Extended Forecast Discussion NWS Weather Prediction Center College Park MD 344 PM EDT Mon Jun 15 2020 Valid 12Z Thu Jun 18 2020 - 12Z Mon Jun 22 2020 ...Overview... A mid/upper low centered over the Carolinas in the short range should lift slowly northward and weaken by the weekend. Another upper low is forecast to press slowly eastward across south-central Canada, while a front ahead of it could focus rain across portions of the Midwest, Plains, and Mississippi Valley. ...Guidance/Predictability Assessment... In the East, model guidance was consistent with the upper low lingering over the Southern/Central Appalachians through Thu, though the extent of its influence varied a bit. Then there is some question when the low joins back up with the northern stream flow. 00Z and 06Z GFS runs keep the low separate through Fri/Sat, while this forecast leaned more toward the consensus of other models that combine the flow more quickly (00Z UKMET, ECMWF, and CMC). Despite those differences, the centroid of the energy did not differ too much by medium range standards through Sat. For the upper low in south-central Canada, recent GFS runs have come into better consensus with other guidance for the positioning and slow movement of the low. Still, questions remain especially with ridging coming in west and north of the low. In the non-NCEP guidance, ridging pinches off into an upper high north of the low which separates the northern stream flow, while the GFS keeps ridging to the west and allows the energy to combine with the northern stream Sat (though ends up separating again by Sun). So continued to lean away from the GFS/GEFS suite with this feature as well, in favor of the ECMWF/EC ensemble mean as well as the UKMET early and a bit of the CMC. ...Weather/Hazard Highlights... It appears that most of the heavy precipitation with the upper low in the East will take place in the short range, but showery and cloudy conditions should persist Thu/Fri over portions of the Southeast and Mid-Atlantic, causing somewhat cooler than average temperatures. Meanwhile, weak ridging is forecast to build behind the upper low across the Southern Plains northeastward, causing above normal temperatures in the Great Lakes through the late week and the Northeast through the weekend. A frontal system stretching across the Midwest to the Plains is expected to slowly track south and eastward ahead of the Canadian upper low. This could provide a focus for modest to locally heavy rainfall and thunderstorms over portions of the Plains and Mississippi Valley through the period. Chances for precipitation will increase across the Great Lakes and Ohio Valley into parts of the eastern U.S. early next week as the front moves eastward. In the West, mainly dry conditions are expected through the period. High temperatures of 5 to 10 degrees below average in the Great Basin and Northern/Central Rockies through the end of the workweek will give way to temperatures 10 to 20 degrees above average spreading east across the Pacific Northwest and northern California into the Intermountain West early next week underneath above normal 500 mb heights. Tate 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 Hazards: - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Mon, Jun 22. - Flooding possible across portions of the Northern Plains and the Northern Rockies. - Flooding occurring or imminent across portions of the Southeast, the Mississippi Valley, and the Northern Plains. - Much above normal temperatures across portions of California, the Central Great Basin, the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Sun-Mon, Jun 21-Jun 22. - Much above normal temperatures across portions of the Great Lakes and the Upper Mississippi Valley, Thu-Fri, Jun 18-Jun 19. - Much above normal temperatures across portions of the Northeast and the Great Lakes, Thu-Sun, Jun 18-Jun 21. 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