Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1141 AM EDT Thu Jul 11 2019 Valid 12Z Sun Jul 14 2019 - 12Z Thu Jul 18 2019 ...Tropical Storm Barry to bring heavy rain to the Lower Mississippi Valley this weekend into early next week... ...Overview and Guidance/Predictability Assessment... ...Weather Highlights/Threats... The National Hurricane Center is issuing advisories on Tropical Storm Barry over the northern Gulf of Mexico. Current forecast shows the system tracking into Louisiana and then continuing northward slowly but steadily in fairly weak flow aloft. Late in the medium range period the southern edge of the westerlies across the northern U.S. may begin to have some influence on the track, with an increasingly large spread among the ensemble members. Guidance clustering has been improving gradually but there is still meaningful spread (with the 00Z UKMET continuing to stray west of the majority). Models/ensembles have generally had greater than average difficulty in forecasting this system's track thus far, so further adjustments to the most likely track are easily possible over coming days. For this forecast the 00Z ECMWF and Canadian were closest to the official NHC track through the first half of the period. Then inclusion of the 00Z GFS was used to help temper the quicker ECMWF as the system lifts through southeastern Missouri and then likely northeastward next week. Barry (and its remnants) should produce an axis of heavy rainfall from the Lower Mississippi Valley into the southern Mid-Mississippi Valley/Lower Ohio Valley as it retains Gulf inflow for several days. Precipitation intensity and coverage should slowly decrease as the remnants of Barry crest the Appalachians, but interaction with a front across the Lakes/Northeast next week may at least enhance precipitation late in the period. A weakening front to the north of the system in the lower MS Valley Sunday could help to enhance rainfall Sun-Mon and lingering Gulf inflow could support pockets of moderate/heavy rainfall along parts of the Gulf Coast away from the center. Please consult latest NHC products for updated information on Barry. Meanwhile upper ridging should remain over the southern Rockies. Shortwaves ejecting from an eastern Pacific into northwestern U.S. mean trough will continue around the ridge, crossing the northern U.S./southern Canada and feeding into a broad/weak mean trough over the Northeast. Strong flow to the south of an upper low tracking across the Gulf of Alaska may reach the Pacific Northwest by day 7 Thu and help to push along the leading trough near the West Coast. There is reasonable continuity for an initial ejecting Northwest shortwave that should support southern Canada low pressure and associated warm/cold front crossing the northern tier. Thus far guidance has had more difficulty in resolving the next shortwave which should be near the Pacific Northwest as of early day 5 Tue. Ensembles have trended quicker with this feature stemming back to its progression across the Aleutians. Continue to expect episodes of showers and thunderstorms across the northern states with the waves/fronts, with locations from the northern Plains into Upper Great Lakes seeing the best potential for some locally heavy rainfall. The Pacific Northwest will see periods of scattered and mostly light rainfall with the shortwaves brushing the region early-mid week. By Thu rainfall could become a little more organized over or just north of the region as flow aloft strengthens. Based on combined preferences for Barry and features in the northern stream, the latest forecast for days 3-4 Sun-Mon started with 00Z ECMWF/Canadian with inclusion of the 00Z GFS by day 5/Tue. Increasing detail uncertainty by days 6-7 Wed-Thu led to a blend of the quicker ECMWF with the slower Canadian as remnant Barry moves through the Ohio Valley with some ensemble mean weighting due to its less-detailed depiction. An area of above normal temperatures will likely expand from the northern Plains into the Northeast during the period with most anomalies in the plus 5-15F range. Clouds and rainfall associated with Barry should produce an area of daytime highs as much as 10-15F below normal over the Lower Mississippi Valley Sun-Mon. Some below normal highs may extend farther northeastward after Mon but with lower confidence. 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