Extended Forecast Discussion NWS Weather Prediction Center College Park MD 211 AM EST Sun Jan 5 2025 Valid 12Z Wed Jan 08 2025 - 12Z Sun Jan 12 2025 ...Arctic blast persists for the central/eastern U.S. this week... ...Overview... The weather pattern into mid-later this week across much of the nation will quiet down in terms of precipitation aside from periodic Great Lake effect snow enhancement with reinforcement of widespread Arctic flow and some areas of mainly light precipitation in the western and central U.S., but much colder than average temperatures will persist in most areas from the Rockies eastward. There then remains an uncertain signal for extent of south-central U.S. rain/winter precipitation development to monitor that leads into a potentially stormy/wintry pattern out through the South and East Caost to monitor heading into/through next weekend as guidance is having trouble with progressions and potential interactions of main systems within separated northern and southern stream flows. ...Guidance/Predictability Assessment... Model and ensemble solutions remain reasonably well clustered valid for Wednesday/Thursday and a GFS/ECMWF/Canadian/UKMET composite model blend seems to mitigate much of lingering smaller scale variances in well defined split flow over the nation as consistent with individual uncertainties. However, forecast spread and cycle to cycle continuity issues have significantly increased heading into and through next weekend in potentially more active flow as guidance grapples with major stream phasing and system timing/focus differences in a pattern with rapidly lowering predictability over time. This seems evident with the models, ensembles and machine learning guidance. Accordingly, WPC medium range products valid for this time frame were primarily derived from the National Blend of Models as adjusted mainly toward the ECMWF ensemble mean as this combination seemed to best maintain WPC continuity and reasonings pending upcoming stabilization of a more common guidance signal. The latest 00 UTC guidance cycle does not seem to yet provide this. ...Weather/Hazards Highlights... It does still remain the case that Great lake effect snows will be periodically rejuvenated with deep cold surges this week given ongoing flow support. The NBM runs remain characteristically underdone with this potential, leading to manual corrective adjustments. Light to modest precipitation including elevation snow will spread focus down through the Rockies and north-central U.S. with an emerging surface system. Farther south, there are some chances for precipitation from the Southwest to Southern Plains and Lower Mississippi Valley and vicinity dependent on uncertain timing/ejection of energies in an at least quite separated southern stream and amplifying northern stream flow. An emerging precipitation pattern may unfold into later week, and with cold air in place from Texas eastward, some areas may need to monitor onset of wintry precipitation. In terms of the WPC Excessive Rainfall Outlooks, no risk areas seemed warranted for either Day 4/Wednesday or Day 5/Thursday given a paucity of deep moisture and instability across the country, but guidance suggests heavier precipitation potential to monitor over the West Gulf Coast states. There are then a few subsequent downstream hazardous scenarios over the ambient cold South and East Coast states to monitor heading into/through next weekend. These primarily revolve around quite uncertain approach and interactions of organized systems in two streams. Some guidance show a threat for potentially significant winter storm development and track versus much more benign solutions. Will continue to monitor for a stronger signal, but for now it seems prudent to prepare/recognize for the threat potential. Colder than normal temperatures will persist across the central and eastern U.S. underneath rounds of upper troughing and with cold surface high pressure systems. Notable cold is possible in the far northern tier, with high temperatures barely reaching 0F and lows in the -10s for some areas. This should not be record breaking, but the cold could still be hazardous as wind chill values may dip into the -20s and -30s. Temperature anomalies of 10-20 degrees below normal are also likely from the central Plains and Mid- Mississippi/Ohio Valleys through the Appalachians, especially as temperatures remain quite cold for snow covered areas from a major lead short range winter storm. Meanwhile, upper ridging in the western U.S. will offer slightly above normal temperatures prior to possible breakdown later period that would also support organized rain/terrain snow potential across the Pacific Northwest/Northwest. 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 (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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