecast. After this, there remains plenty of timing/strength differences with the northern stream shortwave into the Great Lakes late next week, and also placement of the upper low off the California coast and timing of its eventually move inland. This necessitated a shift towards the ensemble means for todays WPC forecast blend. These differences however have bigger implications for resulting QPF across California, with the latest National Blend of Models continuing to appear well overdone with QPF, with not much support for these higher amounts from the better consensus of models. The WPC QPF forecast sided more closely with the ensemble means and the GFS/ECMWF/CMC, which results in a slight reduction in amounts compared to prior shift continuity, and noticeably lower than the NBM. ...Weather/Hazards Highlights... The slow and steady progression of a leading/amplified southern stream upper trough and associated wavy surface front has increasingly shown a signal supportive of some eastern Pacific and enhanced Gulf of Mexico moisture inflow to fuel protracted rainfall potential from the central Gulf Coast states Tuesday through the Southeast/FL with added Atlantic inflow through Wednesday, exiting Thursday. The soaker may lead to some coastal/local and urban runoff issues given potential for several inches of frontal overrunning rains and a threat for some heavier local repeat/training duration amounts. Accordingly, WPC Day 4/5 Excessive Rainfall Outlook Marginal Risk areas continue across these areas. Meanwhile upstream in the active southern stream branch of flow, recent guidance indicates that ample upper trough/closed low development over the eastern Pacific by early next week may prove slow to work until later next week into the West Coast/California in separated flow. There has been a noticeably trend away from any widespread impactful rainfall amounts, but even still, it's likely that moisture should slowly spread organized and periodically moderate to locally terrain enhanced rains into the central California coast, and inland mountain snows for the Sierras Tuesday/Wednesday. Considered a marginal risk on the day 5 ERO for the coastline, but after coordination with Monterey and Los Angeles/Oxnard forecast offices, opted to hold off on any introduction of a risk given dry antecedent conditions and still plenty of uncertainty in the forecast. This activity should eventually expand inland over the Southwest later next week. In the northern stream, lead/amplified upper troughing is slated to increasingly shift from the Northeast to the northern Atlantic Tuesday onward as primarily a maritime low developer with an increasing offshore weather focus. High pressure will linger over much of the East in the wake of this system. Well upstream, upper trough and surface system energies are expected to work across the Pacific Northwest/Northwest through the northern Rockies early-mid next week then again late week to support modest to terrain enhanced moderate rains/snows across the region. Santorelli/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