Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 PM EDT Sun Jul 7 2024 Valid 12Z Wed Jul 10 2024 - 12Z Sun Jul 14 2024 ...Beryl's moisture and energy likely to spread heavy rain into parts of the Great Lakes/Northeast by midweek... ...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. With some continued spread for specifics, latest guidance is holding onto a progressive northeastward track Beryl's surface low with an overall evolution that would make the northeastern quadrant of the U.S. the primary area of concern for heavy rain and flash flooding Wednesday-Thursday. With a strengthening western Atlantic upper ridge helping to stall a front near the Eastern Seaboard later this week, that region should see additional thunderstorm chances into next weekend. ...Guidance/Predictability Assessment... The majority of dynamical guidance is finally settling into the faster northeastward progression of post-tropical Beryl as advertised earlier by the ICON model and machine learning (ML) guidance. Per the 15 UTC National Hurricane Center advisory, this would yield a track from southern Illinois early Wednesday through the central Great Lakes and into southeastern Canada by Thursday- Friday. There are lingering issues related to exact evolution of upper dynamics from Beryl and interacting energy within the larger scale upper trough incorporating Beryl. Specifically, somewhat deeper and more closed upper level energy for a period of time would yield a deeper/westward surface system versus an open upper trough favoring a weaker/eastward surface reflection. A greater number of 00Z ECMWF-initialized machine learning (ML) models side with the more closed evolution aloft and a western surface track that better fits the 15 UTC official track. Among latest/recent runs, the 00Z ECMWF/UKMET, 06Z GFS, and 12Z CMC cluster best among this scenario. Latest ICON runs share a similar evolution but still with faster timing. The 00Z CMC and 12Z GFS/UKMET are somewhat eastward. Beyond this aspect of the forecast, there is continued spread for exactly how this upper level energy ejects and specifics of upstream energy that may filter into the overall Great Lakes/Midwest mean trough. Regardless of the specifics, there is agreement that this trough should steadily weaken through early Saturday as strong Atlantic ridging (anchored by a 600+ dm high near 60W longitude by Friday-Saturday) builds into parts of the East. There is still a signal for some weak energy to approach the East Coast from the Atlantic on the western periphery of the core of strongest ridging with some potential influence on rainfall late in the week. By Sunday, consensus suggests that shallow cyclonic flow may expand into the Northeast while ridging persists over the South. Low predictability for specific details mid-late period would continue to favor a composite/mean approach to represent the larger scale pattern for this part of the forecast. Dynamical/ML guidance continues to agree fairly well for the eastward drift of the western U.S. ridge from California and Nevada into the Four Corners/Central Rockies region over the course of the period. This drift should allow for weak troughing to develop near the West Coast by next weekend. Around the top of the ridge, there is improved agreement for the upper low/trough reaching western Canada by early Friday, but increasing divergence thereafter. There is also spread for low- predictability shortwave details upstream. For now there is no well defined clustering for specifics. Resolution of these issues would improve confidence for surface front details over the far northern tier by next weekend. The first half of the updated forecast based on 00Z/06Z guidance primarily emphasized the 06Z GFS/00Z ECMWF/00Z UKMET to reflect the official track for post-tropical Beryl. The blend added in some 06Z GEFS/00Z ECens means for the latter time frames given the increase in detail uncertainty within a generally agreeable large scale pattern. ...Weather/Hazards Highlights... While guidance still shows meaningful differences for the evolution/track of post-tropical Beryl as the system most likely continues northeastward through the Great Lakes, continuity changes in the best clustering of guidance have at least become less pronounced than in previous cycles. Based on the models closest to the 15Z NHC track for Beryl, expect the flow of tropical moisture to bring highest precipitable water (PWAT) anomalies into the Lower Great Lakes and Northeast during the Wednesday-Wednesday night period covered by the Day 4 Excessive Rainfall Outlook. Some PWAT anomalies within this region will likely exceed the 90th percentile and west-east oriented fronts north/east of post- tropical Beryl may promote training. The general themes of the favored guidance cluster allowed for incorporating the two separate Slight Risk areas from continuity into a single broader Slight Risk. Ongoing spread in the guidance certainly leaves the door open for further changes though. By Day 5/Thursday, above normal moisture and a front lingering across the Eastern Seaboard could enhance thunderstorm development within a broad north-south corridor. Some guidance suggests sufficient moisture/instability for locally high rain rates as far south as the Southeast Coast/north-central Florida, so the prior Marginal Risk area has been extended south to include these regions. Within this broad risk area there are various antecedent ground conditions (such as drought over the Mid-Atlantic, wet conditions over parts of the Northeast). Lack of agreement for best heavy rain focus and relation to initial ground conditions preclude introduction of any Slight Risk area at this time, but the overall pattern supports the possibility once the details become better refined. Additional storms are possible along the East Coast 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. These risk areas in the Days 4-5 EROs remain close to continuity. 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 will remain above normal and the heat will expand into the northern/central Plains by late this week. Meanwhile, slightly below normal temperatures are possible Wednesday in parts of the Midwest 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. Rausch/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