Extended Forecast Discussion NWS Weather Prediction Center College Park MD 326 AM EDT Thu Jun 08 2023 Valid 12Z Sun Jun 11 2023 - 12Z Thu Jun 15 2023 ...A multi-day thunderstorm and local heavy rain threat will continue into early next week from a very saturated Northern Rockies through portions of the Great Plains... ...Heavy rain/strong thunderstorm threat from the Midwest/Mid-South to the East this weekend into early next week with closed low genesis... ...Texas/Lower Mississippi Valley Excessive Heat threat by next midweek may linger beyond day 7... ...Overview... The blocky flow pattern looks to persist through at least this weekend with an anomalously strong upper ridge/high sandwiched between mean troughing/closed lows over the Southwest and the Northeast. This pattern continues to support diurnal showers and storms, some locally heavy, from the southern Plains through the northern Rockies and parts of the Great Basin. The next wave rounding the mid-continental ridge crosses Ontario and approaches the Northeast this weekend, with a likely closed off upper low over the Upper Great Lakes by Sunday. This would prompt an additional and locally enhanced precipitation focus into early next week out across the east-central U.S. and then the Eastern Seaboard. The pattern should finally become more progressive early next week and excessive heat looks to build across Texas and into the lower Mississippi Valley. ...Guidance Evaluation/Predictability Assessment... There remains good agreement on the weather pattern across the CONUS the first half of the period, bolstering forecast confidence. A general model blend was used for Sunday-Tuesday. There's also good synoptic agreement beyond Tuesday that the pattern should finally break down and become more progressive, though still with plenty of differences in timing and details of systems. The Great Lakes closed low is showing better agreement, but the GFS remains on the faster side to move the system of the Northeast next week. The GFS is also considerably faster with the upper low over California as it ejects into the Rockies/Plains late period. Prefer a blend closer to the slower and more amplified ECMWF which also fits well with the ensemble means and WPC continuity. As such, the blend for days 6 and 7 included the ECMWF with the ensemble means. ...Weather/Hazards Highlights... A daily risk for heavy showers and strong to severe thunderstorms from the southern Plains through the northern Rockies and westward into the Great Basin is expected to be slow to dislodge over about the next week as tropical Pacific moisture remains funneled northward between a strong central U.S. ridge and an upper low/trough parked over California/the Southwest. A weakening boundary through the region should also help to enhance rainfall totals, with particular concerns over areas that have been very wet as of late (northern and central Rockies/western Great Plains). Maintained a "slight risk" on the day 4 Excessive Rainfall Outlook in eastern Colorado and far southeast Wyoming with a broad marginal risk elsewhere day 4 and on day 5. Farther into the central U.S. and Ohio Valley, the closed low over the Great Lakes and associated surface cold front should help focus anomalous moisture and plenty of instability to produce at least locally heavy rainfall from the Upper Great Lakes/Midwest, southward into the Tennessee Valley and parts of the Southeast on Sunday. After coordination with the affected WFOs, and considering lingering model uncertainty and also how dry this region has been lately, opted to remove the slight risk on the day 4 ERO across parts of the Tennessee Valley. It is possible a slight risk will need to be reintroduced in future updates if model support increases. The front will push into the Eastern U.S. by Monday with numerous showers and storms to accompany the front as it moves into the Eastern U.S.. Antecedent dry conditions and the progressive nature of the front preclude anything more than a broad marginal risk on the day 5 ERO at this time. Elsewhere, ejecting energies out of the Southwest also look to favor additional rounds of rainfall and convection again around mid-week next week for parts of the south-central Plains along a warm front. Temperatures over the northern tier and back into the Pacific Northwest will continue to be warm, with anomalies 10-15 degrees above normal in some places, through about Tuesday before the upper ridge finally suppresses and pushes east. Underneath possible closed low development over the Great Lakes/Midwest and back into the Southwest/California, temperatures should trend moderately cooler than normal. There continues to be a signal for a building excessive heat threat for Texas into the Lower Mississippi Valley as upper ridging becomes better established over the region. Daytime highs 10-15F above normal, with heat indices possibly in excess of 110F, mainly for central to lower Texas. As per the latest information from the Climate Prediction Center, this threat appears likely to linger beyond day 7/Thursday. Santorelli 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml