Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM 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 before finally moderating, while 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. Initially progressive systems are forecast to slide along the northern periphery of the ridge across the northern tier states before energy consolidates into a deeper upper low moving across south-central and southeastern Canada through the workweek. This energy/flow pattern as well as a surface front draped from the Mid-Atlantic to the central Plains lifting northward ahead of the next cold front should help focus heavy rain potential over parts of the central/eastern U.S., particularly the Ohio Valley/Central Appalachians through around midweek and back into the Middle/Lower Mississippi and Tennessee Valleys as the second front settles southward. This will also support a moderating temperature trend east of the Rockies. Meanwhile 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) that should last into next weekend. Additionally, a period of enhanced monsoonal moisture from the short to medium range period 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, and as another more consolidated trough (stemming from a southern Canada upper low) digs across the Northern Plains/Great Lakes around midweek and into the Midwest/Northeast next Friday-Saturday. Within the northern stream jet there are some differences in guidance with the smaller scale details, but the differences were well within reason for a medium range forecast, and with no particular outliers in the 00/06Z model cycle. Thus the WPC forecast was based on a blend of the deterministic guidance through day 5, with some increasing proportion of the GEFS and EC ensemble means by day 6-7 to smooth out the differences. This maintains good continuity with the previous WPC forecast, with only typical small shifts in fronts and QPF based on the most recent guidance. ...Weather/Hazards Highlights... The south-central U.S. has seen prolonged excessive heat in recent weeks, and this is forecast to last into at least midweek for the southern half of the Plains and Mississippi Valley. Widespread temperatures near or above 100 degrees (with higher heat indices) will continue the dangerous heatwave in this region. However, 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 westward through the northern/central Plains. Initially, the highest rainfall totals seem favored over/near the Ohio Valley into the central/southern Appalachians, where a Slight Risk was maintained and expanded somewhat on the day 4 experimental ERO based on latest forecast trends. Then the second, stronger, front should produce northern Plains convection that extends south/east with time, potentially repeating activity over an already soggy Ohio Valley/central Appalachians region, leading to additional chances of flash flooding. Convection should sink southward with the front, reaching the southern half of the Mississippi Valley and into the Tennessee Valley late week. 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. A Slight Risk of excessive rainfall was introduced for day 4 (Tuesday) as that anomalous moisture stays put over likely wet soil from activity in the short range period. Some of this moisture is expected to interact with the central Plains front to enhance rainfall totals farther north and east into New Mexico and Colorado midweek, which could lead to flash flooding there. 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. Tate/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