Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Fri Nov 18 2022 Valid 12Z Mon Nov 21 2022 - 12Z Fri Nov 25 2022 ...Overview... A more zonal confluent flow regime is forecast to establish itself across the northern tier states by the start of the medium-range period as an upper trough de-amplifies further and exits the Northeast. This will lead to moderating temperatures to expand eastward from the Plains to the East Coast through midweek. Meanwhile, a low pressure wave forming along a stalled front is forecast to bring heavy rain potential along the east coast of Florida early next week. For the West Coast, models are generally trending toward building a stronger ridge late next week while developing a better-defined trough downstream over the Great Plains. This pattern will tend to inhibit heavy precipitation from reaching the Pacific Northwest while spreading moisture northward from the Gulf with unsettled weather likely expanding across the eastern half of the country by the Thanksgiving Holiday weekend. By Friday, there appears to be the potential for the upper trough to interact and amplify the low pressure wave off the Southeast U.S. and then track it up the East Coast. However, details of this interaction are quite uncertain at this time. ...Guidance and Predictability Assessment... Much of the uncertainty will be toward the end of next week with the potential for cyclogenesis to occur near the East Coast. This is in response to a general model trend to build a stronger ridge near the West Coast while promoting a more amplified trough downstream across the Plains states. The last couple of ECMWF runs have been more aggressive in this regard although earlier runs from both the ECMWF and the GFS have hinted at this possibility. The 12Z GFS keeps the trough progressive whereas the CMC does not favor the phasing of the upper trough with the low off the Southeast U.S. The WPC forecast was based on a blend of the 06Z GFS/GEFS with the 00Z ECMWF/EC mean with small contributions from the 00Z CMC/CMC mean, but leaning toward the EC mean by Day 7. ...Weather/Hazard Highlights... Chilly temperatures this weekend are expected to continue into the first part of next week, but should be gradually moderating. Low temperatures on Monday are forecast to be 10-15F below normal from the Lower Mississippi Valley through the East, but only a few degrees below average Tuesday and near to above (especially across the Southeast) normal as the week progresses, though the interior Northeast may see another bout of cold air Thursday-Friday. High temperatures could remain cool for southern Texas on Monday, with highs in the 50s below normal by 15-25F, which should gradually warm through midweek as well. The East may see some below normal highs once again by the latter part of next week. Meanwhile the West could see increasing coverage of above average temperatures by Thursday-Friday given the ridge aloft. Some lingering lake effect snow is possible into Monday downwind of especially the Lower Great Lakes, but the bulk of the significant snow for places like Buffalo, New York is forecast to fall during the short range period. Meanwhile, multiple frontal systems moving into the northwestern U.S. could cause rounds of precipitation there next week, with higher elevation snow. However there is still a fair degree of uncertainty over the southward extent and intensity of rain/mountain snow on a day-to-day basis. Surface high pressure dominating interior parts of the West is likely to keep that region fairly dry. Meanwhile, a shortwave and moisture advecting from the Gulf of Mexico could lead to showers and some thunderstorms across Texas and potentially farther east across the Southeast early in the week. Easterly flow and a frontal system meandering near the Florida Peninsula will enhance shower/thunderstorm coverage there, and isolated flash flooding cannot be ruled out especially over urban areas. Then by the latter half of the week, moisture could stream north ahead of the potential central U.S. trough and increase chances for precipitation across the eastern half of the U.S., though the details remain uncertain and will depend on evolution of the upper and surface systems. Kong/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