Extended Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Tue Jun 06 2023 Valid 12Z Fri Jun 09 2023 - 12Z Tue Jun 13 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... ...Overview... A quite blocky flow pattern should persist through the next week 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, now more likely closing off a low over/near the Ohio Valley into early next week. This would prompt an additional and locally enhanced precipitation focus by later weekend into early next week out across the east-central U.S. and then the Eastern Seaboard. ...Guidance Evaluation/Predictability Assessment... The WPC medium range product suite was primarily derived from a composite blend of well clustered guidance from the latest GFS/ECMWF/UKMET/Canadian, the National Blend of Models and WPC continuity from Friday into the weekend in an active pattern with seemingly above normal predictability and good ensemble support. Models continue to offer some run to run variablility, with trends to hold closed lows over California/Southwest and now more into the Great Lakes with the 12 UTC cycle, but overall remain reasonably clustered into longer time frames. Forecast spread from the models remains below normal into early next week and best in line with ECMWF ensembles that better maintain the blocky flow pattern that seems much more reasonable versus more progressive later period guidance from recent GEFS/Canadian ensemble runs and asscoiated forecast clusters. However, there is at least some run to run trend from GEFS ensembles toward a slower solution. ...Weather/Hazards Highlights... A daily risk for heavy showers and strong thunderstorms from the southern Plains through the northern Rockies and westward into the Great Basin is expected to be slow to dislodge over the next week as tropical Pacific moisture remains funneled northward between a strong central U.S. ridge and an upper low parked over California/Southwest. The days 4 and 5 Excessive Rainfall Outlooks continue to depict a large marginal risk across this entire region with an embedded slight risk over Montana for Day 4 as anomalous moisture focuses along a frontal boundary over an area that has been very wet lately. Additional embedded slight risks are also possible within the larger marginal risk area, especially if heavy rainfall falls over antecedent wet areas. Elsewhere, a front moving southward through the Upper Midwest and Ohio Valley and onward along with favorable leading instability and thetae advection with return flow later this week through the weekend should focus showers and strong thunderstorms. A marginal risk remains expanded into this region by day 5 as models indicate potential for at least locally heavy rainfall and convection. Slight risks are possible as we get closer in time, but at this point, its far too uncertain to pick out where the best focus may be. A leading cold front settling over the Southeast should be a secondary focus for convection, with possibly more widespread/heavy showers across southern Florida later this week along a weakening front. Midwest closed upper trough/low development and associated and wrapping surface low and frontal characteristics trailing over the Appalachians/East/Southeast into early next week may then set the stage for development of a pattern favoring additional widespread threats for heavy rain/thunderstorms to monitor. Warmer than average temperatures, generally +10-15F, from the Northern tier to the Northwest should moderate some this weekend, but may creep up again early next week. Expect near to below normal temperatures over the Northeast and at times into the Mid-Atlantic beneath upper troughing, mainly early in the period. Clouds and periods of rainfall should keep highs 5-10F or so below normal over the southern half of the Rockies/High Plains for most of the period and the second upper low reaching southern California next weekend will bring a reinforcing shot of much cooler temperatures as well. Schichtel/Santorelli Hazards: - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Sat, Jun 10. - Heavy rain across portions of the Northern Plains and the Northern Rockies, Fri-Sat, Jun 9-Jun 10. - Heavy rain across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, the Ohio Valley, and the Tennessee Valley, Sun, Jun 11. - Flooding possible across portions of the Central Rockies and the Central Plains. - Flooding occurring or imminent across portions of the Northern Rockies and the Northern Great Basin. - Flooding likely across portions of the Central Great Basin, the Northern Plains, and the Northern Great Basin. 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