Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1129 AM EDT Fri Jul 12 2019 Valid 12Z Mon Jul 15 2019 - 12Z Fri Jul 19 2019 ...Tropical Storm Barry expected to weaken as it tracks up the Mississippi Valley/Lower Ohio Valley but continue to produce areas of heavy rainfall... ...Overview and Guidance/Predictability Assessment... ...Weather Highlights/Threats... National Hurricane Center forecasts continue to show Barry reaching Louisiana in the short range time frame and making its way northward over the Lower Mississippi Valley leading into the start of the extended time frame by early day 3 Mon. From Mon into Wed Barry should slowly weaken as it tracks into the southern Mid-Mississippi Valley and Lower Ohio Valley. The surface reflection may become less-defined after Wed though the 00Z ECMWF still forecasts a discernible center through the period into next Friday, which is plausible given some similar (or stronger) ensemble members. There are still very stubborn model and ensemble differences overall but the 00Z ECMWF was closest to the official track, closely followed by the Canadian and GFS. Based on this cluster expect highest rainfall totals from 12Z Mon onward to extend from northeastern Arkansas/northern Mississippi through Tennessee/Kentucky, with less confidence to the east-northeast thereafter. There may be a severe threat over some areas to the right of the surface low track but with low predictability in details this far out in time. Later in the week the remnants of Barry could interact with a wavy northern stream front and produce enhanced rainfall over the Northeast but this depends on the strength of Barry in the short term and timing in the northern stream in several days. Please consult latest NHC products for updated information on Barry. Away from Barry the guidance continues to show a fairly typical summertime pattern with an upper ridge prevailing over the southern Rockies/central-southern Plains and progressive low amplitude flow across the northern tier states and southern Canada. Models/means are advertising a change in the pattern's character from the Pacific into western North America though, with a North Pacific jet reaching into the northwestern U.S. mid-late week underneath a Gulf of Alaska into western Canada upper low. Some aspects of the northern stream forecast (shortwaves and associated surface lows/fronts) have maintained consistency to some degree over recent days but others have not. In particular there has been difficulty in resolving the specifics of shortwave energy ejecting from the West Coast upper trough Mon-Wed. Also consensus has generally trended faster over the past day with arrival of the North Pacific jet and closed low to the north. The consensus evolution should bring a period of steadier light to locally terrain-enhanced moderate rainfall between the Pacific Northwest coast and Cascades, after lighter and more scattered activity earlier in the week. The frontal systems affecting the northern tier states will bring periods of showers and thunderstorms with some areas of heavy rainfall, especially from the northern Plains through the Upper Mississippi Valley and northern Great Lakes in association with a front that may stall for a period of time. Over this area the models and ensembles currently show too much spread to depict especially heavy totals in the manual deterministic forecast. However operational runs in principle are showing a decent signal for some multi-inch 5-day totals at some locations so this area will need to be monitored as details come into better focus. Consult the latest WPC Hazards chart for more information. The composite of forecast preferences led to a days 3-5 Mon-Wed blend based mostly on the 00Z ECMWF as well as some ideas from the 00Z-06Z GFS/00Z CMC and 00Z ECMWF mean. Days 6-7 Thu-Fri transitioned to a model/ensemble mean blend (including continuity). This maintained good continuity. Above normal temperatures with some pockets of plus 10F or greater anomalies will spread from the northern Plains into Northeast Mon-Wed with some warmth lingering over the northeast quadrant of the lower 48 into Fri. Clouds/rainfall associated with Barry will likely keep daytime highs well below average over parts of the Lower Mississippi Valley on Mon (perhaps near record low max values). After Mon confidence decreases for how much daytime temperatures may be affected by Barry's moisture from the Ohio/Tennessee Valley into the Mid-Atlantic/Northeast. Expect the central Plains/Mid-Mississippi Valley to trend hotter by the latter half of the week with some highs reaching 10-15F above normal and heat index values potentially high enough to cause concern (105-110F). The southern Rockies/High Plains should be 5-10F above normal most of the period under the upper high. The Northwest will trend cooler by Thu-Fri with highs 5-10F below normal. 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