Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 AM EDT Fri Jul 22 2022 Valid 12Z Mon Jul 25 2022 - 12Z Fri Jul 29 2022 ...Dangerous heat wave persists over the South-Central U.S. into midweek as heat also builds across interior portions of the Northwest next week... ...Overview... The western ridge which is currently centered over the Desert Southwest is expected to steadily drift east through the middle of next week, as progressive systems slide along the northern periphery of the ridge across the northern tier states. A strong ridge developing over the northeastern Pacific through eastern Alaska by the start of the medium range period should shift inland across the West Coast through the middle of next week, establishing a multi-day period of hot weather over the Northwest (with highs looking to reach 15F above normal) into perhaps next weekend. An initial surface front draped from the Mid-Atlantic to the central Plains will become quasi-stationary early next week ahead of the next cold front approaching soon thereafter. This 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 Monday onward will promote daily risk of locally heavy showers and storms that may produce instances of flash flooding. ...Guidance Evaluation/Predictability Assessment... Overall, the latest models and ensembles continue to show very good agreement on the large scale, though with some continued differences for low-predictability shortwave details within northern U.S./southern Canada, particularly by midweek and onward. These differences affect frontal placement across the East and central U.S. with impacts on location and intensity of rainfall, particularly across the Ohio Valley. Models continue to show very good clustering on the expansive ridge across the southern half of the U.S. and building over the Northwest by the middle to latter part of next week. This cycle of the WPC forecast utilized a blend of the deterministic models for days 3-5, with increasing incorporation of the ensemble means by days 6-7 to help mitigate the smaller scale differences. This maintains good continuity with previous WPC forecasts as well. ...Weather/Hazards Highlights... The main weather hazard will be the prolonged excessive heat across especially the southern half of the Plains into at least midweek, with some moderation thereafter. Widespread temperatures near or above 100 degrees (with higher heat indices) will continue the dangerous heatwave in this region. Parts of the Eastern and Southeast U.S. should start the week warm and above normal, but a cold front moving into the region next Monday-Tuesday should bring some relief to the heat in the East. The next front that reaches the northern Plains early next week looks to have a stronger southward push, 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. Both of these fronts will focus episodes of showers and thunderstorms, with some severe weather and heavy rainfall possible. The leading front heading into the East looks to become quasi-stationary and may initially favor highest rainfall totals from the Midwest/lower Ohio Valley into the Northeast/Mid-Atlantic. A slight risk was placed on both the day 4 and 5 experimental EROs across eastern Kentucky into West Virginia where the setup seems most favorable over a somewhat sensitive region and given recent heavy rains. The second 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. Guidance continues to suggest that the pattern evolution will support a more active period with greater coverage and intensity of rainfall, especially for parts of the southern Arizona. As a result, a small slight risk was placed across southeast Arizona on the day 4 ERO where repeat activity from the short range period seems most favorable. Potential still exists for some of this moisture to interact with central Plains fronts to enhance rainfall totals farther north and east into New Mexico and Colorado. Upper ridging that builds over the Northwest next week will bring multiple days of hot weather to that region, with some locations likely to see highs reach up to 10-15F or so above normal, equating to temperatures in the low to mid 100s for especially the Columbia Basin. 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