Extended Forecast Discussion NWS Weather Prediction Center College Park MD 320 PM EDT Fri Jun 02 2023 Valid 12Z Mon Jun 05 2023 - 12Z Fri Jun 09 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 remains parked over the northern Plains/south-central Canada and into the Northwest U.S.. This should support prolonged above normal temperatures from the Northwest into the Northern Plains and the Upper Midwest and Mississippi Valley. Meanwhile, a stationary upper low over/near California will maintain periods of convection over much of the central/southern Plains and Rockies through next week. In the Northeast, an upper low exiting the region on day 3 will be replaced by another upper low which drives lowering heights farther south into the Mid-Atlantic somewhat cooler and more unsettled conditions. ...Guidance Evaluation/Predictability Assessment... This morning's guidance captured the overall synoptic pattern reasonably well during the medium range. A general model blend consisting of the 00z ECMWF/CMC/UKMET and 06z GFS was utilized through day 4, and higher weighting given to the EC due to it's run-to-run consistency in across the CONUS. The 06z GFS lost some favorability on day 3 because of its attempt to break down the West Coast upper low earlier than the rest of the models. Models become more consistent after day 4 due to the predictability of the massive ridge over the central U.S.. The 06z GFS attempts to consolidate the upper level energy over the Northeast while others keep them separated after day 4. The ensemble means are introduced into the blend on day 6 and are favored through day 7 due to the uncertainty of the Northeast system. ...Weather/Hazards Highlights... A central continental ridge with weak troughing over the Intermountain West keeps a mainly diurnal risk for heavy showers and thunderstorms over much of the Rockies/High Plains through Texas and the Sierra Nevada/Great Basin next week. Localized flash flood potential continues through at least Tuesday given broad moist flow from the western Gulf of Mexico along with some instability. Increasing tropical Pacific moisture from the upper low over California early next week brings additional threats for diurnal and locally heavy showers and storms for parts of California and the Great Basin. The Days 4-5 Excessive Rainfall Outlooks continue to depict just large Marginal Risk areas from California/Intermountain West into the Rockies and southward to the southern Plains. Embedded Slight Risk areas may become necessary, particularly if the heavy rain focus is over antecedent wet areas. 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 was added to the days 4 and 5 Excessive Rainfall Outlooks. In the Northeast, the deepening upper trough/lows should favor pockets of rainfall into Friday. The latest advisory from the NHC for T.D. Two has it tracking south and dissipating before next week, but a weakening front/lingering troughing over Florida should allow for continued unsettled wet conditions through most of next week. 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 10-15F anomalies for highs possible most days. Initial warmth over the Great Lakes will moderate early next week after a cold front pushes through from the northeast. The Northwest will be the other focus for very warm temperatures, with highs 10-20F or so above normal. 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. Kebede/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