Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1256 AM EDT Fri Jun 29 2018 Valid 12Z Mon Jul 02 2018 - 12Z Fri Jul 06 2018 ...Long duration heat wave to continue over the northeastern portion of the lower 48... ...Heavy rain threat for the northern Gulf Coast... ...Overview... Models and ensembles remain in good agreement next week with the upper pattern that will feature an expanding upper high that will likely stretch from southern California northeastward to the Appalachians. This will support well above average temperatures over the eastern Great Lakes/Northeast/Mid-Atlantic with daily record highs likely to be broken. One upper low will linger over the Pacific Northwest and another off the southeast coast with yet another to the southwest of the upper high over the Gulf Coast. A surface frontal boundary will lie astride the north/northwest side of the expanding 594-597dm (maybe 600dm?) upper high -- roughly from the Pacific/Interior West through the northern Plains into the Great Lakes. ...Guidance evaluation/preferences... The latest deterministic models formed a good starting point for the forecast (GFS/ECMWF/Canadian/UKMET) though the 12Z/18Z GFS and most GEFS members were slower than the rest of the models/ensembles to bring the upper low southward toward western Washington early next week. After that, GFS/ECMWF fall within the ensemble spread and a blend with their ensembles tempered the differences out to next Friday. Biggest trouble spot may be off the east coast with the upper low -- both in its track and strength (and eventual impact via precipitation). ...Weather threats/highlights... Ascendant upper high will force precipitation around its circulation, firstly in the Northwest in conjunction with southwest flow ahead of the upper low atop the surface boundary. This will extend eastward across Montana into the Plains and Great Lakes as the surface low wanders through southern Canada. A lead front into the Northeast next Mon/Tue will do little but knock temperatures a few degrees and perhaps touch off a shower/storm as it dissipates by Wednesday. The Southeast into Florida may see an increase in precipitation should the Atlantic upper low wobble westward toward the Carolinas later in the week. Finally, the most significant precipitation may lie along the Gulf Coast from LA/MS westward to the upper Texas coast as a weakness drifts westward. ECMWF/UKMET/Canadian seemed a bit aggressive/wet but with plenty of moisture to tap (PW anomalies about +2 to +3 sigma) heavy rainfall is certainly a possibility. Temperatures will be near/above records in the Northeast early in the week with a slow downward trend (but still above average) by late in the week as the core of the upper high moves southwestward. Widespread 90s are forecast for most of the lower 48 states while cooler than average temperatures are expected for the Northwest and also along the Gulf Coast (especially max temps) given extensive cloud cover and rain. Fracasso WPC medium range forecasts of 500 mb heights, surface systems, weather grids, quantitative precipitation, and winter weather outlook probabilities are found at: http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4