Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sat Nov 04 2023 Valid 12Z Tue Nov 07 2023 - 12Z Sat Nov 11 2023 ...Overview... The upper flow pattern across the contiguous U.S. looks to be quasi-zonal and progressive as the medium range period begins Tuesday. But a couple of shortwaves embedded within the flow will be impactful in spinning up low pressure/frontal systems, including one moving through southeastern Canada Tuesday and another tracking from the central to northeastern U.S. Wednesday-Thursday, with some associated precipitation. A cold front with the second low pressure system should track southeastward across much of the country as the week progresses and gradually suppress what starts as a widespread area of above average temperatures. Meanwhile in the West, precipitation is forecast to linger into Tuesday before a likely break around midweek, but rain/snow chances could return late next week as the overall upper pattern starts to amplify, including eastern Pacific troughing. ...Guidance Evaluation/Predictability Assessment... The shortwave moving through the Great Lakes region into the northeastern U.S./southeastern Canada and the associated surface low early in the period are generally agreeable in the model guidance. The next feature shows more detail differences as it tracks eastward, with uncertain energies coming from southern and northern stream sources and interacting/combining. This does have effects on the sensible weather including how far south the precipitation reaches and the temperatures/precipitation type in the north-central to northeastern CONUS. At this point the only real outlier seemed to be the 12Z UKMET, but the other guidance showed variations but generally reasonable solutions, so a blend of the deterministic and ensemble guidance seemed best to handle the differences. It appears that reinforcing energy will maintain troughing across the Great Lakes into late week. Farther west, energy and troughing look to spill southeast across the northeastern Pacific for the latter half of the week, likely moving into the West Coast in some form late week. Models do vary from run to run and cycle to cycle with the character of the troughing. Even the GFS runs themselves have varied considerably, from a more phased trough in the 12/18Z runs to a closed upper low diving south atop California in the 00Z run, and other models and ensemble members have varied similarly. But at least the general idea for somewhat more amplified flow is there by the late period. The WPC forecast was based on a deterministic model blend early in the forecast, favoring the 12Z ECMWF, 18Z GFS, and 12Z CMC with a small portion of the 12Z UKMET initially. Introduced and increased the proportion of the GEFS and EC ensemble means with time to around half by late period to yield compromise solutions for the details of the pattern. ...Weather/Hazards Highlights... The western U.S. can expect precipitation to continue into Tuesday, but with lessening amounts compared to the short range period. Higher elevations like the Cascades and northern Rockies are likely to see snow. Precipitation should trend much lighter for the West on Wednesday as upper-level ridging briefly builds back in, though the central Rockies could have a period of snow. Chances for at least light precipitation may increase again late week for the Pacific Northwest, but with uncertainty in timing. Farther east, the Midwest/Great Lakes region to Northeast should see rounds of precipitation next week as low pressure and frontal systems track across. Amounts and north-south extent of the precipitation remain somewhat uncertain though. One system should exit the Northeast with its precipitation on Tuesday, while the next should push from the north-central U.S. Tuesday into the Great Lakes Wednesday and the Northeast on Thursday, with some precipitation perhaps lingering into Friday. This could be a somewhat colder system, with precipitation in the form of snow possible in areas near the Canadian border and at least the higher elevations of the Interior Northeast, perhaps even into lower elevations of northern New England. There is low confidence in snow levels and amounts at this point though. Some rain is possible farther southwest along the frontal corridor, with the best chance for modest rainfall totals into southern Texas where the available moisture will be the highest. Much of the country will see above average temperatures as the period begins Tuesday, with the greatest anomalies of 15-25F for highs across the southern High Plains as temperatures rise well into the 80s. A corridor of lows that are 20-25F above normal is forecast across the parts of the Mississippi Valley into the Ohio/Tennessee Valleys on Tuesday-Thursday, with warmer than average temperatures across the Gulf Coast states as well. Daily record high temperatures could be set from the south-central to southeastern U.S. especially on Tuesday and Wednesday. Cold fronts tracking south and east should gradually limit the area of above normal temperatures across the CONUS, cooling temperatures across the northern tier, then the central U.S. to Ohio Valley, and finally across the Southeast by around Friday. Areas behind the front should see near to below normal temperatures, spreading progressively from the western U.S. into the south-central U.S. and toward the Ohio Valley, Great Lakes, and the Northeast late 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