Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Fri Jun 19 2020 Valid 12Z Mon Jun 22 2020 - 12Z Fri Jun 26 2020 ...Overview and Weather/Hazard Highlights... The medium range period begins early next week with a pesky upper level low finally exiting the Northeast, while a stronger and slow moving low settles south of Hudson Bay and drifts only slightly eastward through the week. This should bring height falls and a cold front down across the east-central U.S. and eventually the East. Expect much above normal temperatures in advance of this front from the Great Lakes to northern New England. The trailing end of this frontal boundary is expected to stall back through the South to the Plains and linger through much of next week, serving as a focus for shower and thunderstorm development. Precipitation should slowly shift farther south and east, from the Southern Plains/Lower Mississippi Valley to the Ohio Valley/Appalachians and the Eastern Seaboard middle to latter part of next week. The Southern Plains and Lower Mississippi Valley may have the greatest potential for locally heavy rainfall and runoff issues under additional influence of a lingering upper-level trough and this threat is on our Hazards Outlook. Meanwhile out West, upper-level mean ridging should assert over the Southwest for much of next week and early week Northwestern U.S. upper ridging should keep conditions mostly dry. Height falls and cold frontal passage from the Northwest through the Northern Rockies/Plains later next week though may bring some showers over the region, with organized activity most likely to focus along a lingering boundary in the northern Rockies/High Plains. Temperatures across much of the West are forecast to stay above normal, with daytime highs ranging 10 to 15+ degrees above average, especially across the Great Basin and into parts of the interior Northwest. ...Guidance/Predictability Assessment... The 00 UTC ECMWF/ECMWF ensembles show much greater West Gulf Coast/TX spin-up and heavy QPF potential next week than other guidance. 00 UTC ECMWF QPF in particular seems overdone. The newer 12 UTC ECMWF backed off. That said, Gulf moisture and persistent/favorable upper trough proximity common to guidance does offer some heavy rainfall threat. Accordingly, WPC medium range QPF and Hazards Outlook products maintain some risk. There is also some question with a continuity change in the 00 UTC ECMWF that now shows much weaker mid-upper level trough digging over the Northwest and Great Basin later next week on days 6/7. This change is only marginally supported by ECMWF ensembles. A favored GEFS/ECMWF ensemble mean blend shows moderate upper trough development and translation in line with overnight WPC continuity. The newer 12 UTC ECMWF is more amplified. Otherwise, guidance forecast spread seems modest days 3-5 (Mon-Wed), so a GFS/ECMWF/Canadian blend seems fairly reasonable for this period. A GEFS/ECMWF ensemble mean blend offers a good starting point for the forecast by days 6/7 (next Thu/Fri) amid growing aforementioned uncertainties and more numerous and less predictable smaller scale system timing and emphasis variances. Schichtel/Santorelli 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