Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1151 AM EDT Tue Jul 09 2019 Valid 12Z Fri Jul 12 2019 - 12Z Tue Jul 16 2019 ...Overview and Guidance/Predictability Assessment... A strong upper high will slowly weaken over the central/southern Rockies as the jet stream sinks a bit south along the U.S./Canadian border. With a weaker upper ridge off the Southeast coast, troughing over the lower Mississippi Valley/northern Gulf will support a potential tropical system at the surface. This system will pose a heavy rainfall threat to areas along the central and portions of the western Gulf Coast and points northward. Overall the ensembles were in good agreement over the lower 48 (06Z GEFS mean and 00Z ECMWF ensemble mean) in a fairly typical summertime pattern. The deterministic models showed the most disagreement with the track/evolution of the Gulf system but have continued to slowly show more agreement. The 00Z GFS/ECMWF/UKMET/Canadian formed a broad consensus late this week with the Gulf system moving westward then turning northward near the TX/LA coastline in the weaker flow region. The 00Z ECMWF was closest to the ensemble consensus/continuity position with a slight nudge eastward from overnight based on the latest models/trends. Preferred to limit changes to the forecast since the ensembles have been relatively steady in the most recent cycles. By next week, an ensemble consensus/continuity served as a starting point with increasing uncertainty over the middle Mississippi Valley. 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. ...Weather Highlights/Threats... Highest rainfall potential certainly lies near the track of the potential Gulf system, though not necessarily constrained around its center. Combination of Gulf inflow on its east side and the stalled front to the north will modulate other precipitation maxima. Some locally enhanced rainfall 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. Fracasso/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