Extended Forecast Discussion NWS Weather Prediction Center College Park MD 301 PM EDT Mon Jun 05 2023 Valid 12Z Thu Jun 08 2023 - 12Z Mon Jun 12 2023 ...A multi-day thunderstorm and local heavy rain threat will continue rest of this next week from the Northern Rockies through portions of the Great Plains... ...Overview... A very amplified and blocky flow pattern persists over North America with an anomalously strong upper ridge/high sandwiched between mean troughing/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 through Friday. The next wave rounding the mid-continental ridge crosses Ontario and approaches the Northeast this weekend. This allows the precip focus to shift east from the Rockies and approach the Eastern Seaboard by early next week. ...Guidance Evaluation/Predictability Assessment... A general model blend of the 00Z/06Z deterministic solutions worked well for days 4-6 amidst good model agreement on the rather static pattern through Friday and the progression of the next trough rounding the mid-continental ridge and crossing Ontario on approach of the Northeast on Saturday. However, by day 7 spread increases on the progression and depth of the trough/low. Furthermore, 12Z guidance displays greater spread with this feature. The 12Z ECMWF is now more closed/slower with the low over the Great Lakes with all guidance generally maintaining the mid-continental ridge. Out West, the upper low currently over California should weaken and lift north bu Thursday as a second piece of energy cuts off from Eastern Pacific troughing to close off a deep low over southern California by this weekend, likely lingering into next week. The WPC blend increased GEFS/ECENS ensemble means late period given minor model differences as well as the lack of the UKMET beyond Day 5. ...Weather/Hazards Highlights... The daily diurnal risk for heavy showers and thunderstorms from the southern Plains through the northern Rockies and westward into the Great Basin persists through at least Friday as tropical Pacific moisture is funneled northward between a strong central U.S. ridge and the upper low parked over California. The days 4 and 5 Excessive Rainfall Outlooks continue to depict a large marginal risk across this entire region. Embedded slight risks were maintained over west-central Montana 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. However, the Slight Risk areas were withdrawn from the Absarokas/Yellowstone given far lower snow pack in the area compared to last year along with unfocused diurnal rainfall threats. Elsewhere, a front moving southward through the Upper Midwest and Ohio Valley later this week into the weekend should focus showers and thunderstorms along the boundary. A leading cold front settling over the Southeast should be a secondary focus for scattered convection, with possibly more widespread/heavy showers across southern Florida later this week along a weakening front. Anomalous ridging will generally maintain above normal temperatures most days from the Upper Midwest/northern Plains into the Northwest, though temperatures will moderate some across the Great Lakes this weekend as the ridge axis shifts west. 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. Jackson 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