Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sat Jul 16 2022 Valid 12Z Tue Jul 19 2022 - 12Z Sat Jul 23 2022 ...Dangerous heat to persist over much of the Western and especially Central U.S. next week... ...Overview... Hot temperatures will prevail across a large area of the central/western U.S. underneath a strong upper ridge centered over the Four Corners region. Near or record highs will be possible at times, and very warm morning lows may also challenge daily records over some areas. Toward the end of next week and the weekend a potential eastward shift in the upper ridge and arrival of a weak Pacific trough to the West Coast may bring western U.S. high temperatures closer to normal. Flow around the ridge will carry shortwaves that will help to reinforce the long term mean trough over the northeastern U.S. and produce episodes of showers and thunderstorms from the northern tier into the East. For the Southwest U.S. into the Rockies, some monsoonal moisture under the ridge will provide daily chances of showers and storms, some of which could lead to flash flooding. ...Guidance Evaluation/Predictability Assessment... In principle, latest guidance is most agreeable and consistent with the Four Corners upper ridge through about Thursday along with the idea of a compact upper low tracking east along the U.S.-Canadian border, with the overall shortwave feeding into the eastern North America mean trough. Guidance is still shuffling around with the exact timing and track of the upper low/associated low pressure and the 12Z ECMWF most notably strays a bit faster than consensus after early Wednesday (00Z ECMWF has trended slower). Other aspects of the forecast show varying degrees of spread and variability. A shortwave progressing along from western Canada may bring a front into the northern tier and potentially interact with the leading system earlier than previously expected. Meanwhile, models have been all over the place for potential ejection of an initial western Pacific upper low whose energy may play a role in the forecast around the northern periphery of the ridge. On the extremes, ECMWF runs have been quite fast (00Z ECMWF finally trending slower) and the 12Z CMC kept it over the Pacific through the end of the period. The new 00Z CMC has adjusted closer to the intermediate GFS/UKMET. Prefer a conservative approach for depicting this feature until better agreement emerges. By the end of the week, guidance diverges for where the best upper ridge emphasis will be. Current preference is closest to the intermediate 12Z ECMWF and latest GEFS/ECMWF mean runs, between the farther west 12Z CMC and farther east GFS. Also of note, by days 5-7 Thursday-Saturday the new 00Z GFS strays increasingly out of phase with other model/ensemble mean guidance from the North Pacific/Alaska into western Canada and northwestern U.S. Based on guidance available through the 18Z cycle, the updated forecast incorporated a composite of 12Z/18Z operational models for about the first half of the period and then added increasing weight of the 18Z GEFS/12Z ECMWF means so that their total weight reached 50 percent by the end of the period. The resulting forecast yielded good continuity overall with only typical run-to-run detail/timing adjustments. ...Weather/Hazards Highlights... The central Plains and vicinity should see the greatest temperature anomalies during the Tuesday-Saturday period, with each day likely to feature some highs 10-15F above normal. This region will be within a broader area of triple-digit highs expected to persist over much of the southern two-thirds of the Plains. In less extreme fashion, some of the heat may reach the northern Plains/Upper Midwest at times. Some daily records are possible for highs while very warm morning lows could also challenge records especially around Wednesday-Thursday. Over the West, monsoonal moisture and associated diurnally favored showers/storms with locally heavy rainfall may keep parts of the Four Corners/Great Basin region close to normal for highs through the period. Other parts of the West inland from the Pacific Coast should start the period up to 5-10F above normal for highs but then decline more toward normal as an upper low/shortwave eject from the Pacific and the Four Corners upper high eventually shifts eastward. Locally heavy rainfall will be possible with a fairly vigorous system forecast to track from the northern Plains through the Great Lakes and eastern Canada/Northeast U.S. Tuesday onward. Uncertain specifics of energy ejecting from the Pacific may play a role in convective details along a trailing front that may settle into the far northern tier late week into the weekend. The Mid-Atlantic and Northeast will be on the very warm to hot side, with some locations possibly seeing more consecutive days of plus 5-10F anomalies for highs than previously experienced so far this summer. Persistent moisture will allow for multiple episodes of showers/thunderstorms over the Southeast/Florida and central Gulf Coast region. Temperatures should be near normal over those areas. Rausch/Taylor 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, experimental excessive rainfall outlook, 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/#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