Extended Forecast Discussion NWS Weather Prediction Center College Park MD 233 AM EST Tue Jan 09 2024 Valid 12Z Fri Jan 12 2024 - 12Z Tue Jan 16 2024 ...Another major storm to impact the East-Central to Eastern U.S. with snow/rain/wind threats followed by an arctic blast through much of the North-Central U.S.... ...General Overview... An upper trough over the Great Plains will amplify while it propagates through the Midwest and into southeastern Canada this weekend. At the surface, cyclogenesis and a rapidly intensifying mid-latitude cyclone will take shape over the Southern Plains and Lower Mississippi Valley on Friday. This system will continue to intensify as it moves into the Midwest and Northeast on Saturday. Meanwhile, a potent upper low will break-down an East Pacific ridge and make its way into the Northwest this weekend. Arctic high pressure will build in across the Central U.S. behind the departing storm in the East. ...Guidance/Predictability Assessment... The latest numerical models are quite dispersed in their handling of the overall evolution of the synoptic pattern over the lower 48 during the medium range period. There's plenty of run-to-run variance in the deterministic Euro with respect to the incoming East Pac low on day 3. The 12z UKMET/CMC and 18z GFS are also all over the place with their placements of that system so this system's details are yet to be considered certain. The models are in reasonable agreement about the evolution of the wound up eastern U.S. storm through day 5. A general model blend consisting of the 12z EC/UKMET/CMC and 18z GFS were utilized on day 3. The UKMET was removed on day 4 due to its significant divergence from the rest of the guidance regarding the shortwave energy in the East Pac/Northwest U.S.. The Canadian is dropped from the day 5 blend in place of the 12z ECE and 18z GEFS because it (CMC) has the parent low centered over the Upper Midwest while the EC and GFS and Canadian ensemble have it much farther north in Canada. The Canadian ensemble is introduced briefly on day 6 and removed on day 7. ...Weather/Hazards Highlights... The active period continues through this weekend, beginning with yet another major storm over the East-Central to Eastern U.S. this Friday. A deep mid-latitude cyclone will produce a swath of heavy snow and strong winds from eastern Missouri through the Great Lakes on Friday, and into New England on Friday night with lingering lake effect snow occurring on the backside of the arctic cold front downwind Lakes Erie and Ontario on Saturday. Some light to moderate snow may occur down through the Central Appalachians on Friday night and Saturday as well. Rain showers and scattered thunderstorms are likely from the Midwest to the Mid-Atlantic and Southeast/Gulf Coast within the warm sector of the storm on Friday. The Storm Prediction Center highlights a 15% probability of severe thunderstorms from eastern Louisiana across the Southeast, Carolinas and into southern Virginia. Some heavy rainfall is possible over parts of the central Midwest Friday afternoon where some instability may creep in, leading to the threat of excessive rainfall. This threat is marginal (at least 5%). As the system progresses eastward Friday night the Northeast/southern New England Coast may become an area of focused heavy rainfall. A Slight Risk of Excessive Rainfall (at least 15%) is in effect for the area encompassing the I-95 corridor between Baltimore and western Rhode Island where favorable jet dynamics and moisture flux will be present. Heavy rainfall over existing snowpack in northeastern Pennsylvania into northern New Jersey, southern New York and southern New England may also contribute to the flash flooding threat. The deepening cyclone over the Great Lakes will drive another high wind threat across the northeastern quadrant of the country on Saturday. An arctic high pressure will descend on the Central U.S. following the amplified Eastern system this weekend. An arctic airmass will advect into the North-Central to Central U.S. as a result. This airmass will bring with it highs from the teens to negative teens this weekend through the middle of next week. Meanwhile, a potent East Pac shortwave low will break through an entrenched upper ridge over British Columbia and the Pacific Northwest. Despite model uncertainty, this system is still expected to direct subtropical moisture into the West this Friday and Saturday. The result will be heavy to Excessive rainfall along the Northwest coast, from southern Washington to northern California, and Heavy Snow across the Cascades, Olympics, the Intermountain West and Colorado Rockies. Kebede 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 WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw