Extended Forecast Discussion NWS Weather Prediction Center College Park MD 209 PM EST Wed Jan 22 2020 Valid 12Z Sat Jan 25 2020 - 12Z Wed Jan 29 2020 ...Overview... Guidance shows a pattern with moderate progression, highlighted by occasional amplification of energy and associated surface systems over the lower 48 beneath positive height anomalies covering the eastern half or more of Canada. One primary system of interest will affect the Northeast with various precipitation types this weekend while another system should evolve over the central U.S. next Mon-Wed. At the same time expect a strengthening core of negative height anomalies to be anchored near the southern coast of mainland Alaska. Teleconnections relative to these negative height anomalies favor enhanced precipitation potential for the northern/central West Coast. ...Guidance/Predictability Assessment... For this weekend's Northeast system there was generally been better than average clustering over the past day or so. However the centroid of the full model/ensemble envelope has drifted somewhat northward since yesterday and now the 12Z models are diverging more near New England by Sun-Mon. In particular the CMC and to some degree UKMET have become slower than the 00Z ECMWF or typically faster GFS runs. By early Mon the GEFS mean would at least favor slower timing than the GFS. The new 12Z ECMWF is similar to or slower than the 00Z run depending on valid time. Farther south the guidance is still in the process of resolving a southern stream wave that may affect areas from the western Gulf Coast to Florida Peninsula during the weekend and early next week. 00Z/06Z GFS runs were more suppressed than consensus near Florida but at least in terms of its rainfall pattern the 12Z run has adjusted closer to the majority model/ensemble mean cluster--albeit with timing that could be a bit on the fast side. From Sun to Wed the models/ensembles depict eastern Pacific energy feeding into an amplifying central U.S./northern Mexico mean trough aloft, but with poor agreement over which shortwave(s) will be dominant and how they may interact. Thus confidence is lower than desired for specifics of West Coast precipitation events (though within a favorably wet pattern over northern/central areas) as well as for surface low pressure expected to develop over the central U.S. Mon-Wed. Overall the greater clustering of guidance and historical biases favored leaning more toward the 00Z ECMWF/ECMWF mean/CMC details relative to the 06Z GFS/GEFS mean. The GEFS mean did side with the slower cluster for the central U.S. system though. Highlighting the uncertainty, the 12Z CMC has trended at least as fast as the GFS while the UKMET is flatter than other solutions with the Rockies/Plains upper trough by Mon-Tue. The 12Z ECMWF has changed some shortwave details as well. ...Weather/Hazard Highlights... Separate surface waves over the Great Lakes and Mid-Atlantic as of early Sat will consolidate shortly thereafter with the resulting system most likely tracking offshore by Mon. Currently expect the best snow potential (with moderate to meaningful totals) from New York state through interior/northern New England with rain farther south. Recent guidance has been showing a bit of a northern trend, trimming the southern side of winter weather probabilities. Lighter snow will be possible from the central Great Lakes into the central Appalachians. A wave crossing the Gulf of Mexico may bring a brief period of enhanced rainfall to the western Gulf Coast during the weekend and portions of the Florida Peninsula by early next week. Consensus regarding the general event is improving but not yet to the point of being unanimous, plus there are still timing/intensity questions to be resolved. Teleconnections relative to the Alaska/Northeast Pacific pattern provide good support for the significant totals of rain/mountain snow expected over the Pacific Northwest and northern California during the period. Some locations along favored Cascades and coastal terrain may see at least 5-10 inches liquid for the five-day period. Day-to-day specifics have much lower confidence due to low predictability of supporting shortwaves embedded within progressive mean flow. Shortwave energy aloft and associated frontal system will spread lighter precipitation across portions of the Interior West and northern-central Rockies Sun-Tue. Away from the Pacific Northwest/northern California, the northern Rockies should see highest precipitation totals. Amounts over the Central Rockies/High Plains will be sensitive to the exact shape of energy aloft around Mon-Tue. The system expected to affect the Plains into east-central U.S. early-mid week should bring an area of rain south/snow north. Model/ensemble guidance is suggesting potential for some areas of moderate to heavy precipitation but with poor agreement regarding location/coverage/intensity--corresponding to the uncertainty in specifics of system evolution. The forecast pattern will promote near to above average temperatures over most of the lower 48 during the Sat-Wed period. Highest anomalies will likely be across the northern tier states which should average 10-20F above normal for highs and 15-25F above normal for morning lows. Plus 10-20F anomalies for morning lows over the West during the weekend could challenge daily warm records at some locations. The best possibility of near to modestly below normal readings will be over the Southeast/Florida as well as the central-southern Rockies. Rausch Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Heavy precipitation across portions of California and the Pacific Northwest, Sat-Sun, Jan 25-Jan 26. - Heavy precipitation across portions of the Pacific Northwest, and the Northern Great Basin, Wed, Jan 29. - Heavy rain across portions of the Mid-Atlantic and the Northeast, Sat-Sun, Jan 25-Jan 26. - Heavy snow across portions of the Central Great Basin and California, Sun-Mon, Jan 26-Jan 27. - Heavy snow across portions of the Great Lakes, the Mid-Atlantic, the Northeast, the Central Appalachians, and the Ohio Valley, Sat-Mon, Jan 25-Jan 27. - Flooding occurring or imminent across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, the Great Lakes, the Ohio Valley, and the Northern Plains. - Flooding likely across portions of the Pacific Northwest. 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