Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 AM EDT Thu Jul 14 2022 Valid 12Z Sun Jul 17 2022 - 12Z Thu Jul 21 2022 ...Heat Threat to loom over much of the Western and Central U.S.... ...Pattern Overview and Weather/Hazards Highlights... A hot upper high/ridge will settle near Four Corners to support high heat across much of the West well into next week, but predictability is also high for widespread heat to encompass across much of the central U.S. as ridging/heights build downstream. Scattered local record values are possible in these broad areas. In this pattern, moderating monsoonal moisture flow across the Southwest into the central Great Basin/Rockies under the upper ridge will alternately offer daily chances for showers with some locally heavier downpours/runoff issues with slow cell motions. Meanwhile, a series of uncertain upper troughs/impulses will work inland from the Pacific and from southern Canada to track over-top the ridge with associated frontal systems to periodically focus progressive and potentially strong convection from the north-central U.S. and Midwest/Great Lakes to the East where a mean upper trough is reinforced. Deeper moisture will also fuel showers/thunderstorms farther southward down across the Southeast/FL and central Gulf Coast states. ...Guidance Evaluation/Predictability Assessment... While the overall larger scale pattern evolution seems reasonable in guidance through medium range time scales, model embedded system timing/strength differences in the 12/18 UTC guidance cycle were notable all next week with eastern Pacific upper troughs/impulses that work downstream across the U.S. northern tier and southern Canada. Roughly ten to fifteen degree longitude wavelength spacing between organized systems seems right at the critical point to force progression. This along with smaller scale system differences that grow over the rest of the CONUS seemed to overall justify earlier guidance preference focus days 3-7 (Sunday-next Thursday) mainly on the more compatible well blended GEFS/ECMWF ensemble means and the National Blend of Models whose solutions tend to mitigate variance consistent with uncertainty. This also acted to maintain decent WPC product continuity. However, the latest 00 UTC models have come into much better agreement with northern stream system timing as the GFS has sped up to and the Canadian/UKMET slowed down too solutions now in line with the more consistent 12/00 UTC ECMWF runs, bolstering forecast confidence in a solution also pretty compatible with the aforementioned ensemble means. 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, 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