Extended Forecast Discussion NWS Weather Prediction Center College Park MD 359 PM EST Tue Jan 12 2021 Valid 12Z Fri Jan 15 2021 - 12Z Tue Jan 19 2021 ...Overview and Guidance/Predictability Assessment... The Pacific Northwest should catch a break in the prolonged heavy precipitation event this Saturday before additional plumes of moisture reach the region on Sunday and early next week. Farther east, a low pressure system should be near its peak intensity Friday morning as it tracks across the upper Great Lakes with wintry precipitation gradually tapering off from west to east. There has been a general model trend of delaying the eastward progression of the weakening cyclone into southeastern Canada during the weekend. In addition, the slower and more amplified pattern also encourages a wave of low pressure to form along the trailing cold front off the northern Mid-Atlantic coast on Saturday and then rapidly lifts northward across New England. This would increase the chance of heavy rain spreading into interior New England during the day on Saturday after a period of wintry precipitation most likely in the morning. The precipitation should change back to a period of wet snow Saturday night as the system lifts further northward into southeastern Canada by Sunday morning. Near the western Gulf Coast, a couple of upper-level troughs sliding southeast across the southern Plains will help develop a couple of low pressure waves just off the Texas coast. The first wave should be more subtle as it moves across the region on Sunday. By next Tuesday, a more vigorous wave appears to be moving toward the region. The GFS shows a faster progression of the associated rainfall across the Texas Gulf Coast region on both days compared with the ECMWF. The WPC morning forecast package was derived based on a consensus of the 00Z ECMWF/00Z EC mean together with the 06Z GFS/06Z GEFS. The CMC has not been included as its synoptic evolution appears noticeably different from the ECMWF and the GFS. ...Weather/Threats Highlights... Leading closed low energy into the Great Lakes would support a combination of synoptic and lake effect/enhanced snows from the Great Lakes into the northern/central Appalachians, with precipitation also extending into parts of the Northeast. Heavy rain could lead to snow melt issues on Saturday over interior New England on Saturday. Expect rain in the southern part of the moisture shield along the leading cold front into the East as well. In the West, some light precipitation is expected along and over favored terrain as various shortwaves move through. As troughing again deepens over the Rockies/Plains this weekend, precipitation may begin to push out of the mountains and expand into parts of Texas and the lower Mississippi Valley early next week. Above normal temperatures should be fairly widespread across much of the northern half and southwestern portions of the lower 48 on Thursday, though temperatures +5-10 degrees should persist across California and the Desert Southwest through the period. In the East, the mild temperatures on Friday into Saturday will be replaced by more typical mid-January values by early next week, while parts of the Southeast and Rockies will see near to below normal temperatures by about 5 degrees. Another round of above normal temperatures should also move into the Northern Plains by next week, with daytime highs 10 to 15 degrees above normal. Kong/Santorelli/Fracasso 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 Hazards: - Flooding occurring or imminent across portions of the Southeast, the Mid-Atlantic, and the Pacific Northwest. - Flooding likely across portions of the Pacific Northwest and the Northern Great Basin. - High winds across portions of the Northern/Central Plains, Fri, Jan 15. - Heavy precipitation across portions of the Northeast, Fri-Sat, Jan 15-Jan 16. - Much above normal temperatures across portions of the Northeast, Fri-Sat, Jan 15-Jan 16. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Tue, Jan 19. 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