Extended Forecast Discussion NWS Weather Prediction Center College Park MD 303 PM EDT Fri Jun 21 2019 Valid 12Z Mon Jun 24 2019 - 12Z Fri Jun 28 2019 ...Overview... Troughing returns to the Pacific Northwest next week as an upper low slowly sinks southeastward from the Gulf of Alaska then eastward into Washington/Oregon. To the east, a lead system will lift northeastward through the Great Lakes with a ridge developing over the northern Plains in its wake. Upper ridging is forecast to slide westward across the Gulf of Mexico and into the Mexican plateau and far western Texas/southern New Mexico with a weak trough pushing west across Florida to the central Gulf Coast starting in the middle of next week. ...Guidance/Predictability Assessment... A blend of the deterministic 00Z ECMWF/UKMET/06Z GFS guidance offered a good starting point for the Mon-Wed forecast. Differences in timing with the eastern system continued to diminish with these runs for Day 3. Excellent agreement with the system approaching the Pacific Northwest coast ends with divergence on Wed with the shape and depth of the mid-level low center. Differences are also noted in the 00Z ECENS/GEFS with the GEFS deeper. Uncertainty remains with the timing/influence of a reinforcing shortwave from the northern BC coast Thursday. For now went with the less intense solution with the 00Z ECENS which replaced much of the deterministic input for Days 6/7. Farther east, ensembles were in good agreement on moving the weak trough eastward along with its surface cold front and for the ridge over the southeastern 2/3 of the CONUS. It is worth noting that the 00Z and 06Z GEFS both have a mid-level inverted trough shifting west across the northern Gulf of Mexico on Day 7. ...Weather Highlights/Threats... Much of the central and northern Rockies will see below normal temperatures on the order of 5-10 deg F on Monday with cold returning to the West Coast and pushing inland for the rest of next week under the developing trough. Areas from the High Plains to the Northeast will see near to above normal temperatures (up to about +5 to +10 deg F anomalies) through the forecast period, but generally not near record maxes. The cold front will not bring in much colder air to the East but rather a bit drier (briefly). Southern Plains to the Southeast will see 90s most days with a sprinkling of showers/storms during the afternoons. Precipitation forcing will be best Mon/Tue across the northeast ahead of a warm front lifting north from the Great Lakes low. In the Pacific Northwest, an upper low will bring in showers (and some very high elevation snow) that will gradually expand over the northern Plains to the Upper Midwest later in the week as the trough and cold front move eastward. There is potential for notable precipitation along the central Gulf Coast by Fri as a weak upper level disturbance shifts west from Florida, possibly providing forcing to an onshore flow. Jackson 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 Lower Mississippi Valley and the Southern Plains, Mon, Jun 24. - Flooding possible across portions of the Northeast, the Southern Plains, the Middle Mississippi Valley, the Mid-Atlantic, the Great Lakes, and the Ohio Valley. - Flooding occurring or imminent across portions of the Central Plains, the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Mid-Atlantic, and the Ohio Valley. - Flooding likely across portions of the Central Great Basin. - Excessive heat across portions of the Southeast and the Southern Texas, Mon, Jun 24. 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