Extended Forecast Discussion NWS Weather Prediction Center College Park MD 252 AM EDT Wed Jul 01 2020 Valid 12Z Sat Jul 04 2020 - 12Z Wed Jul 08 2020 ...Overview and Guidance Assessment... Today's guidance maintains a similar theme for the overall pattern with multiple embedded detail uncertainties. A mean trough aloft will persist over western Canada and extend into the extreme eastern Pacific/West Coast. Best consensus ejects some of the initial energy over the weekend and then brings upstream energy along or near the Alaska Panhandle down toward Vancouver Island in the form of a closed or nearly closed upper low by days 6-7 Tue-Wed. Along the West Coast this evolution leads to broadening of the overall trough followed by gradual amplification. Meanwhile the upper ridge initially over the Plains/southern Rockies/northern Mexico will retreat southwestward for a time before possibly building back to the northeast in response to late-period West Coast trough amplification. Models/ensembles still advertise some degree of central Canada ridging that will support a mean trough over eastern Canada into the northeastern U.S. through at least the weekend--but there has been a lot of spread and variability over shortwave details and exactly how/when the ridge-trough configuration may break down. The upper weakness developing over the South/Southeast is still in the forecast with ongoing detail differences. A majority of guidance suggests the feature should weaken and/or shear out by midweek. A blend of the 12Z models/18Z GFS early followed by a model/ensemble mean blend represented the consensus pattern evolution over the course of the period. Guidance spread and variability over recent days for West Coast trough details, ejecting energy that will affect specifics of the wavy mean front extending northeast from the northern Rockies into the Plains/Canada, Northeast cyclonic flow and surface features, and weakness over the South/associated surface reflection, make it difficult to have a lot of confidence in one model's specifics over another. There appears to be particularly low predictability/significant randomness in how surface low pressure could evolve/track over the southeastern U.S. western Atlantic. ...Weather/Hazard Highlights... For the time being the forecast has stabilized with the potential for some heavy rainfall in the vicinity of the eastern half of the Gulf Coast and through the southeastern Coast. Low predictability of important details aloft as well as mesoscale convective influences that cannot be resolved very far out in time continue to temper confidence in rainfall details. The Northern Plains will be the other primary region of focus for significant rainfall, with one or more wavy fronts over/near the area during the period supporting the potential for multiple convective events and training. Diurnal convection will be possible over the central/southern Rockies, while cyclonic flow aloft and corresponding waves/fronts may produce some showers/thunderstorms over the Northeast and parts of the Mid-Atlantic/Great Lakes. Confidence in specifics becomes fairly low after the weekend. Expect the most anomalous temperatures to remain centered over the Great Lakes with some highs reaching 10-15F above normal especially during the weekend and early next week. Some of this warmth will extend into the Ohio Valley. Above normal highs initially extending into the Northern Plains/Upper Mississippi Valley should erode from west to east with time. Northeastern temperatures will vary depending on frontal/wave details. Potential amplification of the trough/ridge pattern over the western/central U.S. late in the period may lead to more coverage of below normal highs over the Northwest and above normal highs over parts of the Plains by next Tue-Wed. Areas over the Southeast with clouds/rain should see modestly below normal temperatures while parts of the Florida Peninsula that end up south of most rainfall may be a little above normal. 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