Extended Forecast Discussion NWS Weather Prediction Center College Park MD 323 AM EST Thu Mar 7 2019 Valid 12Z Sun Mar 10 2019 - 12Z Thu Mar 14 2019 ...Weather Pattern Overview... An active weather pattern is expected during much of the medium range period as two large scale troughs originating from the Pacific lead to surface low development across the central U.S. and Midwest states. The first storm system over the Great Lakes region at the beginning of the forecast period Sunday will bring widespread rain and thunderstorms to the eastern U.S. and snow for the Upper Midwest and Great Lakes. The second Pacific disturbance crosses the Desert Southwest on Monday and then undergoes secondary cyclogenesis over the western High Plains by the middle of next week with an evolution that is similar to the first storm system. ...Guidance and Uncertainty Assessment... The deterministic models are in good overall agreement regarding the placement and overall strength of the surface low crossing the Great Lakes region on Sunday, with the GFS slightly faster than the model consensus, and quicker with cold front passage for the East Coast. The speed differences are more apparent with the GFS and also the GEFS mean with the mid week storm system across the Plains. There is good model clustering among the CMC/ECMWF/FV3 solutions, and given that these are closer to WPC continuity compared to the faster GFS/GEFS mean, the forecast was more in line with the CMC/ECMWF/FV3. Taking all of these factors into account, the forecast was primarily derived from the 12Z ECMWF/18Z FV3/12Z UKMET for the first three days, and then a slightly higher percentage of the EC mean while still keeping a significant percentage of the deterministic FV3, ECMWF, and some of the CMC as it relates to the second low pressure system. The FV3 was substituted for the operational GFS for this forecast period given the timing differences noted. The WPC forecast is very similar to the previous forecast in terms of track and expected low evolution. ...Weather Highlights and Hazards... Although the majority of the heavy rain and snow will have likely abated some by the beginning of the forecast period on Sunday, areas of rain and thunderstorm activity will continue across much of the Gulf Coast region and along the immediate East Coast. Heavy snow is still expected across interior portions of New England as the surface low lifts northeastward across eastern Canada, and some lake enhanced snow will be possible. Some severe thunderstorms will also be possible across parts of the Southeast on Sunday ahead of the cold front, and this is something that the Storm Prediction Center is continuing to monitor. Looking ahead for early-mid week, the pattern again favors an amplified mid-upper level trough developing off the West Coast this weekend. This will support another round of precipitation over the southwestern U.S. as the trough moves inland on Monday. Additional widespread rain is expected to develop across the central and southern Plains to the Mississippi Valley/Midwest during the Tuesday and Wednesday time period as the trough induces another deepening surface low east of the Rockies. There is also the potential for severe weather with this storm system, and details on this will become more evident in the upcoming days. Another round of heavy snow and potential blizzard conditions is becoming more probable across parts of the central plains and the Upper Midwest as the surface low intensifies and colder air in drawn in behind the low. D. Hamrick 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