Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Sun Jun 25 2023 Valid 12Z Wed Jun 28 2023 - 12Z Sun Jul 02 2023 ...Prolonged heat wave forecast to expand from Texas to the mid-lower Mississippi Valley... ...Excessive rainfall threat across the Northeast and north-central U.S. states mid-late week... ...Overview with Guidance Evaluation/Predictability Assessment... Models remain in general agreement that a positively-tilted trough lifting out of the western U.S. into the north-central U.S. will spread the excessive heat from over the southern Plains toward the mid-Mississippi during the latter half of this week. However, uncertainties with the details of the lifting trough continue to shift the focus of an area of enhanced rainfall farther east from the northern Plains to the upper Midwest midweek. Meanwhile, models remain in very good agreement to keep a weakening but slow-moving trough over New England through late week before the next low pressure wave moving across the central U.S. may reach New England by next weekend. Therefore, the WPC medium range product suite was primarily derived from a composite blend of the 06Z GFS/00Z ECMWF/00Z Canadian models together with their ensemble means. More of the ensemble mean solutions were included for Days 6 and 7 to handle to higher uncertainty with the timing of the trough ejection across the north-central U.S. late next week. This solution maintains good WPC product continuity except the secondary frontal position across the northern Plains, as well as a significant eastward shift in an area of enhanced rainfall across the northern Plains midweek. ...Weather/Hazards Highlights... An amplified trough slowly progressing through the Northeast will wrap Atlantic moisture around a gradually weakening low pressure system to fuel widespread and lingering precipitation. Locally heavy rainfall will be possible with potential training and embedded thunderstorms in this slow-moving system. A WPC Excessive Rainfall Outlook (ERO) "Marginal Risk" area is maintained over the Northeast for Wednesday and Thursday in an area with antecedent rainfall from the previous slow-moving system. Meanwhile, the ejection of upper trough energies out from the West midweek is expected to bring scattered showers and storm chances eastward across the northern Plains into the upper Midwest with locally heavy rainfall. Models have generally sped up the eastward ejection of the upper energies, resulting in an eastward shift in a marginal risk of excessive rainfall into the upper Midwest on Wednesday. Remaining energies from the positively tilted trough in the western U.S. are forecast to organize another area of marginal risk of excessive rainfall from Thursday into early Friday over the northern High Plains. Meanwhile, scattered showers with embedded thunderstorms and locally heavy rain can be expected from the central U.S. to the East Coast during next weekend with possibly an area of heavier rainfall developing over New England ahead of a warm front as a low pressure wave is forecast to move from the Ohio Valley to the lower Great Lakes. In term of temperatures, excessive heat will continue to plague the south-central U.S. into next week with a mid-week expansion north and east across portions of the central Plains and into the mid- and lower Mississippi Valley. The heat will be oppressive with widespread high temperatures exceeding 100 degrees and heat indices as high as 120 degrees. Heat indices may even exceed 120 degrees in some locations in South Texas. Several temperature records are in danger of being broken during this significant heat wave. The Desert Southwest will also experience temperatures well over 100 degrees next week, but that is not really anomalous for this time of year. Florida will also see hot to record high values. Kong/Schichtel 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, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw