Extended Forecast Discussion NWS Weather Prediction Center College Park MD 204 PM EST Fri Jan 05 2024 Valid 12Z Mon Jan 08 2024 - 12Z Fri Jan 12 2024 ...Powerhouse Storm to track from the Southern Plains to the Great Lakes/Northeast Monday-Wednesday offers widespread threats for Excessive Rain/Runoff, Heavy Snow/Wind and Severe Thunderstorms... ...Dynamic Systems to impact an unsettled/wintry West as Arctic Air digs into the North-Central U.S. mid-later next week... ...Overview... Deep surface cyclogenesis is expected across the south-central Plains by Monday as a major upper trough shifts out from the West, with impressive moisture and instability returning to fuel widespread heavy rainfall/convection and runoff/wind issues across the south-central to eastern U.S. through next midweek. To the north of the deep low's track, there is also a significant snow/ice threat from the central Plains to the Midwest/Great Lakes and Northeast Monday-Wednesday/Thursday, along with strong and gusty winds. Additional dynamic systems in the series look to move into the Pacific Northwest early next week before digging across the West into mid-late next week just as an frigid Arctic airmass slams southward from Canada into the north-central U.S.. ...Guidance/Predictability Assessment... The latest model guidance suite continues to offer a good overall depiction of the synoptic scale weather pattern for the first half of next week including the evolution of the major low pressure system over the Plains and Great Lakes/Northeast. A multi-deterministic composite model blend of well clustered guidance from the GFS/ECMWF/UKMET/Canadian along with the NBM and WPC product continuity was used for the period from Monday-Wednesday to produce max detail consistent with a pattern with seemingly above normal predictability. Going into the latter half of next week, gradually increasing model differences in the wake of the strong low favored some blend inclusion of compatible but smoother input from the GEFS/ECMWF ensemble means along with the models. ...Weather/Hazards Highlights... With the Northeast U.S. storm system moving well out to sea by Monday morning, attention then turns to the developing major low pressure system across the south-central U.S. that has been on the upstream weather horizon for the past several days. Confidence continues to increase for a highly impactful event spanning from Texas to the Great Lakes and Northeast U.S. next week as the surface low becomes anomalously strong over Arkansas and then lifts northeast towards the eastern Great Lakes by Wednesday morning. Heavy rainfall will indeed be one of the things making weather headlines as a very strong low level jet advects deep Gulf of Mexico moisture northward across the central Gulf Coast region on Monday, and with the potential for 2 to 4+ inches of rainfall from multiple rounds of convection, a Slight Risk remains warranted for the new Day 4 ERO for Monday from southern Louisiana to the Florida Peninsula, where hourly rainfall rates could easily exceed one inch per hour. The Slight Risk area was also expanded a bit farther inland given QPF signals. The heavy rainfall threat continues going into Day 5 on Tuesday into Wednesday with widespread 2-3+ inch rainfall totals likely from the southern Appalachians to southern New England. An expansive Slight Risk area is now planned from extreme northeast Georgia through the Mid-Atlantic to the Northeast. A strong southeasterly low level jet will advect highly anomalous moisture inland, especially into terrain and result in enhanced rainfall totals and rates for these areas, increasing the threat of flooding problems. A Moderate Risk area was introduced from extreme eastern PA and northern New Jersey into southeast New York, where there is a strong signal for 2 to 4 inch rainfall totals during this time with impressive IVT values expected as additional/lead Atlantic moisture influx grows. A broader Marginal Risk area includes all areas from southern Georgia to southern New Hampshire. Antecedent/forecast wet conditions and melting snows as applicable will also play a factor. In addition to the heavy rainfall will be the increasing threat of strong to severe thunderstorms in the warm sector of the low where the best combination of kinematics and instability will exist, and this is expected from the central Gulf Coast to the coastal portion of the Carolinas on Monday and into Tuesday. On the northwest side of the low will be the increasing prospects for an impactful winter storm from Kansas to the western Great Lakes, and given the strong pressure gradient expected, some blizzard conditions are expected. Widespread windy conditions are expected across much of the eastern half of the nation Tuesday and going into Wednesday as the surface low likely drops below 980 mb. In terms of temperatures, an Arctic blast forecast with deepest focus 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. Upstream, a continued series of highly dynamic Pacific systems will maintain and periodically rejuvenate a highly unsettled/wintry next week for a good portion of the West. There is a moderate to locally heavier precipitation signal focus 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/Schichtel 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