Extended Forecast Discussion NWS Weather Prediction Center College Park MD 301 AM EDT Fri Jun 23 2023 Valid 12Z Mon Jun 26 2023 - 12Z Fri Jun 30 2023 ...Prolonged heat wave continues across Texas and southeastern New Mexico and will expand northeast next week... ...Overview... The overall upper level pattern will remain fairly stagnant through the period with a strong ridge over the south-central U.S. and mean upper low/troughing over the East and West Coasts. The ridge is responsible for excessive heat in the southern Plains, and heat will gradually expand east and north into the Lower Mississippi Valley and parts of the Middle Mississippi Valley and central Plains by mid-next week. Additional showers and thunderstorms are expected to focus in the eastern third of the country as a few surface low pressure systems move across the region and also out from the West into the north-central U.S.. ...Guidance Evaluation/Predictability Assessment... The latest solutions of the GFS/ECMW/Canadian and GEFS/ECMWF ensemble means seem best clustered for the 3-7 day forecast period and a composite blend is preferred along with WPC continuity and the national Blend of Models. The overall slightly more progressive UKMET solution less likely given amplified and slow moving/repeat flow history. ...Weather/Hazards Highlights... A deep layered low pressure system with wrapping moisture will slowly shift a protracted rain/convection focus from the Great Lakes and Upper Ohio Valley to the north-central Appalachians/Mid-Atlantic and Northeast Monday into Thursday, with some locally heavy amounts possible given potential for training/repeat activity with slow system translations and good dynamical support. Convection also looks to overspread down over much of the East early-mid next week with trailing frontal push, with strong to severe weather also a possibility. A WPC Excessive Rainfall Outlook (ERO) "Marginal Risk" has been maintained for much of the East Monday and lingering across the northern Mid-Atlantic/Northeast Tuesday as there may be multiple opportunities for locally heavy rain with scattered to widespread storms in an unstable environment. Embedded "Slight Risks" are quite possible with future ERO updates given ample early summer upper low/trough development once the guidance signal becomes stronger for a given location. By Tuesday and Wednesday, the front should push slowly eastward with drying behind the front, while additional leading rounds of rain and thunderstorms continue for the Eastern Seaboard. Meanwhile upstream, the ejection of splitting/lead upper trough energies across the West will bring scattered showers and storm chances across the Northern Great Basin/Northwest early next week. Activity will increasingly spread downstream to the Northern Rockies/Plains where an ERO "Marginal Risk" is planned for Tuesday to address potential training/repeat cell runoff concerns, with activity then expanding into the Mid-Upper Mississippi Valley through next midweek. In terms of temperatures, there is really no end in sight for the excessive heat that has plagued particularly Texas/southeastern New Mexico in recent days. Temperatures over 100F and heat indices much higher will continue expanding east into the Lower Mississippi Valley and north toward the central Plains next week. The current forecast calls for temperatures exceeding near to just above 100F in Oklahoma/Kansas/Arkansas by Wednesday-Thursday. Several record temperatures could be set or tied, as temperatures nearing or exceeding 110 degrees could again occur in western and southern Texas. The Desert Southwest starts to see temperatures well over 100F next week too, though not really anomalous for this typically hottest time of the year there. Meanwhile the West should see slightly cooler than normal temperatures particularly for highs with the bouts of upper troughing aloft. The East looks to be slightly cooler than normal overall as well to continue a recent trend, with temperatures 5-10+ degrees below normal from the Great Lakes region through the north-central Appalachians/Mid-Atlantic. 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 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