Extended Forecast Discussion NWS Weather Prediction Center College Park MD 153 PM EST Mon Jan 06 2020 Valid 12Z Thu Jan 09 2020 - 12Z Mon Jan 13 2020 ...Heavy Rain Threat from the Lower-Mid Mississippi Valley into Tennessee/Ohio Valleys Fri-Sat with potential for wintry precipitation across northern Ohio Valley into New England... ...Active pattern over the Northwest... ...Overview/Guidance Assessment... There are embedded details that exhibit some spread and variability but guidance agrees that strong ridges aloft over the east-central Pacific and off the southeastern U.S. coast will hold in place an amplified western U.S. trough at least into early next week. Within this pattern, low level flow of Gulf moisture ahead of an ejecting western shortwave/leading wavy cold front will produce an episode of heavy rainfall from parts of the Lower-Mid Mississippi Valley eastward/northeastward from late this week into the weekend with some wintry weather on the northern side of the precipitation shield. Meanwhile energy flowing around the northeastern side of the Pacific ridge will bring a series of systems into the Northwest. The trajectory of moisture across the Northeast Pacific is not favorable for extreme precipitation totals but the accumulations over several days may still be significant. The first shortwave ejects from the West into the Southern Plains Day 3-4. Operational models and ensemble means show very good agreement on timing of this shortwave and general progression of the low center/frontal boundary. The UKMET was a bit faster/north than the better consensus and the means and was not included in the blend. After day 4, the GFS and ECENS mean were slightly faster as the shortwave lifts into the Ohio Valley compared to the ECMWF/CMC/GEFS mean solutions, but not enough to reject it entirely. Upstream, the next system drops into the Western U.S. this weekend. The GFS/ECMWF and their ensemble means show fairly good agreement for timing of this system, with the CMC notably faster. The energy moves out into the Plains by day 6-7 and there remain some more timing/detail differences with the energy as it moves from the Plains into the Midwest amongst the operational guidance. The ensemble means show much better agreement and thus were leaned more heavily on for the day 6-7 forecast. The day shift WPC progs used a 100% deterministic model blend (mostly GFS/ECMWF with some CMC) for days 3 and 4, steadily increasing contributions from the ECENS/GEFS means days 5-7. The CMC was removed completely after day 5 due to reasoning above. This maintains very good continuity from the previous/overnight WPC forecast. ...Weather Highlights/Threats... Confidence is still above average for the overall heavy rainfall event expected from parts of the Mid-Lower Mississippi Valley into the Ohio/Tennessee Valleys during the late week into weekend time frame. However uncertainty with the timing of supporting dynamics ejecting from the West provides some challenge for resolving the rainfall duration and highest totals. The scenario continues to be favorable with a feed of Gulf moisture interacting with an approaching wavy front, producing areas of heavy rain/embedded convection. The latest WPC QPF shows a widespread area of 3-5" with locally higher amounts from Arkansas to the Ohio Valley and into parts of southwest New York. The Storm Prediction Center is also highlighting a potential for severe weather across the southern tier of states with this event for Friday and Saturday. Meanwhile over the past day the signal for wintry precipitation on the northern periphery of the moisture shield has strengthened. Primary snow potential should extend from parts of the Midwest through the Great Lakes and Northeast. The wavy cold front will eventually cross the East Coast and extend into the Gulf. This trailing part of the front is likely to return north as a warm front around the start of next week and become one focus for another potential rainfall event near the end of the medium range period and beyond. This second event may be just to the south of the first event from roughly Mississippi to Tennessee Valley/Southern Appalachians. Some locations within the heavy rainfall threat area have recently received significant rainfall so effects from this upcoming event will require close monitoring for flash flood and river flood potential. The series of systems coming into the Northwest will focus the highest rain/mountain snow totals over the Pacific Northwest coast/northwest corner of California along with the Cascades. Expect a secondary maximum over the northern Rockies. At times moisture will extend southeastward into the Sierra Nevada/Great Basin/Central Rockies but with lighter amounts in most cases. Amounts should not be extreme given that northwesterly flow should promote only modest anomalies for deep moisture, but multi-day totals over the most favored terrain could reach a few inches liquid. From late week into the weekend expect a surge of very warm air to extend from the central through eastern U.S. with a broad area of plus 10-25F anomalies for highs and plus 20-30F and locally higher anomalies for morning lows. Daily records are possible, especially for warm lows. Most of the West will see moderately below normal highs through the period. The extreme northern Plains/Montana will be a focus for some colder anomalies, including some readings 20-30F below normal Sun-Mon. Santorelli/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 - Heavy precipitation across portions of California, the Pacific Northwest, and the Northern Great Basin, Fri-Mon, Jan 10-Jan 13. - Heavy precipitation across portions of the Northeast, the Central Appalachians, the Middle Mississippi Valley, the Mid-Atlantic, the Great Lakes, and the Ohio Valley, Sat-Mon, Jan 11-Jan 13. - Heavy rain across portions of the Mid-Atlantic, the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Great Lakes, the Middle Mississippi Valley, the Northeast, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Thu-Sun, Jan 9-Jan 12. - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Ohio Valley, Mon, Jan 13. - Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Sat-Mon, Jan 11-Jan 13. - Severe weather across portions of the Lower Mississippi Valley and the Southern Plains, Fri, Jan 10. - Severe weather across portions of the Southeast, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Sat, Jan 11. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Northern Plains, and the Tennessee Valley. - Flooding likely across portions of the Pacific Northwest. - Much below normal temperatures across portions of the Northern Plains, the Northern Rockies, and the Northern Great Basin, Sun-Mon, Jan 12-Jan 13. 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