Extended Forecast Discussion NWS Weather Prediction Center College Park MD 248 AM EDT Fri Jul 07 2023 Valid 12Z Mon Jul 10 2023 - 12Z Fri Jul 14 2023 ...Heat expected to rebuild from the Southwest to the central Gulf Coast into next week... ...Heavy rain concerns likely to focus over portions of the Gulf Coast and the Northeast on Monday, and back into the Midwest by mid-week... ...Overview... Most of the guidance in the medium range period continues to show the large scale flow settling into a fairly persistent pattern through next week. A deep upper low anchored near Hudson Bay looks to send waves of energy across the Midwest into the Northeast to provide a focus for multiple episodes of showers and thunderstorms with some areas of heavy rainfall possible. Meanwhile, an upper level ridge will expand hazardous heat from the Southwest U.S. into the Southern Plains and the central Gulf Coast region, likely persisting into the week two time frame per the latest forecasts from the Climate Prediction Center. ...Guidance Evaluation/Predictability Assessment... Models show very good agreement on the overall large scale pattern across the CONUS through next week. As is typical for these time frames, there remains plenty of uncertainties in the details regarding a couple of shortwaves moving through mean troughing from the Midwest into the Northeast, which has implications for surface features and sensible weather. This is related to rather significant uncertainties in the placement of the parent upper low near Hudson Bay later next week. The GFS (including the new 00z run) is notably the farthest north, although the latest 00z CMC is the greatest outlier bringing the upper low well to the south and east of the consensus. The ensemble means seem to support a solution farther north, closest to that of the GFS and ECMWF. The WPC forecast for tonight blended the deterministic solutions for the first half of the period, trending towards the ensemble means with the GFS/ECMWF for the latter half of the week. ...Weather/Hazards Highlights... A surface front draped across the Southern U.S. should help focus areas of heavy rainfall early in the week, particularly near the central Gulf Coast, where a slight risk is highlighted on the Day 4/Monday Excessive Rainfall Outlook along with a Marginal Risk on Day 5/Tuesday. Guidance continues to trend south with the heaviest rainfall and this is reflected in this latest update. There are also signals for a possible band of confection extending back northwest into the central Plains within an axis of favorable moisture and instability and to the north of the western edge of the front which should lift back north as a warm front. Maintained the marginal risk for this region on Day 4 as there is still a fair bit of uncertainty in the specifics of where the best heavy rainfall will set up. A weak surface low lifting along the Northeast Coast should focus rainfall to the north of it across northern New England/Maine and a marginal risk was maintained on Monday's outlook and continued into the Tuesday as well. Elsewhere, a cold front sagging south across the Northern U.S./Midwest should also focus showers and storms Tuesday and beyond. The new day 5/Tuesday Excessive Rainfall Outlook highlights a marginal risk along this boundary, with potential for an upgrade to a slight eventually especially if heavy rain falls within a region from southeast Nebraska into Illinois which has seen above normal precipitation as of late. Enough uncertainty still to preclude that inclusion for now. 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 and drifts slightly to the west. The greatest high temperature anomalies (of 10-15F above average) should be near the upper high center of western Texas and into New Mexico, with a broadening area of above normal temperatures elsewhere. The oppressive humidity leading to maximum heat indices reaching 110F or greater across southern/eastern Texas into the Lower Mississippi Valley with little relief overnight will result in another period of hazardous to excessive heat across this region, with some records for daytime highs and warm overnight lows possible as well. Humidity will be naturally lower back into the Southwest, though air temperatures could still reach 110-115F in some places. Above normal temperatures will also expand into the West Coast states as well later next week. Elsewhere, a cold front dropping south from Canada should bring temperatures down to 5-10F below average over the northern to central Plains next Wednesday-Friday. The Southeast and up the East Coast may see slightly cooler than average temperatures on Monday, moderating back to near normal Tuesday and beyond. Santorelli 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