Extended Forecast Discussion NWS Weather Prediction Center College Park MD 208 AM EST Sat Mar 12 2022 Valid 12Z Tue Mar 15 2022 - 12Z Sat Mar 19 2022 ...Overview... Several organized systems are noted over the Lower 48 next week in split flow. A leading southern stream system will progress from the lower MS Valley through the Southeast Tuesday/Wednesday before lifting northeast and off the southern Mid-Atlantic coast Thursday in a wet pattern. Another weather focusing upper trough will reach the West Coast Tuesday with a northern component pushing eastward along the U.S./Canadian border mid-later next week as a separate southern stream system meanwhile progresses over the U.S. southern tier that may lead to frontal wave genesis and an increasingly moist pattern into the east-central U.S. heading into next weekend. ...Guidance Evaluation/Predictability Assessment... 12 UTC model and ensemble solutions overall seem reasonably well clustered Tuesday into Friday and a composite of the GFS/ECMWF/UKMET/Canadian along with the 01 UTC NBM provides a good forecast starting point in a pattern with below normal forecast spread. The 12 UTC GFS/ECMWF provide a slightly less progressive solution than the 18 UTC GEFS/GEFS , especially with the lead southern stream system that seems to make sense given flow separation and closed low nature. Latest 00 UTC model and ensemble guidance trends seems supportive of this slightly less progressive solution. Model run to run continuity degrades into days 6/7 and a transition to a blend of best clustered guidance from 12 UTC GFS/ECMWF with the 12 UTC GEFS/ECMWF ensemble means seems reasonable. ...Weather Highlights/Threats... Low pressure shifts to the lower MS Valley into Tuesday and over the Gulf Coast/Southeast mid-week. This system should draw up ample Gulf moisture ahead of it and could combine with sufficient instability to bring widespread thunderstorms capable of producing heavy rainfall, especially along/near the Gulf Coast region. With a bit of a slower solution to the low, there is some threat for excessive rain over north Florida Tuesday/Tuesday night which is an area currently receiving heavy rain and already had above normal rainfall over the past week going into today. The atmospheric river is fairly progressive Monday night into Tuesday as it pushes across northern California, bringing beneficial rainfall and heavy elevation snowfall, with activity spreading inland across the West and into the Rockies into midweek. Later week progression with focus within amplifying southern stream flow will invoke a moderate return of moisture from from the Gulf of Mexico to then support an emerging and expanding area of rain and thunderstorms from the south-central to east-central U.S. Thu into Saturday, albeit in a pattern with increasing forecast spread. Schichtel 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 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