Extended Forecast Discussion NWS Weather Prediction Center College Park MD 307 AM EDT Fri Jul 12 2024 Valid 12Z Mon Jul 15 2024 - 12Z Fri Jul 19 2024 ...Hazardous to dangerous heat for parts of the Central to Eastern U.S. early next week. High heat builds over the West next week... ...Overview... Upper level ridging will be in place next week across the Interior West, Southeast, and south-central U.S. to bring above normal to hazardous temperatures to much of the nation. Upper trough development off the West Coast next week may act to build upper ridging over the West. This would allow energies digging to the lee to increasingly work into downstream ridging over the South. Meanwhile, a series of potent upper level shortwaves will swing across the Upper Midwest, Great Lakes, and Northeast, and a couple of temperature moderating frontal boundaries will sink south across the north-central U.S. and the Northeast, with potential to sink down into the South/Southeast later period. Precipitation chances will increase along these frontal boundaries, and daily precipitation chances will also exist in the Four Corners region as monsoonal moisture focuses over the area. ...Guidance/Predictability Assessment... 18 UTC GFS/GEFS and 12 UTC ECMWF/UKMET/ECMWF ensemble mean guidance seems best clustered Monday into Wednesday. Prefer a composite to smooth the least predictable rough edges. This seems generally in step with the 01 UTC National Blend of Models (NBM) and WPC continuity in a pattern with at least slightly above normal predictability. Forecast spread overall stays managable into later next week, but embedded system timing differences do steadily grow. Leaned WPC blend weighting for this period toward the ECMWF/ECMWF ensemble mean that show somewhat stronger building and maintainance of upper ridging over the West. This seems reasonable given reluctance to uncharacteristically favor weakening given trends for flow amplification. Newer 00 UTC cycle guidance remains overall in line and trends slightly toward this forecast plan. ...Weather/Hazards Highlights... Monsoonal moisture will focus over portions of the Four Corners region, which will allow for daily rounds of precipitation that could result in flash flooding, especially near steep terrain and burn scars. A Marginal Risk of Excessive Rainfall remains planned is for Day 4 (Monday) and Day 5 (Tuesday) for much of the Four Corners region and portions of the south-central Rockies in a region with protracted favorable upper diffluence, with some focus also spilling into the central High Plains and Southwest Texas. Across the Great Lakes and Northeast, upper level shortwaves and well defined and wavy surface fronts will provide support for multiple rounds of showers and thunderstorms. With ample moisture and instability in place across these regions, locally heavy rainfall will be possible and may lead to isolated instances of flash flooding. A WPC Marginal Risk of Excessive Rainfall Outlook (ERO) remains in place for the Great Lakes and Northeast on Day 4 (Monday), especially given the heightened sensitivity in the Northeast following heavy rains this week. The Storm Prediction Center also highlights Midwest parts of this region for some severe weather. A Day 5 (Tuesday) Marginal Risk ERO has also been introduced down across this region and into the Ohio and Mid- Mississippi Valleys as the main frontal zone shifts southeastward. Elsewhere, precipitation chances will progress further southward across much of the rest of the central and eastern U.S. mid-next week as a cold front moves south, and daily precipitation chances will persist in Florida with summertime convection. Locally heavy rain will be possible in these areas with any heavier thunderstorm activity. The West Coast and much of the Pacific Northwest will remain mainly dry through next week. Much of the nation will experience above average temperatures next week and a threat a widespread record values while becoming dangerously hot for many from especially the central to eastern U.S.. Hazardous heat should slowly suppress south and eastward with time as amplified troughing dips into the Great Lakes and Northeast/Mid- Atlantic. Temperatures in the 110s are likely to continue across the Desert Southwest, and highs near or above 100 will be common in the central/southern Plains. Temperatures across the Northwest may be marginally above normal through early next week, but as upper ridging builds back in, anomalies tick upward again in a pattern with increasing hot conditions over the West. Schichtel 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 forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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 https://www.wpc.ncep.noaa.gov/#page=ovw