Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1100 AM EST Sat Jan 05 2019 Valid 12Z Tue Jan 08 2019 - 12Z Sat Jan 12 2019 ...Overview and Guidance Evaluation/Preferences... Broadly speaking the guidance is fairly consistent and agreeable regarding the pattern of progressive Pacific systems with an increasing tendency toward western North America mean ridging by Fri/Sat, perhaps somewhat more pronounced over Canada and Alaska. This developing mean ridge is consistent with teleconnections relative to northern Atlantic positive height anomalies and northern Pacific negative height anomalies in recent D+8 mean charts. By next weekend guidance also appears to be heading toward the teleconnection-favored eastern North America mean troughing. For days 3-5 Tue-Thu a general model blend represents most aspects of significant features well. The 06Z GFS run provides the GFS input as the 00Z cycle brought a shortwave ridge into the Pacific Northwest/southwestern Canada around Thu whereas consensus shows more of a shortwave, albeit a weak one. Also of note the 00Z ECMWF becomes slower/more amplified than about 80 percent of ECMWF ensembles with the upper trough near the East Coast. There is good continuity with low pressure expected to be near the New England Coast as of 12Z Wed. One notable trend over the past 1-2 days is evident upstream as by Thu guidance shows more splitting of shortwave energy moving inland from the West Coast. By days 6-7 Fri-Sat leans more toward the ensemble means, with more 00Z ECMWF mean weight relative to the 06Z GEFS. Lingering operational model weight also sided a little more with the 00Z ECMWF especially along the West Coast. Continuing from mid-period the 00Z ECMWF may still be too slow with the upper trough departing from the East Coast. The split nature of energy progressing from the western U.S. leads to a somewhat more diffuse appearance of central U.S. low pressure by the latter part of next week. Best consensus now suggests a suppressed southern Plains into Gulf of Mexico wave associated with southern stream shortwave energy while a northern stream cool push becomes better defined by next Sat as upper troughing amplifies in response to the western North America ridge. The 06Z GFS may become a little too amplified with the southeast side of this eastern trough aloft late in the period. Meanwhile ECMWF means have had the earlier lead time versus GEFS means on defining the upper trough nearing/reaching the West Coast next Fri-Sat. Thus far the operational GFS idea of closing off a fairly deep southern stream low is in the minority though some GEFS members and a few ECMWF members offer that as a possible solution. Forecast history of preceding systems in this progressive pattern has not favored the slow side of the timing spread (which is currently represented by the 00Z GFS and latest GEFS means). These considerations favor leaning more in the ECMWF/ECMWF mean direction for this part of the forecast. ...Weather Highlights/Hazards... The system affecting the Northeast through midweek may produce some heavy snow over northern New England and lake effect snow will linger for a time after departure of the system. A tight gradient between this system and trailing high pressure will likely produce a couple days of brisk winds over the eastern states. Meanwhile a strong system off the West Coast as of early Tue should track northward and remain offshore but leading flow will bring another episode of heavy rain/mountain snow to the West Coast states with northern California and parts of the Pacific Northwest likely to see the highest totals. Winds may also be strong at times. Expect some of this moisture to reach the northern Rockies through midweek. Associated shortwave energy progressing inland should promote an increase in rainfall coverage/intensity over Texas and possibly some areas to the east/northeast depending on specifics of flow aloft. Any moisture that reaches central latitudes by next weekend could be in the form of snow. There may be a separate area of mostly light snow across extreme northern areas extending into the Great Lakes. The next Pacific system should bring another area of moisture to the West Coast around Fri-Sat. Best precipitation potential may extend farther south through California than with the previous system. Tue into Wed will be quite warm versus average over the eastern half of the U.S. with morning lows 10-25F above normal and Tue highs generally 10-20F above normal. Highs over the East will then trend to near or a little below normal while lows should be a tad more moderate. Upstream progression will bring another area of warmth across the central U.S. mid-late week with highest anomalies over northern locations. Temperatures over the Plains/Mississippi Valley should begin to trend cooler next Sat after cold frontal passage. Over the West the active pattern will tend to keep highs near to below normal, with lows above normal especially Tue-Thu. Rausch WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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