Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EDT Tue Jul 09 2019 Valid 12Z Fri Jul 12 2019 - 12Z Tue Jul 16 2019 ...Overview and Guidance/Predictability Assessment... ...Weather Highlights/Threats... The most significant feature being monitored in the medium range will be a possible tropical system whose supporting energy should already reach the northern Gulf during the short range time frame. As the system tracks over the northern Gulf, westward trends seen in yesterday's 00Z guidance have held up through the latest cycles of guidance with the updated forecast maintaining continuity reflecting yesterday's WPC/NHC coordinated track into southeastern Texas and then northward through the southern Plains. While the guidance spread has decreased compared to previous days, there is enough lingering uncertainty with finer scale details influencing the system's motion that further adjustments to the most likely track will be possible. This system will pose a heavy rainfall threat to areas along the central and portions of the western Gulf Coast and points northward. Elsewhere there is better than average agreement and continuity with the overall pattern. A fairly strong upper high should persist over the southern Rockies/Four Corners region while an eastern Pacific mean trough may drift ever so gradually toward the West Coast. Shortwaves ejecting from the Pacific trough will become embedded in progressive northern U.S./southern Canada flow and likely feed into a broad/shallow mean trough over the Northeast. These shortwaves will support a progression of waves/frontal systems which at times will be accompanied by showers and thunderstorms. Some locally enhanced amounts will be possible over the Northeast with one system late this week while the northern Plains/Upper Mississippi Valley may be another area of interest due to the arrival of another front and its subsequent stalling. The shortwaves brushing the Pacific Northwest may bring one or more periods of light to perhaps isolated moderate rainfall. Western and northern portions of the lower 48 should see above average temperatures during most of the period. The northern Plains to Great Lakes area may see some pockets of plus 10F or greater anomalies for min and/or max readings by early next week. Parts of the interior West may see some mins exceed 10F above normal one or more days. Meanwhile clouds/rainfall associated with the possible Gulf system may hold daytime highs below normal over parts of the southern tier. A blend of 18Z GFS/GEFS mean and 12Z ECMWF/ECMWF mean provided the best initial starting point for the forecast domain this cycle. By the latter half of the period the blend required some adjustment to conform to the desired track of the forecast northern Gulf system (closest to a compromise between the 12Z and old 00Z/08 ECMWF runs). These models/means represented consensus well for individual waves/fronts carried along by northern stream flow while their combination helped to tone down ongoing shortwave uncertainties within the eastern Pacific mean trough. Rausch 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