Extended Forecast Discussion NWS Weather Prediction Center College Park MD 232 AM EDT Sat Jun 03 2023 Valid 12Z Tue Jun 06 2023 - 12Z Sat Jun 10 2023 ...Broad multi-day thunderstorm and local heavy rain threat from the Northern Rockies to the Southern Great Plains continues well into next week... ...Overview... The upper level pattern during the medium range period next week will remain blocky as an anomalously strong upper ridge is sandwiched between stagnant upper lows in the Northeast U.S. and over California. This pattern supports daily showers and storms from the southern Plains into the northern Rockies and parts of the Great Basin, an area which has been quite wet as of late. Prolonged above normal temperatures are also expected from the Northwest into the northern Plains and Upper Midwest/Mississippi Valley. ...Guidance Evaluation/Predictability Assessment... The latest suite of guidance continues to capture the overall synoptic pattern reasonably well and a general model blend sufficed for at least the first half of the period. There are some detail differences to be worked out still, particularly across the Northeast as pieces of energy act to reinforce a mean upper low over the region. Previous runs supported a scenario with a couple of closed lows, but the latest runs seem to be trending towards one consolidated low through most of next week (with the exception of the CMC). There are differences in how far south into the Mid-Atlantic/Southeast the lower heights get too. Out West, the main differences begin to arise after day 5 as the GFS continues to be quickest to erode the upper low over California, and brings troughing farther into the Western U.S. than other solutions (even trying to break down the central U.S. ridge by next weekend). The WPC blend for the second half of the period favors the ECMWF (given the better run-to-run consistency) along with the ensemble means which helps mitigate the detail differences. This approach maintained good continuity with the previous WPC forecast as well. ...Weather/Hazards Highlights... A daily diurnal risk for heavy showers and thunderstorms will be maintained through the period from the southern Plains to the northern Rockies and westward into the Great Basin as tropical Pacific moisture is funneled northward in between a strong central U.S. ridge and an upper low parked over California. For now, the days 4 and 5 Excessive Rainfall Outlooks continue to depict just one large Marginal risk area for this region, however embedded Slight risk areas may become necessary if heavy rains focus over antecedent wet areas. For parts of central Montana, a cold front looks to drop into the region supporting an increased risk for heavy rainfall and flash flooding by days 6 and 7 (this area has been very wet and is more susceptible anyways). Elsewhere, a cold front through the Great Lakes/Upper Midwest early in the week should focus showers and storms ahead of it across the Northern Plains/Upper Mississippi Valley. With decent moisture and instability, a marginal risk remains on the day 4 Excessive Rainfall Outlook. In the Northeast, the deepening upper trough/lows should favor pockets of rainfall into Friday as moisture gets wrapped back into especially northern Maine from a lingering low pressure system near the coast. In Florida, a lingering weak front should support unsettled conditions over the Sunshine State with better heavy rain chances in southern Florida late week as deeper moisture gets pulled north. Central U.S. ridging aloft will maintain an axis of above normal temperatures from the northern Plains south-southeast to the Mid-South, with plus 5-10F anomalies for highs possible most days. The Northwest will be the other focus for very warm temperatures, with highs 10-20F or so above normal and moderation later in the week as troughing begins to push into the region. Expect below normal temperatures over the Northeast and at times into the Mid-Atlantic as upper troughing becomes established. 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 upper low reaching southern California Monday will also bring a cooling trend into the southwestern U.S. next week. 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