Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EST Thu Jan 31 2019 Valid 12Z Sun Feb 3 2019 - 12Z Thu Feb 7 2019 ...Overview... After the recent amplified pattern across much of the continental U.S. this week, a return to a more quasi-zonal flow pattern appears likely by the beginning of the medium range period this weekend. The storm system that will be crossing the Desert Southwest late this week should be present as an open wave across the southeast U.S. by Sunday as a southern stream disturbance. The pattern change continues going into the first part of next week as the large scale Pacific trough works its way inland and supports surface low development across the Great Plains and Upper Midwest. The response to this will likely be a broad upper trough becoming established over the western U.S. by Tuesday with a warmer weather pattern for the eastern U.S. by the end of the forecast period Wednesday. ...Guidance Evaluation/Preferences... Models and ensemble means are in relatively good agreement on Sunday with a couple of shortwave perturbations over the western U.S. and a southern stream shortwave across the southeast U.S. The UKMET indicates less of a surface high pressure ridge building southward out of Canada and slower with the Pacific disturbance approaching California on Monday compared to the model consensus. The CMC continues to be stronger with a surface low developing off the southeast coast early in the forecast period whereas the majority of model solutions support more of an inverted trough feature. Model agreement has improved with the surface low tracking across the Great Lakes Monday night, although the ECMWF is slower with the passage of the trailing cold front across the Plains. By Wednesday, a second surface low is progged to develop along this same boundary and likely track a bit farther to the southeast across the Ohio Valley region and eventually the northeast U.S. by Thursday, with the EC mean providing a good idea on placement for the front with this system. Above average agreement exists for the Canadian high pressure settling southward across the north-central U.S. late in the forecast period. The WPC forecast was based mainly on a GFS/ECMWF blend with some UKMET on Sunday, and then mainly GFS/ECMWF with increasing use of the ensemble means towards the end of the forecast period. ...Weather Highlights/Hazards... A much milder weather pattern will be prevalent across the majority of the central and eastern U.S. by this weekend with high temperatures running about 10 to 20 degrees above climatological averages, and mild overnight lows across the Midwest and Ohio Valley as flow from the Gulf of Mexico advects higher humidity over the region. A couple of well defined low pressure systems are expected to track across the Great Plains and Midwest over the course of the medium range period, with the potential for significant snow to the northwest of the surface lows that develop across the northern plains and Upper Midwest, and arctic airmasses will likely settle southward across the Dakotas and Montana. Based on current projections, the severity of the cold will be less than the ongoing arctic intrusion now. Heavy rain and mountain snow is expected across much of California and the terrain of the Intermountain West this weekend as a strong Pacific disturbance moves inland. Showers and storms are likely to develop from the Gulf Coast to the Midwest in the warm sectors of the two surface lows. Some of this rainfall may be locally heavy, with the highest likelihood for this becoming realized over the Southeast U.S. for next Wednesday and Thursday. Hamrick/Kong WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation and winter weather outlook probabilities are found 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