Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1100 AM EST Mon Jan 28 2019 Valid 12Z Thu Jan 31 2019 - 12Z Mon Feb 04 2019 ...Impressive arctic airmass to affect the north-central U.S. with record breaking temperatures and extreme wind chills expected on Thursday, followed by a moderating trend... ...Overview... The departure of a deep upper level vortex over Quebec at the beginning of the forecast period Thursday and gradual weakening of mean troughing aloft over the eastern U.S. late this week and the weekend will promote a significant warming trend over the eastern U.S. At the same time the short-range West Coast mean ridge aloft will give way to a series of Pacific systems that will bring a return of significant precipitation to parts of the West with moisture then spreading farther eastward. By the latter half of the period the mean pattern should evolve toward a positively tilted mean trough over the West and positive height anomalies/some degree of ridging over the East. This configuration is consistent with what teleconnections suggest based on the core of positive height anomalies which D+8 multi-day means show over east-central Pacific. ...Guidance Evaluation/Preferences... Decent clustering exists for the leading compact Pacific system reaching California by day 3 Thu. The 00Z UKMET is the one extreme with slower timing than most other solutions. Guidance is still in the process of consolidating for the next somewhat larger scale system expected to reach the West Coast in the Fri-Sat time frame. Much of this narrowing of the spread has been by way of GFS/GEFS mean runs trending significantly slower and more amplified toward the ECMWF/ECMWF mean which have been fairly steady over the past couple days. As of day 5 Sat the 00Z UKMET/CMC are close to the ECMWF scenario. The 06Z GFS/GEFS mean are favorably slower than their respective 00Z runs but still not quite as slow as the ECMWF cluster. The 00Z FV3 GFS better reflects the slower timing but the operational 06Z GFS run compares closer to consensus depth. So overall preferences remain closer to the ECMWF cluster with minority input from the 06Z GFS/00Z FV3 GFS to balance timing/depth considerations. As the upper level energy progresses northeastward expect a significant low pressure system to track across the Plains into the Great Lakes region by Sun-Mon. Track will depend on the timing/evolution of ejecting western energy as well as possible interaction with northern stream flow. Timing considerations upstream favor leaning somewhat more toward the ECMWF/ECMWF through day 7 Mon although the CMC does eventually gravitate toward the faster and northward GFS/GEFS mean. Ahead of this system there will likely be a wave tracking along the U.S.-Canadian border with some notable timing/track differences. The favored blend maintains a forecast close to continuity. Finally, the next system to reach the West by Sun-Mon becomes a little faster in GFS/FV3 GFS runs while the GEFS mean is slower to align better with the ECMWF/ECMWF mean--also favoring a blend that tilts more than 2/3 to the slower half of the envelope. ...Weather Highlights/Hazards... Expect the extreme arctic air intrusion affecting areas from the Upper Midwest through the Great Lakes/Ohio Valley into Northeast to continue into Thursday. The coldest temperatures of this event are likely on Wednesday (now in the short range time frame) over the Upper Midwest and northern Great Lakes but frigid temperatures will continue into the next day with highs running 20-30F below normal over the Upper Midwest/Great Lakes-Ohio Valley/Northeast. Also expect some readings to approach or fall below record low/record cold high values. Dangerously low wind chill values will be possible as well. A pronounced warming trend will move into the central and then eastern states during the weekend and early next week, with low temperatures in particular possibly reaching 10-25F above normal. Multiple Pacific systems will bring precipitation (rain and mountain snow) to a large portion of the West and then to areas east of the Rockies. The first system will be compact and confine its moisture mostly to California and the Southwest on Thursday-Thursday night. As the shortwave continues onward some locally enhanced rainfall may be possible over parts of the Gulf Coast states with some rainfall extending northeastward. The next system will first spread rain/snow into the Northwest and gradually move south/southeast. Expect heaviest totals over favored terrain in California and Arizona. During the latter half of the period the moisture from this system will spread across the Rockies and then low pressure tracking northeast from the central Plains may produce a significant snow event over northern areas with rain in the warm sector. Additional rainfall may develop over portions of the South. Rausch/Hamrick 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