Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Sun Apr 07 2019 Valid 12Z Wed Apr 10 2019 - 12Z Sun Apr 14 2019 ...Major winter storm likely from the Northern High Plains to the Upper Midwest by mid to late this week... ...Overview and Guidance Assessment/Preferences... A vigorous upper-level trough moving from the Rockies to the central U.S. on Wed is expected to quickly deepen and spin up a significant low pressure system. The surface low is expected to move from the Central High Plains Wed morning to the Midwest on Thu and the Great Lakes by Fri, before quickly moving northeast into Quebec by Fri night/Sat. Confidence in the forecast for this system has improved significantly over the past 24-48 hours. Deterministic model solutions and ensemble members are now very well-clustered with respect to the surface low track Wed-Fri, with the ECMWF and UKMET the two solutions most well-centered within the broad consensus. The UKMET has performed particularly well with this system over the past few days, showing a highly consistent structure and track for the system for at least the past 4-5 runs. Farther west, additional shortwave energy is expected to dive south across the western U.S. before amplifying and perhaps closing off across the Great Basin Thu-Fri. Models consensus has improved significantly on this system as well, with a large reduction in spread noted over the past 12-24 hours. Given these considerations, the WPC forecast during days 3-5 (Wed-Fri) was based on a multi-model blend of deterministic solutions including the 00Z ECMWF/UKMET/CMC and 06Z FV3 (which was closer to consensus than the GFS with the central U.S. system). Particular weight was placed toward the highly consistent ECMWF/UKMET solutions. By next weekend, the primary forecast concern becomes how quickly the energy across the Southwest Thu-Fri ejects eastward into the central U.S. Models seem to be demonstrating their usual biases with this system, with the 06Z GFS racing the shortwave eastward faster than most other solutions, and the ECMWF on the slow side of the spread. The GFS has shown run-to-run inconsistency, flipping between a fast solution (06Z run) and a slower more ECMWF-like idea (00Z run). In most cases such as this, the actual verification often ends up in between the two camps, perhaps a bit more toward the slower solutions. Ensembles provide strong support for the slower solutions (including even the GEFS mean), despite a very slight faster trend over the past couple runs. Thus, leaned heavily toward the ECENS/NAEFS ensemble means and the 00Z ECMWF during days 6-7 (Sat-Sun). Most solutions, regardless of their timing, spin up a low pressure system across the central Gulf Coast/lower Mississippi Valley by next Sun ahead of the upper trough. ...Weather Highlights/Hazards... The low pressure system crossing the central U.S. Wed-Fri is expected to bring significant winter weather impacts from portions of the central/northern Rockies and adjacent High Plains to the Upper Midwest/Great Lakes. Models show strong signal for a band of dynamically forced moderate to heavy snow north of the surface low track. Strong and gusty winds due to the deep nature of the low pressure system will likely result in blowing snow and perhaps blizzard conditions for some areas. Farther south, a strong capping inversion will initially prevent much in the way of convection in the warm sector across the Southern Plains on Wed. By Thu-Fri, increasing moisture return as the system enters the Mississippi Valley should lead to scattered to numerous showers and thunderstorms, some of which could be strong to severe. The system across the western U.S. Wed-Fri should produce scattered areas of rain and mountain snow from the West Coast to the Great Basin and Rockies. As the system enters the central U.S. by next weekend, a developing frontal wave along the Gulf Coast/lower Mississippi Valley should promote strong moisture return and widespread rain and thunderstorms from the lower Mississippi Valley to the Tennessee/Ohio Valleys and the Southeast, with areas of heavy rainfall possible. Above average temperatures are expected in the warm sector ahead of the deep low pressure system. High temperatures are forecast to be 10 to 20 deg F above average across Southern/Central Plains and lower/mid Mississippi Valley on Wed, and 10-15 deg above average across portions of the Southeast and Tennessee/Ohio Valleys on Thu. In the wake of the low pressure system, much colder air is expected to spread into the Rockies and the central U.S., with high temperatures 15-25 deg below average possible through late in the week. Ryan 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