Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1240 AM EDT Sun Jun 16 2019 Valid 12Z Wed Jun 19 2019 - 12Z Sun Jun 23 2019 ...Overview and Guidance/Predictability Assessment... Latest guidance indicates a persistent southeast Canada trough with confluent flow south in the the MS Valley and Oh Valley to the northeast and mid Atlantic. This allows multiple frontal waves to progress across these areas. The models have similar depictions with different timing of the waves. For days 3-4 the 18z GFS and 12z UKMET are on the slow side of the guidance spread with the wave progressing from the mid MS valley Wed to the Oh Valley Thu and New England Fri. Given the faster jet usually promotes faster wave progression, more weighting was given the 12z ECMWF/ECMWF Ensemble Mean/12z Canadian/18z GEFS Mean solutions. Consensus shows a closed anticyclone over the Pacific west of northern CA that remains slowly moving through next weekend. Teleconnections from this anomalously strong high in the northeast Pacific lead to a downstream trough over the northern Plains with an embedded closed low near the US Canadian border through the middle of next week before retreating into southern Canada next weekend. Prefer a blended approach giving more weight to the ensemble means of the 12z ECMWF and 18z GEFS Ensemble Means, with less weighting to the operational 12z/18z GFS, which forecast a more progressive upper trough than the 12z ECMWF/Canadian and the ensemble means of the 18z GEFS and 12z ECMWF. The GFS is known to have a fast bias in moving closed lows aloft, which is suspected to be the case here, especially with the GEFS Mean slower and in much better agreement with the ECMWF and ECMWF Ensemble Mean. The 18z GEFS Mean and 12z ECMWF Ensemble Means continue to show better than average agreement over the northern Rockies and northern Plains, so more weighting was given to the Ensemble Means of the 18z GEFS and 12z ECMWF. ...Sensible Weather Highlights/Threats... The expected progression of waves of low pressure along a front continues to be favorable for multiple episodes of convection from the southern half of the Plains across the lower-mid MS Valley, followed by the Ohio Valley/Tn Valley/ Appalachians/Mid Atlantic/Northeast. The Florida peninsula should see diurnal convection day 3-6, possibly declining day 7 as an upper ridge strengthens. During Wed-Thu expect showers/storms to spread into the northern Plains/Upper Mississippi Valley with the system forecast to affect those regions, with another round of showers/storms near where moisture and instability focus across eastern OK/AR/TN/northern MS/AL/GA. From Fri 21 Jun-Sun 23 Jun the showers/storms may extend from eastern OK across the mid-upper MS Valley into the Great Lakes and Ohio Valley, with more than one round possible as the frontal system moves slowly east in the blocking pattern. Over the West, expect broad coverage of above normal temperatures Wed and Thu in CA/OR/NV with some pockets of greater than plus 10F anomalies centered on interior northern CA. The anomalies might taper a bit but temps remain above normal from CA into the southwest Sun 23 Jun. The other area of persistent above normal temperatures is expected to be Texas. WA and ID/northern OR cool with height falls in the middle of the week, remaining cool through next weekend. Areas across the northern Plains starting with eastern MT and WY and spreading into the western Dakotas will see below normal highs by as much as 10 to 15 degrees below normal Wed 19 Jun through Sun 23 Jun. The central US trough builds up the southeast ridge with above normal temps next weekend expected for coastal SC across southeast GA and much of Fl. Petersen 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