Extended Forecast Discussion NWS Weather Prediction Center College Park MD 347 PM EST Fri Jan 15 2021 Valid 12Z Mon Jan 18 2021 - 12Z Fri Jan 22 2021 ...Heavy rainfall event likely for portions of the interior South next week... ...An anomalous upper low expected to bring unsettled weather over parts of the Desert Southwest for much of next week... ...Pattern Overview and Guidance/Predictability Assessment... An increasingly complex synoptic pattern appears to be in store for much of next week as many of the southern tier states will likely experience an extended period of unsettled weather. Model consensus continues to indicate a trend toward more robust amplification of an upper-level trough dipping across the Desert Southwest, and possibly developing into a closed low by the time it reaches the northern Baja. This anomalous upper low will likely bring unsettled weather from the central Rockies down into the Southwest on Monday into Tuesday, as moisture from the Gulf returns into Texas. The GFS and ECMWF agree quite well with this general scenario. The CMC, on the other hand, continues to take the upper low further off the coast of Baja into the subtropical Pacific--a scenario being ruled out at this point. A consensus of the 00Z ECMWF/00Z EC mean with the 06Z GFS/06Z GEFS formed the basis for this morning's WPC forecast charts. This brings the anomalous upper low slowly eastward into northern Mexico for the latter part of next week, keeping a good chance of unsettled weather over the Desert Southwest while a threat of heavy rain lingers from eastern Texas across the interior Deep South into the interior Southeast. ...Weather/Threats Highlights... The main weather story next week will be the potential for a multi-day heavy rainfall event, extending from central Texas to the southern Appalachians, mainly during the Tuesday-Thursday time period. A prolonged period of moist southerly flow from the Gulf and Caribbean ahead of a slow moving low pressure system over southern Texas, in combination with moisture convergence along a quasi-stationary front, may result in several inches of rainfall for parts of this region and some potential for flooding. Moderate to heavy snow is likely for portions of the central and northern Rockies early in the week. Meanwhile, there appears to be an increasing chance of wintry precipitation spreading into the higher elevations of central Arizona and rain over the lower elevations of southeastern Arizona and southwestern New Mexico. By Thursday and Friday, the chance for snow returns to the Northeast, the Great Lakes, as well as the Cascades as the next storm systems arrive. In terms of temperatures, readings should be near to slightly above normal for most areas to begin the week, and some 10-20 degree positive anomalies are possible across the northern Plains by Wednesday ahead of the next front. By the end of the week, there are some hints of an Arctic airmass affecting the northwestern quadrant of the U.S., although the core of the Arctic high should remain north of the Canadian border. Kong/Hamrick 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: - Flooding occurring or imminent across portions of the Southeast and the Pacific Northwest. - High winds across portions of the Central Great Basin, California, and the Southwest, Mon-Tue, Jan 18-Jan 19. - High winds across portions of the Northern Plains and the Northern Rockies, Tue, Jan 19. - High winds across portions of the Central Rockies and the Central Plains, Wed, Jan 20. - Heavy rain across portions of the Southern Plains, the Lower Mississippi Valley, the Tennessee Valley, the Southern Appalachians, and the Southeast, Thu-Fri, Jan 21-Jan 22. - Enhanced wildfire risk across portions of California, Mon-Tue, Jan 18-Jan 19. 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