Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sun Jul 24 2022 Valid 12Z Wed Jul 27 2022 - 12Z Sun Jul 31 2022 ...Dangerous heat wave over the south-central U.S. to moderate some by midweek, while heat also builds across the Northwest into next weekend... ...Heavy to excessive rainfall likely in parts of the central/southern Rockies as well as the Tennessee Valley and central Appalachians... ...Overview... A west-east oriented ridge will persist across the southern and western U.S. through next weekend as somewhat amplified troughing slides across the Midwest/Ohio Valley and into the Northeast. This energy/flow pattern as well as a surface front settling into the East-Central U.S. should finally bring some modest relief to the heat across the south-central Plains with excessive heat across the Northwest continuing into next weekend. The potential for a multi-day period of heavy to excessive rainfall is increasing in places along this boundary from especially the central Appalachians into the Tennessee/lower Ohio Valleys. Additionally, enhanced monsoonal moisture from the short to medium range period will continue to promote daily risks of locally heavy showers and storms that may produce instances of flash flooding in parts of the Southwest and southern/central Rockies. ...Guidance Evaluation/Predictability Assessment... On the large scale, the latest model and ensemble guidance remains in agreement with the overall pattern showing expansive and persistent ridging from the Northwest to the southern half of the U.S., with a more consolidated trough (stemming from a southern Canada upper low) digging across the Upper Midwest/Great Lakes around midweek and into the Northeast by next Friday-Saturday. Within this northern stream energy there are some differences in guidance with the smaller scale details, with most differences well within reason for a medium range forecast. The pattern across the northern tier becomes a little more messy and uncertain by days 6-7, mostly related to additional shortwave energy dropping into central Canada behind the departing larger upper low earlier in the period, and also addiitonal weak energy entering the Pacific Northwest. Given good agreement, the WPC forecast was based on a blend of the deterministic guidance through day 5, through transitioned to move weighting on the ensemble means by 6 and 7 to smooth out the variability in the deterministic solutions. This maintains good continuity with the previous WPC forecast, with only typical small shifts in fronts and QPF based on the most recent guidance, although models have shown a notable increase in QPF amounts along the main frontal boundary from the central High Plains all the way into the central Appalachians. ...Weather/Hazards Highlights... The south-central U.S. has seen prolonged excessive heat in recent weeks, and this is forecast to last into the beginning of the medium range period for the southern half of the Plains and Mississippi Valley. Widespread temperatures near or above 100 degrees (with higher heat indices) will continue in this region through at least Wednesday. The next front that reaches the northern Plains early next week looks to bring moderately below normal highs to the northern-central Plains Wednesday-Thursday, and should have a strong enough southward push to finally bring some moderating temperatures back towards normal for the southern Plains as well for the latter half of the week. Meanwhile, a building upper ridge over the Northwest this week will bring multiple days of hot weather, with some locations likely to see highs as much as 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. The latest guidance continues to suggest increasing potential for a mulitple day period of heavy to possible excessive rainfall along intially a warm front draped from the Mid-Atlantic to the middle Mississippi Valley, but then again as the next front through the Plains settles into mid-South and central Plains. Sufficient moisture and instability pooled along this boundary as it becomes quasi-stationary should support rounds of heavy rainfall and convection across some of the same regions over multiple days. The days 4 and 5 experimental EROs have expanded the slight risks across the central Appalachians and back into the Tennessee Valley and parts of the middle Mississippi Valley. Heavy rainfall will expand into the southern Mid-Atlantic and the central Plains later in the week as well. Persistent monsoonal moisture 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 on the day 4 ERO was introduced across a good portion of central and eastern Arizona as that anomalous moisture stays put over likely wet soil from activity in the short range period. Some of this moisture is also expected to interact with the central Plains front to enhance rainfall totals farther north and east into New Mexico and Colorado midweek, with potential for flash flooding as well (and the presence of a slight risk on both the days 4 and 5 ERO). 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