Extended Forecast Discussion NWS Weather Prediction Center College Park MD 417 PM 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 next week to linger beyond day 7... ...Overview... The ongoing blocky flow pattern looks to persist into the 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 to work into the Great Lakes/Northeast later this weekend to re-energize that portion of the block with a likely closed off upper low to linger as it translates slowly eastward across the region early next week. This would prompt an additional and locally enhanced precipitation focus into early next week out across the east-central U.S. as aided by southern stream energies and then up the Eastern Seaboard along with wrapping moisture around a deepening surface low/frontal system. The pattern should finally become more progressive next week, with excessive heat likley to build looks to build to the South across Texas and into the lower Mississippi Valley this period. ...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-early Tuesday. There's also good synoptic agreement beyond Tuesday that the pattern should finally, but only gradually, break down and become more progressive. Great Lakes/Midwest to Northeast closed low translation is showing better agreement in guidance. However, the GFS and to a lesser extent the GEFS remain on the faster side of the full envelope of guidance to eject the bulk of energy associated with the upper low over California and the Southwest out across the Rockies/Plains and east-central states next week within southern stream flow. Prefer a blend closer to the slower and more amplified ECMWF/Canadian and ECMWF ensembles which also fits well with WPC continuity and the nature of closed systems/blocky flow that to tend to linger. Latest 12 UTC cycle guidance has overall trended a bit slower in this southern stream. ...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 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 not depict any slight risk areas on the day 4 ERO across parts of the Tennessee Valley despite some guidance signal. 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 onward to the east-central states with flow/frontal progression and lead intability/moisture feed. 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 to the south of a frontal drape. Daytime highs 10-15F above normal, with heat indices possibly in excess of 110F, mainly for central to lower Texas. Some record values are possible. As per the latest information from the Climate Prediction Center, this threat appears likely to linger beyond day 7/Thursday. Schichtel/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 Hazards: - Heavy rain across portions of the Central High Plains and the Great Lakes, Sun-Mon, Jun 11-Jun 12. - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Southern Appalachians, and the Ohio Valley, Sun, Jun 11 and Wed-Thu, Jun 14-Jun 15. - Heavy rain across portions of the Central Appalachians, the Mid-Atlantic, and the Great Lakes Mon, Jun 12. - Flooding possible across portions of the Northern Plains. - Flooding occurring or imminent across portions of the Northern Rockies and the Northern Great Basin. - Excessive heat across portions of the Lower Mississippi Valley and the Southern Plains, Tue-Thu, Jun 13-Jun 15. 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