Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Fri Feb 10 2023 Valid 12Z Mon Feb 13 2023 - 12Z Fri Feb 17 2023 ...Stormy flow with a series of upper lows in split southern stream flow from the Western U.S. northeastward... ...Overview... The early to middle part of next week will feature a continuation of the short range tendency for upper lows to close off in the southern stream and then track northeastward, followed by the potential for more phased troughing to reach the eastern half of the country as a ridge moves into the West. Within this pattern, a leading system will track away from the East Coast as a northern stream shortwave approaches. Another upper low should track out of the Southwest and reach the Great Lakes by Wednesday while a trailing upper trough digging into the West will likely close off a low around Tuesday-Wednesday with the upper dynamics and potentially fairly strong surface system tracking from the Plains into eastern Canada mid-late week. Expect the latter two systems to produce a broad area of active weather across the lower 48 during next week. There is uncertainty over how upstream eastern Pacific trough energy may evolve later in the week, lowering confidence in how much moisture could reach the West Coast at that time. ...Guidance/Predictability Assessment... Overall the guidance shows better than average agreement with the sequence of significant systems. Consensus shows the system off the East Coast as of early Monday continuing onward with most moisture staying offshore, helped along by an approaching Great Lakes/Northeast shortwave. Then clustering is somewhat better than average for the next system tracking from the Southwest through the Great Lakes Monday-Wednesday. Agreement is also reasonably good for the final system of the series through Wednesday as a developing upper low tracks over the Four Corners region. However there is some complexity to the forecast after Wednesday, with guidance suggesting some phasing with northern stream flow somewhere over the central or east-central U.S. The 12Z/18Z GFS runs stray somewhat to the fast side of the spread with low pressure by days 6-7 Thursday-Friday with other guidance including the GEFS mean recommending timing that is slower and closer to continuity. Thus prefer a solution more in line with the 12Z ECMWF/CMC and 18Z GEFS/12Z ECMWF means at that time. The new 00Z GFS has trended closer to the favored cluster. Models and ensembles are showing mixed messages over the eastern Pacific/West Coast during the latter half of the week. Operational model runs as a whole suggest that eastern Pacific trough energy should try to separate, yielding decent upper ridging along/inland from the West Coast (though with GFS runs tending to close off the upper low farther west than the others), while enough ensembles are more open and progressive to result in the means bringing an open trough fairly close to the West Coast by next Friday. Prefer an intermediate solution between the model and ensemble ideas given typical uncertainty with such evolutions at the day 7 time frame. A composite of 12Z/18Z operational models represented consensus well during the first half of the period. Then forecast considerations favored transitioning the forecast to a blend of the 12Z ECMWF/CMC and 18Z GEFS/12Z ECMWF means, with the models and means evenly weighted by day 7 Friday. ...Weather/Hazard Highlights... Expect most of the moisture associated with the system departing from the East Coast to stay offshore, though it may be a close call for southeastern New England where minor changes in track could make the difference between dry conditions or meaningful precipitation. The system initially tracking out of the Southwest early next week should initially produce some rain and higher elevation snow over Arizona and the southern Rockies, followed by an area of precipitation spreading across the central-southern Plains and most of the east-central U.S. This should be a fairly warm system with most of any snow confined to the northern Plains/Upper Midwest. Some rainfall may be moderate to heavy over the Plains/Mississippi Valley but fairly progressive. However the supporting front may stall over the central Gulf Coast/Southeast by around Tuesday night, raising the possibility for some training and heavier totals. This potential as well as soil moisture expected to result from short-range rainfall led to the introduction of a Marginal Risk area on the day 5 experimental Excessive Rainfall Outlook. The next system moving into the West should bring a brief period of enhanced rainfall/mountain snow to the Pacific Northwest and to some degree northern Rockies early next week, with moisture then continuing southeastward through Tuesday/early Wednesday with the highest precipitation totals likely to be over favored terrain of Arizona/Utah/Colorado as an upper low passes over the region. Expected system emergence over the south-central Plains and then a track northeastward into eastern Canada mid-late week will likely renew a heavy precipitation pattern over the eastern half of the country. More meaningful snow is possible in the cold sector of this system relative to its predecessor, with the most probable axis for significant accumulations currently extending from the central High Plains into the central/upper Great Lakes. Meanwhile leading Gulf inflow ahead of the system's trailing front should promote areas of heavy rainfall. Guidance is also signaling this storm could become deep enough to produce fairly strong winds. The upper trough/low digging over the West early-mid week will bring highs down to 10-25F below normal for a couple days or so over the southern two-thirds of the region during Tuesday-Thursday. Cool temperatures should persist into Friday but with more moderate anomalies. Warm flow ahead of the two primary systems next week will bring well above normal temperatures to parts of the central U.S. during the first half of the week and the eastern U.S. through at least Thursday. Some readings may reach at least 20-25F above normal for highs and/or lows. Record warm lows are possible especially Wednesday-Friday (if they hold through the end of the calendar day), while some record highs could be possible around Thursday over New England and the Florida Peninsula. Rausch 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, experimental excessive rainfall outlook, 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/#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