Extended Forecast Discussion NWS Weather Prediction Center College Park MD 151 AM EDT Fri Jun 04 2021 Valid 12Z Mon Jun 07 2021 - 12Z Fri Jun 11 2021 ...Record Heat Threat from the Northern Plains to the Northeast.... ...Multi-Day Heavy Rainfall Event For the Southern Plains and Lower Mississippi Valley... ...Overview and Guidance Evaluation/Preferences... The large scale pattern remains locked on the amplification and persistence of a West Coast upper trough next week while downstream ridging is forecast to build and anchor over much of the Southeast to Mid-Atlantic. A weakness in the ridge over the central U.S. and an associated surface boundary will be the focus/lift for widespread precipitation, some of which could be locally heavy and result in flash flooding over portions of Texas, Louisiana, and the ArkLaTex region. With troughing established over the West Coast, storm systems are expected to track along a quasi-stationary boundary from the central/northern Rockies into the northern Plains. While the model guidance is reasonably clustered and agreeable for days 3-5 (Mon-Wed), there is considerable uncertainty for the Western U.S. with the evolution of shortwave energy coming out of the Gulf of Alaska and Eastern Pacific. The ECMWF is actually fast to eject energy out of the Gulf of Alaska through the base of the trough into the Pacific Northwest by Friday while the GFS bottles this energy back offshore into a closed low. By day 7, the deterministic runs of the GFS/ECMWF are almost out of phase over the Northwest. The ensembles (ECENS/GEFS) are a bit slower and depict a solution toward the GFS idea instead of the faster ECMWF. With this in mind, the WPC blend this cycle used mostly a ECMWF/GFS/UKMET blend early on then mostly GEFS/ECENS blend for day 6-7 to help offset some of the higher uncertainty for the Pacific Northwest. ...Weather Highlights/Hazards... The combination of deep flow from the Gulf of Moisture interacting with a surface boundary along the western/central Gulf Coast will continue to provide episodes of heavy rainfall and possible flash flooding late this weekend into early next week from portions of Texas, Louisiana, and gradually northward across the ArkLaTex and Lower/Mid Mississippi River Valley where the greatest risk area for several inches of rainfall totals exists. Over time next week, the associated surface trough is forecast to weaken and lift northward which will bring numerous to widespread showers and thunderstorms to portions of the Ohio Valley and Great Lakes regions, although with lighter rainfall amounts expected at this time. Meanwhile, diurnally driven showers and storms will be possible across the southern to central Appalachians and perhaps into portions of the Mid-Atlantic with the flow around a strong Bermuda high. The West will remain dry aside from some light precipitation across the Pacific Northwest and far northern Rockies. The greatest temperature anomalies during the period are expected to be across the northern tier of the CONUS where daytime highs 15F to 20F above normal. Record highs will be possible, especially across the Northeast Monday and Tuesday. The South will see normal to even slightly below normal temperatures thanks to increased cloud cover and precipitation chances while the West Coast will experience slightly below normal readings in response to the troughing in place over the region. Taylor 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