Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1143 AM EDT Mon Jul 08 2019 Valid 12Z Thu Jul 11 2019 - 12Z Mon Jul 15 2019 ...Overview and Guidance/Predictability Assessment... Models consensus remains relatively poor as to the eventual evolution of low pressure expected across the Gulf of Mexico later this week into the weekend. In general, a westward trend was noted in the guidance from overnight, especially among the GFS/ECMWF and their respective ensembles, while the 00Z UKMET/CMC maintained solutions that keep the area of low pressure farther to the east. After assessing the trends and the current ensemble/model spread, a solutions close to the 00Z ECMWF was preferred at this time, subject to adjustment this afternoon pending new model guidance and collaboration with NHC. Fortunately, models showed slightly above average agreement at the larger scales elsewhere, with the primary storm track focused within a relatively active jet across the CONUS northern tier. Timing/amplitude differences were minor with a series of upper shortwaves crossing the Midwest/Great Lakes/Northeast through the period. Differences grow through time, and shortwave energy expected to reach the Pacific Northwest Sun-Mon, then moving east from there showed somewhat larger differences among the guidance. Given these considerations, a multi-model deterministic blend was used initially during days 3-4, with a shift toward a three-way blend of the ECMWF and ECENS/GEFS ensemble means during days 5-7. Ryan ...Weather Highlights/Threats... The heavy rainfall threat continues for some areas along and inland from the Gulf Coast, with specifics depending on the very uncertain path of the system expected to track over a portion of the northern Gulf. Given the diverse guidance spread thus far, it is important to note that a meaningful potential exists over a greater area than represented on any single deterministic model or manual forecast. Latest trends are suggesting there may be a westward shift in highest rainfall potential but further runs will be needed for confirmation. Elsewhere, low pressure and trailing front will bring showers/thunderstorms to the Northeast and Mid-Atlantic late this week with best dynamics aloft supporting highest rainfall totals over parts of the Northeast. Some showers/storms may also accompany another frontal system tracking from the northern Plains into the East late week through the weekend. The trailing part of the front may stall over the northern Plains to provide a longer-term rainfall focus. Locations along and just inland from the Pacific Northwest coast may see one or more periods of scattered light rainfall depending on strength of shortwaves ejecting from the mean trough aloft over the eastern Pacific. Portions of the Rockies may see scattered diurnal convection on one or more days. Most temperature anomalies should be in the single digits through the period. Aided by warm morning lows in particular, areas from the interior West through the northern Plains should be consistently above normal. Frontal progression will provide some temperature variability over the northeastern quadrant of the lower 48. Clouds/rainfall may keep high temperatures a little below normal over some areas along and inland from the Gulf Coast, depending on the track of the possible Gulf system. 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