Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Fri Jun 18 2021 Valid 12Z Mon Jun 21 2021 - 12Z Fri Jun 25 2021 ...High Heat over the West spreads to the Plains next week... ...Wet remnants of "Three" exits Carolinas Monday to lift off East Coast... ...Trailing frontal heavy rains across the South to the East early next week... ...Guidance/Predictability Evaluation... Recent GFS/ECMWF and GEFS/ECMWF ensemble mean runs for days 3-7 are mainly well clustered and along with the overall representative National Blend of Models seem to act as a reasonable forecast base in a pattern with above normal forecast predictability. ...Weather Highlights/Hazards... Ongoing record-breaking and dangerous heat over the Southwest/California may slowly moderate next week, but it will still be hot. High heat is also expected for the Northwest and Great Basin and will also spread into the Plains. Potential Tropical Cyclone "Three" is forecast by the NHC to develop and reach the central Gulf Coast Saturday and track across the South/Southeast this weekend. By Monday, the moist remnant system and heavy rains are subsequently expected to move offshore the Carolinas before lifting off the East Coast as mainly a maritime threat. Early next week upper support, frontal approach and Gulf moisture/instability return in the wake of "Three" will support periods of strong convection with heavy downpours across the already wet South that would lead to additional runoff issues, especially with lead training. Generally progressive frontal focusing rains will meanwhile also spread through the Ohio Valley, Appalachians and the Eastern Seaboard, lingering over the Southeast/Florida midweek with the trailing front. Upstream, additional digging upper energies and return frontal support may combine to favor a moderate convective rain focus from the eastern Plains and north-central Mid-Mississippi Valley/Midwest later next week. 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 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