Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1058 AM EST Sat Feb 23 2019 Valid 12Z Tue Feb 26 2019 - 12Z Sat Mar 02 2019 ...Pattern Overview... The Rex block will continue to persist over the east-central Pacific with ridging stretching into Alaska and northwestern Canada, allowing features to drop quickly across the western U.S. That feature, along with troughing over eastern North America, has good consensus among models. However, details about systems dropping across the west and as they progress eastward are still quite uncertain. There is still a signal for precipitation across the West Coast and parts of the Intermountain West along with very cold temperatures in the northern half of the Plains. The eastern U.S. can expect an active period with precipitation--but uncertainties with the multiple systems impacting this region does not bring confidence in the details at this time. ...Guidance/Predictability Assessment and Preferences... In the beginning of the medium range period, a mid-level closed low/trough will remain over western British Columbia/Pacific Northwest through Day 5 (Thursday). The detailing of this trough and the timing of this feature moving inland is still unclear. The 00Z CMC and 00Z UKMET have closed lows by Day 3/Tue, with the 06Z GFS and 00Z ECMWF showing an elongated open trough. By Day 4, these models show the mid-level low closing off and beginning to meander inland. However, the 06Z and 00Z GFS, along with the 06Z GEFS mean, are much faster than all the guidance by day 5 with this closed low--with the UKMET much slower. Because of this, the evolution of this feature with the GFS is such an outlier (even the 06Z GEFS mean)--by Day 7/Sat, the GFS has a 1050 mb high pressure spilling into the Plains with a very strong surface low moving into the Ohio Valley. Once again, the other pieces of guidance are more in agreement not to be as potent as the GFS. With the shortwaves dropping southward along the edge of the Rex in the Pacific through the eastern U.S., the timing and details of these features also differ among the 00Z ECMWF/06Z GFS/00Z CMC and 00Z UKMET throughout the medium range period. With this in mind, began with a multi-model blend through Day 3-4/Tue-Wed using the 06Z GFS/00Z ECMWF/00Z UKMET and CMC. By Day 5, because of how much an outlier the GFS and the GEFS mean are, opted to not include it at all. Instead, the 00Z CMC overall had fair agreement with the ECMWF, so included some of it through Day 7. Additionally, from Days 5-7, increased the usage of 00Z ECMWF ensemble mean and the 00Z NAEFS mean--which seemed to be a nice compromise between the 00Z ECMWF ensemble mean and the 06Z GEFS mean. ...Weather Highlights/Hazards... From Tue-Wed, expect widespread, significant precipitation across the Pacific Northwest and northern California--in the form of rain and higher elevation snow. This precipitation will also stretch into the Intermountain West, including the northern Rockies. By Thu-Fri, a lull in precipitation can be expected with potential for light to scattered precipitation mostly for the Pacific Northwest and northern Rockies. As the weekend comes, another round of significant precipitation will approach the West Coast--especially in California/Sierra Nevada and into the Intermountain West/Central Great Basin. Precipitation coverage and intensity from the Plains to East Coast continue to be difficult to pinpoint due to significant differences in shortwave energy and surface evolution. From Tue - Wed night, expect light snow to progress from Montana and into the Plains, potentially the Upper Midwest. Meanwhile, the southern stream impulses may promote periods of rainfall across the Gulf Coast states over the course of the period. By Fri-Sat, there may be an expansion of precipitation coverage over the eastern states (snow north and rain south) in association with some degree of surface development over the East and/or extreme western Atlantic. Within the area of much below normal temperatures centered over the northern half of the Plains, coldest anomalies (at least 30F below normal at some locations) will remain through midweek, with a slight rebound in temperatures by Thu-Fri. However, with another Arctic high pressure dropping, cold temperatures in the northern Plains will arrive once again by the weekend. Flow from the Pacific will keep morning lows above normal over all but the extreme northern parts of the West, as well as over the southern tier, while clouds and precipitation will tend to keep highs closer to normal. Reinhart/Rausch 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