Extended Forecast Discussion NWS Weather Prediction Center College Park MD 152 PM EST Tue Feb 06 2024 Valid 12Z Fri Feb 09 2024 - 12Z Tue Feb 13 2024 ...Overview... A reloading upper trough position should mainly hold on over the West into the weekend, before beginning to slowly shift eastward as upper ridging tries to build in near the West Coast again and a couple of organized systems push through the East Pacific. The trough will continue to keep this region active with rounds of lower elevation rains and mountain snow. Meanwhile, a strong upper ridge shifting out of the Central U.S. will continue to support well above normal temperatures that could be record-setting across the parts of the Upper Great Lakes-Northeast on Friday-Saturday before it becomes suppressed and shifts eastward off the coast. A fairly strong storm system tracking out of the Great Lakes on Friday will produce some cold sector snow and brisk winds. Then additional shortwaves/energy from the mean upper trough over the West will periodically eject into the central U.S. There is significant uncertainty over how associated systems will reflect at the surface to the east of the Rockies, but the general pattern appears favorable for increasing rainfall across the Mid-South/Southeast by late week/weekend prior to a potential lifting of a deepening East Coast to western Atlantic low to monitor for into early next week. ...Guidance/Predictability Assessment... There has been some narrowing of forecast spread across the lower 48 and vicinity into the weekend, bolstering forecast spread. The GFS/ECMWF/UKMET solutions seem best clustered in this period and ensemble support in a favored model composite is reasonable. Forecast spread and growing uncertainties with embedded system details and the degree of potential phasing of northern and southern stream energies over time still need to be worked out for into early next week. The 00 UTC run cycle was trending in a common direction with phasing, but 12 UTC models do not offer stellar run to run continuity with a trend away from phasing. ...Weather/Hazards Highlights... General broad troughing over the Southwest should keep the Western U.S. periodically active with widespread lower elevation rain/mountain snows into next weekend. Best snow potential should be over the favored terrain of the Four Corners states. Additional rounds of rain and mountain snows could come into California through Friday, though with very low confidence on exact amounts and locations of heaviest precipitation. Given extreme rainfall across much of California recently, the area is more sensitive than usual to additional rainfall, but the fact that any digging dynamics aloft should take an along-coast or inland path should not be supportive of a heavy precipitation threat. Precipitation may clear out of much of the Intermountain West by Saturday, but one or more progressive systems could bring episodes of light to moderate totals to the Pacific Northwest. Fairly strong low pressure will be tracking out of the Great Lakes Friday into Saturday, though with still some lingering snow and gusty wind threat on the backside of the system. The trailing cold front should focus moisture and some weak instability to produce rain across the Mid-South late week, but especially into the weekend aided by shortwave energy out of the Southwest. This may increase potential for training/repeat showers and thunderstorms over some areas, but with still a lot of spread in the details and corresponding location/magnitude/timing of the heaviest rainfall. Ensembles suggest the primary region that requires monitoring extends from the Tennessee Valley into Lower Mississippi Valley and Southeast. This overall area has a mix of antecedent soil moisture conditions. Despite the presence of anamolous moisture and some instability, confidence remains too low though to introduce any risk areas in the Days 4-5 EROs at this time, but again the general pattern may ultimately support an axis of heavy rainfall sometime in the weekend time frame. Meanwhile, the far northern fringe of the southern tier moisture shield could produce some snow from the weekend into early next week, but highly uncertain and dependent on the exact track of the very uncertain low pressure system out of the south-central states. There is with the past guidance cycle some trend toward low development up and off the East Coast into Monday and Tuesday, albeit mainly contingent on still uncertain stream phasings. Accordingly, latest WPC progs now show a more organized low track, but not to the extent of some of the latest models. This type of scenario does offer more potential for lifting/wrapping rains with focus up the Mid-Atlantic and some window for snow for marginally cooler areas from the Appalachians through the interior Northeast. The upper ridge progressing from the eastern U.S. into the western Atlantic late this week will support a broad area of unseasonably warm temperatures which will gradually shift from the Great Lakes/Midwest toward the East Coast. Departures from normal should eventually become somewhat less extreme with time. The Upper Midwest/Great Lakes should be warmest versus normal on Friday with anomalies up to plus 30F for morning lows and plus 25F for daytime highs, leading to widespread daily temperature records. By the weekend expect the East to see lows of 15-30F above normal and highs 10-20F above normal while the central U.S. trends closer to normal. In contrast, the Southwest U.S./California should be persistently cool, especially for daytime highs that may be up to 10-15F below normal into the weekend. This region should begin to see a moderating trend by Sunday or Monday. Clouds/precipitation over the West should keep most morning lows within a few degrees on either side of normal but a few localized cooler spots are possible. Santorelli/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