Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Sat Jul 08 2023 Valid 12Z Tue Jul 11 2023 - 12Z Sat Jul 15 2023 ...Heat expected to rebuild from the Southwest to the Gulf Coast next week... ...Heavy rain concerns likely to focus over parts of the Midwest and Mid-Mississippi Valley... ...Overview... The upper-level pattern over the CONUS next week remains rather unchanged as a deep upper low remains entrenched over Hudson Bay, and upper ridging expands across the southern tier states. Multiple waves of energy will rotate around the southern periphery of the low and drive rounds of showers and storms that could result in areas of heavy rainfall and flooding across the Midwest and Northeast. Underneath the ridge, hazardous heat will build over the Southwest and Texas and expand eastward to the Gulf Coast region through next week. Hazardous heat will likely persist into the week two time frame as well, per the latest forecast from the Climate Prediction Center. ...Guidance Evaluation/Predictability Assessment... Guidance is in reasonable agreement regarding the broad scale evolution of the synoptic pattern during the medium range period. A general model blend consisting of the 00z EC/CMC/UKMET and 06z GFS was used through day 4. The GFS was given less weighting on day 3 due to to an inconsistency between it and the 00z guidance with respect to the shortwave trough moving through the Northeast. The 00z ECE and 06z GEFS were introduced on day 5 while the Canadian and UKMET were removed due to failure to identify a southern stream ridge and over amplification of shortwave energy over the Great Lakes, respectively. The 00z CMCE was introduced on day 6 and the ensemble guidance made up much of the blend through the remainder of the period. ...Weather/Hazards Highlights... A front settling from the central Plains into the Midwest should provide the best focus for daily rounds of showers and storms through much of the medium range period, with areas of heavy rainfall increasingly likely in some areas. For the Day 4 Excessive Rainfall Outlook, there was enough model agreement for the addition of a slight risk area from eastern South Dakota into far northwest Iowa given high moisture and instability and that some of this region has seen above normal rainfall over the past week or two. A marginal risk surrounds this area into the Upper Midwest as well as back into the northern High Plains. By Day 5/Wednesday, the heavy rainfall axis should shift east with the boundary from the Mid-Mississippi Valley into the Upper Great Lakes. It seems likely there will be heavy to excessive rainfall somewhere within this region, but there is still a considerable amount of uncertainty on where. For this reason, the day 5 ERO at this point only depicts a broad marginal risk, but future upgrades to a slight risk are possible as models come into better focus. Elsewhere, showers and storms will continue across parts of the Southeast and central Gulf Coast into Wednesday near a lingering frontal boundary. Weak low pressure lifting along the Northeast coast will also continue to bring wrap around showers across parts of the Northeast. A slight risk area was added with this afternoon's update over portions of northern/central Maine on day 4 as well, due to sensitive surfaces caused by the previous day's heavy rainfall threat. Additional rainfall looks to impact this region and south into the Mid-Atlantic later in the week as well. Hazardous heat is expected to return and expand across the southern tier through at least next week (and likely extending beyond per latest CPC forecasts) as the upper ridge strengthens over the South. The greatest high temperature anomalies (of 10-15F above average) are forecast under the center of the upper high over West Texas and New Mexico, with a broadening area of above normal temperatures elsewhere. Increasing humidity will result in oppressive heat indices possibly exceeding 110F from the eastern half of Texas to the Gulf Coast, and hazardously high heat indices could expand to the Florida peninsula as well late next week. Humidity will be naturally lower back into the Southwest, though air temperatures could still reach 110-115F in some places. Little relief is expected in these areas overnight with anomalously warm nighttime lows in the forecast. Above normal temperatures will also expand into the West Coast states late next week. Elsewhere, a cold front dropping south from Canada should bring temperatures down to 5-10F below average over parts of the northern and central Plains, while the Southeast and up the East Coast should stay near normal for this time of the year. Kebede/Santorelli 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