Extended Forecast Discussion NWS Weather Prediction Center College Park MD 203 AM EDT Wed Jul 10 2019 Valid 12Z Sat Jul 13 2019 - 12Z Wed Jul 17 2019 ...Overview and Guidance/Predictability Assessment... ...Weather Highlights/Threats... A significant focus of the medium range forecast continues to be with the eventual track and sensible weather effects of a tropical system that may develop over the northern Gulf of Mexico in the short range time frame. Not surprising given the behavior of guidance up to this point, solutions are still showing some variability and spread. Over the past 24 hours the majority cluster has settled a bit eastward of where it had quickly adjusted a couple days ago, but the past couple UKMET runs still provide a representative on the western fringe of the envelope. Meanwhile the CMC which had been consistently on the eastern side of the spread has come back to the west in the new 00Z run. The manual forecast reflects yesterday's WPC/NHC coordinated track which takes the system through western Louisiana/Arkansas into early Tue followed by northeastward extrapolation across Missouri. Expect heavy rainfall to accompany this system from the Gulf Coast northward, with highest totals likely to be near the central Gulf Coast/Lower Mississippi Valley. Gulf inflow to the east of the system as well as a stalled front to the north may promote relative maxima in addition to the rainfall closer to the center. Elsewhere the guidance continues to agree rather well with the overall pattern. An upper ridge will prevail over the southern half of the Rockies, likely with a very slow southward drift with time. At the same time an eastern Pacific mean trough will make slow progress toward the Pacific Northwest coast. Individual shortwaves will eject from the trough and be carried along in progressive flow across the northern U.S./southern Canada then into a shallow mean trough that covers the Northeast. Continuity looks good at the moment for the best-defined waves/frontal systems affecting the northern states. These fronts will provide a focus for episodes of showers and thunderstorms. The northern Plains into Upper Mississippi Valley still appear to have the best potential for some locally heavy activity due to fronts stalling for a time before lifting northward ahead of the next wave in the series. For the upper trough nearing the Pacific Northwest, the ECMWF mean has been the most consistent over recent runs though latest GEFS means are now similar. As expected the operational model runs vary with shortwave details that have low predictability, ultimately favoring a model/mean blend for a deterministic forecast. The overall mean trough will keep the chances for occasional light to isolated moderate rain in the forecast over parts of the Pacific Northwest. A majority of the western and northern U.S. should see above normal temperatures during the period with anomalies for morning lows tending to be somewhat greater than for daytime highs. Some pockets of plus 10F or greater anomalies are possible. Expect the best emphasis for warmest readings versus average to shift from the western states during the weekend into the northern Plains/Upper Mississippi Valley and expanding toward the Northeast during Mon-Wed. Clouds and rainfall near and east of the system tracking northward from northern Gulf should keep daytime highs below normal for a period of time. 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