Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Tue Nov 07 2023 Valid 12Z Fri Nov 10 2023 - 12Z Tue Nov 14 2023 ...Overview... The upper flow pattern across the contiguous U.S. late week into the weekend looks to be progressive with multiple embedded shortwaves that will be impactful in spinning up low pressure/frontal systems. The first system of concern is a positively tilted shortwave over the north-central U.S. Friday combining with Canadian flow to produce troughing across parts of the central and eastern U.S. late week. Eastward progression of the upper trough and an associated wavy front will gradually suppress an area of above average temperatures across the Southeast late week, while spreading rain across the southern and eastern U.S. that could linger into early next week. Upstream, a quickly moving shortwave and frontal system or two coming through the Northwest should increase rain/snow chances there, followed by a larger scale eastern Pacific upper trough that may generate additional precipitation over the Pacific Northwest during the weekend and beyond. This eastern Pacific trough will promote upper ridging farther east into the north-central U.S. with warmer temperatures, and overall a more longwave-dominated pattern into next week. ...Guidance Evaluation/Predictability Assessment... Despite some relatively minor detail differences, there remains good enough agreement the first half of the period for a multi-model blend of the latest deterministic guidance. By Sunday and beyond, bigger issues begin to arise regarding a shortwave traversing the northern half of the country reaching the Great Lakes around Sunday. The ECMWF by this point becomes faster and more amplified as it tries to combine energies with a separate shortwave moving into the Great Lakes on Sunday from central Canada and also spins up a deep surface low off the East Coast on Monday. The better consensus suggests more separation of features and weaker systems, and by Day 7, the ECMWF becomes completely out of phase across the East compared to the GFS/CMC. This has implications for QPF across the East/Southeast this weekend/early next week. The ensemble means show better agreement and suggests a trough position in between the GFS/CMC and the ECMWF. Timing issues begin to arise by Monday and especially into Tuesday with amplified troughing towards the West Coast with the ECMWF quite a bit faster bringing this energy (and the resulting QPF) inland. The ensemble means generally follow suit with their deterministic counterparts. The WPC forecast for today used a general model blend for days 3-5, leaning more heavily on the ensemble means by Day 6 and 7/Monday-Tuesday. Maintained a slight preference towards the slower GFS/GEFS which maintained better continuity with the previous WPC forecast as well. ...Weather/Hazards Highlights... Moisture overrunning the cold front that is likely to push through the Southeast and then stall over the northern Gulf will lead to some rain across the south-central to southeastern quadrant of the U.S. for late week into early next week. The highest rainfall totals are likely to be over southern Texas near a meandering surface low along the front, with eastern Pacific and Gulf moisture combining. On Friday, some instability could be in place especially early in the day before the front pushes through. This could lead to locally heavy rainfall rates, but are likely to stay below any flash flooding thresholds, so maintained no risk area on the Day 4/Friday Excessive Rainfall Outlook. By Saturday, since the front is likely to have passed, lack of instability should mean rain rates will not be too high, so no risk area is planned for the Day 5/Saturday ERO either. Into next week though, there may be more support for convection as mid-upper level energy approaches, so this will continue to be monitored. Farther north, lake effect precipitation is likely with troughing and westerly flow over the Great Lakes, likely maximized Friday. Additional upper-level energy could spread light precipitation to the Northeast early next week. Rounds of frontal systems and shortwaves pushing through the Northwest will maintain precipitation chances across the Pacific Northwest and the northern Rockies. Moderate to heavy amounts are likely to be directed into the northern parts of the Olympics and Cascades, with lower elevation rain and higher elevation snow. Southeastern portions of the country will remain warmer than average ahead of the frontal boundary on Friday, with a corridor of lows that are 10-20F above normal extending from the Lower Mississippi Valley into the Southeast to the Mid-Atlantic Friday morning before the cold front passes and limits above normal highs to the Southeast/Florida. The Florida Peninsula should be the main area above average by Saturday, with highs well into the 80s actually close to daily record highs. Elsewhere, temperatures should be near average to cooler than average through late week in the post-frontal cool high pressure. But as upper ridging builds across the north-central U.S. early next week, above normal temperatures by around 10-15F will overspread the central and northern Plains into the Midwest. Meanwhile below normal highs should linger in the south-central U.S. with lower heights overhead and clouds and rain possible, and interestingly lead to similar highs from Texas all the way north to South Dakota or so (in the upper 50s and 60s). Near to cooler than normal over the Eastern Seaboard this weekend should gradually moderate through the early part of next week. Tate 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