Extended Forecast Discussion NWS Weather Prediction Center College Park MD 333 AM EDT Sun Jul 7 2024 Valid 12Z Wed Jul 10 2024 - 12Z Sun Jul 14 2024 ...Beryl's moisture and energy will spread heavy rain into the Ohio Valley/Great Lakes to Northeast by midweek, faster than previously forecast... ...Dangerous heat wave in the West persists through the 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 through the week, and a positively tilted Mississippi Valley/Great Lakes mean trough in part comprised of energy from Beryl, which will be post-tropical by midweek. Guidance continues to track faster/farther northeast with Beryl's low, making the northeastern quadrant of the U.S. the primary area of concern for heavy rain and flash flooding Wednesday-Thursday. A stalling front near the Eastern Seaboard could promote additional thunderstorm chances there into next weekend. ...Guidance/Predictability Assessment... Model guidance has certainly struggled over the past several days with the timing and track of Beryl even/especially as it becomes post-tropical interacting and phasing with the northern stream. Overall the trend has been for a faster/farther northeast track of the low. In terms of the 12Z/18Z model cycle, the 12Z CMC, UKMET, and GFS were slow compared to the faster trend of the 12Z ECMWF, and then the 18Z GFS made a switch to an even faster/northeast position. In terms of AI/ML models, all of them were faster than the 12Z ECMWF even though it was on the faster side of the operational models. The ICON model has also been maintaining a fast track. So the early part of the WPC forecast, to support a faster track for Beryl (but also worked well for other aspects of the forecast), was comprised of a 12Z ECMWF/18Z GFS blend. This seems to be a good way to go, as newer 00Z guidance maintains this northeast trend, including the CMC and UKMET with a jump northeast. There is some spread for the upper trough that lingers in the Great Lakes/Northeast into late week/weekend. In varying ways, most guidance suggests that Great Lakes into Plains/Mississippi Valley upper troughing should persist into Sunday but with a gradual weakening trend. This will occur as strong Atlantic ridging (anchored by a 600+ dm high over 50-65W longitude by Friday- Saturday) builds into parts of the East. A modest upper weakness (with predictability low enough not to reflect yet in a deterministic forecast by Saturday) could approach the East Coast from the Atlantic on the western periphery of the ridge. A composite of model/ensemble guidance appears reasonable for aforementioned troughing and the retrograding Atlantic ridge. Aside from typical detail differences, dynamical/ML guidance shows good agreement with eastward drift of the western U.S. ridge from California/Nevada into the Four Corners region over the course of the period. However around the top of the ridge there has been a fair amount of spread and run-to-run variability for Northeast Pacific into western Canada dynamics, though recent guidance has shown some convergence in solutions. A model/ensemble mean blend worked to temper individual differences there as well. ...Weather/Hazards Highlights... With Beryl trending much faster than previous forecasts indicated, by midweek the tropical moisture and the post-tropical frontal low is currently forecast to be pushing into the Ohio Valley and Great Lakes region and streaming east into the Northeast. For the Day 4/Wednesday ERO, have introduced a Slight Risk for parts of Indiana/Michigan near Post-Tropical Cyclone Beryl, and another into the Northeast where precipitable water values will likely be above the 90th percentile and west-east oriented fronts in the vicinity may promote training. This is a significant change from the previous ERO forecast, but necessary due to the model trends. By Day 5/Thursday, above normal moisture and a front lingering across the Eastern Seaboard could allow for more thunderstorms to develop, and a Marginal Risk is delineated for potential for flash flooding. Additional storms are possible there Friday and Saturday. Farther west, some moisture may feed into the Four Corners states in a monsoonal pattern. Marginal Risks are in place for Wednesday and Thursday 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 through this 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, slightly below normal temperatures are possible Wednesday in parts of the central U.S. with the rain/clouds from Beryl. These areas should moderate to near normal, with near average temperatures for this time of year likely across the Southeast as well--which is still hot and humid. Near to a bit above average max/min temperatures are forecast for the Northeast. Tate/Rausch 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