Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Tue Nov 22 2022 Valid 12Z Fri Nov 25 2022 - 12Z Tue Nov 29 2022 ...Meaningful precipitation is possible across the southeastern U.S. late this week and potentially into the Northeast early next week... ...Overview... Fortunately, model guidance has come into better agreement with the overall pattern across the country late this week into early next week. Unfortunately, models have trended toward the solution that has not been favored in the WPC forecast over the last few days since this pattern was formerly in the minority. The new model guidance and the WPC forecast indicate that a closed upper low will track across the south-central U.S. along with a developing surface low pressure system for Friday-Saturday. This should lead to widespread rain chances across the southern half of the Plains and Mississippi Valley and farther east into the Southeast, Ohio and Tennessee Valleys, and the East Coast for late week into the weekend. There is some chance of snow on the backside of the closed low in the southern High Plains on Friday. By early next week, the upper pattern is likely to transition to more zonal flow, but with troughing and fronts coming into the Northwest promoting increasing precipitation chances across the West Coast into the Great Basin and Rockies Sunday-Tuesday. ...Guidance and Predictability Assessment... It has been quite difficult to make a deterministic forecast the past few days given the model spread and no notable middle ground type solutions between a cluster of models led by the ECMWF and EC ensemble members that showed a phased upper trough marching through the central-eastern U.S. along with a strengthening Northeast surface low around the Thursday-Saturday timeframe, and one led by the GFS/some GEFS members/UKMET that spilled energy into the southern stream enough to create a closed upper low over Texas or so with a slower track. The significant differences seemed to arise from energy in the eastern Pacific handled differently by each model. The WPC forecast had been leaning toward the former cluster which had fit continuity better. However, now pretty much all the guidance has trended toward the slow southern stream upper low type of solution. There still remain some wiggles the placement of the upper low from model to model and run to run, but there is much less spread than there has been. Thus the WPC forecast, after a trend in that direction by the previous shift, was pretty much "all in" on showing a closed low over the Southern Plains day 3/Friday and a slight shift eastward day 4/Saturday. This affected the frontal positions and QPF and other weather grids with some necessary changes to continuity. The forecast blend for fronts/pressures was based on a multi-model deterministic blend of the 12/18Z guidance to provide a middle ground between slightly slower or faster solutions. Farther west, there continues to be a general trend toward troughing in the West early next week. Some guidance like the 12Z ECMWF was aggressive in bringing in a shortwave to the western U.S. by Sunday before the main trough feature, and there are certainly model differences that basically average out to zonal flow, before better agreement for troughing coming in around Tuesday--though of course there are some model differences in the details of how fast the trough moves inland and its depth etc. The WPC forecast utilized a deterministic model and GEFS/EC ensemble mean blend (just over half ensemble means) for the latter part of the period to alleviate these differences. ...Weather/Hazard Highlights... Ahead of the closed upper low in the Southern Plains and a couple of low pressure/frontal systems, Gulf moisture is likely to stream into central and eastern parts of the lower 48. Precipitation is expected from Texas/Oklahoma (which could be in the form of snow for some portions) with rain and perhaps some thunderstorms farther east across the Lower Mississippi Valley and Southeast on Friday. Locally heavy rainfall causing isolated flash flooding is possible. The low is forecast to track northeastward and spread precipitation across the Middle Mississippi Valley and Ohio/Tennessee Valleys as well on Saturday, and into the Eastern Seaboard by Sunday. With this low track, most areas are likely to see rain rather than wintry precipitation, but higher elevations of the Interior Northeast could be an exception. There could be some lake effect rain/snow showers early next week behind the upper trough. The Pacific Northwest into the Northern Rockies can expect some light to moderate precipitation late this week in conjunction with a couple of frontal systems. As upper troughing shifts into the region, precipitation is forecast to spread southward across California and into the Great Basin and Rockies for early next week. Lower elevation rain and higher elevation snow will be likely. The upper low now forecast atop the south-central U.S. late week will cause some cooler than normal temperatures there, particularly in terms of highs that could be 10-20F below normal mainly in Texas on Friday. Meanwhile lows are likely to be warmer than normal for the central/eastern Gulf Coast states and northward into the Tennessee/Ohio Valleys Friday given the Gulf inflow ahead of the upper low, shifting into the East by Sunday. Slightly milder than normal high temperatures for the north-central U.S. Friday-Saturday should moderate to near normal by Sunday. As upper troughing influences the West early next week, expanding coverage of below average temperatures is likely there, while the south-central U.S. flips to slightly above normal ahead of the trough. 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, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices 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