Extended Forecast Discussion NWS Weather Prediction Center College Park MD 157 AM EST Sun Jan 7 2024 Valid 12Z Wed Jan 10 2024 - 12Z Sun Jan 14 2024 ...Another low pressure system is likely to close out the work week across the central and eastern U.S. with more wind, snow, and heavy rain, and an Arctic blast for the northern Plains... ...General Overview... The powerful low pressure system that hammers the Eastern U.S. early in the week is expected to reach southern Ontario by Wednesday morning, with the cold front exiting the East Coast except for New England, where strong onshore flow will produce heavy rain and high winds. An improving weather trend commences in the wake of this storm system going into Thursday across the Eastern U.S. as high pressure briefly settles in. However, another potent low pressure system likely gets organized across the south-central U.S. by Friday morning in response to an amplifying upper trough approaching from the Rockies, and this low should track in the general direction of the Ohio Valley and Great Lakes region by next weekend with more bad weather expected for many areas. In addition, a pattern change will result in a strong arctic front heralding the coldest weather of the season thus far across much of the north-central U.S. for the second half of the week and beyond. ...Guidance/Predictability Assessment... The 00Z model guidance suite remains in good overall agreement on the exiting low pressure system across the Northeast U.S. on Wednesday, although the GFS is a little slower with pivoting the axis of the upper trough across New England compared to the ECMWF/CMC. The 00z CMC has trended in line with the model consensus, but at the time of fronts/pressures preparation, the 12Z CMC was considerably faster with the trailing trough over the Midwest and Ohio Valley through Thursday, so the model blend was initialized from a GFS/ECMWF/UKMET blend through the end of the week. For the next system developing across the southern Plains Friday, the GFS is slower and more amplified with the upper trough compared to the much more progressive ECMWF/CMC, and therefore considerable timing differences with the surface low track (GFS slowest and ECMWF fastest by Friday night). Both the EC and GEFS ensemble means are between these two solutions, and therefore these served as a good proxy for the expected location of the surface low. Model spread becomes high across the eastern Pacific and adjacent portions of the West going into next weekend, and this leads to below average confidence for that region. The ensemble means accounted for 40-60% of the forecast blend going into next weekend to account for the growing model differences. ...Weather/Hazards Highlights... Heavy rain and strong winds will likely be ongoing across central and eastern portions of New England Wednesday morning into the afternoon ahead of the strong cold front exiting the East Coast. An impressive south-southeasterly low level jet ahead of the front will likely mix down enough to produce surface wind gusts in excess of 50 mph at times across Maine, and storm force winds across the coastal waters. Rainfall will be maximized across the upslope portions of the northern Appalachians of Maine where 1 to 2 inches of rainfall is likely, and much of this will likely be falling over areas with some snowpack. Given some existing uncertainty in snow levels and overall precipitation type, a broad Marginal Risk area for Day 4 is planned, although this could eventually be upgraded to a Slight Risk once things become more certain. For the Day 5 period Thursday, no risk areas are planned for this forecast cycle. Looking ahead to the Friday-Saturday time period, another potentially strong low pressure system is looking increasingly likely and this could affect similar areas of the central and eastern U.S. compared to the low on Tuesday/Wednesday, tracking from Texas to the Great Lakes based on the latest guidance. There will likely be a band of significant snow extending from Missouri to Michigan associated with the deformation zone northwest of the surface low, and the highest probabilities of this are generally southeast of the highest snowfall totals expected with the system early in the week. Heavy rain and strong thunderstorms are also likely for much of the Deep south and extending eastward across portions of the Carolinas. In terms of temperatures, an Arctic blast is expected for the Northern Plains to close out next week with widespread subzero lows for the Dakotas and into Montana, and highs only in the 0s and 10s for many of those same areas, with anomalies upward to 30 degrees below normal. Some subzero highs are likely for northern Montana into North Dakota. Upstream, a continued series of highly dynamic Pacific systems will maintain and periodically rejuvenate a highly unsettled/wintry pattern next week for a good portion of the West. There is a moderate to locally heavier precipitation signal to spread down from the Pacific Northwest to north-central California into the Sierra. There should also be widespread terrain/mountain focusing snows further inland across the Intermountain West into the Rockies with continued system progressions. Hamrick 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