Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM EDT Fri Sep 03 2021 Valid 12Z Mon Sep 06 2021 - 12Z Fri Sep 10 2021 ...Overview... Upper ridging will drift out of the Great Basin early next week toward the southern Plains as troughing moves into the Pacific Northwest. Troughing in the Northeast on Monday will lift out by Tuesday but will be quickly replaced by incoming troughing from southern Canada. That trough should exit the East Coast around the end of next week, likely keeping Hurricane Larry over the Atlantic. The pattern is largely quiet and drier than average after a very active and wet several weeks. ...Guidance Evaluation and Preferences... Through the 12Z/18Z cycle, the models and ensembles showed relatively good clustering through the period, with expected differences that grew with time. Recent GFS runs were a bit on the southern side of the spread with low pressure through the Great Lakes Tue-Wed, but not implausible. Larger differences over the Pacific translated into the West (particularly the Northwest) due to system disagreement on existence/timing/track. Ensemble consensus seemed to favor an area of low pressure approaching the coast by the end of next week (with its cold front perhaps onshore) in between the quicker 18Z GFS and 12Z Canadian and the slower 12Z ECMWF (12Z GFS was also as slow as the ECMWF). Multi-day ensemble trend has been toward a bit slower and more amplified trough-ridge-trough pattern over the CONUS, so weighed the slower ECMWF a bit more than the GFS but with a majority ensemble mean blend. Over the Southwest, the movement of the upper high southeastward may allow for an increase in moisture into the lower CO River basin late next week. GFS/GEFS were a bit wetter than the ECMWF/Canadian and their ensembles. Favored a slightly drier scenario for now. In the Gulf, any limited tropical activity is forecast to be weak/disorganized, but may spread moisture/rainfall into the Gulf Coast. Continued to favor the weaker solutions vs the more robust models. ...Weather/Hazard Highlights... Rainfall will focus over the Upper Midwest/Great Lakes Monday in advance of a system out of the northern Plains, which may promote some heavier rainfall on Tuesday across Michigan. Rainfall along the cold front may be lighter and continued southward into the Southeast in a warmer and more humid environment. Temperatures will be near to above normal over most areas, especially the West to the Northern Rockies ahead of the incoming Pacific trough. Temperatures 5-15 degrees above normal are possible as the area of warmth moves into the southern Plains late next week. Temperatures in the Northeast will be near to a bit below normal thanks to generally northwest flow. Fracasso 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