Extended Forecast Discussion NWS Weather Prediction Center College Park MD 401 PM EDT Fri Jun 04 2021 Valid 12Z Mon Jun 07 2021 - 12Z Fri Jun 11 2021 ...Record Heat Threat from the Northern Rockies/Plains to the Northeast.... ...Lingering Multi-Day Heavy Rainfall Event For the Southern Plains and Lower Mississippi Valley... ...Overview and Guidance Evaluation/Preferences... Models and ensembles highlight the amplification and persistence of a eastern Pacific to West Coast mean upper trough next week while hot downstream ridging is forecast to build over much of the East, albeit eroding southward from the Great Lakes/Northeast mid-later next week with northern stream upper trough digging as upper ridging builds upstream over the north-central states. An upper weakness stuck over the east-central U.S. and associated surface boundaries 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, but forecast spread is highest with this portion of the forecast. While model guidance is reasonably clustered and agreeable for much of the lower 48 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. This then offers ample challenge with the timing and extent of height falls working inland over the West mid-later next week. The WPC medium range product suite is primarily derived from a composite blend of the 06 UTC GFS, 00 UTC ECMWF/Canadian and by days 6/7 the less progressive and more amplified 06 UTC GEFS and 00 UTC ECMWF ensemble means. Lo and behold the the latest 12 UTC models now also show a strong trend toward amplification and slower progression then that will be monitored for future forecast cycles, but this trend seems reasonable considering the blocky nature of the pattern. ...Weather Highlights/Hazards... The interaction of deep/moist flow from the Gulf of Mexico with weakening surface boundaries up from the western/central Gulf Coast and lingering upper troughing will continue to provide episodes of heavy rainfall and possible flash flooding into early-mid next week for 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/storms will be possible eastward to the southern to central Appalachians and parts of the Mid-Atlantic with the flow around a strong Bermuda high. The West will remain dry aside from some light precipitation for the Pacific Northwest and northern Rockies. The greatest temperature anomalies during the period are expected to be across the northern tier of the CONUS where daytime highs will range from 15F to 20+F above normal. Record highs will be possible, especially across the Northeast Monday and Tuesday prior to expected backdoor cold front passage. 12 UTC model trends for more amplified upper flow downstream from the West Coast mid-later next week may also act to prolong a threat of record conditions over the north-central U.S. under a stronger upper ridge than anticipated for this forecast package. This trend also blend wells with the hot CPC week 2 forecast. 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. Schichtel/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 - Heavy rain across portions of the Middle/Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Mon-Wed, Jun 7-Jun 9. - Flooding possible across portions of the Lower Mississippi Valley and the Southern Plains. - Flooding occurring or imminent across portions of the Southern Plains and the Northern Rockies. - Flooding likely across portions of the Northern Great Basin. - Much above normal temperatures across portions of the Central Plains, the Great Basin, the Northern Plains, the Northern/Central Rockies, and the Upper Mississippi Valley, Mon-Fri, Jun 7-Jun 11. - Much above normal temperatures across portions of the Great Lakes and the Upper Mississippi Valley, Mon-Tue, Jun 7-Jun 8. - Much above normal temperatures across portions of the Great Lakes, the Mid-Atlantic, the Northeast, and the Central Appalachians, Mon-Wed, Jun 7-Jun 9. 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