Extended Forecast Discussion NWS Weather Prediction Center College Park MD 224 AM EST Fri Jan 27 2023 Valid 12Z Mon Jan 30 2023 - 12Z Fri Feb 03 2023 ...Dangerously cold temperatures and wind chills are forecast across the Northern Plains and Upper Midwest through early next week... ...Overview... A persistent closed upper low atop the Hudson Bay will send a series of shortwaves into the U.S., and its extension of troughing will lead to colder than average temperatures that could be most dangerous for the north-central U.S. in particular. Meanwhile ridging/an upper high over Cuba during much of next week should keep the Southwest warmer than normal. Between these upper-level features and temperature regimes, active weather is expected as shortwave energy and the combination of a couple wavy fronts along with periods of Gulf inflow support a couple of significant precipitation events east of the Rockies with rainfall to the south/southeast and some wintry weather in the colder air. Some locally enhanced rain and higher elevation snow are possible in the Southwest around Monday as an upper low/trough digs into the mean trough, while the West Coast may see increasing precipitation chances by later next week. ...Guidance/Predictability Assessment... As the medium range period begins Monday, a feature of concern will be a possible upper low around California embedded within the mean positively tilted trough. There has been some model waffling as to whether a closed low develops and the degree at which it stays phased with the northern stream through Tuesday and beyond. In the 12/18Z model cycle, most guidance all indicated a closed low other than the UKMET. But there remained some significant timing differences even with models that show the closed low, with GFS runs faster and ECMWF and CMC runs slower to move it eastward--in fact, slower than most ensemble members. In the newer 00Z model guidance, the UKMET does now show closed low development, and ECMWF and CMC runs sped up a bit. So hopefully models are coming to a better consensus with the track and timing of the upper energy/low. Upstream, there continues to be considerable variability for the overall flow across the Pacific and if/when it presses the northwestern U.S. ridge eastward, particularly later in the week. Individual models vary as do the ensemble members, with no real emerging consensus at this point. The ensemble means were favored here. Additionally, there remain some model differences with placement of frontal boundaries particularly in the southeastern U.S. While these are relatively minor for the forecast lead times, the locations of the fronts will be important for axes of any heavy rain as well as transitions to snow and/or ice and thus impactful. These frontal positions will continue to be refined going forward. The WPC model blend was based on a consensus of the 12/18Z GFS and 12Z ECMWF and CMC runs early in the period and tried to aim for a middle ground forecast for the upper low for example by blending in some ensemble mean guidance as well. An increasing proportion of ensemble mean guidance was used later in the period amid increasing uncertainty. ...Weather/Hazard Highlights... As the workweek begins next week, the north-central U.S. will continue to be quite cold after a chilly weekend as well, as a strong cold front produces a surge of arctic air behind it. Highs in the single digits and even below zero are possible in the Dakotas into Minnesota while bitterly cold lows combined with wind will produce dangerous wind chills. Much below normal temperatures should extend across much of the central U.S. through midweek especially, as well as across much of the Interior West with temperatures 15-25F below normal through Monday-Tuesday with gradual moderation thereafter. Meanwhile the far Southeast and Florida Peninsula should see the most consistent above average temperatures with highs 10-15F above average and lows with +20F anomalies. The embedded possible upper low within the trough could produce some enhanced precipitation across southern California continuing into Monday and across the Southwest Monday-Tuesday. Then this feature and the overall troughing and other shortwaves will provide support for frontal boundaries with waves of low pressure through the south-central to southeastern U.S., which combined with Gulf moisture streaming in could lead to multiple rounds of precipitation. On the southern side locally heavy rain and localized flooding are possible, especially at times when there is sufficient instability for higher rain rates. With colder than normal air in place on the northern side, winter weather could also be a threat. There are uncertain chances of snow across parts of the southern half of the Plains and Mississippi Valley into the Ohio/Tennessee Valleys and the Mid-Atlantic at times. This is also a pattern that could support freezing rain with ice accumulations with the cold air in place at the surface and potential for warm moist air to flow overtop it. The placement of heaviest rain, freezing rain, and snow all remain in question given small-scale details like the frontal positions are quite uncertain. A couple rounds of likely mainly light snow are also possible in the Northeast next week. By later next week, precipitation looks to return to the West Coast but with uncertainty in the specifics there as well. 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