Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Fri Jan 14 2022 Valid 12Z Mon Jan 17 2022 - 12Z Fri Jan 21 2022 ...Major winter storm to impact the Northeast through Monday... ...Overview... A potent closed low moving through the Mid-Atlantic as the period starts Monday will continue to spread heavy snow into parts of the Northeast. Behind this, general troughiness will continue across the Great Lakes next week as the next amplified shortwave drops through the Plains and into the East next Thursday and Friday. Out West, a closed low off the southern California coast will weaken as it slides East, with weak shortwaves periodically acting to break down ridging situated over the Northwest before a stronger shortwave tries to move in late in the week. ...Guidance/Predictability Assessment... Models and ensembles have come into closer agreement regarding the ongoing major winter storm as the period starts moving into the Northeast. This lends to increased confidence in the specifics, though some uncertainty still lingers. Most if not all of the guidance now shows the low inland over the Mid-Atlantic Monday morning (near Philadelphia), although the UKMET is still displaced a little south and the GEFS mean remains a bit farther east showing the low right along the coast. Of course, even minor changes in the low track can have bigger effects on winter precip and type across especially eastern portions of the Mid-Atlantic and the Northeast. Elsewhere, there's fairly good agreement on general and reinforced troughing across the Great Lakes next week, with some minor differences in the details. A stronger shortwave looks to drop through the Plains mid to late next week and eventually into the East. Some recent model runs (mostly the CMC) indicate another potential low pressure area near the East Coast, but uncertainty in the strength of this system is highly uncertain at this time. Out West, the greatest differences begin to pop up next Thursday-Friday with the handling of Pacific system energy into an upper ridge off/over the West Coast. The 06z GFS is more ernest with a shortwave through the east Pacific and even shows a closed low off the Pacific Northwest coast next Friday. Meanwhile, the CMC and ECMWF are both weaker and more deflects the energy over the ridge. The ensemble means tend to favor a solution closer to the ECMWF and CMC. The WPC forecast for today used a composite blend of the deterministic models days 3-5, with increasing ensemble means thereafter to account for detail differences across the East late period and the energy off/over the Northwest. This provided a consistent forecast with overnight WPC continuity. ...Weather Highlights/Hazards... A major winter low developing over the weekend seems set to lift from the northern Mid-Atlantic/lower Great Lakes through the Northeast on Monday. This will present a continuing full array of weather hazards and threats. Heavy wrapping snows will spread in earnest along/on the backside of the deepening low and west of the I-95 corridor into interior areas. For locations closer to the coast, precipitation may start out as some brief snow, with a changeover to sleet and rain as warmer air filters in from the east. Gusty winds surrounding the surface low may create high waves off the coast leading to possible coastal flood concerns along the Northeast coastline. After the main low exits the Northeast by Tuesday, another low pressure system is forecast to track over the north-central U.S. in response to a mid-upper shortwave and bring some snow to the Upper Midwest and Great Lakes then northern New England, with possibly higher totals near typical lake enhancement areas. The West could see some light precipitation during the period, particularly over the Pacific Northwest and into the Northern Rockies, with mainly dry conditions elsewhere. Rain may develop across the Lower Mississippi Valley and Southeast for mid-later next week with modest return Gulf flow with induced wave passages. For temperatures, the East should moderate back towards normal after Monday's storm with colder temperatures moving back in by the end of the week. The Central U.S. will start mild and above normal early in the week, though as strong Canadian high pressure sinks southward, will quickly trend below to well below normal Wednesday and Thursday. Daytime highs could be near or below zero across parts of the northern Plains and northern Mississippi Valley. West of the Rockies should be mostly near or slightly above normal influenced by the upper level ridge. 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, winter weather outlook probabilities and heat indices 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml