Extended Forecast Discussion NWS Weather Prediction Center College Park MD 439 PM EDT Mon Jul 29 2019 Valid 12Z Thu Aug 01 2019 - 12Z Mon Aug 05 2019 ...Overview and Guidance/Predictability Assessment... The North American medium range upper flow pattern will feature a closed high over the southern Rockies, with an amplified ridge up over the west-central U.S. The ridge is sandwiched by persistent mean troughing from the northeastern Pacific into WA/OR and also downstream over the east-central U.S. underneath more dynamic eastern Canadian troughing. Models/ensembles continue to show forecast spread with respect to incoming/evolving Pacific flow inland, but most variance occurs from the weekend into early next week. Confidence remains low there, but is about average elsewhere. A composite blend of the latest and reasonably well clustered GFS/ECMWF and GEFS/ECMWF ensemble means seems reasonable Thu-Sat. Used GEFS/ECMWF ensemble mean guidance that seem more compatable later Sat into Monday amid growing forecast spread and embedded feature uncertainty. ...Weather Highlights/Threats... Below average temperatures in AZ/UT due to monsoonal moisture (and an abundance of clouds/showers/storms) will moderate with time as the upper high drifts just enough eastward to focus rainfall over CO/NM this coming weekend into Monday. Coastal Washington may flirt with some mainly offshore rain as a cold front moves inland but most of the dynamics lift into Canada. Downstream, a wavy frontal boundary draped over the east-central states will be a focus for convective rainfall including some locally heavier downpours/runoff issues through the period. Abundant moisture and modest instability under the mean trough aloft will support less organized precipitation away from the boundary in the Southeast. East of Florida, an emerging tropical wave may bring increased rainfall to parts of the Sunshine State, the Bahamas, and perhaps into the coastal Carolinas. Finally, the High Plains/Upper Midwest will see the Canadian system pull its front eastward along with higher chances of rain/convection Sat-Mon. Fracasso/Schichtel 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: - Heavy rain across portions of the Southeast, the Southern Appalachians, the Mid-Atlantic, and the Central Appalachians, Thu-Fri, Aug 1-Aug 2. - Heavy rain across southern Florida, Thu-Sun, Aug 1-Aug 4. - Heavy rain across portions of the central Plains into the Middle Mississippi Valley, Sat, Aug 3. - Heavy rain across portions of the central and southern Rockies as well as the central and southern Plains, Sun-Mon, Aug 4-Aug 5. - Heavy rain across portions of the central High Plains, as well as over the interior Southeast, the Mid-Atlantic, and the Southern Appalachians, Mon, Aug 5. 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