Extended Forecast Discussion NWS Weather Prediction Center College Park MD 234 PM 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... Little change to the upper pattern is forecast during the medium range period. A strong ridge will persist over the south-central U.S. while mean upper low/troughing remains in place over the East and West Coasts. The ridge is responsible for excessive heat in the southern Plains, and heat will expand north and east into parts of the Lower and Middle Mississippi Valley and Central Plains next week. Showers and thunderstorms are expected to impact the eastern third of the country and the north-central U.S. through the period. ...Guidance Evaluation/Predictability Assessment... Model solutions are in good agreement for the the first half of the period, after which solutions begin to diverge. A general deterministic model blend was used for days 3 and 4, then ensemble guidance was introduced to the blend for days 5, 6, and 7. The main differences between the solutions were associated with a shortwave trough that is forecast to move through the western trough, round the top of the ridge, then dive southeast across the northern Plains and Upper Midwest. Uncertainty is quite large on the strength and position of this feature, which in turns creates uncertainty in the sensible weather forecast. Uncertainty also remains on the strength of the western ridge in the wake of this feature and how the ridge placement will be affected. The GFS and CMC maintain a stronger trough that shifts the center of the ridge slightly east from over Texas to Louisiana. However, the ECMWF significantly weakens the trough and keeps the ridge position nearly stationary. For this forecast, a blend was used to create a middle ground scenario. ...Weather/Hazards Highlights... The frontal system currently bringing precipitation to the eastern U.S. will move offshore and dissipate Monday morning, then the next system will follow hot on its heels. The second system will push across the eastern U.S. early in the week accompanied by ample moisture that will support widespread precipitation. Moisture will focus ahead of and along the cold front and wrap around the low pressure center in the Great Lakes region. Severe weather will be possible in the warm sector and along the cold front, and the Storm Prediction Center has highlighted an area of potential severe weather on Monday from the Chesapeake Bay to the interior Carolinas. Locally heavy rainfall will be possible as well with potential training/repeat activity associated with this system. For Monday, there is a Marginal Risk of Excessive Rainfall for parts of the Upper Midwest, Northeast, Mid-Atlantic, and interior Southeast. For Tuesday, there is another Marginal Risk for parts of the Northeast and Mid-Atlantic where heavy rainfall potential will linger. Embedded Slight Risk areas may be possible for the Northeast and/or Mid-Atlantic in future ERO updates when confidence in the location of heavier rainfall totals increases. For now, too much uncertainty remains in the forecast to highlight a specific area. The system will slow down as is approaches the East Coast, and precipitation chances will linger along the eastern seaboard through the end of the period. In the West, the ejection of the splitting/lead upper trough energies will bring scattered showers and storm chances across the Northern Great Basin and Northwest early next week. Activity will increase and spread downstream to the Northern Rockies and northern Plains, and heavy rainfall may be a concern. There is a Marginal Risk of Excessive Rainfall for parts of this region on Tuesday to address potential training/repeat cell runoff concerns. Precipitation will spread into the Upper Midwest and Ohio and Tennessee Valleys mid-to-late next week as the system progresses. In term of temperatures, excessive heat is forecast to continue to plague the south-central U.S. through at least next week with a mid-week expansion north and east into the Central Plains and Middle 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. Elsewhere in the country, near normal high temperatures are forecast with below normal highs likely in areas of precipitation each day. Dolan/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