Extended Forecast Discussion NWS Weather Prediction Center College Park MD 241 PM EDT Mon Jul 18 2022 Valid 12Z Thu Jul 21 2022 - 12Z Mon Jul 25 2022 ...Dangerous heat to persist over the Central U.S. through the start of next week... ...Overview... A strong upper ridge centered over the Southwest/Four Corners region as of early Thursday may shift its emphasis somewhat eastward by the weekend, though with increasing uncertainty over exactly where ridging will be located. This ridge will keep hot and humid weather over the central/southern Plains for a majority of the period. Some southern locations could see readings approach or break daily records for highs and very warm nighttime lows. With somewhat less extreme anomalies, areas from the Tennessee/Ohio Valleys through Mid-Atlantic/New England will experience multiple hot days as well. The West should moderate after midweek with the approach/ejection of eastern Pacific upper trough energy. This energy and other features across southern Canada and the northern tier U.S. will flow around the ridge and feed into a broad northeastern U.S. mean trough, supporting one or more waves/frontal systems and episodes of showers and thunderstorms from the northern tier into the East. Monsoonal moisture over the Southwest/southern Rockies will promote daily chances of showers and storms, some of which could lead to flash flooding. Some increase of this activity will be possible during the weekend if the Four Corners ridge does indeed adjust eastward for a time. ...Guidance Evaluation/Predictability Assessment... The overall synoptic pattern of troughing along the northern tier states and ridging in the South during the medium range was captured well by the deterministics through day 4 and ensembles later in the period. A general model blend of the 00z EC/UK/CMC and 06z GFS suite were utilized to capture the incoming upper-level low in the Pacific Northwest. There were some differences in position and intensity of the upper trough as it moves across the Northwest on day 5, so ensembles were incorporated here. By days 6 & 7, a primarily ensemble mean spread was used to account for uncertainties posed by the deterministic guidance. ...Weather/Hazards Highlights... The most anomalous heat over the central U.S. will likely focus over the central Plains where the best potential exists for multiple days of highs 10-15F above normal. Some of the heat may also eventually drift into parts of the Tennessee Valley. Toward Sunday-Monday a cold front may suppress the heat over the north-central Plains. Typically hotter southern Plains locations will see less extreme anomalies but overall there will be a broad area with highs reaching or exceeding 100F for highs, while very warm lows in the upper 70s to low 80s will provide little nighttime relief. This heat wave will likely bring scattered records, most likely over the southern Plains to lower/mid MS Valley. 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 within a few degrees on either side of normal during through the period. The most likely scenario of an eastward shift of upper ridging after late this week would lead to an increase of moisture/rainfall next weekend and perhaps a bit of a westward shift in the overall moisture axis. However there is a lower probability potential for the Four Corners upper ridge to be more persistent, which would tend to maintain the existing late week pattern. The approach/ejection of Pacific trough energy should bring highs down to near normal levels over an increasing portion of the West by Friday-Saturday. A rebound of upper ridging over the Northwest may bring highs to 5-10F or so above normal over that region by Sunday-Monday. The fairly vigorous late week system over eastern Canada and its trailing front into the eastern U.S. may produce some locally heavy rainfall. There will likely be other areas of enhanced rainfall from the northern tier into the East during the rest of the period, but with much less confidence in specifics due to guidance difficulty in resolving the details within southern Canada/northern U.S. flow aloft, including ejecting Pacific energy that joins this stream. 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. The front reaching the East Coast by Friday could lead to a brief and slight dip in temperatures before it weakens during the weekend. Persistent moisture will allow for multiple episodes of showers/thunderstorms over the Southeast/Florida and central Gulf Coast region. Continues to expect near normal temperatures over those areas. Kebede/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, 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