Extended Forecast Discussion NWS Weather Prediction Center College Park MD 324 PM EDT Thu Sep 05 2019 Valid 12Z Sun Sep 08 2019 - 12Z Thu Sep 12 2019 ...Record heat to continue for the Lower Mississippi Valley/Gulf Coast into next week... ...Overview...Guidance Evaluation and Preferences... Upper ridging will remain anchored over the Lower Mississippi Valley and Southeast into next week. The West will see a series of upper troughs moving through the region with the waves gradually deamplifying as the head across the Plains and upper MS Valley and Great Lakes. Low pressure emerging from the West early in the week should track eastward along the US/Canadian border to the east coast around next Thursday. The models have good agreement on the timing of the initial wave departing the northern Rockies on day 3 across the northern high Plains, with primarily an amplitude difference. A blend few the models/means was sued to resolve differences, with slightly more weighting given to the operational ECMWF/GFS/Canadian. On days 5-7, the model and ensemble differences grow. In the Great lakes to the northeast, the 06z GFS became an outlier on a faster and stronger low located further north than other solutions. With the GEFS Means suppressed further south like the other guidance and the 00z GFS run, the 00z GFS was used int he blend instead. Out west, the 00z ECMWF became one of the fastest solutions in moving the trough east across the Great Basin and northern Rockies, followed by the high Plains. Most ECMWF ensembles were slower, as were the GFS, Canadian, and their ensemble members. Consequently, less weighting was given to the operational ECMWF days 6-7. With the GEFS and ECMWF members showing a bi-modal clustering of solutions, confidence is low in picking a correct cluster. An intermediate solution was chosen between the ensemble means of the 06z GEFS and 00z ECMWF until the solutions start to cluster better. ...Sensible Weather... The Southern tier of the CONUS from east Texas eastward to the Florida panhandle will generally see well above average temperatures in the upper-90s to lower 100s F that are forecast to tie or break record highs, especially on Sunday and Monday. Above normal temperatures with a few possible records still continue through at least Wednesday. Much of the northwest and CA/AZ will see below average temperatures. Rainfall will mostly favor the northern areas from the Pacific Northwest eastward across the northern Rockies, northern Plains, upper MS Valley, Great Lakes, and northeast in conjunction with the frontal waves moving across these regions. Pockets of heavier rain may be possible across the High Plains into the western Great Lakes region around the surface low and in advance of the warm front. In the Mid-Atlantic region, stalling front late this weekend into early Monday may help expand an area of generally light rain before high pressure to the north moves in by Tuesday. In the Southwest, moisture out of Mexico will likely lead to a daily chance of mountain showers/storms that could move into desert valley locations (southern Arizona and portions of New Mexico) and perhaps into extreme western Texas. Petersen/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 Hazards: - Heavy rain across portions of the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Mon-Tue, Sep 9-Sep 10and Thu, Sep 12. - Heavy rain across portions of the Middle Mississippi Valley, the Great Lakes, and the Ohio Valley, Sun, Sep 8. - Flooding possible across portions of the Southeast and the Mid-Atlantic. - Flooding occurring or imminent across portions of the Southeast and the Northern Plains. - Flooding likely across portions of the Southeast and the Mid-Atlantic. - Excessive heat across portions of the Southeast, the Lower Mississippi Valley, and the Southern Plains, Sun-Mon, Sep 8-Sep 9. 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