Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1149 AM EDT Tue Jul 30 2019 Valid 12Z Fri Aug 02 2019 - 12Z Tue Aug 06 2019 ...16Z update... No major changes were needed to the overnight medium range package. Model guidance continues to handle the overall pattern well over the CONUS, while struggling a bit with energy over the eastern Pacific and Gulf of Alaska, especially late in the period. Decided the best compromise was the 06Z GFS, 00Z EC mean, and the 00Z NAEFS. The 00Z ECMWF kept the energy more northward toward the Gulf of Alaska. Downstream, model differences exist with another upper trough over south-central Canada. The 00Z GFS is stronger with this low compared to other guidance, but on the other hand, the 00Z and 06Z GEFS means have less troughing extending southward from this feature into the Great Lakes region. Therefore, chose to lean away from those solutions in favor of better clustering other guidance. For additional information and details about sensible weather, please see the previous discussion. Tate ...Previous Discussion... ...Overview and Guidance/Predictability Assessment... Fairly typical summertime pattern will feature an upper high over New Mexico with troughing lifting out of the Pacific Northwest, through Canada, and settling into the Great Lakes by next week. A break in the subtropical ridge will favor a trough over the northeastern Gulf of Mexico as well. The models/ensembles have had a tough time resolving the Pacific flow into western North America which continued through the 12Z/18Z cycle. However, the 18Z GFS and 12Z ECMWF clustered well enough with their ensemble means so that a consensus blend sufficed as a starting point Fri-Sun. By next week, the ensembles were much quicker to dig height falls into the Great Lakes/Northeast than the deterministic runs but the trend in the ensembles is for a more-defined and slower solution. In light of quicker continuity, a position midway between the two camps was reasonable for now since there continues to be uncertainty upstream with ridging into the Gulf of Alaska which may modulate the orientation of the flow across southern Canada. Elsewhere, a blended solution worked well with fewer changes in lower latitudes. ...Weather Highlights/Threats... Monsoonal moisture will focus rainfall over CO/NM around the upper high this weekend before possibly shifting back westward into eastern Arizona next week. Coastal Washington will see some rain as a cold front moves inland Friday before drying out. Downstream, a wavy frontal boundary from the central Plains eastward to the mid-Atlantic will favor precipitation along and to the south of it with scattered mainly afternoon shower/storms. 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 fronts eastward along with higher chances of rain/convection Sat-Tue. Temperatures will be a bit cooler than average over the central states with higher chances of precipitation. Milder than average temperatures are expected over the Great Lakes and Northeast ahead of the northern tier system this weekend. Elsewhere, temperatures will be within a few degrees of typical early August values. 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 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