Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1140 AM EDT Mon Jun 24 2019 Valid 12Z Thu Jun 27 2019 - 12Z Mon Jul 01 2019 1600 UTC Update... No significant changes were made from the previous shift. Models continue to show relatively good agreement on the overall synoptic scale pattern over the CONUS in the medium range. This cycle for the WPC progs used a blend of the latest deterministic guidance with previous shift continuity through Day 5, with increasing weighting of the ensemble means thereafter to mitigate the less predictable detail and timing differences. See previous discussion below for pattern assessment and notable weather highlights and threats. Santorelli ...Overview and Guidance/Predictability Assessment... An initially deep closed upper low is forecast to slowly but steadily move through the Pacific Northwest and then into British Columbia later this week and weekend. Upper ridging will build downstream over the High Plains into the western Great Lakes while troughing in eastern Canada (Hudson Bay) will dig into the Northeast next weekend. Along the Gulf Coast, an inverted trough develops and will move westward as an upper high settles into AZ/NM. The latest deterministic models offer a reasonably well-clustered starting point for the Thu-Sat period. Thereafter, incorporated the GEFS/ECMWF ensemble means which smoothed out smaller-scale timing and amplitude differences for the lower 48. ...Weather Highlights/Threats... The amplified upper low and lingering troughing will favor cooler than average temperatures in most of the West (especially Pacific Northwest into the Great Basin/Intermountain West) and scattered rain/storms with some very high elevation snow. Temperatures initially 5-15 deg F below average will moderate back toward typical late-June values by late next weekend as heights rise. Temperatures in the northern Plains/Upper Midwest will be 5-10 deg F above average (80s to low or even mid 90s), but with a daily risk of showers/storms with locally heavy downpours in the vicinity of a warm front. The Storm Prediction Center highlights a 15% area for severe thunderstorms on Thursday across parts of the Northern High Plains along the warm front before it lifts north and eastward into the Upper Midwest by this weekend. The Northeast will see cooler temperatures by Sunday as a front sinks through the region. The Southeast and lower MS Valley/Gulf Coast region will see a daily chance of showers/storms in typical summertime fashion, but that may be enhanced as the upper trough moves westward as lower level moisture slowly increases from the Gulf. 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