Extended Forecast Discussion...amended NWS Weather Prediction Center College Park MD 257 AM EST Sat Jan 6 2024 Valid 12Z Tue Jan 9 2024 - 12Z Sat Jan 13 2024 ***Intense low pressure to bring widespread rain, wind, and snow for much of the eastern half of the nation through Wednesday, followed by an arctic airmass settling south across the Northern Plains*** ...General Overview... The weather pattern across the continental U.S. will continue to be extremely active with multiple high impact weather events expected next week. The first and biggest event will be the rapidly deepening surface low across the south-central U.S. that will quickly reach the Great Lakes and Northeast by Wednesday morning, with widespread heavy rain and strong winds accompanying it, and potential blizzard conditions northwest of the low track. Once this storm departs, an arctic front will herald the arrival of the coldest temperatures so far this season across the north-central U.S. with a pattern change emerging. There are also increasing prospects for another well organized storm system to develop over the Deep South/Gulf Coast region by the end of the week that could very well produce more impactful weather for the Eastern U.S. by Saturday. ...Guidance/Predictability Assessment... The 00Z model guidance suite now agrees very well on the intensity and overall evolution of the major eastern U.S. storm system during the Tuesday-Wednesday time period, and the CMC has trended closer to the model consensus compared to yesterday, where this solution was well south of the other guidance. The models agree that the low should bottom out in the high 970s to low 980s for pressure. For the Pacific system moving in across the northwestern U.S., some differences become apparent as the shortwave reaches the Great Lakes, with the UKMET weaker and more suppressed with the surface low. Looking ahead to the end of the week, the CMC is faster with the southern stream shortwave ejecting across the southern Plains, and the GFS is the slower and stronger solution with the ECMWF between these two solutions. This trough will be the main driver for the next organized storm to affect the eastern U.S. by the end of the forecast period. The fronts/pressures were primarily derived from a multi-deterministic model blend through Wednesday, and then a gradually increasing percentage of the ensemble means to account for 40-50% of the forecast by next Saturday. ...Weather/Hazards Highlights... Confidence continues to increase for a highly impactful event spanning from Texas to the Great Lakes and Northeast U.S. early in the week as a 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 East Coast states on Tuesday. Widespread 1-3 inch rainfall totals are likely from the southern Appalachians to southern New England, with scattered higher amounts possible. The new Day 4 outlook continues with a Slight Risk area stretched from the southern Appalachians to southern New England, and maintaining the existing Moderate Risk area between Philadelphia and New York city, where there is a strong signal for 2 to 3 inch rainfall totals during this time with impressive IVT values expected from the western Atlantic. Parts of this region may also have some snow on the ground at the onset of this event, and this will tend to be an aggravating factor in the flooding potential along with reduced flash flood guidance. A broader Marginal Risk area includes all areas from southern Georgia to southern New Hampshire. 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 northern Florida to southeastern North Carolina on Tuesday. On the northwest side of the low will be the increasing prospects for an impactful winter storm from northern Missouri to Michigan, and given the strong pressure gradient expected, there will likely be some blizzard conditions at times. Widespread windy conditions are expected across much of the eastern half of the nation Tuesday and going into Wednesday with winds gusting 30-50 mph at times, and perhaps even higher across the highest terrain of the central/southern Appalachians. 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 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. Looking ahead to the Friday-Saturday time period, it is looking more likely that another potentially strong low pressure system could affect similar areas of the central and eastern U.S. compared to the low on Tuesday, tracking from Texas to the Great Lakes based on the latest guidance. This would once again increase the potential for strong thunderstorms, heavy rainfall, and winter weather to close out the week, and this will continue to be monitored closely. 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