Extended Forecast Discussion NWS Weather Prediction Center College Park MD 311 AM EDT Sat Jul 6 2024 Valid 12Z Tue Jul 09 2024 - 12Z Sat Jul 13 2024 ...Beryl will spread heavy rainfall across the south-central U.S. as it transitions to post-tropical... ...Dangerous heat wave in the West persists into next week... ...Overview... The most prominent large scale features during the period will be a persistent upper ridge over the West supporting a dangerous and likely record-setting heat wave across much of the region into next week, and a positively tilted Plains/Mississippi Valley/Great Lakes mean trough whose southern periphery will interact with Beryl as it transitions to post-tropical. Heavy rain is likely to spread from parts of Texas into the Lower Mississippi Valley and possibly northeastward into midweek as Beryl's low pressure and moisture interacts with a frontal boundary. Meanwhile, seasonably hot and humid conditions along with scattered thunderstorms at times should persist across the Southeast to East Coast. ...Guidance/Predictability Assessment... Model guidance continues to indicate that Beryl will track faster and farther northeastward compared to model runs from a day or two ago. Confidence in this trend is rising, though there is still some spread in the timing. The 12Z ECMWF was faster than consensus while the 12Z CMC was slower. GFS runs were close to the NHC 03Z track for Beryl but its QPF pattern was not ideal. The 12Z UKMET was an okay proxy for QPF but a bit northwest of the preferred track. The newer 00Z ECMWF and CMC fortunately converged toward each other with the timing/track of Beryl's low and QPF. Beryl's track being faster allows for it to get picked up by the northern stream troughing and recurve as it merges with a surface front. This northern stream trough shows reasonably good agreement in models as its positively tilted axis stretches across the Great Lakes into the Plains/Mississippi Valley into midweek and beyond, gradually weakening late week with fairly typical spread. This spread does affect the positioning of an East Coast surface front. Meanwhile, models continue to show good agreement on an upper high drifting from the Desert Southwest into the Four Corners as the week progresses, causing the prolonged heat wave. The most uncertain aspect of the forecast continues to be the flow pattern farther north across the northeast Pacific into western Canada mid- late week with no dominant clustering for the time being. This feature may help to push a frontal system into the far northwestern U.S. by late next week. A blended/intermediate solution looks like a good starting point here. The WPC forecast used a blend of deterministic models favoring the 12Z ECMWF early in the period, transitioning toward a half models/half ensemble means blend by the end of the period. ...Weather/Hazards Highlights... By the start of the medium range period early Tuesday, Beryl is forecast to be tracking inland in east Texas as a tropical storm, and then looks to phase with a frontal system to its north by midweek. These features should lead to the potential for heavy rain causing flash flooding concerns in eastern Texas and the Lower Mississippi Valley Tuesday and Tuesday night, and a Slight Risk remains in place in the Day 4/Tuesday ERO. The persistent model trend of Beryl being faster necessitates an expansion of the Slight farther northeast compared to the previous issuance, and trimming off on the southern side in south Texas. As Beryl's low gets strung along a frontal boundary into Wednesday, the focus for the placement of heavy rainfall is less clear. However the ingredients for isolated flash flooding like above normal moisture are in place across the south-central U.S. and northeastward into the Ohio/Tennessee Valleys and much of the Eastern Seaboard, so a broad Marginal Risk is in place for Day 5/Wednesday for these areas. A Slight Risk upgrade may be necessary in future cycles if the placement of higher totals comes into better agreement. This appears most likely in the Ohio Valley. Meanwhile farther north, the upper trough pushing one or more cold fronts across the northeastern U.S. will also lead to some thunderstorm chances. Some focus of the convective rain ahead of the front(s) and sufficient instability for heavy rain rates in the northern Mid-Atlantic to Northeast have prompted a Marginal Risk in the ERO for Day 4/Tuesday. Stalling fronts and persistent moist conditions will promote scattered storms continuing into later week across the Southeast/Carolinas and into the Mid-Atlantic. Farther west, some moisture may feed into the Four Corners states in a monsoonal pattern. Marginal Risks are in place for Tuesday and Wednesday mainly for New Mexico--especially considering sensitivities due to burn scars and areas that have seen ample rainfall recently. The West will continue to see a major to extreme and long-lived heat wave into next week. Highs exceeding 110F should be widespread in the Desert Southwest, with typically hotter locations exceeding 120F. Farther north, highs into the 100s are forecast into Oregon and Washington and east into the Intermountain West, as temperatures soar 10-20F above normal with locally higher anomalies. Numerous daily records are likely to be broken during this heat wave, with monthly/all-time records not out of the question. The prolonged nature of the heat wave and record warm overnight temperatures will increase heat stress. The Pacific Northwest looks to moderate closer to normal later week with possible troughing aloft, but interior areas and expanding into the north-central U.S. will be above normal. Meanwhile, warmer than average temperatures in the Northeast Tuesday should moderate by midweek. The Southeast can expect near normal heat for this time of year-- which is still hot and humid. The south-central U.S. should see some minor heat relief through Thursday or so with below average temperatures given the clouds and rain chances. 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 forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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