Extended Forecast Discussion NWS Weather Prediction Center College Park MD 240 AM 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 very amplified and blocky flow pattern should persist through at least this coming weekend 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. The next wave rounding the mid-continental ridge crosses Ontario and approaches the Northeast this weekend, possibly closing off a low over/near the Ohio Valley late period. This would allow 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 latest deterministic solutions worked well for days 3-5 amidst good model agreement on the rather static pattern in place into the weekend. Out West, models show good synoptic agreement on the next upper low settling over California and troughing maintained over the Western U.S.. There greatest area of uncertainty late in the period is with the wave dropping towards the Great Lakes this weekend and models seem to be trending more aggressive with this feature with many showing a closed low around Sunday/Monday. There is disagreement on placement of this low and still considerable run to run inconsistencies. There are scenarios where the low gets held up over the Great Lakes, drops south into the Appalachians or the Southeast, or progresses quickly into the Northeast. Obviously, this has implications on eventual precipitation into the Eastern U.S. late period and will need to be watched. The ensemble means are more subdued but do offer a nice middle ground solution at this point. Overall, models are showing increasing potential that this stubborn and blocky pattern over the CONUS may finally begin to break down and shift east by next week. ...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 into at least the weekend as tropical Pacific moisture is funneled northward between a strong central U.S. ridge and an upper low parked over California. 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 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 later this week into the weekend should focus showers and thunderstorms along the boundary. A marginal risk was 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 scattered convection, with possibly more widespread/heavy showers across southern Florida later this week along a weakening front. 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. 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