Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Fri Jul 28 2023 Valid 12Z Mon Jul 31 2023 - 12Z Fri Aug 04 2023 ...Hot temperatures and high heat indices are likely across the south-central Plains and Mississippi Valley into the Southeast next week... ...Overview... It remains evident that the persistent upper high that has stayed atop the southwest/south-central U.S. for weeks now is finally forecast to drift eastward next week, finally bringing temperatures in the Desert Southwest closer to normal (though still hot). Ridging stretching north from the upper high will also promote above normal temperatures across the central Plains to Mid-Mississippi Valley with the Southeast also likely to warm above normal, with high heat indices. A "ring of fire" type of pattern is likely in the precipitation forecast, as monsoonal moisture leads to diurnally driven convection in the Four Corners states and vicinity, shortwaves push through northwest flow and spark strong to severe thunderstorms in the north-central U.S., and a defined cold front pressing unusually far south before stalling helps to focus rain and storms at least the southern half of the Eastern Seaboard. There is a risk of heavy rainfall and flash flooding in these areas where high rain rates occur and where storms train/occur over the same areas. ...Guidance Evaluation/Predictability Assessment... The WPC medium range product suite was primarily derived from a composite blend of reasonably clustered mid-larger scale guidance from the 18 UTC GFS/GEFS and 12 UTC ECMWF/Canadian/UKMET along with the generally compatible 01 UTC National Blend of Models. This solution maintains decent product continuity in a pattern with above average overall predictability. A composite of newer 00 UTC guidance offers a similar forecast basis. While the larger scale flow/feature/guidance signal for the convective pattern remains decent for mid-summer, there is, as usual, lingering uncertainties through these medium range time scales with the more local focus of thunderstorms and associated heavy downpours impacts. ...Weather/Hazards Highlights... Shortwave energy in northwest flow aloft from the north-central U.S. to the eastern U.S. will carry showers and thunderstorms early to mid-next week. A lead cold front should push unseasonably far south to offer a more defined than normal summertime convective focus over the Southeast. A Marginal Risk has been drawn up in the Day 4/5 EROs for portions of Georgia and Florida as there could be high rain rates possibly causing excessive rainfall given stalling moisture pooling/instability focus and upper support. The combination of an additional frontal passage as well as the lingering/wavy southern front is then likely to favor periodic activity through mid-later next week. Meanwhile, the north-central U.S. can also expect scattered storms as shortwaves track through the region and moisture increases. A heavy rain/flash flooding threat will likely be tied to the potential for organized convective systems in the northwesterly flow. Day to day positions of heavy rain and MCSs are uncertain at this point, but the pattern is there. Marginal Risks have been included on both Days 4 and 5 to cover this potential, with eventual more concentrated Slight Risk areas possible. The Four Corners states and into Wyoming are likely to see diurnally driven convection each day as monsoonal moisture comes in, and as the upper high shifts eastward with time this may increase moist southerly flow and allow for additional shortwave energy to work into the region. There is also a notable trend of QPF becoming more widespread and locally heavier as the week progresses, and Marginal Risks are in place and become broader with time. The latest risk areas attempt to reflect channels with best potential moisture and instability. By early next week, the persistent upper high that has been centered over the southwest/south-central U.S. will start drifting eastward, allowing for high temperatures in the Desert Southwest to finally ease to near normal. Highs should still be over 100F in many areas but at least there should be minor relief compared to the past few weeks. Meanwhile with the core of the upper high/ridge tracking east, temperatures are likely to increase to above normal. The most persistent/greatest anomalies should be in the central Plains to the Mid-Mississippi Valley, where above normal temperatures by 5 to 15 degrees are likely as actual temperatures near or exceed 100F. The southern Plains to Lower Mississippi Valley and Southeast may see slightly lower anomalies of 5-10F above normal, but the heat combined with high dewpoints will lead to heat indices soaring above 105F, even above 110-115F in some areas. Record hot highs and warm minimum temperatures are possible in these regions. 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 forecast, 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