Extended Forecast Discussion NWS Weather Prediction Center College Park MD 249 PM EDT Wed Aug 19 2020 Valid 12Z Sat Aug 22 2020 - 12Z Wed Aug 26 2020 ...Hot temperatures to continue for much of the West into next week... ...Overview and Weather/Hazard Highlights... A strong upper ridge centered over the Four Corners region should remain in place through the period. It will likely be strongest around Sun-Mon followed by modest erosion of its northern periphery as some energy ejects from the Northeast Pacific across the northern tier U.S./southern Canada. The ridge will maintain well above normal temperatures over many locations from the West into the Rockies and parts of the Plains. Best potential for record highs with readings up to 10-12F above normal will be this weekend from the Great Basin/Southwest into the southern High Plains. Expect morning lows to be somewhat more extreme Sat-Wed with broader coverage of plus 10-15F anomalies and potential daily record warm values over California and the Southwest/Great Basin. There should be isolated to scattered showers/storms over the West each day, aided by shortwaves flowing around the upper high center. The most prominent focus for rainfall will be over the Gulf of Mexico and adjacent areas. First there will be lingering moisture ahead of a dissipating stationary front associated with an east-central U.S. upper trough that will weaken after early Sat. The best moisture and highest rainfall totals should be over/near the northern Gulf with more modest moisture and generally lighter rain extending into the eastern states during the weekend ahead of the upper trough. Then two separate tropical features may enhance rainfall, one over parts of the western half of the Gulf/Gulf Coast and another that may affect Florida and portions of the eastern Gulf. Clouds and rain should lead to somewhat below normal highs over the Southeast and vicinity especially on Sat-Sun. Low amplitude upper flow across southern Canada and northern U.S. will support multiple waves/fronts across the northern states and episodes of showers and thunderstorms between the Northern Plains and Northeast. Most features will be fairly transient so rainfall totals should generally be on the moderate side, though locally more intense activity could be possible at times. Locations to the north of a front on a particular day may see below normal temperatures while above normal readings (up to plus 5-10F anomalies) are possible over the north-central latitudes that will tend to be in the warm sector ahead/south of the fronts. ...Tropical Features... The forecast is consistent for Hurricane Genevieve in the eastern Pacific as National Hurricane Center advisories show the system weakening while it tracks northwestward into colder waters. Flow around the Four Corners upper high may still bring a reflection of Genevieve's remaining shortwave energy into California but with little moisture remaining. The two features of interest in the Atlantic basin have fairly high uncertainty for specifics, more so the one that may affect areas over/near the western Gulf. This feature emerges from the Caribbean with guidance varying considerably over strength, timing, and track by next Mon-Wed. The spread reflects the sensitivity to the degree of development and where the feature is at a particular valid time relative to evolution of flow aloft. Meanwhile the system farther east originates from an elongated area of low pressure near 45-50W. The daily 17Z NHC/WPC tropical coordination reflects the most consistent signal in guidance as a whole with a track reaching just north of Cuba and then into the eastern Gulf of Mexico. However the full solution envelope remains broad, with tracks between the Gulf and Bahamas along with surface reflections ranging between a mere trough and a well-developed low. Please consult latest NHC products for further information. ...Guidance/Predictability Assessment... The latest forecast started with a blend of the 00Z operational models for this weekend and then transitioned to half models/half means by next Tue-Wed. The 00Z GFS/CMC and 06Z GEFS mean were closest in principle to continuity for the system that may track north of Cuba and into the eastern Gulf after the weekend. The blended solution with minor edits yielded a conservative solution for the western Gulf feature. For both systems the final issuance later today will reflect adjustments from 17Z NHC/WPC coordination. The low amplitude of northern tier flow aloft continues to provide challenges in resolving northern U.S.-southern Canada wave/front specifics. Over the past day there have been some convergent trends with energy ejecting from the northeastern Pacific--ensemble means starting to hint at some ejection and some operational runs backing off with shortwave amplitude. Now the GFS runs are the most amplified with northern tier energy though at least the 12Z run shows a flatter trend by day 7 Wed. Rausch/Fracasso Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml