Extended Forecast Discussion NWS Weather Prediction Center College Park MD 249 PM EST Fri Jan 17 2020 Valid 12Z Mon Jan 20 2020 - 12Z Fri Jan 24 2020 ...Overview... A progressive flow in the upper levels will take the western ridge/eastern trough eastward next week which will bring back ridging to the East later in the week. A system will push through the Pacific Northwest Tuesday, eventually reorganizing over the Southern Plains by Thursday and into the Lower Mississippi Valley next Friday. This would likely increase the threat of some heavier rain to this region in an otherwise quieter pattern between storms. ...Guidance/Predictability Assessment... The flow out of the Pacific, across the West and eventually into the Central states continues to be the biggest forecast issue of the medium range period. Beyond day 4, models begin to diverge on the details, but at least can all agree on some sort of amplified trough axis across the Central U.S. by day 6. The ECMWF takes the shortwave energy due east, with the trough splitting into a northern and southern stream flow, and a surface low developing along the Gulf Coast. Meanwhile, the GFS and the Canadian drag the energy southeastward, developing a closed upper level low over the south/central High Plains by 12z next Thursday. This results in a well developed surface low lifting from the High Plains overnight Wednesday into the Mid-Mississippi Valley by early Friday. The ensembles generally follow their deterministic counterparts, though at the expense of detail. For the WPC blend, a general model compromise worked well for day 3-5, but began increasing the weighting of the ensemble means by the end of the period. Continued the usage of at least 50% deterministic (some combo of the GFS/ECMWF/CMC) just for a bit more definition on the emerging shortwave in the Plains. This blend resulted in a forecast very close to previous shift continuity. ...Weather/Hazard Highlights... Troughing east of the Rockies early in the week will favor below normal temperatures especially over the Upper Midwest/Corn Belt (owing to new snowfall in the short term) but also to the Gulf region and through Florida. Above normal temperatures in the West and Rockies Mon/Tue will slide eastward to the Plains on Wednesday then Great Lakes/Midwest Thursday and to the East Coast Friday. Precipitation will be limited in the East to around the Great Lakes and across southern Florida early in the period. Out West, modest lower elevation rain/higher elevation snow Tuesday will be followed by lighter precipitation Wednesday before increasing again next Thu-Fri with another Pacific front. By next Wed-Thu, Gulf moisture should increase rain chances over Texas northward and northeastward as a front approaches the area from the northwest. Models and ensembles continue to show the potential for heavy rainfall, from along the northwestern Gulf Coast into the ArkLaTex region. Some wintry precipitation may also be supported on the northern edge of the precipitation shield from the Central Plains to the Mid-Mississippi Valley. Santorelli 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 and the Pacific Northwest, Tue-Wed, Jan 21-Jan 22. - Heavy precipitation across portions of the Central Plains, the Middle Mississippi Valley, the Southern Plains, and the Ohio Valley, Thu-Fri, Jan 23-Jan 24. - Heavy rain across portions of the Central and Southern Plains, the Lower and Middle Mississippi Valley, the Tennessee Valley, the Southeast, and the Ohio Valley, Thu-Fri, Jan 23-Jan 24. - Heavy snow across portions of the Central Great Basin and California, Tue-Wed, Jan 21-Jan 22. - Flooding possible across portions of the Central Plains, the Tennessee Valley, the Great Lakes, the Middle Mississippi Valley, the Southeast, the Southern Plains, and the Ohio Valley. - Flooding occurring or imminent across portions of the Lower and Middle Mississippi Valley, the Northern Plains, the Tennessee Valley, the Southeast, the Great Lakes, and the Ohio Valley. - Flooding likely across portions of the Middle Mississippi Valley. - Much below normal temperatures across portions of the Central Plains, the Northern Plains, the Middle and Upper Mississippi Valley, the Great Lakes, and the Ohio Valley, Mon-Tue, Jan 20-Jan 21. - High significant wave heights for coastal portions of California and the Pacific Northwest, Tue, Jan 21. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Jan 20-Jan 21. - Much below normal temperatures across portions of mainland Alaska, Mon, Jan 20. 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