Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Tue Sep 28 2021 Valid 12Z Fri Oct 01 2021 - 12Z Tue Oct 05 2021 ... Heavy rain threat over portions of Texas late this week... ...Overview... The medium range period will feature a slow-moving frontal boundary across the Plains with a heavy rain threat most likely over portions of Texas late this week. This system should then move more quickly to the northeast early next week as a closed upper low exits the Northeast while the next upper trough from the Pacific Northwest reaches the northern Plains. ...Guidance Evaluation/Preferences... The main area of concern remains centered over the mid-section of the country where models continue to indicate noticeable differences regarding the eventual outcome of a stalled frontal boundary in an amplified and blocky upper-level pattern across North America. The GFS continues to indicate a faster solution with this system heading toward the Ohio Valley beginning later this weekend. Meanwhile, the slower ECMWF has been showing a clear tendency of pushing this system faster toward the northeast across the Plains for a past few runs. The latest (12Z) ECMWF solution calls for a low to drift southeastward across the Great Lakes. It appears that the model has not yet settled with a preferred solution with this system. A consensus approach was used to handle this system. A blend of the ensemble and deterministic solutions from the 00Z ECMWF, 06Z GFS, and the 00Z CMC yielded a general southeastward drift of a low center from the upper Great Lakes/upper Midwest this weekend, reaching the Ohio Valley by early next week. For the late week heavy rain threat across the southern Plains, models and ensembles are in relatively good agreement for heavy rain to occur through the western to central section of Texas Friday and into the Saturday ahead of a stalled front. Therefore, a consensus approach was adopted to handle this system. This yielded a QPF axis oriented slightly more toward the northeast across the southern Plains compared with WPC continuity. ...Weather and Potential Hazards... Widespread and potentially heavy rainfall should culminate on Friday across portions of the southern Plains as an slow-moving upper trough interacts with tropical moisture streaming up from the Gulf of Mexico. 2 to 4 inches of rain with locally higher amounts can be expected to extend through a good portion of Texas. Periods of rain can be expected farther north across the rest of the Plains and the Midwest in the vicinity of the stalled front, with a tendency for the rain to slowly shift eastward into the Ohio Valley as the surface low pressure system stalls by early next week. Meanwhile, a round of showers is possible for the Northern Rockies/Plains on Friday as a front passes through, scattered showers and thunderstorms are possible for southern Florida through the period, and some moisture may return to the Four Corners states by Monday/Tuesday. Warmer than normal temperatures are forecast across the north-central tier of the CONUS through the end of the week, with highs in the 70s through the Midwest underneath upper ridging. On the other hand, cooler than average temperatures (especially highs) are expected for the Rockies into southern/central portions of the High Plains. Friday should be particularly cool over New Mexico/Colorado/Texas given the clouds and precipitation over the region. The West Coast can expect temperatures a few degrees above normal by the weekend, while slightly below average temperatures are expected for the Northeast with the lingering upper low. Tate 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, 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