Extended Forecast Discussion NWS Weather Prediction Center College Park MD 232 AM EDT Wed Jun 26 2019 Valid 12Z Sat Jun 29 2019 - 12Z Wed Jul 03 2019 ...Overview and Weather Highlights/Threats... Transition to quasi-zonal flow marks the arrival of a typical summertime pattern but that will be punctuated by an inverted trough over Texas. That leaves the northern stream to waver along the US/Canadian border with bouts of rainfall and mostly afternoon thunderstorms. No clear signal exists for organized heavy rainfall though the potential is there on a local level. Temperatures will be well above average in the northern Plains/Upper Midwest (80s to upper 90s, warmest on Saturday), but with a daily risk of showers/storms with locally heavy downpours in the vicinity of a warm front Saturday and a persistent stationary front Sunday onward. The Southeast and lower MS Valley/Gulf Coast region will see a daily chance of showers/storms in typical summertime fashion that may be enhanced via the upper trough and lower-level moisture increases from the Gulf. ...Guidance/Predictability Assessment... The deterministic models mostly clustered together for the first few days before uncertainty in timing/evolution (mostly off the West Coast) resulted in decreased confidence in specifics. Trended to a majority ensemble mean weighting by next Tue/Wed. Largest question remains west of the WA/OR and how the positively-tilted (and latitudinally-elongated) trough evolves downstream of a significant positive height anomaly over southern Alaska. These scenarios often present mutually exclusive forecasts (e.g., vorticity either sliding westward under the upper high or coaxed eastward into the in-situ trough) and a blend would result in a less than realistic solution. However, a blended mean starting point sufficed for now which indicates less amplitude over the Pacific Northwest that does not favor any singular deterministic model. Fracasso 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 Hazards: - Flooding possible across portions of the Central Plains and the Middle Mississippi Valley. - Flooding occurring or imminent across portions of the Central/Southern Plains, the Middle/Lower Mississippi Valley, and the Ohio Valley. - Flooding likely across portions of the Central Plains and the Middle Mississippi Valley. 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