Extended Forecast Discussion NWS Weather Prediction Center College Park MD 209 PM EST Sat Mar 13 2021 Valid 12Z Tue Mar 16 2021 - 12Z Sat Mar 20 2021 ...Bouts of heavy rainfall possible across the southeastern quadrant of the CONUS next week... ...Overview... A robust, upper low will track east from the Four Corners region through the extended period; which will keep the potential for widespread rainfall with embedded areas of locally heavy amounts across the South and into the Tennessee Valley. Multiple weakening low pressure systems will approach the West, keeping a majority of the precipitation in British Columbia. Prior to the passage of the cold front, most of the CONUS will experience near seasonal average for mid-March. ...Model Guidance/Predictability Assessment... The 6Z and 12Z model guidance was fairly clustered with respect to the deep mid/upper low exiting the Four Corners region into the central US. The GFS was more open and faster than the ECWMF, CMC and UKMET solutions to track the front through the Plains- especially in the initial and middle periods. Preferred a heavier weighting to non-NCEP guidance for this issuance. The blend mainly was nearly equal parts of the ECWMF/CMC/UKMET with light weighting of the 00Z/06Z runs of the GFS increasing inclusion of the EC ensemble means and the GEFS means by mid and late periods as there is timing uncertainty as the low/front tracks through the eastern U.S. and offshore. ...Weather/Threats Highlights... The leading system will spread light to modest rain/snow over the Central Rockies and into the adjacent Plains Tuesday while the rainfall increases areal coverage over the Southeast along the warm front. Areas north of the frontal boundary will have light snow from the Corn Belt to points east into the higher terrain of the Central Appalachians, spreading to the Northeast toward the end of the forecast period. Rainfall could be heavy in some locations in the warm air mass near and inland from the Gulf Coast Tuesday through Thursday. Farther west, approaching Pacific system will spread low elevation rain and higher elevation snow to the West Coast (NorCal and northern Sierra into coastal OR/WA) especially Wednesday onward. The Southeast will have mild temperatures through Wednesday with numerous locations in the 70s. Meanwhile, colder than average temperatures will be ushered in by the cold front exiting the Rockies. The daily high temperatures will average 5 to 15 degrees colder across most of the the Interior West and into the High Plains toward the end of the extended period. With ridging expected to build back into the West, warmer temperatures will slowly return. Campbell 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 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