Extended Forecast Discussion NWS Weather Prediction Center College Park MD 140 AM EST Sat Nov 09 2019 Valid 12Z Tue Nov 12 2019 - 12Z Sat Nov 16 2019 ...Record cold next week for much of the central/eastern states... ...Pattern Overview and Guidance/Predictability Assessment... Punctuated upper ridging will meander off the coast of California, favoring troughing east of the Rockies. Over Mexico, a slow-moving closed low will eventually rejoin the southern edge of the westerlies after Wednesday and track across the northern Gulf of Mexico. The models/ensembles were in good agreement overall but with varying degrees of speed/track/evolution differences in a fairly perturbed pattern. The 12Z GFS/ECMWF and 00Z ECMWF formed much of the base for the forecast with the 12Z NAEFS/ECMWF ensemble mean as a needed smoother. Largest differences were in the Southeast as the Mexican upper low and a northern stream shortwave merge/phase/interact which may induce cyclogenesis and increase precipitation over the region. 12Z ECMWF appeared too aggressive but the 12Z GFS too quick (both their biases). 12Z ECMWF ensemble mean and NAEFS mean were weaker but perhaps better placed, along with the 00Z/08 ECMWF (just offshore). Secondarily, troughing in the eastern Pacific may approach California in some fashion as a shortwave may crest the upper ridge along 140W. Ensembles have trended more bullish but will need to wait to see if any precipitation can be realized south of NorCal. ...Weather Highlights/Threats... Cold Canadian high pressure will move out of the central/southern Plains Tuesday and into the Ohio Valley by Wednesday, bringing in well below average temperatures that will likely break daily records across a sizable area of the eastern half of the CONUS Tue-Wed. This equates to high temperatures in the 40s from Texas into the lower MS Valley, 30s in the TN Valley, 20s in the Midwest, and teens in the northern Great Lakes, which is more typical of mid-winter in some locations. For some, this could be the earliest in the season such cold will be observed in the period of record. Temperatures will moderate for later in the week as the high moves offshore and weakens, but highs will remain about 10-15 degrees below average along and east of the Mississippi into next Friday. West of the Rockies (but including parts of the Front Range), temperatures will stay above average by about 5-10 degrees. Low pressure will move out of New England Tuesday with a swath of snow to the northwest of the track and lake-effect snows for the Great Lakes with very cold temperatures aloft over still warm water. By the end of the week, the upper low once over Mexico will reach the Gulf and its interaction with a frontal boundary could spread increasingly heavier precipitation over the Southeast as low pressure develops near Florida. This may lift northeastward into next Saturday along the coast with some high elevation snow possible for the southern Appalachians per the current evolution in the lingering cold air mass. Fracasso Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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