Extended Forecast Discussion NWS Weather Prediction Center College Park MD 227 PM EDT Thu Jul 07 2022 Valid 12Z Sun Jul 10 2022 - 12Z Thu Jul 14 2022 ...A prolonged heat wave will last through early next week across the southern Plains and Mid-South... ...Overview... A persistent and strong upper level high drifting west from the southern High Plains and then meandering atop the Four Corners states next week will keep very hot temperatures in place across much of the central U.S. particularly through around Tuesday. Combined with the humidity, oppressive heat indices are likely in places and with very little nighttime relief in temperatures, a prolonged heat wave is expected to continue across the southern half of the Plains and Mississippi Valley. On the periphery of the upper ridge, troughing is forecast over the Northeast this weekend while another trough across the Northwest Sunday will track quickly across the north-central U.S. and redevelop troughing centered in the northeast quadrant of the lower 48 by Tuesday-Thursday. Rain and thunderstorms are forecast for the Southeast near a cold front that should stall and dissipate through the first half of the week. The northern Plains to Upper Midwest should also see chances of rain and potentially severe thunderstorms ahead of another cold front, and some showers and storms could shift southeastward with the front stretching from the Northeast back into the central/southern Plains Tuesday-Thursday. Meanwhile some monsoonal moisture continues to flow into the Southwest. ...Guidance Evaluation/Predictability Assessment... Recent deterministic and ensemble guidance remains in good agreement for the large scale setup and evolution through much of the period. There are some smaller scale timing differences, particularly affecting the shortwave as it drops towards the Great Lakes, and then evolution of the deepening trough over the East. These differences, which could take into the short range to fully resolve, would impact frontal placement and QPF amounts as well. Regardless, the WPC forecast remained very close to continuity and was comprised of a blend of latest deterministic model guidance days 3-5, with increasing contributions from the ensemble means on days 6-7. ...Sensible Weather and Hazards... As the eastern part of a cold front continues to drop southward and then stall early next week in the Southeast/central Gulf Coast/Florida, it will provide a focus for anomalously high moisture to pool and lead to rain and thunderstorms chances continuing from the short range period. While rain totals are expected to gradually drop as the front dissipates, localized areas of flash flooding cannot be ruled out especially if multiple rounds of heavy rain affect the same areas. Farther north, shortwave energy and a frontal system or two are forecast to lead to rain and thunderstorms across the northern Plains and Upper Midwest Sunday-Monday. Although moisture and instability levels will be sufficient, the possibly quicker storm motions and the uncertainty in the details of the shortwaves/frontal placement preclude Slight Risk issuance in the WPC experimental Excessive Rainfall Outlook at this point. However, the Storm Prediction Center currently delineates parts of the Dakotas into much of Minnesota in a Slight Risk for severe weather. Rainfall activity should shift toward the Great Lakes region and then the Northeast Monday-Wednesday, with scattered storms also possible along the trailing cold front in the Ohio Valley and even back into central and then southern parts of the Plains and Mississippi Valley. Elsewhere, monsoonal moisture could persist even into next week with moist southwesterly flow/embedded shortwaves leading to mainly diurnally driven showers and storms over the Four Corners states. An upper level weakness near the central Gulf Coast early to mid next week could bring some locally heavy rainfall to coastal locations. The West Coast should be the most consistently dry area through the period. Very hot weather is expected to persist across the southern half of the Plains/Mississippi Valley underneath the strong upper ridge/high early next week, before finally some slight moderation around midweek. High temperatures near or exceeding 100F are expected, which is between 5 and 15 degrees above normal. Combined with the humidity, daily maximum heat indices 105-110F+ are likely at times across the southern Plains and Lower Mississippi Valley through early next week. The repeating days of high heat/humidity and lack of any appreciable nighttime relief (lows in the upper 70s to low 80s for some areas) will increase the potential for impacts from this prolonged heatwave to the more sensitive and vulnerable populations. Several daily record high temperatures are possible, particularly for warm lows but a few highs may be close to records in Texas. A briefer period of temperatures 10-20F above average is forecast for the central/northern Plains on Sunday before approaching closer to average as the workweek begins. As the upper ridge drifts westward, the West should see temperatures warming from slightly below normal to above normal (by 10+ degrees in the Northwest) as next week progresses. The East can expect slightly cooler than normal temperatures early in the week behind the cold front, before warming to near/just above normal. Santorelli/Tate 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