Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sat Jul 23 2022 Valid 12Z Tue Jul 26 2022 - 12Z Sat Jul 30 2022 ...Dangerous heat wave persists over the south-central U.S. into midweek as heat also builds across the Northwest next week... ...Overview... A west-east oriented ridge will persist across the southern tier of the U.S. through much of next week, as progressive systems slide along the northern periphery of the ridge across the northern tier states. A strong ridge over the northeastern Pacific will shift inland across the West Coast, establishing a multi-day period of hot weather over the Northwest (with highs looking to reach 15-20F above normal) which should last into next weekend. An initial surface front draped from the Mid-Atlantic to the central Plains will become quasi-stationary early next week before eventually lifting north as a warm front ahead of the next cold front approaching around Thursday which may again settle across parts of the mid-South by next weekend. These boundaries should help to focus heavy rain potential over parts of the central/eastern U.S. and support a moderating temperature trend east of the Rockies. A period of enhanced monsoonal moisture from Tuesday onward will promote daily risks of locally heavy showers and storms that may produce instances of flash flooding in parts of the Southwest. ...Guidance Evaluation/Predictability Assessment... The latest model and ensemble guidance remains agreeable with the large scale pattern showing expansive and persistent ridging from the Northwest to the Southern half of the U.S., with an initial shortwave shifting off the East Coast on Tuesday, as another trough digs across the Northern Plains/Great Lakes and into the Midwest/Northeast next Friday-Saturday. Its within these shortwaves where the guidance differs on some of the smaller scale details. Larger differences come into play by day 6-7 concerning a closed low near/over Hudson Bay, and additional energy dropping down the west side of the trough into central Canada and possibly the far northern U.S. tier next weekend. The CMC seems to be an outlier in showing a second closed low into central Canada, with weaker troughing into the Northeast next Saturday. The ensembles and ECMWF and GFS suggest a much weaker secondary wave with more amplified troughing across the Northeast. As such, the CMC was excluded from the model blend beyond day 5. The WPC forecast for tonight used a composite blend of the latest deterministic runs for days 3-5, amidst good model agreement. After this, the ECMWF and GFS were blended with the ensemble means to help mitigate some of the smaller scale differences. This maintains good continuity with the previous WPC forecast. ...Weather/Hazards Highlights... The main weather hazard will be the prolonged excessive heat across especially the southern half of the Plains and Mississippi Valley into at least midweek. Widespread temperatures near or above 100 degrees (with higher heat indices) will continue the dangerous heatwave in this region. The next front that reaches the northern Plains early next week looks to have a stronger southward push with more upper-level support, bringing moderately below normal highs to the northern-central Plains Tuesday onward, with finally some moderating temperatures back towards normal for the southern Plains as well for the latter half of the week. Meanwhile, a lingering quasi-stationary front through the Mid-Atlantic and Tennessee Valley and points westward, will focus daily rounds of showers and thunderstorms along it across a good portion of the Mid-Atlantic/Midwest, and northern/central Plains. Initially, the highest rainfall totals seem favored over/near the Ohio Valley, where a slight risk was maintained on the day 4 experimental ERO across eastern Kentucky/Tennessee and into West Virginia and far western Virginia. The second, stronger, front should produce northern Plains convection that extends south/east with time, potentially repeating activity over an already soggy Ohio Valley. Expect periods of showers and thunderstorms over portions of Florida and the Gulf Coast as well as an area of enhanced moisture passes through from east to west. Over the West, persistent monsoonal moisture and various shortwave impulses will support diurnally favored showers/storms with some locally heavy rainfall over the Four Corners/Great Basin region through next week. Potential still exists for some of this moisture to eventually interact with central Plains front to enhance rainfall totals farther north and east into New Mexico and Colorado. Meanwhile, upper ridging that builds over the Northwest next week will bring multiple days of hot weather, with some locations likely to see highs reach up to 10-20F above normal. This equates to highs in the low to mid 100s for the Columbia Basin, and 90s are expected to reach as far west as Portland and Seattle. Some daily records for highs/warm lows will be possible across interior portions of the Northwest. Santorelli 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