Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1156 AM EDT Sat Jul 11 2020 Valid 12Z Tue Jul 14 2020 - 12Z Sat Jul 18 2020 ...Record high temperatures possible across portions of Texas through early next week... 1600 UTC Update... Overall, no major changes were made to the ongoing forecast during the extended period. A blend of the 00Z ECMWF/06Z GFS served as forecast starting point during days 3-4 (Tue-Wed). During days 5-7 (Thu-Sat), a blend of the ECMWF along with increasing ensemble means (ECENS and NAEFS) through time was used to counteract increasing spread. The 06Z GFS had some significant differences from consensus during the latter portion of the forecast period, including more amplification than consensus with a trough across the north central U.S. on Thu, and ridging across the Pacific Northwest late in the week, where the consensus of other guidance, along with hemispheric teleconnections support some degree of trough. Ryan Previous Discussion (issued at 0621 UTC)... ...Overview and Guidance/Predictability Assessment... Classic summertime upper high will meander over the southern Plains and lower Mississippi Valley with an extension toward the East Coast next Tue-Sat. Models/ensembles show excellent agreement in the lower latitudes with a weakness off California in between another upper high well offshore. Jet stream will be relegated to along the U.S./Canadian border with an increasingly zonal flow, lowering predictability in shortwave timing. Lead-in pattern will feature one closed upper low over Saskatchewan/Manitoba that is forecast to slowly drift northeastward toward Hudson Bay. A second upper low over southern Quebec/northern New England will move into Atlantic Canada by Thursday. The frontal system attached to each upper low will progress from west to east and generally lift northward in time as height rise across the mid-latitudes. A consensus blend sufficed for much of the period, though the 12Z Canadian departed most from the ensemble majority with the flow out of the northeast Pacific by midweek, and was discounted. Otherwise, trended toward a blend of the GFS/ECMWF and their ensemble means by the start of next weekend with an expansive area > 588dam heights. ...Weather Pattern/Hazard Highlights... A potent cold front will push through the Upper Midwest/Great Lakes Tue-Wed with a chance of showers/thunderstorms and locally heavy rain. The unsettled weather will continue along and to the south of the boundary (Plains/Corn Belt/Midwest) but with overall modest rainfall amounts. Generally dry conditions are expected elsewhere over the CONUS except Florida which will see afternoons showers/storms. Temperatures near and above record highs are likely over parts of the Southwest and across much of Texas on Tuesday with widespread 100+ readings. Above normal temperatures are likely from the Rockies to the East Coast much of next week with the largest anomalies over Texas (5-10 deg above normal but 10-15 deg above normal Tue). Widespread mid-90s to low 100s are likely with higher heat indices from Oklahoma eastward to the Southeast. A few hotter days are likely for the Northeast/Mid-Atlantic into the upper 80s to mid 90s. Overnight temperatures may only fall into the mid 70s to near 80 in urban areas under the influence of the upper high. Fracasso Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml