Extended Forecast Discussion NWS Weather Prediction Center College Park MD 310 PM EDT Sat Oct 30 2021 Valid 12Z Tue Nov 02 2021 - 12Z Sat Nov 06 2021 ...Overview... An omega block centered over North America will likely maintain broad troughing across the eastern U.S. while general ridging will tend to re-establish itself over the western U.S. during the medium range period. Periodic shortwave energies coming from the eastern Pacific will attempt to pass under the omega block and then across the western U.S. towards the central Plains. This is where much of the model uncertainty lies. A more prominent shortwave is forecast to track through the central Plains midweek before reaching the East Coast late next week with some potential for cyclogenesis to occur off the coast. Another shortwave may make its way through the western U.S. and move into the southern Plains by next weekend. ...Guidance/Predictability Assessment... With the omega block in place over North America, model solutions appear to split into their own flavors as they try to handle the relatively amplified pattern with time. The ECMWF solutions tend to be slower while the GFS faster with bringing the broad upper trough progressively through the eastern U.S. later next week. In the mean time, the CMC shows elements seen from both the ECMWF and the GFS. The slower ECMWF solutions would therefore open up the possibility for a closed upper low to form over the central U.S. followed by cyclogenesis off the New England coast by next weekend. On the other hand, the faster GFS would tend to kick the energy farther offshore. Meanwhile, recent ECMWF runs have shown a tendency to speed up this incipient trough progression. Given this relatively typical biases of these models in the medium-range, a general model compromise was used to compose the WPC medium-range forecasts. This consisted of mainly an even blend of the deterministic and ensemble means from the 00Z ECMWF/EC mean, the 06Z GFS/GEFS, with smaller percentages from the 00Z CMC/CMC means. ...Weather/Hazards Highlights... A frontal system with occasional upper-level shortwaves passing through the West will result in periods of enhanced precipitation across the area during the second half of the week. One such shortwave is forecast to make its way into the central to southern Plains where moderate to heavy rainfall is possible Wednesday into Thursday. Then the combination of moisture and southern stream shortwave energy interacting with a frontal system across the south-central U.S. will increase rainfall chances Tuesday-Wednesday for the southern Plains and possibly into parts of the lower Mississippi Valley, with some heavy rain possible. Some precipitation could spread east/northeast during the latter part of the week, with the higher elevations of the central Appalachians and the interior Northeast seeing some possibility for snow, but with low confidence in the specifics. On the other hand, the slower ECMWF solution continues to indicate the possibility of cyclogenesis near the East Coast by next weekend. Meanwhile, unsettled weather is expected to continue along the West Coast. Northern California and far southwestern Oregon should see the heaviest precipitation with normal terrain enhancements and higher elevation snow. Some of these activities are expected to spread into the Pacific Northwest with lesser totals eastward into the Intermountain West and Rockies. Some snow/rain can be expected in the central High Plains Tuesday night into Wednesday morning as the upper shortwave heads further toward the northeast. Behind the cold front, a cold high pressure system will maintain well below normal temperatures across the central and eastern U.S. This will especially be the case for highs which should be 10-20F below average from the central and eventually southern parts of the Plains and spreading across the Mississippi Valley and eastern U.S. Chilly lows in the 20s may reach as far south as Kansas and Iowa, which would only be minus 5-10F anomalies but would still bring the first freeze around next Tuesday or so. Expect above normal low temperatures under the western ridge aloft, but periods of unsettled weather will keep highs somewhat below normal over California on most days and near normal elsewhere. Kong 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, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml