Extended Forecast Discussion NWS Weather Prediction Center College Park MD 310 PM 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 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 developing over the northeastern Pacific through eastern Alaska by the start of the medium range period should shift inland across the West Coast by the middle of next week, establishing a multi-day period of hot weather over the Northwest (with highs looking to reach 15-20F 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 risks of locally heavy showers and storms that may produce instances of flash flooding. ...Guidance Evaluation/Predictability Assessment... The latest model and ensemble guidance remains agreeable with the large scale pattern of high heights in the southern tier and shortwave impulses moving through the quasi-zonal jet stream in the northern tier through the middle of next week. Guidance varies somewhat with the small-scale details of individual shortwaves, which can affect frontal and rainfall placement, but nothing too egregious for the medium range time frame. The early part of the forecast period was based on a blend of the 00/06Z deterministic models as they showed good overall agreement. The pattern looks to transition to slightly more amplified by later in the week as ridging builds in the Northwest, and meanwhile energy could consolidate around midweek to strengthen an upper low centered in south-central Canada, with troughing stemming into the northern half of the Plains and shifting eastward through the latter part of the workweek. The 00Z UKMET was slightly weaker than consensus with low/trough feature by day 5/Wed. 00/06Z GFS runs show the upper low tracking east just a bit more quickly than the 00Z ECMWF by Thursday-Friday, though still within reason, but the 12Z GFS and ECMWF have converged even a bit more with the GFS slowing down and the ECMWF speeding up a bit. The WPC forecast was able to maintain over half deterministic guidance in the forecast blend through the period, though with some inclusion of the GEFS and EC ensemble means. This maintained good continuity with previous WPC forecasts, with just some typical slight shifts in frontal placement based on the newer guidance. ...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, 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 U.S. should also start the week warm and above normal, but a cold front passing through next Monday-Tuesday should bring some relief to the heat in the East. Then 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. 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 will spread rain and storms to the Northeast and Mid-Atlantic, while the front farther west looks to become quasi-stationary and may initially favor highest rainfall totals over the Midwest and Ohio Valley. Slight Risks were placed on both the day 4 and 5 experimental EROs across eastern Kentucky/Tennessee and into West Virginia and western 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 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. Meanwhile, 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 10-20F or so 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 Hazards: - Heavy rain across portions of the Central/Southern Plains, the Central/Southern Rockies, the Central Great Basin, the Tennessee Valley, the Middle Mississippi Valley, the Central/Southern Appalachians, the Ohio Valley, and the Southwest, Mon-Thu, Jul 25-Jul 28. - Flooding occurring or imminent across portions of the Northern Plains. - Flooding likely across portions of the Northern Plains. - Excessive heat across portions of California, the Central Great Basin, the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Mon-Fri, Jul 25-Jul 29. - Excessive heat across portions of the Central/Southern Plains, the Lower/Middle Mississippi Valley, the Tennessee Valley, and the Southeast, Mon-Thu, Jul 25-Jul 28. 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