Extended Forecast Discussion NWS Weather Prediction Center College Park MD 254 AM EDT Tue Aug 17 2021 Valid 12Z Fri Aug 20 2021 - 12Z Tue Aug 24 2021 ...Weather Pattern Overview... A well defined upper level trough should be in place across the Intermountain West and Northern Rockies to begin the forecast period Friday, and an upper level ridge situated over the Southeast U.S. in the wake of Tropical Storm Fred. The upper trough then reaches the Upper Midwest by the weekend and drives a cold front and surface low eastward, with a building ridge across the Northeast states that will force the main surface low northward into Canada. A more robust ridge axis developing over the Gulf Coast region will tend to steer Tropical Storm Grace farther westward across the Gulf and eventually making landfall south of Brownsville, Texas. ...Model Analysis and preferences... The 00Z model guidance suite is still indicating some timing differences with the trough exiting the Rockies and crossing the northern Plains, and the 18Z/00Z runs of the GFS have been faster compared to the better clustered CMC/ECMWF/UKMET guidance. This also holds true with the next shortwave across the north-central U.S. by Sunday night. The model spread with the path of Grace has improved since yesterday, with latest trends suggesting a more southern track owing to the strength of the ridge to its north. The WPC fronts/pressures forecast was primarily derived from a 12Z ECMWF/ECENS/UKMET/CMC blend through Saturday, and then primarily ECMWF/ECENS/and some GFS for the end of the forecast period. ...Sensible weather and potential hazards... Improving weather conditions are expected for the East Coast to close out the work week after the remnants of Tropical Storm Fred exit the region, with some lingering showers remaining over portions of the Mid-Atlantic and Northeast. Moderate to heavy rainfall is likely across portions of North Dakota and Minnesota ahead of the developing storm system to close out the work week, with the potential for some scattered 1 to 3 inch totals where mesoscale convective complexes develop. Another corridor of enhanced showers and storms may materialize across portions of the Mid-South this weekend owing to a slow moving front in the vicinity. In the temperature department, expect readings to be up to 20 degrees below normal across portions of the northern Rockies and western portions of the northern Plains for the end of the week, and some high elevation snow for Wyoming and Montana is within the realm of possibility. Except for some slightly above average temperatures across the Great Lakes and New England, no serious heat waves are currently expected. Hamrick 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