Extended Forecast Discussion NWS Weather Prediction Center College Park MD 356 PM EST Thu Jan 19 2023 Valid 12Z Sun Jan 22 2023 - 12Z Thu Jan 26 2023 ...Two deep lows with a heavy snow threat focus for the Appalachians/interior Northeast Sunday/Monday, then again Wednesday into next Thursday... ...Overview... It remains the case that an established pattern into next week will feature a strong eastern Pacific ridge and a sequence of shortwaves dropping into the West, then ejecting beyond the Rockies to produce individual systems generating various types of significant weather. These shortwaves/systems will likely produce some locally focused rain/mountain snow from the Northwest east and southeast into the Rockies, and then heaviest rainfall potential over the Southeast and winter weather potential from the Plains into the Northeast, with more moderate rainfall totals between these two areas. Confidence is steadily increasing for a lead system forecast to reach the Northeast Sunday-Monday given improvement in guidance clustering. There are still differences for the energy dropping into the West Sunday-Monday, ultimately causing continued forecast challenges for precipitation specifics over the West and the system that may affect the central-eastern U.S. about three days on the heels of the lead one. However, forecast spread is steadily improving with latest guidance, bolstering forecast confidence in development and track. Guidance suggests that subsequent energy dropping into the West will be a lot weaker into later next week, yielding a broader mean trough aloft, but there is room for additional digging. ...Guidance/Predictability Assessment... For the leading system reaching the Northeast Sunday-Monday, following a majority model/ensemble cluster has held up well continuity-wise over the past day or so since guidance fully adjusted to the currently depicted phasing aloft over the central U.S. during the weekend. Recent UKMET/CMC runs have adjusted closer to the majority scenario for the surface low track after some earlier runs were on the south/southeast side of the spread previously. Overall an operational model composite with greater emphasis on the latest GFS/ECMWF provide a reasonable starting point. Models/ensembles have been diverse and inconsistent for days with the trailing shortwave digging into the West, highlighted by pronounced reversals in the ECMWF and GFS runs over the past day or so. The latest few runs of the ECMWF/Canadian/UKMET have slowly converged upon a better cluster forecast evolution. Recent GFS and to a lesser extent GEFS runs have been on the open and progressive side of the spread through Monday, but the latest 12 UTC version has finally trended a bit slower at least toward the rest of model guidance, bolstering forecast confidence across the region and also with corresponding the evolution of downstream system development and threats across the central-eastern U.S. through next Thursday. Even with some lingering differences along the way, storm developent and impact now has a good guidance signal. Recent GEFS/ECens/CMCens means along with the GFS/ECMWF/CMC found a way to show remarkably similar/deepened surface low positions near New England by early day 7 Thursday and a blend provides good continuity for the upper system and surface reflection through the period. ...Weather/Hazard Highlights... Two significant systems will work out from the West to traverse the south-central U.S. and then impact the eastern half of the country during this period. The first system will likely track from the Mississippi Valley/Gulf Coast into New England Sunday-Monday, bringing the potential for some wintry weather from the Midwest into the central-northern Appalachians and interior New England. The Appalachians/New England area has the best potential for meaningful to heavy snow totals. Expect rain to the south of the snow area, with heaviest rainfall most likely over the Southeast. Currently expect the next system to develop over the southern Plains/Gulf Coast around Tuesday and then reach near New England by Thursday, but some changes are possible in the details. Depending on exactly how this system evolves, there may be similarities in precipitation distribution/amounts, including the best heavy rainfall potential over the Southeast and a band of wintry weather from the Plains northeastward into New England. The exact rain-snow line will depend on finer details of system strength/track that are still not resolved well. Both of these systems may be strong enough to produce enhanced winds over the Northeast. Across the West, rain and mountain snow of mostly moderate amounts (but perhaps locally enhanced) should extend south-southeast across the Rockies and nearby areas with upper trough/low support and lower level upslope flow. Southwestward extent of the precipitation will depend on exact track/amplitude of the weekend/early next week feature whose details remain uncertain. Most areas from the northern three-fourths of the West into the central-southern High Plains should remain chilly through the period with highs generally 5-15F below normal but possibly up to several degrees colder around Monday underneath or in the wake of an upper trough/low over the Four Corners states. Far northern parts of the West should be within a few degrees on either side of normal, while highs at locations along the central-northern West Coast may drift a few degrees above normal as the eastern Pacific upper ridge extends a tad eastward. Meanwhile the eastern U.S. will tend to see above normal lows, occasionally by more than 10F, while highs should be near to moderately above normal. The northern Plains and vicinity will tend to be above normal into midweek and then trend colder by Thursday after passage of a cold front dropping south from Canada. Rausch/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 Hazards: - Heavy precipitation across portions of the Great Lakes, the Mid-Atlantic, the Northeast, the Central Appalachians, and the Ohio Valley, Sun-Mon, Jan 22-Jan 23 and Wed, Jan 25. - Heavy rain across portions of the Southeast and the Mid-Atlantic, Sun, Jan 22. - Heavy rain across portions of the Southeast, the Mid-Atlantic, and the Southern Appalachians, Tue, Jan 24. - Heavy snow across portions of the Northeast and the Great Lakes, Sun-Mon, Jan 22-Jan 23 and Wed, Jan 25. - Much below normal temperatures across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Southern Rockies, the Southern Plains, and the Southwest, Mon-Wed, Jan 23-Jan 25. 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