Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Fri Jul 5 2024 Valid 12Z Mon Jul 08 2024 - 12Z Fri Jul 12 2024 ...Beryl likely to affect Texas early next week... ...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 may interact with Tropical Storm Beryl (forecast by the National Hurricane Center to strengthen back to hurricane status as it tracks into the western Gulf of Mexico this weekend). Beryl should bring a period of windy conditions and heavy rainfall to parts of Texas, with potential for northeastward progression of rainfall next week. For now the uncertainty in how Beryl interacts with the mean trough aloft is leading to lower than desired confidence regarding important details of the forecast. Meanwhile, hot and humid conditions will likely continue for much of the southern states and extending to the East Coast. ...Guidance/Predictability Assessment... Latest guidance is showing some significant trends for Beryl, with a northward adjustment as the system reaches the western Gulf Coast and then greater potential for northeastward recurvature thereafter. Upon reaching eastern Texas, the degree of interaction with the mean trough aloft (and shortwave details within the trough) would affect the track and timing of Beryl's surface reflection. The past couple ICON runs have been very progressive while CMC runs still seem to be catching up from being on the far left side of the envelope. 00Z machine learning (ML) models generally favored the recurvature scenario, between the slower 00Z ECMWF and faster 00Z/06Z GFS (12Z UKMET leaning somewhat faster as well). Eastward and then much faster trend of the new 12Z ECMWF highlights the forecast uncertainty. The updated manual forecast reflects this trend in principle while staying somewhat conservative with deterministic QPF given the lower than average confidence for the time being. Consult National Hurricane Center products for the latest information regarding Beryl. As for other aspects of the forecast, there is moderate spread among the dynamical/ML guidance for a trough with embedded low tracking from the northeastern 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. Meanwhile some differences arise for upper trough details from eastern Canada into the central U.S. by late next week. Some GFS runs and the new 12Z ECMWF show weaker troughing over the Plains/Mississippi Valley by next Friday versus most other guidance, while guidance is split over the depth of troughing over southeastern Canada by then. The latter issue will affect a surface front likely to be near the East Coast late next week. There is also some indication that strong Atlantic upper ridging may build westward somewhat and serve to stall the East Coast front. With adjustments to account for the official track of Beryl, the updated forecast started with an operational model composite early in the period (more ECMWF/GFS emphasis relative to the UKMET/CMC) and then transitioned toward half GEFS/ECens input by the end of the period next Friday. ...Weather/Hazards Highlights... Ongoing model trends for Beryl temper confidence in exact details of magnitude and axis of heaviest rainfall, with sensitivity to both track and speed. Current consensus would suggest at least several inches of rainfall in South/East Texas during the first half of next week with potential for southwesterly flow aloft to spread some degree of enhanced rainfall northeastward from Texas after midweek. The Days 4-5 Excessive Rainfall Outlooks for Monday and Tuesday reflect Slight Risk areas where the relatively higher potential for heavy rainfall exists. Reflecting latest model trends, the Day 4 Slight Risk extends a little farther northeastward versus continuity while the Day 5 Slight Risk reflects a more pronounced northeastward extent. Monday's Slight Risk continues to be a higher-end Slight before increasing divergence in guidance for Beryl's track and especially timing. A nearby front will also provide a focus for potentially significant convection/heavy rainfall. There is certainly potential for upgrades to Moderate Risks in future updates if placement of higher totals comes into better agreement. This front and moisture could linger into and beyond midweek, but with steadily decreasing confidence in the specifics. Scattered thunderstorms are likely across the Gulf Coast states through much of next week given a moist and unstable airmass in place. Also, early in the week parts of the Southeast will likely see lingering anomalous moisture with sufficient instability to support some localized convection with high rainfall rates-- supporting addition of a Marginal Risk area on Day 4 given some carryover of the pattern from the Day 3 time frame. Farther north, the upper trough pushing one or more cold fronts through the north-central to northeastern U.S. also will lead to some storms, with the bulk of the activity moving east with time from the Midwest/Great Lakes Monday toward the eastern U.S. Tuesday- Thursday. Some focus of the convective rain and sufficient instability for heavy rain rates in much of New York and Pennsylvania have prompted a Marginal Risk in the ERO for Day 5/Tuesday. Meanwhile, by Tuesday and beyond, some moisture may feed into the Four Corners states in a monsoonal pattern, and have a Marginal Risk in place for Day 5/Tuesday 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 records not out of the question. The prolonged nature of the heat wave and record warm overnight temperatures will increase heat stress. Meanwhile, warmer than average temperatures in the Northeast early in the week should moderate by midweek. The Southeast should see 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 with below average temperatures given the clouds and rain chances. 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